i915 will soon gain an eviction path that trylock a whole lot of locks
for eviction, getting dmesg failures like below:
BUG: MAX_LOCK_DEPTH too low!
turning off the locking correctness validator.
depth: 48 max: 48!
48 locks held by i915_selftest/5776:
#0: ffff888101a79240 (&dev->mutex){....}-{3:3}, at: __driver_attach+0x88/0x160
#1: ffffc900009778c0 (reservation_ww_class_acquire){+.+.}-{0:0}, at: i915_vma_pin.constprop.63+0x39/0x1b0 [i915]
#2: ffff88800cf74de8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_vma_pin.constprop.63+0x5f/0x1b0 [i915]
#3: ffff88810c7f9e38 (&vm->mutex/1){+.+.}-{3:3}, at: i915_vma_pin_ww+0x1c4/0x9d0 [i915]
#4: ffff88810bad5768 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915]
#5: ffff88810bad60e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915]
...
#46: ffff88811964d768 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915]
#47: ffff88811964e0e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915]
INFO: lockdep is turned off.
Fixing eviction to nest into ww_class_acquire is a high priority, but
it requires a rework of the entire driver, which can only be done one
step at a time.
As an intermediate solution, add an acquire context to
ww_mutex_trylock, which allows us to do proper nesting annotations on
the trylocks, making the above lockdep splat disappear.
This is also useful in regulator_lock_nested, which may avoid dropping
regulator_nesting_mutex in the uncontended path, so use it there.
TTM may be another user for this, where we could lock a buffer in a
fastpath with list locks held, without dropping all locks we hold.
[peterz: rework actual ww_mutex_trylock() implementations]
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/YUBGPdDDjKlxAuXJ@hirez.programming.kicks-ass.net
Readers of rwbase can lock and unlock without taking any inner lock, if
that happens, we need the ordering provided by atomic operations to
satisfy the ordering semantics of lock/unlock. Without that, considering
the follow case:
{ X = 0 initially }
CPU 0 CPU 1
===== =====
rt_write_lock();
X = 1
rt_write_unlock():
atomic_add(READER_BIAS - WRITER_BIAS, ->readers);
// ->readers is READER_BIAS.
rt_read_lock():
if ((r = atomic_read(->readers)) < 0) // True
atomic_try_cmpxchg(->readers, r, r + 1); // succeed.
<acquire the read lock via fast path>
r1 = X; // r1 may be 0, because nothing prevent the reordering
// of "X=1" and atomic_add() on CPU 1.
Therefore audit every usage of atomic operations that may happen in a
fast path, and add necessary barriers.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20210909110203.953991276@infradead.org
The code in rwbase_write_lock() is a little non-obvious vs the
read+set 'trylock', extract the sequence into a helper function to
clarify the code.
This also provides a single site to fix fast-path ordering.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/YUCq3L+u44NDieEJ@hirez.programming.kicks-ass.net
Noticed while looking at the readers race.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lkml.kernel.org/r/20210909110203.828203010@infradead.org
When running locktorture as a module, any lock_torture_init() issues will be
reflected in the error code from modprobe or insmod, as the case may be.
However, these error codes are not available when running locktorture
built-in, for example, when using the kvm.sh script. This commit
therefore adds WARN_ON_ONCE() to allow distinguishing lock_torture_init()
errors when running locktorture built-in.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Dan reported that rt_mutex_adjust_prio_chain() can be called with
.orig_waiter == NULL however commit a055fcc132 ("locking/rtmutex: Return
success on deadlock for ww_mutex waiters") unconditionally dereferences it.
Since both call-sites that have .orig_waiter == NULL don't care for the
return value, simply disable the deadlock squash by adding the NULL check.
Notably, both callers use the deadlock condition as a termination condition
for the iteration; once detected, it is sure that (de)boosting is done.
Arguably step [3] would be a more natural termination point, but it's
dubious whether adding a third deadlock detection state would improve the
code.
Fixes: a055fcc132 ("locking/rtmutex: Return success on deadlock for ww_mutex waiters")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/YS9La56fHMiCCo75@hirez.programming.kicks-ass.net
The regular pile:
- A few improvements to the mutex code
- Documentation updates for atomics to clarify the difference between
cmpxchg() and try_cmpxchg() and to explain the forward progress
expectations.
- Simplification of the atomics fallback generator
- The addition of arch_atomic_long*() variants and generic arch_*()
bitops based on them.
- Add the missing might_sleep() invocations to the down*() operations of
semaphores.
The PREEMPT_RT locking core:
- Scheduler updates to support the state preserving mechanism for
'sleeping' spin- and rwlocks on RT. This mechanism is carefully
preserving the state of the task when blocking on a 'sleeping' spin- or
rwlock and takes regular wake-ups targeted at the same task into
account. The preserved or updated (via a regular wakeup) state is
restored when the lock has been acquired.
- Restructuring of the rtmutex code so it can be utilized and extended
for the RT specific lock variants.
- Restructuring of the ww_mutex code to allow sharing of the ww_mutex
specific functionality for rtmutex based ww_mutexes.
- Header file disentangling to allow substitution of the regular lock
implementations with the PREEMPT_RT variants without creating an
unmaintainable #ifdef mess.
- Shared base code for the PREEMPT_RT specific rw_semaphore and rwlock
implementations. Contrary to the regular rw_semaphores and rwlocks the
PREEMPT_RT implementation is writer unfair because it is infeasible to
do priority inheritance on multiple readers. Experience over the years
has shown that real-time workloads are not the typical workloads which
are sensitive to writer starvation. The alternative solution would be
to allow only a single reader which has been tried and discarded as it
is a major bottleneck especially for mmap_sem. Aside of that many of
the writer starvation critical usage sites have been converted to a
writer side mutex/spinlock and RCU read side protections in the past
decade so that the issue is less prominent than it used to be.
- The actual rtmutex based lock substitutions for PREEMPT_RT enabled
kernels which affect mutex, ww_mutex, rw_semaphore, spinlock_t and
rwlock_t. The spin/rw_lock*() functions disable migration across the
critical section to preserve the existing semantics vs. per CPU
variables.
- Rework of the futex REQUEUE_PI mechanism to handle the case of early
wake-ups which interleave with a re-queue operation to prevent the
situation that a task would be blocked on both the rtmutex associated
to the outer futex and the rtmutex based hash bucket spinlock.
While this situation cannot happen on !RT enabled kernels the changes
make the underlying concurrency problems easier to understand in
general. As a result the difference between !RT and RT kernels is
reduced to the handling of waiting for the critical section. !RT
kernels simply spin-wait as before and RT kernels utilize rcu_wait().
- The substitution of local_lock for PREEMPT_RT with a spinlock which
protects the critical section while staying preemptible. The CPU
locality is established by disabling migration.
The underlying concepts of this code have been in use in PREEMPT_RT for
way more than a decade. The code has been refactored several times over
the years and this final incarnation has been optimized once again to be
as non-intrusive as possible, i.e. the RT specific parts are mostly
isolated.
It has been extensively tested in the 5.14-rt patch series and it has
been verified that !RT kernels are not affected by these changes.
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Merge tag 'locking-core-2021-08-30' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking and atomics updates from Thomas Gleixner:
"The regular pile:
- A few improvements to the mutex code
- Documentation updates for atomics to clarify the difference between
cmpxchg() and try_cmpxchg() and to explain the forward progress
expectations.
- Simplification of the atomics fallback generator
- The addition of arch_atomic_long*() variants and generic arch_*()
bitops based on them.
- Add the missing might_sleep() invocations to the down*() operations
of semaphores.
The PREEMPT_RT locking core:
- Scheduler updates to support the state preserving mechanism for
'sleeping' spin- and rwlocks on RT.
This mechanism is carefully preserving the state of the task when
blocking on a 'sleeping' spin- or rwlock and takes regular wake-ups
targeted at the same task into account. The preserved or updated
(via a regular wakeup) state is restored when the lock has been
acquired.
- Restructuring of the rtmutex code so it can be utilized and
extended for the RT specific lock variants.
- Restructuring of the ww_mutex code to allow sharing of the ww_mutex
specific functionality for rtmutex based ww_mutexes.
- Header file disentangling to allow substitution of the regular lock
implementations with the PREEMPT_RT variants without creating an
unmaintainable #ifdef mess.
- Shared base code for the PREEMPT_RT specific rw_semaphore and
rwlock implementations.
Contrary to the regular rw_semaphores and rwlocks the PREEMPT_RT
implementation is writer unfair because it is infeasible to do
priority inheritance on multiple readers. Experience over the years
has shown that real-time workloads are not the typical workloads
which are sensitive to writer starvation.
The alternative solution would be to allow only a single reader
which has been tried and discarded as it is a major bottleneck
especially for mmap_sem. Aside of that many of the writer
starvation critical usage sites have been converted to a writer
side mutex/spinlock and RCU read side protections in the past
decade so that the issue is less prominent than it used to be.
- The actual rtmutex based lock substitutions for PREEMPT_RT enabled
kernels which affect mutex, ww_mutex, rw_semaphore, spinlock_t and
rwlock_t. The spin/rw_lock*() functions disable migration across
the critical section to preserve the existing semantics vs per-CPU
variables.
- Rework of the futex REQUEUE_PI mechanism to handle the case of
early wake-ups which interleave with a re-queue operation to
prevent the situation that a task would be blocked on both the
rtmutex associated to the outer futex and the rtmutex based hash
bucket spinlock.
While this situation cannot happen on !RT enabled kernels the
changes make the underlying concurrency problems easier to
understand in general. As a result the difference between !RT and
RT kernels is reduced to the handling of waiting for the critical
section. !RT kernels simply spin-wait as before and RT kernels
utilize rcu_wait().
- The substitution of local_lock for PREEMPT_RT with a spinlock which
protects the critical section while staying preemptible. The CPU
locality is established by disabling migration.
The underlying concepts of this code have been in use in PREEMPT_RT for
way more than a decade. The code has been refactored several times over
the years and this final incarnation has been optimized once again to be
as non-intrusive as possible, i.e. the RT specific parts are mostly
isolated.
It has been extensively tested in the 5.14-rt patch series and it has
been verified that !RT kernels are not affected by these changes"
* tag 'locking-core-2021-08-30' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (92 commits)
locking/rtmutex: Return success on deadlock for ww_mutex waiters
locking/rtmutex: Prevent spurious EDEADLK return caused by ww_mutexes
locking/rtmutex: Dequeue waiter on ww_mutex deadlock
locking/rtmutex: Dont dereference waiter lockless
locking/semaphore: Add might_sleep() to down_*() family
locking/ww_mutex: Initialize waiter.ww_ctx properly
static_call: Update API documentation
locking/local_lock: Add PREEMPT_RT support
locking/spinlock/rt: Prepare for RT local_lock
locking/rtmutex: Add adaptive spinwait mechanism
locking/rtmutex: Implement equal priority lock stealing
preempt: Adjust PREEMPT_LOCK_OFFSET for RT
locking/rtmutex: Prevent lockdep false positive with PI futexes
futex: Prevent requeue_pi() lock nesting issue on RT
futex: Simplify handle_early_requeue_pi_wakeup()
futex: Reorder sanity checks in futex_requeue()
futex: Clarify comment in futex_requeue()
futex: Restructure futex_requeue()
futex: Correct the number of requeued waiters for PI
futex: Remove bogus condition for requeue PI
...
Pull RCU updates from Paul McKenney:
"RCU changes for this cycle were:
- Documentation updates
- Miscellaneous fixes
- Offloaded-callbacks updates
- Updates to the nolibc library
- Tasks-RCU updates
- In-kernel torture-test updates
- Torture-test scripting, perhaps most notably the pinning of
torture-test guest OSes so as to force differences in memory
latency. For example, in a two-socket system, a four-CPU guest OS
will have one pair of its CPUs pinned to threads in a single core
on one socket and the other pair pinned to threads in a single core
on the other socket. This approach proved able to force race
conditions that earlier testing missed. Some of these race
conditions are still being tracked down"
* 'core-rcu.2021.08.28a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (61 commits)
torture: Replace deprecated CPU-hotplug functions.
rcu: Replace deprecated CPU-hotplug functions
rcu: Print human-readable message for schedule() in RCU reader
rcu: Explain why rcu_all_qs() is a stub in preemptible TREE RCU
rcu: Use per_cpu_ptr to get the pointer of per_cpu variable
rcu: Remove useless "ret" update in rcu_gp_fqs_loop()
rcu: Mark accesses in tree_stall.h
rcu: Make rcu_gp_init() and rcu_gp_fqs_loop noinline to conserve stack
rcu: Mark lockless ->qsmask read in rcu_check_boost_fail()
srcutiny: Mark read-side data races
rcu: Start timing stall repetitions after warning complete
rcu: Do not disable GP stall detection in rcu_cpu_stall_reset()
rcu/tree: Handle VM stoppage in stall detection
rculist: Unify documentation about missing list_empty_rcu()
rcu: Mark accesses to ->rcu_read_lock_nesting
rcu: Weaken ->dynticks accesses and updates
rcu: Remove special bit at the bottom of the ->dynticks counter
rcu: Fix stall-warning deadlock due to non-release of rcu_node ->lock
rcu: Fix to include first blocked task in stall warning
torture: Make kvm-test-1-run-qemu.sh check for reboot loops
...
ww_mutexes can legitimately cause a deadlock situation in the lock graph
which is resolved afterwards by the wait/wound mechanics. The rtmutex chain
walk can detect such a deadlock and returns EDEADLK which in turn skips the
wait/wound mechanism and returns EDEADLK to the caller. That's wrong
because both lock chains might get EDEADLK or the wrong waiter would back
out.
Detect that situation and return 'success' in case that the waiter which
initiated the chain walk is a ww_mutex with context. This allows the
wait/wound mechanics to resolve the situation according to the rules.
[ tglx: Split it apart and added changelog ]
Reported-by: Sebastian Siewior <bigeasy@linutronix.de>
Fixes: add461325e ("locking/rtmutex: Extend the rtmutex core to support ww_mutex")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/YSeWjCHoK4v5OcOt@hirez.programming.kicks-ass.net
rtmutex based ww_mutexes can legitimately create a cycle in the lock graph
which can be observed by a blocker which didn't cause the problem:
P1: A, ww_A, ww_B
P2: ww_B, ww_A
P3: A
P3 might therefore be trapped in the ww_mutex induced cycle and run into
the lock depth limitation of rt_mutex_adjust_prio_chain() which returns
-EDEADLK to the caller.
Disable the deadlock detection walk when the chain walk observes a
ww_mutex to prevent this looping.
[ tglx: Split it apart and added changelog ]
Reported-by: Sebastian Siewior <bigeasy@linutronix.de>
Fixes: add461325e ("locking/rtmutex: Extend the rtmutex core to support ww_mutex")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/YSeWjCHoK4v5OcOt@hirez.programming.kicks-ass.net
The rt_mutex based ww_mutex variant queues the new waiter first in the
lock's rbtree before evaluating the ww_mutex specific conditions which
might decide that the waiter should back out. This check and conditional
exit happens before the waiter is enqueued into the PI chain.
The failure handling at the call site assumes that the waiter, if it is the
top most waiter on the lock, is queued in the PI chain and then proceeds to
adjust the unmodified PI chain, which results in RB tree corruption.
Dequeue the waiter from the lock waiter list in the ww_mutex error exit
path to prevent this.
Fixes: add461325e ("locking/rtmutex: Extend the rtmutex core to support ww_mutex")
Reported-by: Sebastian Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210825102454.042280541@linutronix.de
The new rt_mutex_spin_on_onwer() loop checks whether the spinning waiter is
still the top waiter on the lock by utilizing rt_mutex_top_waiter(), which
is broken because that function contains a sanity check which dereferences
the top waiter pointer to check whether the waiter belongs to the
lock. That's wrong in the lockless spinwait case:
CPU 0 CPU 1
rt_mutex_lock(lock) rt_mutex_lock(lock);
queue(waiter0)
waiter0 == rt_mutex_top_waiter(lock)
rt_mutex_spin_on_onwer(lock, waiter0) { queue(waiter1)
waiter1 == rt_mutex_top_waiter(lock)
...
top_waiter = rt_mutex_top_waiter(lock)
leftmost = rb_first_cached(&lock->waiters);
-> signal
dequeue(waiter1)
destroy(waiter1)
w = rb_entry(leftmost, ....)
BUG_ON(w->lock != lock) <- UAF
The BUG_ON() is correct for the case where the caller holds lock->wait_lock
which guarantees that the leftmost waiter entry cannot vanish. For the
lockless spinwait case it's broken.
Create a new helper function which avoids the pointer dereference and just
compares the leftmost entry pointer with current's waiter pointer to
validate that currrent is still elegible for spinning.
Fixes: 992caf7f17 ("locking/rtmutex: Add adaptive spinwait mechanism")
Reported-by: Sebastian Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210825102453.981720644@linutronix.de
Semaphore is sleeping lock. Add might_sleep() to down*() family
(with exception of down_trylock()) to detect atomic context sleep.
Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20210809021215.19991-1-nixiaoming@huawei.com
The consolidation of the debug code for mutex waiter intialization sets
waiter::ww_ctx to a poison value unconditionally. For regular mutexes this
is intended to catch the case where waiter_ww_ctx is dereferenced
accidentally.
For ww_mutex the poison value has to be overwritten either with a context
pointer or NULL for ww_mutexes without context.
The rework broke this as it made the store conditional on the context
pointer instead of the argument which signals whether ww_mutex code should
be compiled in or optiized out. As a result waiter::ww_ctx ends up with the
poison pointer for contextless ww_mutexes which causes a later dereference of
the poison pointer because it is != NULL.
Use the build argument instead so for ww_mutex the poison value is always
overwritten.
Fixes: c0afb0ffc0 ("locking/ww_mutex: Gather mutex_waiter initialization")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210819193030.zpwrpvvrmy7xxxiy@linutronix.de
Add the static and runtime initializer mechanics to support the RT variant
of local_lock, which requires the lock type in the lockdep map to be set
to LD_LOCK_PERCPU.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211305.967526724@linutronix.de
Going to sleep when locks are contended can be quite inefficient when the
contention time is short and the lock owner is running on a different CPU.
The MCS mechanism cannot be used because MCS is strictly FIFO ordered while
for rtmutex based locks the waiter ordering is priority based.
Provide a simple adaptive spinwait mechanism which currently restricts the
spinning to the top priority waiter.
[ tglx: Provide a contemporary changelog, extended it to all rtmutex based
locks and updated it to match the other spin on owner implementations ]
Originally-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211305.912050691@linutronix.de
The current logic only allows lock stealing to occur if the current task is
of higher priority than the pending owner.
Significant throughput improvements can be gained by allowing the lock
stealing to include tasks of equal priority when the contended lock is a
spin_lock or a rw_lock and the tasks are not in a RT scheduling task.
The assumption was that the system will make faster progress by allowing
the task already on the CPU to take the lock rather than waiting for the
system to wake up a different task.
This does add a degree of unfairness, but in reality no negative side
effects have been observed in the many years that this has been used in the
RT kernel.
[ tglx: Refactored and rewritten several times by Steve Rostedt, Sebastian
Siewior and myself ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211305.857240222@linutronix.de
On PREEMPT_RT the futex hashbucket spinlock becomes 'sleeping' and rtmutex
based. That causes a lockdep false positive because some of the futex
functions invoke spin_unlock(&hb->lock) with the wait_lock of the rtmutex
associated to the pi_futex held. spin_unlock() in turn takes wait_lock of
the rtmutex on which the spinlock is based which makes lockdep notice a
lock recursion.
Give the futex/rtmutex wait_lock a separate key.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211305.750701219@linutronix.de
Add the necessary defines, helpers and API functions for replacing struct mutex on
a PREEMPT_RT enabled kernel with an rtmutex based variant.
No functional change when CONFIG_PREEMPT_RT=n
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211305.081517417@linutronix.de
Add the actual ww_mutex API functions which replace the mutex based variant
on RT enabled kernels.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211305.024057938@linutronix.de
Add a ww acquire context pointer to the waiter and various functions and
add the ww_mutex related invocations to the proper spots in the locking
code, similar to the mutex based variant.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.966139174@linutronix.de
Provide the defines for RT mutex based ww_mutexes and fix up the debug logic
so it's either enabled by DEBUG_MUTEXES or DEBUG_RT_MUTEXES on RT kernels.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.908012566@linutronix.de
RT mutex based ww_mutexes cannot order based on timestamps. They have to
order based on priority. Add the necessary decision logic.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.847536630@linutronix.de
Provide the type defines and the helper inlines for rtmutex based ww_mutexes.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.790760545@linutronix.de
Accessing the internal wait_lock of mutex and rtmutex is slightly
different. Provide helper functions for that.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.734635961@linutronix.de
Some ww_mutex helper functions use pointers for the underlying mutex and
mutex_waiter. The upcoming rtmutex based implementation needs to share
these functions. Add and use defines for the types and replace the direct
types in the affected functions.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.678720245@linutronix.de
Move the mutex related access from various ww_mutex functions into helper
functions so they can be substituted for rtmutex based ww_mutex later.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.622477030@linutronix.de
The upcoming rtmutex based ww_mutex needs a different handling for
enqueueing a waiter. Split it out into a helper function.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.566318143@linutronix.de
Split out the waiter iteration functions so they can be substituted for a
rtmutex based ww_mutex later.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.509186185@linutronix.de
None of these functions will be on the stack when blocking in
schedule(), hence __sched is not needed.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.453235952@linutronix.de
Split the W/W mutex helper functions out into a separate header file, so
they can be shared with a rtmutex based variant later.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.396893399@linutronix.de
Split the ww related part out into a helper function so it can be reused
for a rtmutex based ww_mutex implementation.
[ mingo: Fixed bisection failure. ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.340166556@linutronix.de
The wait_lock of mutex is really a low level lock. Convert it to a
raw_spinlock like the wait_lock of rtmutex.
[ mingo: backmerged the test_lockup.c build fix by bigeasy. ]
Co-developed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.166863404@linutronix.de
Move the mutex waiter declaration from the public <linux/mutex.h> header
to the internal kernel/locking/mutex.h header.
There is no reason to expose it outside of the core code.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.054325923@linutronix.de
Having two header files which contain just the non-debug and debug variants
is mostly waste of disc space and has no real value. Stick the debug
variants into the common mutex.h file as counterpart to the stubs for the
non-debug case.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.995350521@linutronix.de
Ensure all !RT tasks have the same prio such that they end up in FIFO
order and aren't split up according to nice level.
The reason why nice levels were taken into account so far is historical. In
the early days of the rtmutex code it was done to give the PI boosting and
deboosting a larger coverage.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.938676930@linutronix.de
Similar to rw_semaphores, on RT the rwlock substitution is not writer fair,
because it's not feasible to have a writer inherit its priority to
multiple readers. Readers blocked on a writer follow the normal rules of
priority inheritance. Like RT spinlocks, RT rwlocks are state preserving
across the slow lock operations (contended case).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.882793524@linutronix.de
Provide the actual locking functions which make use of the general and
spinlock specific rtmutex code.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.826621464@linutronix.de
A simplified version of the rtmutex slowlock function, which neither handles
signals nor timeouts, and is careful about preserving the state of the
blocked task across the lock operation.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.770228446@linutronix.de
Guard the regular sleeping lock specific functionality, which is used for
rtmutex on non-RT enabled kernels and for mutex, rtmutex and semaphores on
RT enabled kernels so the code can be reused for the RT specific
implementation of spinlocks and rwlocks in a different compilation unit.
No functional change.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.311535693@linutronix.de
Add an rtlock_task pointer to rt_mutex_wake_q, which allows to handle the RT
specific wakeup for spin/rwlock waiters. The pointer is just consuming 4/8
bytes on the stack so it is provided unconditionaly to avoid #ifdeffery all
over the place.
This cannot use a regular wake_q, because a task can have concurrent wakeups which
would make it miss either lock or the regular wakeups, depending on what gets
queued first, unless task struct gains a separate wake_q_node for this, which
would be overkill, because there can only be a single task which gets woken
up in the spin/rw_lock unlock path.
No functional change for non-RT enabled kernels.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.253614678@linutronix.de
Prepare for the required state aware handling of waiter wakeups via wake_q
and switch the rtmutex code over to the rtmutex specific wrapper.
No functional change.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.197113263@linutronix.de
To handle the difference between wakeups for regular sleeping locks (mutex,
rtmutex, rw_semaphore) and the wakeups for 'sleeping' spin/rwlocks on
PREEMPT_RT enabled kernels correctly, it is required to provide a
wake_q_head construct which allows to keep them separate.
Provide a wrapper around wake_q_head and the required helpers, which will be
extended with the state handling later.
No functional change.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.139337655@linutronix.de
Regular sleeping locks like mutexes, rtmutexes and rw_semaphores are always
entering and leaving a blocking section with task state == TASK_RUNNING.
On a non-RT kernel spinlocks and rwlocks never affect the task state, but
on RT kernels these locks are converted to rtmutex based 'sleeping' locks.
So in case of contention the task goes to block, which requires to carefully
preserve the task state, and restore it after acquiring the lock taking
regular wakeups for the task into account, which happened while the task was
blocked. This state preserving is achieved by having a separate task state
for blocking on a RT spin/rwlock and a saved_state field in task_struct
along with careful handling of these wakeup scenarios in try_to_wake_up().
To avoid conditionals in the rtmutex code, store the wake state which has
to be used for waking a lock waiter in rt_mutex_waiter which allows to
handle the regular and RT spin/rwlocks by handing it to wake_up_state().
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.079800739@linutronix.de
The RT specific R/W semaphore implementation used to restrict the number of
readers to one, because a writer cannot block on multiple readers and
inherit its priority or budget.
The single reader restricting was painful in various ways:
- Performance bottleneck for multi-threaded applications in the page fault
path (mmap sem)
- Progress blocker for drivers which are carefully crafted to avoid the
potential reader/writer deadlock in mainline.
The analysis of the writer code paths shows that properly written RT tasks
should not take them. Syscalls like mmap(), file access which take mmap sem
write locked have unbound latencies, which are completely unrelated to mmap
sem. Other R/W sem users like graphics drivers are not suitable for RT tasks
either.
So there is little risk to hurt RT tasks when the RT rwsem implementation is
done in the following way:
- Allow concurrent readers
- Make writers block until the last reader left the critical section. This
blocking is not subject to priority/budget inheritance.
- Readers blocked on a writer inherit their priority/budget in the normal
way.
There is a drawback with this scheme: R/W semaphores become writer unfair
though the applications which have triggered writer starvation (mostly on
mmap_sem) in the past are not really the typical workloads running on a RT
system. So while it's unlikely to hit writer starvation, it's possible. If
there are unexpected workloads on RT systems triggering it, the problem
has to be revisited.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.016885947@linutronix.de
On PREEMPT_RT, rw_semaphores and rwlocks are substituted with an rtmutex and
a reader count. The implementation is writer unfair, as it is not feasible
to do priority inheritance on multiple readers, but experience has shown
that real-time workloads are not the typical workloads which are sensitive
to writer starvation.
The inner workings of rw_semaphores and rwlocks on RT are almost identical
except for the task state and signal handling. rw_semaphores are not state
preserving over a contention, they are expected to enter and leave with state
== TASK_RUNNING. rwlocks have a mechanism to preserve the state of the task
at entry and restore it after unblocking taking potential non-lock related
wakeups into account. rw_semaphores can also be subject to signal handling
interrupting a blocked state, while rwlocks ignore signals.
To avoid code duplication, provide a shared implementation which takes the
small difference vs. state and signals into account. The code is included
into the relevant rw_semaphore/rwlock base code and compiled for each use
case separately.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211302.957920571@linutronix.de
Split the inner workings of rt_mutex_slowlock() out into a separate
function, which can be reused by the upcoming RT lock substitutions,
e.g. for rw_semaphores.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211302.841971086@linutronix.de
RT builds substitutions for rwsem, mutex, spinlock and rwlock around
rtmutexes. Split the inner working out so each lock substitution can use
them with the appropriate lockdep annotations. This avoids having an extra
unused lockdep map in the wrapped rtmutex.
No functional change.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211302.784739994@linutronix.de
Prepare for reusing the inner functions of rtmutex for RT lock
substitutions: introduce kernel/locking/rtmutex_api.c and move
them there.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211302.726560996@linutronix.de
Allows the compiler to generate better code depending on the architecture.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211302.668958502@linutronix.de
Inlines are type-safe...
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211302.610830960@linutronix.de
RT mutexes belong to the LD_WAIT_SLEEP class. Make them so.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211302.031014562@linutronix.de
Currently, the lock_is_read_held variable is bool, so that a reader sets
it to true just after lock acquisition and then to false just before
lock release. This works in a rough statistical sense, but can result
in false negatives just after one of a pair of concurrent readers has
released the lock. This approach does have low overhead, but at the
expense of the setting to true potentially never leaving the reader's
store buffer, thus resulting in an unconditional false negative.
This commit therefore converts this variable to atomic_t and makes
the reader use atomic_inc() just after acquisition and atomic_dec()
just before release. This does increase overhead, but this increase is
negligible compared to the 10-microsecond lock hold time.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The lock_stress_stats structure's ->n_lock_fail and ->n_lock_acquired
fields are incremented and sampled locklessly using plain C-language
statements, which KCSAN objects to. This commit therefore marks the
statistics gathering with data_race() to flag the intent. While in
the area, this commit also reduces the number of accesses to the
->n_lock_acquired field, thus eliminating some possible check/use
confusion.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The 2nd parameter 'count' is not used in this function.
The places where the function is called are also modified.
Signed-off-by: xuyehan <xuyehan@xiaomi.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/1625547043-28103-1-git-send-email-yehanxu1@gmail.com
Yanfei reported that it is possible to loose HANDOFF when we race with
mutex_unlock() and end up setting HANDOFF on an unlocked mutex. At
that point anybody can steal it, losing HANDOFF in the process.
If this happens often enough, we can in fact starve the top waiter.
Solve this by folding the 'set HANDOFF' operation into the trylock
operation, such that either we acquire the lock, or it gets HANDOFF
set. This avoids having HANDOFF set on an unlocked mutex.
Reported-by: Yanfei Xu <yanfei.xu@windriver.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Reviewed-by: Yanfei Xu <yanfei.xu@windriver.com>
Link: https://lore.kernel.org/r/20210630154114.958507900@infradead.org
Yanfei reported that setting HANDOFF should not depend on recomputing
@first, only on @first state. Which would then give:
if (ww_ctx || !first)
first = __mutex_waiter_is_first(lock, &waiter);
if (first)
__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
But because 'ww_ctx || !first' is basically 'always' and the test for
first is relatively cheap, omit that first branch entirely.
Reported-by: Yanfei Xu <yanfei.xu@windriver.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Reviewed-by: Yanfei Xu <yanfei.xu@windriver.com>
Link: https://lore.kernel.org/r/20210630154114.896786297@infradead.org
When enabling CONFIG_LOCK_STAT=y, then CONFIG_LOCKDEP=y is forcedly enabled,
but CONFIG_PROVE_LOCKING is disabled.
We can get output from /proc/lockdep, which currently includes usages of
lock classes. But the usages are meaningless, see the output below:
/ # cat /proc/lockdep
all lock classes:
ffffffff9af63350 ....: cgroup_mutex
ffffffff9af54eb8 ....: (console_sem).lock
ffffffff9af54e60 ....: console_lock
ffffffff9ae74c38 ....: console_owner_lock
ffffffff9ae74c80 ....: console_owner
ffffffff9ae66e60 ....: cpu_hotplug_lock
Only one usage context for each lock, this is because each usage is only
changed in mark_lock() that is in the CONFIG_PROVE_LOCKING=y section,
however in the test situation, it's not.
The fix is to move the usages reading and seq_print from the
!CONFIG_PROVE_LOCKING section to its defined section.
Also, locks_after list of lock_class is empty when !CONFIG_PROVE_LOCKING,
so do the same thing as what have done for usages of lock classes.
With this patch with !CONFIG_PROVE_LOCKING we can get the results below:
/ # cat /proc/lockdep
all lock classes:
ffffffff85163290: cgroup_mutex
ffffffff85154dd8: (console_sem).lock
ffffffff85154d80: console_lock
ffffffff85074b58: console_owner_lock
ffffffff85074ba0: console_owner
ffffffff85066d60: cpu_hotplug_lock
... a class key and the relevant class name each line.
Signed-off-by: Xiongwei Song <sxwjean@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20210629135916.308210-1-sxwjean@me.com
Pull RCU updates from Paul McKenney:
- Bitmap parsing support for "all" as an alias for all bits
- Documentation updates
- Miscellaneous fixes, including some that overlap into mm and lockdep
- kvfree_rcu() updates
- mem_dump_obj() updates, with acks from one of the slab-allocator
maintainers
- RCU NOCB CPU updates, including limited deoffloading
- SRCU updates
- Tasks-RCU updates
- Torture-test updates
* 'core-rcu-2021.07.04' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (78 commits)
tasks-rcu: Make show_rcu_tasks_gp_kthreads() be static inline
rcu-tasks: Make ksoftirqd provide RCU Tasks quiescent states
rcu: Add missing __releases() annotation
rcu: Remove obsolete rcu_read_unlock() deadlock commentary
rcu: Improve comments describing RCU read-side critical sections
rcu: Create an unrcu_pointer() to remove __rcu from a pointer
srcu: Early test SRCU polling start
rcu: Fix various typos in comments
rcu/nocb: Unify timers
rcu/nocb: Prepare for fine-grained deferred wakeup
rcu/nocb: Only cancel nocb timer if not polling
rcu/nocb: Delete bypass_timer upon nocb_gp wakeup
rcu/nocb: Cancel nocb_timer upon nocb_gp wakeup
rcu/nocb: Allow de-offloading rdp leader
rcu/nocb: Directly call __wake_nocb_gp() from bypass timer
rcu: Don't penalize priority boosting when there is nothing to boost
rcu: Point to documentation of ordering guarantees
rcu: Make rcu_gp_cleanup() be noinline for tracing
rcu: Restrict RCU_STRICT_GRACE_PERIOD to at most four CPUs
rcu: Make show_rcu_gp_kthreads() dump rcu_node structures blocking GP
...
- Changes to core scheduling facilities:
- Add "Core Scheduling" via CONFIG_SCHED_CORE=y, which enables
coordinated scheduling across SMT siblings. This is a much
requested feature for cloud computing platforms, to allow
the flexible utilization of SMT siblings, without exposing
untrusted domains to information leaks & side channels, plus
to ensure more deterministic computing performance on SMT
systems used by heterogenous workloads.
There's new prctls to set core scheduling groups, which
allows more flexible management of workloads that can share
siblings.
- Fix task->state access anti-patterns that may result in missed
wakeups and rename it to ->__state in the process to catch new
abuses.
- Load-balancing changes:
- Tweak newidle_balance for fair-sched, to improve
'memcache'-like workloads.
- "Age" (decay) average idle time, to better track & improve workloads
such as 'tbench'.
- Fix & improve energy-aware (EAS) balancing logic & metrics.
- Fix & improve the uclamp metrics.
- Fix task migration (taskset) corner case on !CONFIG_CPUSET.
- Fix RT and deadline utilization tracking across policy changes
- Introduce a "burstable" CFS controller via cgroups, which allows
bursty CPU-bound workloads to borrow a bit against their future
quota to improve overall latencies & batching. Can be tweaked
via /sys/fs/cgroup/cpu/<X>/cpu.cfs_burst_us.
- Rework assymetric topology/capacity detection & handling.
- Scheduler statistics & tooling:
- Disable delayacct by default, but add a sysctl to enable
it at runtime if tooling needs it. Use static keys and
other optimizations to make it more palatable.
- Use sched_clock() in delayacct, instead of ktime_get_ns().
- Misc cleanups and fixes.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'sched-core-2021-06-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler udpates from Ingo Molnar:
- Changes to core scheduling facilities:
- Add "Core Scheduling" via CONFIG_SCHED_CORE=y, which enables
coordinated scheduling across SMT siblings. This is a much
requested feature for cloud computing platforms, to allow the
flexible utilization of SMT siblings, without exposing untrusted
domains to information leaks & side channels, plus to ensure more
deterministic computing performance on SMT systems used by
heterogenous workloads.
There are new prctls to set core scheduling groups, which allows
more flexible management of workloads that can share siblings.
- Fix task->state access anti-patterns that may result in missed
wakeups and rename it to ->__state in the process to catch new
abuses.
- Load-balancing changes:
- Tweak newidle_balance for fair-sched, to improve 'memcache'-like
workloads.
- "Age" (decay) average idle time, to better track & improve
workloads such as 'tbench'.
- Fix & improve energy-aware (EAS) balancing logic & metrics.
- Fix & improve the uclamp metrics.
- Fix task migration (taskset) corner case on !CONFIG_CPUSET.
- Fix RT and deadline utilization tracking across policy changes
- Introduce a "burstable" CFS controller via cgroups, which allows
bursty CPU-bound workloads to borrow a bit against their future
quota to improve overall latencies & batching. Can be tweaked via
/sys/fs/cgroup/cpu/<X>/cpu.cfs_burst_us.
- Rework assymetric topology/capacity detection & handling.
- Scheduler statistics & tooling:
- Disable delayacct by default, but add a sysctl to enable it at
runtime if tooling needs it. Use static keys and other
optimizations to make it more palatable.
- Use sched_clock() in delayacct, instead of ktime_get_ns().
- Misc cleanups and fixes.
* tag 'sched-core-2021-06-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (72 commits)
sched/doc: Update the CPU capacity asymmetry bits
sched/topology: Rework CPU capacity asymmetry detection
sched/core: Introduce SD_ASYM_CPUCAPACITY_FULL sched_domain flag
psi: Fix race between psi_trigger_create/destroy
sched/fair: Introduce the burstable CFS controller
sched/uclamp: Fix uclamp_tg_restrict()
sched/rt: Fix Deadline utilization tracking during policy change
sched/rt: Fix RT utilization tracking during policy change
sched: Change task_struct::state
sched,arch: Remove unused TASK_STATE offsets
sched,timer: Use __set_current_state()
sched: Add get_current_state()
sched,perf,kvm: Fix preemption condition
sched: Introduce task_is_running()
sched: Unbreak wakeups
sched/fair: Age the average idle time
sched/cpufreq: Consider reduced CPU capacity in energy calculation
sched/fair: Take thermal pressure into account while estimating energy
thermal/cpufreq_cooling: Update offline CPUs per-cpu thermal_pressure
sched/fair: Return early from update_tg_cfs_load() if delta == 0
...
- Core locking & atomics:
- Convert all architectures to ARCH_ATOMIC: move every
architecture to ARCH_ATOMIC, then get rid of ARCH_ATOMIC
and all the transitory facilities and #ifdefs.
Much reduction in complexity from that series:
63 files changed, 756 insertions(+), 4094 deletions(-)
- Self-test enhancements
- Futexes:
- Add the new FUTEX_LOCK_PI2 ABI, which is a variant that
doesn't set FLAGS_CLOCKRT (.e. uses CLOCK_MONOTONIC).
[ The temptation to repurpose FUTEX_LOCK_PI's implicit
setting of FLAGS_CLOCKRT & invert the flag's meaning
to avoid having to introduce a new variant was
resisted successfully. ]
- Enhance futex self-tests
- Lockdep:
- Fix dependency path printouts
- Optimize trace saving
- Broaden & fix wait-context checks
- Misc cleanups and fixes.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'locking-core-2021-06-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Ingo Molnar:
- Core locking & atomics:
- Convert all architectures to ARCH_ATOMIC: move every architecture
to ARCH_ATOMIC, then get rid of ARCH_ATOMIC and all the
transitory facilities and #ifdefs.
Much reduction in complexity from that series:
63 files changed, 756 insertions(+), 4094 deletions(-)
- Self-test enhancements
- Futexes:
- Add the new FUTEX_LOCK_PI2 ABI, which is a variant that doesn't
set FLAGS_CLOCKRT (.e. uses CLOCK_MONOTONIC).
[ The temptation to repurpose FUTEX_LOCK_PI's implicit setting of
FLAGS_CLOCKRT & invert the flag's meaning to avoid having to
introduce a new variant was resisted successfully. ]
- Enhance futex self-tests
- Lockdep:
- Fix dependency path printouts
- Optimize trace saving
- Broaden & fix wait-context checks
- Misc cleanups and fixes.
* tag 'locking-core-2021-06-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (52 commits)
locking/lockdep: Correct the description error for check_redundant()
futex: Provide FUTEX_LOCK_PI2 to support clock selection
futex: Prepare futex_lock_pi() for runtime clock selection
lockdep/selftest: Remove wait-type RCU_CALLBACK tests
lockdep/selftests: Fix selftests vs PROVE_RAW_LOCK_NESTING
lockdep: Fix wait-type for empty stack
locking/selftests: Add a selftest for check_irq_usage()
lockding/lockdep: Avoid to find wrong lock dep path in check_irq_usage()
locking/lockdep: Remove the unnecessary trace saving
locking/lockdep: Fix the dep path printing for backwards BFS
selftests: futex: Add futex compare requeue test
selftests: futex: Add futex wait test
seqlock: Remove trailing semicolon in macros
locking/lockdep: Reduce LOCKDEP dependency list
locking/lockdep,doc: Improve readability of the block matrix
locking/atomics: atomic-instrumented: simplify ifdeffery
locking/atomic: delete !ARCH_ATOMIC remnants
locking/atomic: xtensa: move to ARCH_ATOMIC
locking/atomic: sparc: move to ARCH_ATOMIC
locking/atomic: sh: move to ARCH_ATOMIC
...
If there is no matched result, check_redundant() will return BFS_RNOMATCH.
Signed-off-by: Xiongwei Song <sxwjean@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lkml.kernel.org/r/20210618130230.123249-1-sxwjean@me.com
Even the very first lock can violate the wait-context check, consider
the various IRQ contexts.
Fixes: de8f5e4f2d ("lockdep: Introduce wait-type checks")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Joerg Roedel <jroedel@suse.de>
Link: https://lore.kernel.org/r/20210617190313.256987481@infradead.org
In the step #3 of check_irq_usage(), we seach backwards to find a lock
whose usage conflicts the usage of @target_entry1 on safe/unsafe.
However, we should only keep the irq-unsafe usage of @target_entry1 into
consideration, because it could be a case where a lock is hardirq-unsafe
but soft-safe, and in check_irq_usage() we find it because its
hardirq-unsafe could result into a hardirq-safe-unsafe deadlock, but
currently since we don't filter out the other usage bits, so we may find
a lock dependency path softirq-unsafe -> softirq-safe, which in fact
doesn't cause a deadlock. And this may cause misleading lockdep splats.
Fix this by only keeping LOCKF_ENABLED_IRQ_ALL bits when we try the
backwards search.
Reported-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210618170110.3699115-4-boqun.feng@gmail.com
In print_bad_irq_dependency(), save_trace() is called to set the ->trace
for @prev_root as the current call trace, however @prev_root corresponds
to the the held lock, which may not be acquired in current call trace,
therefore it's wrong to use save_trace() to set ->trace of @prev_root.
Moreover, with our adjustment of printing backwards dependency path, the
->trace of @prev_root is unncessary, so remove it.
Reported-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210618170110.3699115-3-boqun.feng@gmail.com
We use the same code to print backwards lock dependency path as the
forwards lock dependency path, and this could result into incorrect
printing because for a backwards lock_list ->trace is not the call trace
where the lock of ->class is acquired.
Fix this by introducing a separate function on printing the backwards
dependency path. Also add a few comments about the printing while we are
at it.
Reported-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210618170110.3699115-2-boqun.feng@gmail.com
Change the type and name of task_struct::state. Drop the volatile and
shrink it to an 'unsigned int'. Rename it in order to find all uses
such that we can use READ_ONCE/WRITE_ONCE as appropriate.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20210611082838.550736351@infradead.org
Replace a bunch of 'p->state == TASK_RUNNING' with a new helper:
task_is_running(p).
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20210611082838.222401495@infradead.org
When a interruptible mutex locker is interrupted by a signal
without acquiring this lock and removed from the wait queue.
if the mutex isn't contended enough to have a waiter
put into the wait queue again, the setting of the WAITER
bit will force mutex locker to go into the slowpath to
acquire the lock every time, so if the wait queue is empty,
the WAITER bit need to be clear.
Fixes: 040a0a3710 ("mutex: Add support for wound/wait style locks")
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Zqiang <qiang.zhang@windriver.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210517034005.30828-1-qiang.zhang@windriver.com
The reason that lockdep_rcu_suspicious() prints the value of debug_locks
is because a value of zero indicates a likely false positive. This can
work, but is a bit obtuse. This commit therefore explicitly calls out
the possibility of a false positive.
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Make the code more readable by replacing the atomic_cmpxchg_acquire()
by an equivalent atomic_try_cmpxchg_acquire() and change atomic_add()
to atomic_or().
For architectures that use qrwlock, I do not find one that has an
atomic_add() defined but not an atomic_or(). I guess it should be fine
by changing atomic_add() to atomic_or().
Note that the previous use of atomic_add() isn't wrong as only one
writer that is the wait_lock owner can set the waiting flag and the
flag will be cleared later on when acquiring the write lock.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lkml.kernel.org/r/20210426185017.19815-1-longman@redhat.com
- rtmutex cleanup & spring cleaning pass that removes ~400 lines of code
- Futex simplifications & cleanups
- Add debugging to the CSD code, to help track down a tenacious race (or hw problem)
- Add lockdep_assert_not_held(), to allow code to require a lock to not be held,
and propagate this into the ath10k driver
- Misc LKMM documentation updates
- Misc KCSAN updates: cleanups & documentation updates
- Misc fixes and cleanups
- Fix locktorture bugs with ww_mutexes
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'locking-core-2021-04-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Ingo Molnar:
- rtmutex cleanup & spring cleaning pass that removes ~400 lines of
code
- Futex simplifications & cleanups
- Add debugging to the CSD code, to help track down a tenacious race
(or hw problem)
- Add lockdep_assert_not_held(), to allow code to require a lock to not
be held, and propagate this into the ath10k driver
- Misc LKMM documentation updates
- Misc KCSAN updates: cleanups & documentation updates
- Misc fixes and cleanups
- Fix locktorture bugs with ww_mutexes
* tag 'locking-core-2021-04-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (44 commits)
kcsan: Fix printk format string
static_call: Relax static_call_update() function argument type
static_call: Fix unused variable warn w/o MODULE
locking/rtmutex: Clean up signal handling in __rt_mutex_slowlock()
locking/rtmutex: Restrict the trylock WARN_ON() to debug
locking/rtmutex: Fix misleading comment in rt_mutex_postunlock()
locking/rtmutex: Consolidate the fast/slowpath invocation
locking/rtmutex: Make text section and inlining consistent
locking/rtmutex: Move debug functions as inlines into common header
locking/rtmutex: Decrapify __rt_mutex_init()
locking/rtmutex: Remove pointless CONFIG_RT_MUTEXES=n stubs
locking/rtmutex: Inline chainwalk depth check
locking/rtmutex: Move rt_mutex_debug_task_free() to rtmutex.c
locking/rtmutex: Remove empty and unused debug stubs
locking/rtmutex: Consolidate rt_mutex_init()
locking/rtmutex: Remove output from deadlock detector
locking/rtmutex: Remove rtmutex deadlock tester leftovers
locking/rtmutex: Remove rt_mutex_timed_lock()
MAINTAINERS: Add myself as futex reviewer
locking/mutex: Remove repeated declaration
...
Peter Zijlstra asked us to find bad annotation that blows up the lockdep
storage [1][2][3] but we could not find such annotation [4][5], and
Peter cannot give us feedback any more [6]. Since we tested this patch
on linux-next.git without problems, and keeping this problem unresolved
discourages kernel testing which is more painful, I'm sending this patch
without forever waiting for response from Peter.
[1] https://lkml.kernel.org/r/20200916115057.GO2674@hirez.programming.kicks-ass.net
[2] https://lkml.kernel.org/r/20201118142357.GW3121392@hirez.programming.kicks-ass.net
[3] https://lkml.kernel.org/r/20201118151038.GX3121392@hirez.programming.kicks-ass.net
[4] https://lkml.kernel.org/r/CACT4Y+asqRbjaN9ras=P5DcxKgzsnV0fvV0tYb2VkT+P00pFvQ@mail.gmail.com
[5] https://lkml.kernel.org/r/4b89985e-99f9-18bc-0bf1-c883127dc70c@i-love.sakura.ne.jp
[6] https://lkml.kernel.org/r/CACT4Y+YnHFV1p5mbhby2nyOaNTy8c_yoVk86z5avo14KWs0s1A@mail.gmail.com
kernel/locking/lockdep.c | 2 -
kernel/locking/lockdep_internals.h | 8 +++----
lib/Kconfig.debug | 40 +++++++++++++++++++++++++++++++++++++
3 files changed, 45 insertions(+), 5 deletions(-)
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Merge tag 'tomoyo-pr-20210426' of git://git.osdn.net/gitroot/tomoyo/tomoyo-test1
Pull lockdep capacity limit updates from Tetsuo Handa:
"syzbot is occasionally reporting that fuzz testing is terminated due
to hitting upper limits lockdep can track.
Analysis via /proc/lockdep* did not show any obvious culprits, allow
tuning tracing capacity constants"
* tag 'tomoyo-pr-20210426' of git://git.osdn.net/gitroot/tomoyo/tomoyo-test1:
lockdep: Allow tuning tracing capacity constants.
While this code is executed with the wait_lock held, a reader can
acquire the lock without holding wait_lock. The writer side loops
checking the value with the atomic_cond_read_acquire(), but only truly
acquires the lock when the compare-and-exchange is completed
successfully which isn’t ordered. This exposes the window between the
acquire and the cmpxchg to an A-B-A problem which allows reads
following the lock acquisition to observe values speculatively before
the write lock is truly acquired.
We've seen a problem in epoll where the reader does a xchg while
holding the read lock, but the writer can see a value change out from
under it.
Writer | Reader
--------------------------------------------------------------------------------
ep_scan_ready_list() |
|- write_lock_irq() |
|- queued_write_lock_slowpath() |
|- atomic_cond_read_acquire() |
| read_lock_irqsave(&ep->lock, flags);
--> (observes value before unlock) | chain_epi_lockless()
| | epi->next = xchg(&ep->ovflist, epi);
| | read_unlock_irqrestore(&ep->lock, flags);
| |
| atomic_cmpxchg_relaxed() |
|-- READ_ONCE(ep->ovflist); |
A core can order the read of the ovflist ahead of the
atomic_cmpxchg_relaxed(). Switching the cmpxchg to use acquire
semantics addresses this issue at which point the atomic_cond_read can
be switched to use relaxed semantics.
Fixes: b519b56e37 ("locking/qrwlock: Use atomic_cond_read_acquire() when spinning in qrwlock")
Signed-off-by: Ali Saidi <alisaidi@amazon.com>
[peterz: use try_cmpxchg()]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Steve Capper <steve.capper@arm.com>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
Tested-by: Steve Capper <steve.capper@arm.com>
ambiguous/confusing kernel log message.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'locking-urgent-2021-04-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking fixlets from Ingo Molnar:
"Two minor fixes: one for a Clang warning, the other improves an
ambiguous/confusing kernel log message"
* tag 'locking-urgent-2021-04-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
lockdep: Address clang -Wformat warning printing for %hd
lockdep: Add a missing initialization hint to the "INFO: Trying to register non-static key" message
The signal handling in __rt_mutex_slowlock() is open coded.
Use signal_pending_state() instead.
Aside of the cleanup this also prepares for the RT lock substituions which
require support for TASK_KILLABLE.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210326153944.533811987@linutronix.de
The warning as written is expensive and not really required for a
production kernel. Make it depend on rt mutex debugging and use !in_task()
for the condition which generates far better code and gives the same
answer.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210326153944.436565064@linutronix.de
Preemption is disabled in mark_wakeup_next_waiter(,) not in
rt_mutex_slowunlock().
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210326153944.341734608@linutronix.de
The indirection via a function pointer (which is at least optimized into a
tail call by the compiler) is making the code hard to read.
Clean it up and move the futex related trylock functions down to the futex
section.
Move the wake_q wakeup into rt_mutex_slowunlock(). No point in handing it
to the caller. The futex code uses a different function.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210326153944.247927548@linutronix.de
rtmutex is half __sched and the other half is not. If the compiler decides
to not inline larger static functions then part of the code ends up in the
regular text section.
There are also quite some performance related small helpers which are
either static or plain inline. Force inline those which make sense and mark
the rest __sched.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210326153944.152977820@linutronix.de
There is no value in having two header files providing just empty stubs and
a C file which implements trivial debug functions which can just be inlined.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210326153944.052454464@linutronix.de
The conditional debug handling is just another layer of obfuscation. Split
the function so rt_mutex_init_proxy_locked() can invoke the inner init and
__rt_mutex_init() gets the full treatment.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210326153943.955697588@linutronix.de
None of these functions are used when CONFIG_RT_MUTEXES=n.
Remove the gunk. Remove pointless comments and clean up the coding style
mess while at it.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210326153943.863379182@linutronix.de
There is no point for this wrapper at all.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210326153943.754254046@linutronix.de
No users or useless and therefore just ballast.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210326153943.549192485@linutronix.de
The rtmutex specific deadlock detector predates lockdep coverage of rtmutex
and since commit f5694788ad ("rt_mutex: Add lockdep annotations") it
contains a lot of redundant functionality:
- lockdep will detect an potential deadlock before rtmutex-debug
has a chance to do so
- the deadlock debugging is restricted to rtmutexes which are not
associated to futexes and have an active waiter, which is covered by
lockdep already
Remove the redundant functionality and move actual deadlock WARN() into the
deadlock code path. The latter needs a seperate cleanup.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210326153943.320398604@linutronix.de
The following debug members of 'struct rtmutex' are unused:
- save_state: No users
- file,line: Printed if ::name is NULL. This is only used for non-futex
locks so ::name is never NULL
- magic: Assigned to NULL by rt_mutex_destroy(), no further usage
Remove them along with unused inline and macro leftovers related to
the long gone deadlock tester.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210326153943.195064296@linutronix.de
rt_mutex_timed_lock() has no callers since:
c051b21f71 ("rtmutex: Confine deadlock logic to futex")
Remove it.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210326153943.061103415@linutronix.de
Clang doesn't like format strings that truncate a 32-bit
value to something shorter:
kernel/locking/lockdep.c:709:4: error: format specifies type 'short' but the argument has type 'int' [-Werror,-Wformat]
In this case, the warning is a slightly questionable, as it could realize
that both class->wait_type_outer and class->wait_type_inner are in fact
8-bit struct members, even though the result of the ?: operator becomes an
'int'.
However, there is really no point in printing the number as a 16-bit
'short' rather than either an 8-bit or 32-bit number, so just change
it to a normal %d.
Fixes: de8f5e4f2d ("lockdep: Introduce wait-type checks")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210322115531.3987555-1-arnd@kernel.org
Since this message is printed when dynamically allocated spinlocks (e.g.
kzalloc()) are used without initialization (e.g. spin_lock_init()),
suggest to developers to check whether initialization functions for objects
were called, before making developers wonder what annotation is missing.
[ mingo: Minor tweaks to the message. ]
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210321064913.4619-1-penguin-kernel@I-love.SAKURA.ne.jp
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The ww_acquire_ctx structure for ww_mutex needs to persist for a complete
lock/unlock cycle. In the ww_mutex test in locktorture, however, both
ww_acquire_init() and ww_acquire_fini() are called within the lock
function only. This causes a lockdep splat of "WARNING: Nested lock
was not taken" when lockdep is enabled in the kernel.
To fix this problem, we need to move the ww_acquire_fini() after
the ww_mutex_unlock() in torture_ww_mutex_unlock(). This is done by
allocating a global array of ww_acquire_ctx structures. Each locking
thread is associated with its own ww_acquire_ctx via the unique thread
id it has so that both the lock and unlock functions can access the
same ww_acquire_ctx structure.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210318172814.4400-6-longman@redhat.com
To allow the lock and unlock functions in locktorture to access
per-thread information, we need to pass some hint on how to locate
those information. One way to do this is to pass in a unique thread
id which can then be used to access a global array for thread specific
information.
Change the lock and unlock method to add a thread id parameter which
can be determined by the offset of the lwsp/lrsp pointer from the global
lwsa/lrsa array.
There is no other functional change in this patch.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210318172814.4400-5-longman@redhat.com
In order to avoid false positive circular locking lockdep splat
when runnng the ww_mutex torture test, we need to make sure that
the ww_mutexes have the same lock class as the acquire_ctx. This
means the ww_mutexes must have the same lockdep key as the
acquire_ctx. Unfortunately the current DEFINE_WW_MUTEX() macro fails
to do that. As a result, we add an init method for the ww_mutex test
to do explicit ww_mutex_init()'s of the ww_mutexes to avoid the false
positive warning.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210318172814.4400-3-longman@redhat.com
The use_ww_ctx flag is passed to mutex_optimistic_spin(), but the
function doesn't use it. The frequent use of the (use_ww_ctx && ww_ctx)
combination is repetitive.
In fact, ww_ctx should not be used at all if !use_ww_ctx. Simplify
ww_mutex code by dropping use_ww_ctx from mutex_optimistic_spin() an
clear ww_ctx if !use_ww_ctx. In this way, we can replace (use_ww_ctx &&
ww_ctx) by just (ww_ctx).
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Link: https://lore.kernel.org/r/20210316153119.13802-2-longman@redhat.com
Update wake_futex_pi() and kill the call altogether. This is possible because:
(i) The case of fixup_owner() in which the pi_mutex was stolen from the
signaled enqueued top-waiter which fails to trylock and doesn't see a
current owner of the rtmutex but needs to acknowledge an non-enqueued
higher priority waiter, which is the other alternative. This used to be
handled by rt_mutex_next_owner(), which guaranteed fixup_pi_state_owner('newowner')
never to be nil. Nowadays the logic is handled by an EAGAIN loop, without
the need of rt_mutex_next_owner(). Specifically:
c1e2f0eaf0 (futex: Avoid violating the 10th rule of futex)
9f5d1c336a (futex: Handle transient "ownerless" rtmutex state correctly)
(ii) rt_mutex_next_owner() and rt_mutex_top_waiter() are semantically
equivalent, as of:
c28d62cf52 (locking/rtmutex: Handle non enqueued waiters gracefully in remove_waiter())
So instead of keeping the call around, just use the good ole rt_mutex_top_waiter().
No change in semantics.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210226175029.50335-1-dave@stgolabs.net
Adds defines for lock state returns from lock_is_held_type() based on
Johannes Berg's suggestions as it make it easier to read and maintain
the lock states. These are defines and a enum to avoid changes to
lock_is_held_type() and lockdep_is_held() return types.
Updates to lock_is_held_type() and __lock_is_held() to use the new
defines.
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/linux-wireless/871rdmu9z9.fsf@codeaurora.org/
Some kernel functions must be called without holding a specific lock.
Add lockdep_assert_not_held() to be used in these functions to detect
incorrect calls while holding a lock.
lockdep_assert_not_held() provides the opposite functionality of
lockdep_assert_held() which is used to assert calls that require
holding a specific lock.
Incorporates suggestions from Peter Zijlstra to avoid misfires when
lockdep_off() is employed.
The need for lockdep_assert_not_held() came up in a discussion on
ath10k patch. ath10k_drain_tx() and i915_vma_pin_ww() are examples
of functions that can use lockdep_assert_not_held().
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/linux-wireless/871rdmu9z9.fsf@codeaurora.org/
Drop repeated words in kernel/events/.
{if, the, that, with, time}
Drop repeated words in kernel/locking/.
{it, no, the}
Drop repeated words in kernel/sched/.
{in, not}
Link: https://lkml.kernel.org/r/20210127023412.26292-1-rdunlap@infradead.org
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Will Deacon <will@kernel.org> [kernel/locking/]
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
- Support for userspace to emulate Xen hypercalls
- Raise the maximum number of user memslots
- Scalability improvements for the new MMU. Instead of the complex
"fast page fault" logic that is used in mmu.c, tdp_mmu.c uses an
rwlock so that page faults are concurrent, but the code that can run
against page faults is limited. Right now only page faults take the
lock for reading; in the future this will be extended to some
cases of page table destruction. I hope to switch the default MMU
around 5.12-rc3 (some testing was delayed due to Chinese New Year).
- Cleanups for MAXPHYADDR checks
- Use static calls for vendor-specific callbacks
- On AMD, use VMLOAD/VMSAVE to save and restore host state
- Stop using deprecated jump label APIs
- Workaround for AMD erratum that made nested virtualization unreliable
- Support for LBR emulation in the guest
- Support for communicating bus lock vmexits to userspace
- Add support for SEV attestation command
- Miscellaneous cleanups
PPC:
- Support for second data watchpoint on POWER10
- Remove some complex workarounds for buggy early versions of POWER9
- Guest entry/exit fixes
ARM64
- Make the nVHE EL2 object relocatable
- Cleanups for concurrent translation faults hitting the same page
- Support for the standard TRNG hypervisor call
- A bunch of small PMU/Debug fixes
- Simplification of the early init hypercall handling
Non-KVM changes (with acks):
- Detection of contended rwlocks (implemented only for qrwlocks,
because KVM only needs it for x86)
- Allow __DISABLE_EXPORTS from assembly code
- Provide a saner follow_pfn replacements for modules
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Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm
Pull KVM updates from Paolo Bonzini:
"x86:
- Support for userspace to emulate Xen hypercalls
- Raise the maximum number of user memslots
- Scalability improvements for the new MMU.
Instead of the complex "fast page fault" logic that is used in
mmu.c, tdp_mmu.c uses an rwlock so that page faults are concurrent,
but the code that can run against page faults is limited. Right now
only page faults take the lock for reading; in the future this will
be extended to some cases of page table destruction. I hope to
switch the default MMU around 5.12-rc3 (some testing was delayed
due to Chinese New Year).
- Cleanups for MAXPHYADDR checks
- Use static calls for vendor-specific callbacks
- On AMD, use VMLOAD/VMSAVE to save and restore host state
- Stop using deprecated jump label APIs
- Workaround for AMD erratum that made nested virtualization
unreliable
- Support for LBR emulation in the guest
- Support for communicating bus lock vmexits to userspace
- Add support for SEV attestation command
- Miscellaneous cleanups
PPC:
- Support for second data watchpoint on POWER10
- Remove some complex workarounds for buggy early versions of POWER9
- Guest entry/exit fixes
ARM64:
- Make the nVHE EL2 object relocatable
- Cleanups for concurrent translation faults hitting the same page
- Support for the standard TRNG hypervisor call
- A bunch of small PMU/Debug fixes
- Simplification of the early init hypercall handling
Non-KVM changes (with acks):
- Detection of contended rwlocks (implemented only for qrwlocks,
because KVM only needs it for x86)
- Allow __DISABLE_EXPORTS from assembly code
- Provide a saner follow_pfn replacements for modules"
* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (192 commits)
KVM: x86/xen: Explicitly pad struct compat_vcpu_info to 64 bytes
KVM: selftests: Don't bother mapping GVA for Xen shinfo test
KVM: selftests: Fix hex vs. decimal snafu in Xen test
KVM: selftests: Fix size of memslots created by Xen tests
KVM: selftests: Ignore recently added Xen tests' build output
KVM: selftests: Add missing header file needed by xAPIC IPI tests
KVM: selftests: Add operand to vmsave/vmload/vmrun in svm.c
KVM: SVM: Make symbol 'svm_gp_erratum_intercept' static
locking/arch: Move qrwlock.h include after qspinlock.h
KVM: PPC: Book3S HV: Fix host radix SLB optimisation with hash guests
KVM: PPC: Book3S HV: Ensure radix guest has no SLB entries
KVM: PPC: Don't always report hash MMU capability for P9 < DD2.2
KVM: PPC: Book3S HV: Save and restore FSCR in the P9 path
KVM: PPC: remove unneeded semicolon
KVM: PPC: Book3S HV: Use POWER9 SLBIA IH=6 variant to clear SLB
KVM: PPC: Book3S HV: No need to clear radix host SLB before loading HPT guest
KVM: PPC: Book3S HV: Fix radix guest SLB side channel
KVM: PPC: Book3S HV: Remove support for running HPT guest on RPT host without mixed mode support
KVM: PPC: Book3S HV: Introduce new capability for 2nd DAWR
KVM: PPC: Book3S HV: Add infrastructure to support 2nd DAWR
...
[ NOTE: unfortunately this tree had to be freshly rebased today,
it's a same-content tree of 82891be90f3c (-next published)
merged with v5.11.
The main reason for the rebase was an authorship misattribution
problem with a new commit, which we noticed in the last minute,
and which we didn't want to be merged upstream. The offending
commit was deep in the tree, and dependent commits had to be
rebased as well. ]
- Core scheduler updates:
- Add CONFIG_PREEMPT_DYNAMIC: this in its current form adds the
preempt=none/voluntary/full boot options (default: full),
to allow distros to build a PREEMPT kernel but fall back to
close to PREEMPT_VOLUNTARY (or PREEMPT_NONE) runtime scheduling
behavior via a boot time selection.
There's also the /debug/sched_debug switch to do this runtime.
This feature is implemented via runtime patching (a new variant of static calls).
The scope of the runtime patching can be best reviewed by looking
at the sched_dynamic_update() function in kernel/sched/core.c.
( Note that the dynamic none/voluntary mode isn't 100% identical,
for example preempt-RCU is available in all cases, plus the
preempt count is maintained in all models, which has runtime
overhead even with the code patching. )
The PREEMPT_VOLUNTARY/PREEMPT_NONE models, used by the vast majority
of distributions, are supposed to be unaffected.
- Fix ignored rescheduling after rcu_eqs_enter(). This is a bug that
was found via rcutorture triggering a hang. The bug is that
rcu_idle_enter() may wake up a NOCB kthread, but this happens after
the last generic need_resched() check. Some cpuidle drivers fix it
by chance but many others don't.
In true 2020 fashion the original bug fix has grown into a 5-patch
scheduler/RCU fix series plus another 16 RCU patches to address
the underlying issue of missed preemption events. These are the
initial fixes that should fix current incarnations of the bug.
- Clean up rbtree usage in the scheduler, by providing & using the following
consistent set of rbtree APIs:
partial-order; less() based:
- rb_add(): add a new entry to the rbtree
- rb_add_cached(): like rb_add(), but for a rb_root_cached
total-order; cmp() based:
- rb_find(): find an entry in an rbtree
- rb_find_add(): find an entry, and add if not found
- rb_find_first(): find the first (leftmost) matching entry
- rb_next_match(): continue from rb_find_first()
- rb_for_each(): iterate a sub-tree using the previous two
- Improve the SMP/NUMA load-balancer: scan for an idle sibling in a single pass.
This is a 4-commit series where each commit improves one aspect of the idle
sibling scan logic.
- Improve the cpufreq cooling driver by getting the effective CPU utilization
metrics from the scheduler
- Improve the fair scheduler's active load-balancing logic by reducing the number
of active LB attempts & lengthen the load-balancing interval. This improves
stress-ng mmapfork performance.
- Fix CFS's estimated utilization (util_est) calculation bug that can result in
too high utilization values
- Misc updates & fixes:
- Fix the HRTICK reprogramming & optimization feature
- Fix SCHED_SOFTIRQ raising race & warning in the CPU offlining code
- Reduce dl_add_task_root_domain() overhead
- Fix uprobes refcount bug
- Process pending softirqs in flush_smp_call_function_from_idle()
- Clean up task priority related defines, remove *USER_*PRIO and
USER_PRIO()
- Simplify the sched_init_numa() deduplication sort
- Documentation updates
- Fix EAS bug in update_misfit_status(), which degraded the quality
of energy-balancing
- Smaller cleanups
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'sched-core-2021-02-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler updates from Ingo Molnar:
"Core scheduler updates:
- Add CONFIG_PREEMPT_DYNAMIC: this in its current form adds the
preempt=none/voluntary/full boot options (default: full), to allow
distros to build a PREEMPT kernel but fall back to close to
PREEMPT_VOLUNTARY (or PREEMPT_NONE) runtime scheduling behavior via
a boot time selection.
There's also the /debug/sched_debug switch to do this runtime.
This feature is implemented via runtime patching (a new variant of
static calls).
The scope of the runtime patching can be best reviewed by looking
at the sched_dynamic_update() function in kernel/sched/core.c.
( Note that the dynamic none/voluntary mode isn't 100% identical,
for example preempt-RCU is available in all cases, plus the
preempt count is maintained in all models, which has runtime
overhead even with the code patching. )
The PREEMPT_VOLUNTARY/PREEMPT_NONE models, used by the vast
majority of distributions, are supposed to be unaffected.
- Fix ignored rescheduling after rcu_eqs_enter(). This is a bug that
was found via rcutorture triggering a hang. The bug is that
rcu_idle_enter() may wake up a NOCB kthread, but this happens after
the last generic need_resched() check. Some cpuidle drivers fix it
by chance but many others don't.
In true 2020 fashion the original bug fix has grown into a 5-patch
scheduler/RCU fix series plus another 16 RCU patches to address the
underlying issue of missed preemption events. These are the initial
fixes that should fix current incarnations of the bug.
- Clean up rbtree usage in the scheduler, by providing & using the
following consistent set of rbtree APIs:
partial-order; less() based:
- rb_add(): add a new entry to the rbtree
- rb_add_cached(): like rb_add(), but for a rb_root_cached
total-order; cmp() based:
- rb_find(): find an entry in an rbtree
- rb_find_add(): find an entry, and add if not found
- rb_find_first(): find the first (leftmost) matching entry
- rb_next_match(): continue from rb_find_first()
- rb_for_each(): iterate a sub-tree using the previous two
- Improve the SMP/NUMA load-balancer: scan for an idle sibling in a
single pass. This is a 4-commit series where each commit improves
one aspect of the idle sibling scan logic.
- Improve the cpufreq cooling driver by getting the effective CPU
utilization metrics from the scheduler
- Improve the fair scheduler's active load-balancing logic by
reducing the number of active LB attempts & lengthen the
load-balancing interval. This improves stress-ng mmapfork
performance.
- Fix CFS's estimated utilization (util_est) calculation bug that can
result in too high utilization values
Misc updates & fixes:
- Fix the HRTICK reprogramming & optimization feature
- Fix SCHED_SOFTIRQ raising race & warning in the CPU offlining code
- Reduce dl_add_task_root_domain() overhead
- Fix uprobes refcount bug
- Process pending softirqs in flush_smp_call_function_from_idle()
- Clean up task priority related defines, remove *USER_*PRIO and
USER_PRIO()
- Simplify the sched_init_numa() deduplication sort
- Documentation updates
- Fix EAS bug in update_misfit_status(), which degraded the quality
of energy-balancing
- Smaller cleanups"
* tag 'sched-core-2021-02-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (51 commits)
sched,x86: Allow !PREEMPT_DYNAMIC
entry/kvm: Explicitly flush pending rcuog wakeup before last rescheduling point
entry: Explicitly flush pending rcuog wakeup before last rescheduling point
rcu/nocb: Trigger self-IPI on late deferred wake up before user resume
rcu/nocb: Perform deferred wake up before last idle's need_resched() check
rcu: Pull deferred rcuog wake up to rcu_eqs_enter() callers
sched/features: Distinguish between NORMAL and DEADLINE hrtick
sched/features: Fix hrtick reprogramming
sched/deadline: Reduce rq lock contention in dl_add_task_root_domain()
uprobes: (Re)add missing get_uprobe() in __find_uprobe()
smp: Process pending softirqs in flush_smp_call_function_from_idle()
sched: Harden PREEMPT_DYNAMIC
static_call: Allow module use without exposing static_call_key
sched: Add /debug/sched_preempt
preempt/dynamic: Support dynamic preempt with preempt= boot option
preempt/dynamic: Provide irqentry_exit_cond_resched() static call
preempt/dynamic: Provide preempt_schedule[_notrace]() static calls
preempt/dynamic: Provide cond_resched() and might_resched() static calls
preempt: Introduce CONFIG_PREEMPT_DYNAMIC
static_call: Provide DEFINE_STATIC_CALL_RET0()
...
Reduce rbtree boiler plate by using the new helpers.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Pull RCU updates from Paul E. McKenney:
- Documentation updates.
- Miscellaneous fixes.
- kfree_rcu() updates: Addition of mem_dump_obj() to provide allocator return
addresses to more easily locate bugs. This has a couple of RCU-related commits,
but is mostly MM. Was pulled in with akpm's agreement.
- Per-callback-batch tracking of numbers of callbacks,
which enables better debugging information and smarter
reactions to large numbers of callbacks.
- The first round of changes to allow CPUs to be runtime switched from and to
callback-offloaded state.
- CONFIG_PREEMPT_RT-related changes.
- RCU CPU stall warning updates.
- Addition of polling grace-period APIs for SRCU.
- Torture-test and torture-test scripting updates, including a "torture everything"
script that runs rcutorture, locktorture, scftorture, rcuscale, and refscale.
Plus does an allmodconfig build.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
include/asm-generic/qrwlock.h was trying to get arch_spin_is_locked via
asm-generic/qspinlock.h. However, this does not work because architectures
might be using queued rwlocks but not queued spinlocks (csky), or because they
might be defining their own queued_* macros before including asm/qspinlock.h.
To fix this, ensure that asm/spinlock.h always includes qrwlock.h after
defining arch_spin_is_locked (either directly for csky, or via
asm/qspinlock.h for other architectures). The only inclusion elsewhere
is in kernel/locking/qrwlock.c. That one is really unnecessary because
the file is only compiled in SMP configurations (config QUEUED_RWLOCKS
depends on SMP) and in that case linux/spinlock.h already includes
asm/qrwlock.h if needed, via asm/spinlock.h.
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Waiman Long <longman@redhat.com>
Fixes: 26128cb6c7 ("locking/rwlocks: Add contention detection for rwlocks")
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Ben Gardon <bgardon@google.com>
[Add arch/sparc and kernel/locking parts per discussion with Waiman. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
There are not users of mutex_trylock_recursive() in tree as of
v5.11-rc7.
Remove it.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210210085248.219210-2-bigeasy@linutronix.de
vmlinux.o: warning: objtool: lock_is_held_type()+0x107: call to warn_bogus_irq_restore() leaves .noinstr.text section
As per the general rule that WARNs are allowed to violate noinstr to
get out, annotate it away.
Fixes: 997acaf6b4 ("lockdep: report broken irq restoration")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Link: https://lkml.kernel.org/r/YCKyYg53mMp4E7YI@hirez.programming.kicks-ass.net
Commit f6f48e1804 ("lockdep: Teach lockdep about "USED" <- "IN-NMI"
inversions") overlooked that print_usage_bug() releases the graph_lock
and called it without the graph lock held.
Fixes: f6f48e1804 ("lockdep: Teach lockdep about "USED" <- "IN-NMI" inversions")
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Link: https://lkml.kernel.org/r/YBfkuyIfB1+VRxXP@hirez.programming.kicks-ass.net
This is a leftover from 7f26482a87 ("locking/percpu-rwsem: Remove the embedded rwsem")
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lkml.kernel.org/r/20210126101721.976027-1-nborisov@suse.com
To fix the following issues:
kernel/locking/rtmutex.c:1612: warning: Function parameter or member
'lock' not described in '__rt_mutex_futex_unlock'
kernel/locking/rtmutex.c:1612: warning: Function parameter or member
'wake_q' not described in '__rt_mutex_futex_unlock'
kernel/locking/rtmutex.c:1675: warning: Function parameter or member
'name' not described in '__rt_mutex_init'
kernel/locking/rtmutex.c:1675: warning: Function parameter or member
'key' not described in '__rt_mutex_init'
[ tglx: Change rt lock to rt_mutex for consistency sake ]
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/1605257895-5536-2-git-send-email-alex.shi@linux.alibaba.com
Nothing uses the argument. Remove it as preparation to use
pi_state_update_owner().
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org
We generally expect local_irq_save() and local_irq_restore() to be
paired and sanely nested, and so local_irq_restore() expects to be
called with irqs disabled. Thus, within local_irq_restore() we only
trace irq flag changes when unmasking irqs.
This means that a sequence such as:
| local_irq_disable();
| local_irq_save(flags);
| local_irq_enable();
| local_irq_restore(flags);
... is liable to break things, as the local_irq_restore() would mask
irqs without tracing this change. Similar problems may exist for
architectures whose arch_irq_restore() function depends on being called
with irqs disabled.
We don't consider such sequences to be a good idea, so let's define
those as forbidden, and add tooling to detect such broken cases.
This patch adds debug code to WARN() when raw_local_irq_restore() is
called with irqs enabled. As raw_local_irq_restore() is expected to pair
with raw_local_irq_save(), it should never be called with irqs enabled.
To avoid the possibility of circular header dependencies between
irqflags.h and bug.h, the warning is handled in a separate C file.
The new code is all conditional on a new CONFIG_DEBUG_IRQFLAGS symbol
which is independent of CONFIG_TRACE_IRQFLAGS. As noted above such cases
will confuse lockdep, so CONFIG_DEBUG_LOCKDEP now selects
CONFIG_DEBUG_IRQFLAGS.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210111153707.10071-1-mark.rutland@arm.com
The purpose of local_lock_t is to abstract: preempt_disable() /
local_bh_disable() / local_irq_disable(). These are the traditional
means of gaining access to per-cpu data, but are fundamentally
non-preemptible.
local_lock_t provides a per-cpu lock, that on !PREEMPT_RT reduces to
no-ops, just like regular spinlocks do on UP.
This gives rise to:
CPU0 CPU1
local_lock(B) spin_lock_irq(A)
<IRQ>
spin_lock(A) local_lock(B)
Where lockdep then figures things will lock up; which would be true if
B were any other kind of lock. However this is a false positive, no
such deadlock actually exists.
For !RT the above local_lock(B) is preempt_disable(), and there's
obviously no deadlock; alternatively, CPU0's B != CPU1's B.
For RT the argument is that since local_lock() nests inside
spin_lock(), it cannot be used in hardirq context, and therefore CPU0
cannot in fact happen. Even though B is a real lock, it is a
preemptible lock and any threaded-irq would simply schedule out and
let the preempted task (which holds B) continue such that the task on
CPU1 can make progress, after which the threaded-irq resumes and can
finish.
This means that we can never form an IRQ inversion on a local_lock
dependency, so terminate the graph walk when looking for IRQ
inversions when we encounter one.
One consequence is that (for LOCKDEP_SMALL) when we look for redundant
dependencies, A -> B is not redundant in the presence of A -> L -> B.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
[peterz: Changelog]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
In preparation for adding an TRACE_IRQFLAGS dependent skip function to
check_redundant(), move it below the TRACE_IRQFLAGS #ifdef.
While there, provide a stub function to reduce #ifdef usage.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Some __bfs() walks will have additional iteration constraints (beyond
the path being strong). Provide an additional function to allow
terminating graph walks.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
The local_lock_t's are special, because they cannot form IRQ
inversions, make sure we can tell them apart from the rest of the
locks.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
When the compiler doesn't feel like inlining, it causes a noinstr
fail:
vmlinux.o: warning: objtool: lock_is_held_type()+0xb: call to lockdep_enabled() leaves .noinstr.text section
Fixes: 4d004099a6 ("lockdep: Fix lockdep recursion")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210106144017.592595176@infradead.org
- A few extensions to the rwsem API and support for opportunistic
spinning and lock stealing
- lockdep selftest improvements
- Documentation updates
- Cleanups and small fixes all over the place
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Merge tag 'locking-core-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Thomas Gleixner:
"A moderate set of locking updates:
- A few extensions to the rwsem API and support for opportunistic
spinning and lock stealing
- lockdep selftest improvements
- Documentation updates
- Cleanups and small fixes all over the place"
* tag 'locking-core-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (21 commits)
seqlock: kernel-doc: Specify when preemption is automatically altered
seqlock: Prefix internal seqcount_t-only macros with a "do_"
Documentation: seqlock: s/LOCKTYPE/LOCKNAME/g
locking/rwsem: Remove reader optimistic spinning
locking/rwsem: Enable reader optimistic lock stealing
locking/rwsem: Prevent potential lock starvation
locking/rwsem: Pass the current atomic count to rwsem_down_read_slowpath()
locking/rwsem: Fold __down_{read,write}*()
locking/rwsem: Introduce rwsem_write_trylock()
locking/rwsem: Better collate rwsem_read_trylock()
rwsem: Implement down_read_interruptible
rwsem: Implement down_read_killable_nested
refcount: Fix a kernel-doc markup
completion: Drop init_completion define
atomic: Update MAINTAINERS
atomic: Delete obsolete documentation
seqlock: Rename __seqprop() users
lockdep/selftest: Add spin_nest_lock test
lockdep/selftests: Fix PROVE_RAW_LOCK_NESTING
seqlock: avoid -Wshadow warnings
...
RCU:
- Avoid cpuinfo-induced IPI pileups and idle-CPU IPIs.
- Lockdep-RCU updates reducing the need for __maybe_unused.
- Tasks-RCU updates.
- Miscellaneous fixes.
- Documentation updates.
- Torture-test updates.
KCSAN:
- updates for selftests, avoiding setting watchpoints on NULL pointers
- fix to watchpoint encoding
LKMM:
- updates for documentation along with some updates to example-code
litmus tests
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Merge tag 'core-rcu-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull RCU updates from Thomas Gleixner:
"RCU, LKMM and KCSAN updates collected by Paul McKenney.
RCU:
- Avoid cpuinfo-induced IPI pileups and idle-CPU IPIs
- Lockdep-RCU updates reducing the need for __maybe_unused
- Tasks-RCU updates
- Miscellaneous fixes
- Documentation updates
- Torture-test updates
KCSAN:
- updates for selftests, avoiding setting watchpoints on NULL pointers
- fix to watchpoint encoding
LKMM:
- updates for documentation along with some updates to example-code
litmus tests"
* tag 'core-rcu-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (72 commits)
srcu: Take early exit on memory-allocation failure
rcu/tree: Defer kvfree_rcu() allocation to a clean context
rcu: Do not report strict GPs for outgoing CPUs
rcu: Fix a typo in rcu_blocking_is_gp() header comment
rcu: Prevent lockdep-RCU splats on lock acquisition/release
rcu/tree: nocb: Avoid raising softirq for offloaded ready-to-execute CBs
rcu,ftrace: Fix ftrace recursion
rcu/tree: Make struct kernel_param_ops definitions const
rcu/tree: Add a warning if CPU being onlined did not report QS already
rcu: Clarify nocb kthreads naming in RCU_NOCB_CPU config
rcu: Fix single-CPU check in rcu_blocking_is_gp()
rcu: Implement rcu_segcblist_is_offloaded() config dependent
list.h: Update comment to explicitly note circular lists
rcu: Panic after fixed number of stalls
x86/smpboot: Move rcu_cpu_starting() earlier
rcu: Allow rcu_irq_enter_check_tick() from NMI
tools/memory-model: Label MP tests' producers and consumers
tools/memory-model: Use "buf" and "flag" for message-passing tests
tools/memory-model: Add types to litmus tests
tools/memory-model: Add a glossary of LKMM terms
...
Reader optimistic spinning is helpful when the reader critical section
is short and there aren't that many readers around. It also improves
the chance that a reader can get the lock as writer optimistic spinning
disproportionally favors writers much more than readers.
Since commit d3681e269f ("locking/rwsem: Wake up almost all readers
in wait queue"), all the waiting readers are woken up so that they can
all get the read lock and run in parallel. When the number of contending
readers is large, allowing reader optimistic spinning will likely cause
reader fragmentation where multiple smaller groups of readers can get
the read lock in a sequential manner separated by writers. That reduces
reader parallelism.
One possible way to address that drawback is to limit the number of
readers (preferably one) that can do optimistic spinning. These readers
act as representatives of all the waiting readers in the wait queue as
they will wake up all those waiting readers once they get the lock.
Alternatively, as reader optimistic lock stealing has already enhanced
fairness to readers, it may be easier to just remove reader optimistic
spinning and simplifying the optimistic spinning code as a result.
Performance measurements (locking throughput kops/s) using a locking
microbenchmark with 50/50 reader/writer distribution and turbo-boost
disabled was done on a 2-socket Cascade Lake system (48-core 96-thread)
to see the impacts of these changes:
1) Vanilla - 5.10-rc3 kernel
2) Before - 5.10-rc3 kernel with previous patches in this series
2) limit-rspin - 5.10-rc3 kernel with limited reader spinning patch
3) no-rspin - 5.10-rc3 kernel with reader spinning disabled
# of threads CS Load Vanilla Before limit-rspin no-rspin
------------ ------- ------- ------ ----------- --------
2 1 5,185 5,662 5,214 5,077
4 1 5,107 4,983 5,188 4,760
8 1 4,782 4,564 4,720 4,628
16 1 4,680 4,053 4,567 3,402
32 1 4,299 1,115 1,118 1,098
64 1 3,218 983 1,001 957
96 1 1,938 944 957 930
2 20 2,008 2,128 2,264 1,665
4 20 1,390 1,033 1,046 1,101
8 20 1,472 1,155 1,098 1,213
16 20 1,332 1,077 1,089 1,122
32 20 967 914 917 980
64 20 787 874 891 858
96 20 730 836 847 844
2 100 372 356 360 355
4 100 492 425 434 392
8 100 533 537 529 538
16 100 548 572 568 598
32 100 499 520 527 537
64 100 466 517 526 512
96 100 406 497 506 509
The column "CS Load" represents the number of pause instructions issued
in the locking critical section. A CS load of 1 is extremely short and
is not likey in real situations. A load of 20 (moderate) and 100 (long)
are more realistic.
It can be seen that the previous patches in this series have reduced
performance in general except in highly contended cases with moderate
or long critical sections that performance improves a bit. This change
is mostly caused by the "Prevent potential lock starvation" patch that
reduce reader optimistic spinning and hence reduce reader fragmentation.
The patch that further limit reader optimistic spinning doesn't seem to
have too much impact on overall performance as shown in the benchmark
data.
The patch that disables reader optimistic spinning shows reduced
performance at lightly loaded cases, but comparable or slightly better
performance on with heavier contention.
This patch just removes reader optimistic spinning for now. As readers
are not going to do optimistic spinning anymore, we don't need to
consider if the OSQ is empty or not when doing lock stealing.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Link: https://lkml.kernel.org/r/20201121041416.12285-6-longman@redhat.com
If the optimistic spinning queue is empty and the rwsem does not have
the handoff or write-lock bits set, it is actually not necessary to
call rwsem_optimistic_spin() to spin on it. Instead, it can steal the
lock directly as its reader bias is in the count already. If it is
the first reader in this state, it will try to wake up other readers
in the wait queue.
With this patch applied, the following were the lock event counts
after rebooting a 2-socket system and a "make -j96" kernel rebuild.
rwsem_opt_rlock=4437
rwsem_rlock=29
rwsem_rlock_steal=19
So lock stealing represents about 0.4% of all the read locks acquired
in the slow path.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Link: https://lkml.kernel.org/r/20201121041416.12285-4-longman@redhat.com
The lock handoff bit is added in commit 4f23dbc1e6 ("locking/rwsem:
Implement lock handoff to prevent lock starvation") to avoid lock
starvation. However, allowing readers to do optimistic spinning does
introduce an unlikely scenario where lock starvation can happen.
The lock handoff bit may only be set when a waiter is being woken up.
In the case of reader unlock, wakeup happens only when the reader count
reaches 0. If there is a continuous stream of incoming readers acquiring
read lock via optimistic spinning, it is possible that the reader count
may never reach 0 and so the handoff bit will never be asserted.
One way to prevent this scenario from happening is to disallow optimistic
spinning if the rwsem is currently owned by readers. If the previous
or current owner is a writer, optimistic spinning will be allowed.
If the previous owner is a reader but the reader count has reached 0
before, a wakeup should have been issued. So the handoff mechanism
will be kicked in to prevent lock starvation. As a result, it should
be OK to do optimistic spinning in this case.
This patch may have some impact on reader performance as it reduces
reader optimistic spinning especially if the lock critical sections
are short the number of contending readers are small.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Link: https://lkml.kernel.org/r/20201121041416.12285-3-longman@redhat.com
The atomic count value right after reader count increment can be useful
to determine the rwsem state at trylock time. So the count value is
passed down to rwsem_down_read_slowpath() to be used when appropriate.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Link: https://lkml.kernel.org/r/20201121041416.12285-2-longman@redhat.com
In preparation for converting exec_update_mutex to a rwsem so that
multiple readers can execute in parallel and not deadlock, add
down_read_interruptible. This is needed for perf_event_open to be
converted (with no semantic changes) from working on a mutex to
wroking on a rwsem.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/87k0tybqfy.fsf@x220.int.ebiederm.org
In preparation for converting exec_update_mutex to a rwsem so that
multiple readers can execute in parallel and not deadlock, add
down_read_killable_nested. This is needed so that kcmp_lock
can be converted from working on a mutexes to working on rw_semaphores.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/87o8jabqh3.fsf@x220.int.ebiederm.org
A warning was hit when running xfstests/generic/068 in a Hyper-V guest:
[...] ------------[ cut here ]------------
[...] DEBUG_LOCKS_WARN_ON(lockdep_hardirqs_enabled())
[...] WARNING: CPU: 2 PID: 1350 at kernel/locking/lockdep.c:5280 check_flags.part.0+0x165/0x170
[...] ...
[...] Workqueue: events pwq_unbound_release_workfn
[...] RIP: 0010:check_flags.part.0+0x165/0x170
[...] ...
[...] Call Trace:
[...] lock_is_held_type+0x72/0x150
[...] ? lock_acquire+0x16e/0x4a0
[...] rcu_read_lock_sched_held+0x3f/0x80
[...] __send_ipi_one+0x14d/0x1b0
[...] hv_send_ipi+0x12/0x30
[...] __pv_queued_spin_unlock_slowpath+0xd1/0x110
[...] __raw_callee_save___pv_queued_spin_unlock_slowpath+0x11/0x20
[...] .slowpath+0x9/0xe
[...] lockdep_unregister_key+0x128/0x180
[...] pwq_unbound_release_workfn+0xbb/0xf0
[...] process_one_work+0x227/0x5c0
[...] worker_thread+0x55/0x3c0
[...] ? process_one_work+0x5c0/0x5c0
[...] kthread+0x153/0x170
[...] ? __kthread_bind_mask+0x60/0x60
[...] ret_from_fork+0x1f/0x30
The cause of the problem is we have call chain lockdep_unregister_key()
-> <irq disabled by raw_local_irq_save()> lockdep_unlock() ->
arch_spin_unlock() -> __pv_queued_spin_unlock_slowpath() -> pv_kick() ->
__send_ipi_one() -> trace_hyperv_send_ipi_one().
Although this particular warning is triggered because Hyper-V has a
trace point in ipi sending, but in general arch_spin_unlock() may call
another function having a trace point in it, so put the arch_spin_lock()
and arch_spin_unlock() after lock_recursion protection to fix this
problem and avoid similiar problems.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20201113110512.1056501-1-boqun.feng@gmail.com
Chris Wilson reported a problem spotted by check_chain_key(): a chain
key got changed in validate_chain() because we modify the ->read in
validate_chain() to skip checks for dependency adding, and ->read is
taken into calculation for chain key since commit f611e8cf98
("lockdep: Take read/write status in consideration when generate
chainkey").
Fix this by avoiding to modify ->read in validate_chain() based on two
facts: a) since we now support recursive read lock detection, there is
no need to skip checks for dependency adding for recursive readers, b)
since we have a), there is only one case left (nest_lock) where we want
to skip checks in validate_chain(), we simply remove the modification
for ->read and rely on the return value of check_deadlock() to skip the
dependency adding.
Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20201102053743.450459-1-boqun.feng@gmail.com
When executing the LOCK06 locktorture scenario featuring percpu-rwsem,
the RCU callback rcu_sync_func() may still be pending after locktorture
module is removed. This can in turn lead to the following Oops:
BUG: unable to handle page fault for address: ffffffffc00eb920
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 6500a067 P4D 6500a067 PUD 6500c067 PMD 13a36c067 PTE 800000013691c163
Oops: 0000 [#1] PREEMPT SMP
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.9.0-rc5+ #4
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
RIP: 0010:rcu_cblist_dequeue+0x12/0x30
Call Trace:
<IRQ>
rcu_core+0x1b1/0x860
__do_softirq+0xfe/0x326
asm_call_on_stack+0x12/0x20
</IRQ>
do_softirq_own_stack+0x5f/0x80
irq_exit_rcu+0xaf/0xc0
sysvec_apic_timer_interrupt+0x2e/0xb0
asm_sysvec_apic_timer_interrupt+0x12/0x20
This commit avoids tis problem by adding an exit hook in lock_torture_ops
and using it to call percpu_free_rwsem() for percpu rwsem torture during
the module-cleanup function, thus ensuring that rcu_sync_func() completes
before module exits.
It is also necessary to call the exit hook if lock_torture_init()
fails half-way, so this commit also adds an ->init_called field in
lock_torture_cxt to indicate that exit hook, if present, must be called.
Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
If an locktorture torture-test run is given a bad kvm.sh argument, the
test will complain to the console, which is good. What is bad is that
from the user's perspective, it will just hang for the time specified
by the --duration argument. This commit therefore forces an immediate
kernel shutdown if a lock_torture_init()-time error occurs, thus avoiding
the appearance of a hang. It also forces a console splat in this case
to clearly indicate the presence of an error.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Exclusive locks do not have readlock support, which means that a
locktorture run with the following module parameters will do nothing:
torture_type=mutex_lock nwriters_stress=0 nreaders_stress=1
This commit therefore rejects this combination for exclusive locks by
returning -EINVAL during module init.
Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds a last_lock_release variable that tracks the time of
the last ->writeunlock() call, which allows easier diagnosing of lock
hangs when using a kernel debugger.
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
- Fix incorrect failure injection handling on the fuxtex code
- Prevent a preemption warning in lockdep when tracking local_irq_enable()
and interrupts are already enabled
- Remove more raw_cpu_read() usage from lockdep which causes state
corruption on !X86 architectures.
- Make the nr_unused_locks accounting in lockdep correct again.
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Merge tag 'locking-urgent-2020-11-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking fixes from Thomas Gleixner:
"A couple of locking fixes:
- Fix incorrect failure injection handling in the fuxtex code
- Prevent a preemption warning in lockdep when tracking
local_irq_enable() and interrupts are already enabled
- Remove more raw_cpu_read() usage from lockdep which causes state
corruption on !X86 architectures.
- Make the nr_unused_locks accounting in lockdep correct again"
* tag 'locking-urgent-2020-11-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
lockdep: Fix nr_unused_locks accounting
locking/lockdep: Remove more raw_cpu_read() usage
futex: Fix incorrect should_fail_futex() handling
lockdep: Fix preemption WARN for spurious IRQ-enable
Chris reported that commit 24d5a3bffef1 ("lockdep: Fix
usage_traceoverflow") breaks the nr_unused_locks validation code
triggered by /proc/lockdep_stats.
By fully splitting LOCK_USED and LOCK_USED_READ it becomes a bad
indicator for accounting nr_unused_locks; simplyfy by using any first
bit.
Fixes: 24d5a3bffef1 ("lockdep: Fix usage_traceoverflow")
Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://lkml.kernel.org/r/20201027124834.GL2628@hirez.programming.kicks-ass.net
I initially thought raw_cpu_read() was OK, since if it is !0 we have
IRQs disabled and can't get migrated, so if we get migrated both CPUs
must have 0 and it doesn't matter which 0 we read.
And while that is true; it isn't the whole store, on pretty much all
architectures (except x86) this can result in computing the address for
one CPU, getting migrated, the old CPU continuing execution with another
task (possibly setting recursion) and then the new CPU reading the value
of the old CPU, which is no longer 0.
Similer to:
baffd723e4 ("lockdep: Revert "lockdep: Use raw_cpu_*() for per-cpu variables"")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20201026152256.GB2651@hirez.programming.kicks-ass.net
It is valid (albeit uncommon) to call local_irq_enable() without first
having called local_irq_disable(). In this case we enter
lockdep_hardirqs_on*() with IRQs enabled and trip a preemption warning
for using __this_cpu_read().
Use this_cpu_read() instead to avoid the warning.
Fixes: 4d004099a6 ("lockdep: Fix lockdep recursion")
Reported-by: syzbot+53f8ce8bbc07924b6417@syzkaller.appspotmail.com
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Pull RCU changes from Ingo Molnar:
- Debugging for smp_call_function()
- RT raw/non-raw lock ordering fixes
- Strict grace periods for KASAN
- New smp_call_function() torture test
- Torture-test updates
- Documentation updates
- Miscellaneous fixes
[ This doesn't actually pull the tag - I've dropped the last merge from
the RCU branch due to questions about the series. - Linus ]
* tag 'core-rcu-2020-10-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (77 commits)
smp: Make symbol 'csd_bug_count' static
kernel/smp: Provide CSD lock timeout diagnostics
smp: Add source and destination CPUs to __call_single_data
rcu: Shrink each possible cpu krcp
rcu/segcblist: Prevent useless GP start if no CBs to accelerate
torture: Add gdb support
rcutorture: Allow pointer leaks to test diagnostic code
rcutorture: Hoist OOM registry up one level
refperf: Avoid null pointer dereference when buf fails to allocate
rcutorture: Properly synchronize with OOM notifier
rcutorture: Properly set rcu_fwds for OOM handling
torture: Add kvm.sh --help and update help message
rcutorture: Add CONFIG_PROVE_RCU_LIST to TREE05
torture: Update initrd documentation
rcutorture: Replace HTTP links with HTTPS ones
locktorture: Make function torture_percpu_rwsem_init() static
torture: document --allcpus argument added to the kvm.sh script
rcutorture: Output number of elapsed grace periods
rcutorture: Remove KCSAN stubs
rcu: Remove unused "cpu" parameter from rcu_report_qs_rdp()
...
Steve reported that lockdep_assert*irq*(), when nested inside lockdep
itself, will trigger a false-positive.
One example is the stack-trace code, as called from inside lockdep,
triggering tracing, which in turn calls RCU, which then uses
lockdep_assert_irqs_disabled().
Fixes: a21ee6055c ("lockdep: Change hardirq{s_enabled,_context} to per-cpu variables")
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Basically print_lock_class_header()'s for loop is out of sync with the
the size of of ->usage_traces[].
Also clean things up a bit while at it, to avoid such mishaps in the future.
Fixes: 23870f1227 ("locking/lockdep: Fix "USED" <- "IN-NMI" inversions")
Reported-by: Qian Cai <cai@redhat.com>
Debugged-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Qian Cai <cai@redhat.com>
Link: https://lkml.kernel.org/r/20200930094937.GE2651@hirez.programming.kicks-ass.net
Pull v5.10 RCU changes from Paul E. McKenney:
- Debugging for smp_call_function().
- Strict grace periods for KASAN. The point of this series is to find
RCU-usage bugs, so the corresponding new RCU_STRICT_GRACE_PERIOD
Kconfig option depends on both DEBUG_KERNEL and RCU_EXPERT, and is
further disabled by dfefault. Finally, the help text includes
a goodly list of scary caveats.
- New smp_call_function() torture test.
- Torture-test updates.
- Documentation updates.
- Miscellaneous fixes.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Qian Cai reported a BFS_EQUEUEFULL warning [1] after read recursive
deadlock detection merged into tip tree recently. Unlike the previous
lockep graph searching, which iterate every lock class (every node in
the graph) exactly once, the graph searching for read recurisve deadlock
detection needs to iterate every lock dependency (every edge in the
graph) once, as a result, the maximum memory cost of the circular queue
changes from O(V), where V is the number of lock classes (nodes or
vertices) in the graph, to O(E), where E is the number of lock
dependencies (edges), because every lock class or dependency gets
enqueued once in the BFS. Therefore we hit the BFS_EQUEUEFULL case.
However, actually we don't need to enqueue all dependencies for the BFS,
because every time we enqueue a dependency, we almostly enqueue all
other dependencies in the same dependency list ("almostly" is because
we currently check before enqueue, so if a dependency doesn't pass the
check stage we won't enqueue it, however, we can always do in reverse
ordering), based on this, we can only enqueue the first dependency from
a dependency list and every time we want to fetch a new dependency to
work, we can either:
1) fetch the dependency next to the current dependency in the
dependency list
or
2) if the dependency in 1) doesn't exist, fetch the dependency from
the queue.
With this approach, the "max bfs queue depth" for a x86_64_defconfig +
lockdep and selftest config kernel can get descreased from:
max bfs queue depth: 201
to (after apply this patch)
max bfs queue depth: 61
While I'm at it, clean up the code logic a little (e.g. directly return
other than set a "ret" value and goto the "exit" label).
[1]: https://lore.kernel.org/lkml/17343f6f7f2438fc376125384133c5ba70c2a681.camel@redhat.com/
Reported-by: Qian Cai <cai@redhat.com>
Reported-by: syzbot+62ebe501c1ce9a91f68c@syzkaller.appspotmail.com
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200917080210.108095-1-boqun.feng@gmail.com
The __this_cpu*() accessors are (in general) IRQ-unsafe which, given
that percpu-rwsem is a blocking primitive, should be just fine.
However, file_end_write() is used from IRQ context and will cause
load-store issues on architectures where the per-cpu accessors are not
natively irq-safe.
Fix it by using the IRQ-safe this_cpu_*() for operations on
read_count. This will generate more expensive code on a number of
platforms, which might cause a performance regression for some of the
other percpu-rwsem users.
If any such is reported, we can consider alternative solutions.
Fixes: 70fe2f4815 ("aio: fix freeze protection of aio writes")
Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lkml.kernel.org/r/20200915140750.137881-1-houtao1@huawei.com
During the LPC RCU BoF Paul asked how come the "USED" <- "IN-NMI"
detector doesn't trip over rcu_read_lock()'s lockdep annotation.
Looking into this I found a very embarrasing typo in
verify_lock_unused():
- if (!(class->usage_mask & LOCK_USED))
+ if (!(class->usage_mask & LOCKF_USED))
fixing that will indeed cause rcu_read_lock() to insta-splat :/
The above typo means that instead of testing for: 0x100 (1 <<
LOCK_USED), we test for 8 (LOCK_USED), which corresponds to (1 <<
LOCK_ENABLED_HARDIRQ).
So instead of testing for _any_ used lock, it will only match any lock
used with interrupts enabled.
The rcu_read_lock() annotation uses .check=0, which means it will not
set any of the interrupt bits and will thus never match.
In order to properly fix the situation and allow rcu_read_lock() to
correctly work, split LOCK_USED into LOCK_USED and LOCK_USED_READ and by
having .read users set USED_READ and test USED, pure read-recursive
locks are permitted.
Fixes: f6f48e1804 ("lockdep: Teach lockdep about "USED" <- "IN-NMI" inversions")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/20200902160323.GK1362448@hirez.programming.kicks-ass.net
Currently, the chainkey of a lock chain is a hash sum of the class_idx
of all the held locks, the read/write status are not taken in to
consideration while generating the chainkey. This could result into a
problem, if we have:
P1()
{
read_lock(B);
lock(A);
}
P2()
{
lock(A);
read_lock(B);
}
P3()
{
lock(A);
write_lock(B);
}
, and P1(), P2(), P3() run one by one. And when running P2(), lockdep
detects such a lock chain A -> B is not a deadlock, then it's added in
the chain cache, and then when running P3(), even if it's a deadlock, we
could miss it because of the hit of chain cache. This could be confirmed
by self testcase "chain cached mixed R-L/L-W ".
To resolve this, we use concept "hlock_id" to generate the chainkey, the
hlock_id is a tuple (hlock->class_idx, hlock->read), which fits in a u16
type. With this, the chainkeys are different is the lock sequences have
the same locks but different read/write status.
Besides, since we use "hlock_id" to generate chainkeys, the chain_hlocks
array now store the "hlock_id"s rather than lock_class indexes.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-15-boqun.feng@gmail.com
Since we have all the fundamental to handle recursive read locks, we now
add them into the dependency graph.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-13-boqun.feng@gmail.com
Currently, in safe->unsafe detection, lockdep misses the fact that a
LOCK_ENABLED_IRQ_*_READ usage and a LOCK_USED_IN_IRQ_*_READ usage may
cause deadlock too, for example:
P1 P2
<irq disabled>
write_lock(l1); <irq enabled>
read_lock(l2);
write_lock(l2);
<in irq>
read_lock(l1);
Actually, all of the following cases may cause deadlocks:
LOCK_USED_IN_IRQ_* -> LOCK_ENABLED_IRQ_*
LOCK_USED_IN_IRQ_*_READ -> LOCK_ENABLED_IRQ_*
LOCK_USED_IN_IRQ_* -> LOCK_ENABLED_IRQ_*_READ
LOCK_USED_IN_IRQ_*_READ -> LOCK_ENABLED_IRQ_*_READ
To fix this, we need to 1) change the calculation of exclusive_mask() so
that READ bits are not dropped and 2) always call usage() in
mark_lock_irq() to check usage deadlocks, even when the new usage of the
lock is READ.
Besides, adjust usage_match() and usage_acculumate() to recursive read
lock changes.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-12-boqun.feng@gmail.com
check_redundant() will report redundancy if it finds a path could
replace the about-to-add dependency in the BFS search. With recursive
read lock changes, we certainly need to change the match function for
the check_redundant(), because the path needs to match not only the lock
class but also the dependency kinds. For example, if the about-to-add
dependency @prev -> @next is A -(SN)-> B, and we find a path A -(S*)->
.. -(*R)->B in the dependency graph with __bfs() (for simplicity, we can
also say we find an -(SR)-> path from A to B), we can not replace the
dependency with that path in the BFS search. Because the -(SN)->
dependency can make a strong path with a following -(S*)-> dependency,
however an -(SR)-> path cannot.
Further, we can replace an -(SN)-> dependency with a -(EN)-> path, that
means if we find a path which is stronger than or equal to the
about-to-add dependency, we can report the redundancy. By "stronger", it
means both the start and the end of the path are not weaker than the
start and the end of the dependency (E is "stronger" than S and N is
"stronger" than R), so that we can replace the dependency with that
path.
To make sure we find a path whose start point is not weaker than the
about-to-add dependency, we use a trick: the ->only_xr of the root
(start point) of __bfs() is initialized as @prev-> == 0, therefore if
@prev is E, __bfs() will pick only -(E*)-> for the first dependency,
otherwise, __bfs() can pick -(E*)-> or -(S*)-> for the first dependency.
To make sure we find a path whose end point is not weaker than the
about-to-add dependency, we replace the match function for __bfs()
check_redundant(), we check for the case that either @next is R
(anything is not weaker than it) or the end point of the path is N
(which is not weaker than anything).
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-11-boqun.feng@gmail.com
Currently, lockdep only has limit support for deadlock detection for
recursive read locks.
This patch support deadlock detection for recursive read locks. The
basic idea is:
We are about to add dependency B -> A in to the dependency graph, we use
check_noncircular() to find whether we have a strong dependency path
A -> .. -> B so that we have a strong dependency circle (a closed strong
dependency path):
A -> .. -> B -> A
, which doesn't have two adjacent dependencies as -(*R)-> L -(S*)->.
Since A -> .. -> B is already a strong dependency path, so if either
B -> A is -(E*)-> or A -> .. -> B is -(*N)->, the circle A -> .. -> B ->
A is strong, otherwise not. So we introduce a new match function
hlock_conflict() to replace the class_equal() for the deadlock check in
check_noncircular().
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-10-boqun.feng@gmail.com
The "match" parameter of __bfs() is used for checking whether we hit a
match in the search, therefore it should return a boolean value rather
than an integer for better readability.
This patch then changes the return type of the function parameter and the
match functions to bool.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-9-boqun.feng@gmail.com
Now we have four types of dependencies in the dependency graph, and not
all the pathes carry real dependencies (the dependencies that may cause
a deadlock), for example:
Given lock A and B, if we have:
CPU1 CPU2
============= ==============
write_lock(A); read_lock(B);
read_lock(B); write_lock(A);
(assuming read_lock(B) is a recursive reader)
then we have dependencies A -(ER)-> B, and B -(SN)-> A, and a
dependency path A -(ER)-> B -(SN)-> A.
In lockdep w/o recursive locks, a dependency path from A to A
means a deadlock. However, the above case is obviously not a
deadlock, because no one holds B exclusively, therefore no one
waits for the other to release B, so who get A first in CPU1 and
CPU2 will run non-blockingly.
As a result, dependency path A -(ER)-> B -(SN)-> A is not a
real/strong dependency that could cause a deadlock.
From the observation above, we know that for a dependency path to be
real/strong, no two adjacent dependencies can be as -(*R)-> -(S*)->.
Now our mission is to make __bfs() traverse only the strong dependency
paths, which is simple: we record whether we only have -(*R)-> for the
previous lock_list of the path in lock_list::only_xr, and when we pick a
dependency in the traverse, we 1) filter out -(S*)-> dependency if the
previous lock_list only has -(*R)-> dependency (i.e. ->only_xr is true)
and 2) set the next lock_list::only_xr to true if we only have -(*R)->
left after we filter out dependencies based on 1), otherwise, set it to
false.
With this extension for __bfs(), we now need to initialize the root of
__bfs() properly (with a correct ->only_xr), to do so, we introduce some
helper functions, which also cleans up a little bit for the __bfs() root
initialization code.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-8-boqun.feng@gmail.com
To add recursive read locks into the dependency graph, we need to store
the types of dependencies for the BFS later. There are four types of
dependencies:
* Exclusive -> Non-recursive dependencies: EN
e.g. write_lock(prev) held and try to acquire write_lock(next)
or non-recursive read_lock(next), which can be represented as
"prev -(EN)-> next"
* Shared -> Non-recursive dependencies: SN
e.g. read_lock(prev) held and try to acquire write_lock(next) or
non-recursive read_lock(next), which can be represented as
"prev -(SN)-> next"
* Exclusive -> Recursive dependencies: ER
e.g. write_lock(prev) held and try to acquire recursive
read_lock(next), which can be represented as "prev -(ER)-> next"
* Shared -> Recursive dependencies: SR
e.g. read_lock(prev) held and try to acquire recursive
read_lock(next), which can be represented as "prev -(SR)-> next"
So we use 4 bits for the presence of each type in lock_list::dep. Helper
functions and macros are also introduced to convert a pair of locks into
lock_list::dep bit and maintain the addition of different types of
dependencies.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-7-boqun.feng@gmail.com
lock_list::distance is always not greater than MAX_LOCK_DEPTH (which
is 48 right now), so a u16 will fit. This patch reduces the size of
lock_list::distance to save space, so that we can introduce other fields
to help detect recursive read lock deadlocks without increasing the size
of lock_list structure.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-6-boqun.feng@gmail.com
Currently, __bfs() will do a breadth-first search in the dependency
graph and visit each lock class in the graph exactly once, so for
example, in the following graph:
A ---------> B
| ^
| |
+----------> C
a __bfs() call starts at A, will visit B through dependency A -> B and
visit C through dependency A -> C and that's it, IOW, __bfs() will not
visit dependency C -> B.
This is OK for now, as we only have strong dependencies in the
dependency graph, so whenever there is a traverse path from A to B in
__bfs(), it means A has strong dependencies to B (IOW, B depends on A
strongly). So no need to visit all dependencies in the graph.
However, as we are going to add recursive-read lock into the dependency
graph, as a result, not all the paths mean strong dependencies, in the
same example above, dependency A -> B may be a weak dependency and
traverse A -> C -> B may be a strong dependency path. And with the old
way of __bfs() (i.e. visiting every lock class exactly once), we will
miss the strong dependency path, which will result into failing to find
a deadlock. To cure this for the future, we need to find a way for
__bfs() to visit each dependency, rather than each class, exactly once
in the search until we find a match.
The solution is simple:
We used to mark lock_class::lockdep_dependency_gen_id to indicate a
class has been visited in __bfs(), now we change the semantics a little
bit: we now mark lock_class::lockdep_dependency_gen_id to indicate _all
the dependencies_ in its lock_{after,before} have been visited in the
__bfs() (note we only take one direction in a __bfs() search). In this
way, every dependency is guaranteed to be visited until we find a match.
Note: the checks in mark_lock_accessed() and lock_accessed() are
removed, because after this modification, we may call these two
functions on @source_entry of __bfs(), which may not be the entry in
"list_entries"
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-5-boqun.feng@gmail.com
__bfs() could return four magic numbers:
1: search succeeds, but none match.
0: search succeeds, find one match.
-1: search fails because of the cq is full.
-2: search fails because a invalid node is found.
This patch cleans things up by using a enum type for the return value
of __bfs() and its friends, this improves the code readability of the
code, and further, could help if we want to extend the BFS.
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-4-boqun.feng@gmail.com
On the archs using QUEUED_RWLOCKS, read_lock() is not always a recursive
read lock, actually it's only recursive if in_interrupt() is true. So
change the annotation accordingly to catch more deadlocks.
Note we used to treat read_lock() as pure recursive read locks in
lib/locking-seftest.c, and this is useful, especially for the lockdep
development selftest, so we keep this via a variable to force switching
lock annotation for read_lock().
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-2-boqun.feng@gmail.com
The lockdep tracepoints are under the lockdep recursion counter, this
has a bunch of nasty side effects:
- TRACE_IRQFLAGS doesn't work across the entire tracepoint
- RCU-lockdep doesn't see the tracepoints either, hiding numerous
"suspicious RCU usage" warnings.
Pull the trace_lock_*() tracepoints completely out from under the
lockdep recursion handling and completely rely on the trace level
recusion handling -- also, tracing *SHOULD* not be taking locks in any
case.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Marco Elver <elver@google.com>
Link: https://lkml.kernel.org/r/20200821085348.782688941@infradead.org
Sven reported that commit a21ee6055c ("lockdep: Change
hardirq{s_enabled,_context} to per-cpu variables") caused trouble on
s390 because their this_cpu_*() primitives disable preemption which
then lands back tracing.
On the one hand, per-cpu ops should use preempt_*able_notrace() and
raw_local_irq_*(), on the other hand, we can trivialy use raw_cpu_*()
ops for this.
Fixes: a21ee6055c ("lockdep: Change hardirq{s_enabled,_context} to per-cpu variables")
Reported-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200821085348.192346882@infradead.org
The sparse tool complains as follows:
kernel/locking/locktorture.c:569:6: warning:
symbol 'torture_percpu_rwsem_init' was not declared. Should it be static?
And this function is not used outside of locktorture.c,
so this commit marks it static.
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
- Untangle the header spaghetti which causes build failures in various
situations caused by the lockdep additions to seqcount to validate that
the write side critical sections are non-preemptible.
- The seqcount associated lock debug addons which were blocked by the
above fallout.
seqcount writers contrary to seqlock writers must be externally
serialized, which usually happens via locking - except for strict per
CPU seqcounts. As the lock is not part of the seqcount, lockdep cannot
validate that the lock is held.
This new debug mechanism adds the concept of associated locks.
sequence count has now lock type variants and corresponding
initializers which take a pointer to the associated lock used for
writer serialization. If lockdep is enabled the pointer is stored and
write_seqcount_begin() has a lockdep assertion to validate that the
lock is held.
Aside of the type and the initializer no other code changes are
required at the seqcount usage sites. The rest of the seqcount API is
unchanged and determines the type at compile time with the help of
_Generic which is possible now that the minimal GCC version has been
moved up.
Adding this lockdep coverage unearthed a handful of seqcount bugs which
have been addressed already independent of this.
While generaly useful this comes with a Trojan Horse twist: On RT
kernels the write side critical section can become preemtible if the
writers are serialized by an associated lock, which leads to the well
known reader preempts writer livelock. RT prevents this by storing the
associated lock pointer independent of lockdep in the seqcount and
changing the reader side to block on the lock when a reader detects
that a writer is in the write side critical section.
- Conversion of seqcount usage sites to associated types and initializers.
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Merge tag 'locking-urgent-2020-08-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Thomas Gleixner:
"A set of locking fixes and updates:
- Untangle the header spaghetti which causes build failures in
various situations caused by the lockdep additions to seqcount to
validate that the write side critical sections are non-preemptible.
- The seqcount associated lock debug addons which were blocked by the
above fallout.
seqcount writers contrary to seqlock writers must be externally
serialized, which usually happens via locking - except for strict
per CPU seqcounts. As the lock is not part of the seqcount, lockdep
cannot validate that the lock is held.
This new debug mechanism adds the concept of associated locks.
sequence count has now lock type variants and corresponding
initializers which take a pointer to the associated lock used for
writer serialization. If lockdep is enabled the pointer is stored
and write_seqcount_begin() has a lockdep assertion to validate that
the lock is held.
Aside of the type and the initializer no other code changes are
required at the seqcount usage sites. The rest of the seqcount API
is unchanged and determines the type at compile time with the help
of _Generic which is possible now that the minimal GCC version has
been moved up.
Adding this lockdep coverage unearthed a handful of seqcount bugs
which have been addressed already independent of this.
While generally useful this comes with a Trojan Horse twist: On RT
kernels the write side critical section can become preemtible if
the writers are serialized by an associated lock, which leads to
the well known reader preempts writer livelock. RT prevents this by
storing the associated lock pointer independent of lockdep in the
seqcount and changing the reader side to block on the lock when a
reader detects that a writer is in the write side critical section.
- Conversion of seqcount usage sites to associated types and
initializers"
* tag 'locking-urgent-2020-08-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (25 commits)
locking/seqlock, headers: Untangle the spaghetti monster
locking, arch/ia64: Reduce <asm/smp.h> header dependencies by moving XTP bits into the new <asm/xtp.h> header
x86/headers: Remove APIC headers from <asm/smp.h>
seqcount: More consistent seqprop names
seqcount: Compress SEQCNT_LOCKNAME_ZERO()
seqlock: Fold seqcount_LOCKNAME_init() definition
seqlock: Fold seqcount_LOCKNAME_t definition
seqlock: s/__SEQ_LOCKDEP/__SEQ_LOCK/g
hrtimer: Use sequence counter with associated raw spinlock
kvm/eventfd: Use sequence counter with associated spinlock
userfaultfd: Use sequence counter with associated spinlock
NFSv4: Use sequence counter with associated spinlock
iocost: Use sequence counter with associated spinlock
raid5: Use sequence counter with associated spinlock
vfs: Use sequence counter with associated spinlock
timekeeping: Use sequence counter with associated raw spinlock
xfrm: policy: Use sequence counters with associated lock
netfilter: nft_set_rbtree: Use sequence counter with associated rwlock
netfilter: conntrack: Use sequence counter with associated spinlock
sched: tasks: Use sequence counter with associated spinlock
...
x86:
* Report last CPU for debugging
* Emulate smaller MAXPHYADDR in the guest than in the host
* .noinstr and tracing fixes from Thomas
* nested SVM page table switching optimization and fixes
Generic:
* Unify shadow MMU cache data structures across architectures
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Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm
Pull KVM updates from Paolo Bonzini:
"s390:
- implement diag318
x86:
- Report last CPU for debugging
- Emulate smaller MAXPHYADDR in the guest than in the host
- .noinstr and tracing fixes from Thomas
- nested SVM page table switching optimization and fixes
Generic:
- Unify shadow MMU cache data structures across architectures"
* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (127 commits)
KVM: SVM: Fix sev_pin_memory() error handling
KVM: LAPIC: Set the TDCR settable bits
KVM: x86: Specify max TDP level via kvm_configure_mmu()
KVM: x86/mmu: Rename max_page_level to max_huge_page_level
KVM: x86: Dynamically calculate TDP level from max level and MAXPHYADDR
KVM: VXM: Remove temporary WARN on expected vs. actual EPTP level mismatch
KVM: x86: Pull the PGD's level from the MMU instead of recalculating it
KVM: VMX: Make vmx_load_mmu_pgd() static
KVM: x86/mmu: Add separate helper for shadow NPT root page role calc
KVM: VMX: Drop a duplicate declaration of construct_eptp()
KVM: nSVM: Correctly set the shadow NPT root level in its MMU role
KVM: Using macros instead of magic values
MIPS: KVM: Fix build error caused by 'kvm_run' cleanup
KVM: nSVM: remove nonsensical EXITINFO1 adjustment on nested NPF
KVM: x86: Add a capability for GUEST_MAXPHYADDR < HOST_MAXPHYADDR support
KVM: VMX: optimize #PF injection when MAXPHYADDR does not match
KVM: VMX: Add guest physical address check in EPT violation and misconfig
KVM: VMX: introduce vmx_need_pf_intercept
KVM: x86: update exception bitmap on CPUID changes
KVM: x86: rename update_bp_intercept to update_exception_bitmap
...
static priority level knowledge from non-scheduler code.
The three APIs for non-scheduler code to set SCHED_FIFO are:
- sched_set_fifo()
- sched_set_fifo_low()
- sched_set_normal()
These are two FIFO priority levels: default (high), and a 'low' priority level,
plus sched_set_normal() to set the policy back to non-SCHED_FIFO.
Since the changes affect a lot of non-scheduler code, we kept this in a separate
tree.
When merging to the latest upstream tree there's a conflict in drivers/spi/spi.c,
which can be resolved via:
sched_set_fifo(ctlr->kworker_task);
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'sched-fifo-2020-08-04' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull sched/fifo updates from Ingo Molnar:
"This adds the sched_set_fifo*() encapsulation APIs to remove static
priority level knowledge from non-scheduler code.
The three APIs for non-scheduler code to set SCHED_FIFO are:
- sched_set_fifo()
- sched_set_fifo_low()
- sched_set_normal()
These are two FIFO priority levels: default (high), and a 'low'
priority level, plus sched_set_normal() to set the policy back to
non-SCHED_FIFO.
Since the changes affect a lot of non-scheduler code, we kept this in
a separate tree"
* tag 'sched-fifo-2020-08-04' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (24 commits)
sched,tracing: Convert to sched_set_fifo()
sched: Remove sched_set_*() return value
sched: Remove sched_setscheduler*() EXPORTs
sched,psi: Convert to sched_set_fifo_low()
sched,rcutorture: Convert to sched_set_fifo_low()
sched,rcuperf: Convert to sched_set_fifo_low()
sched,locktorture: Convert to sched_set_fifo()
sched,irq: Convert to sched_set_fifo()
sched,watchdog: Convert to sched_set_fifo()
sched,serial: Convert to sched_set_fifo()
sched,powerclamp: Convert to sched_set_fifo()
sched,ion: Convert to sched_set_normal()
sched,powercap: Convert to sched_set_fifo*()
sched,spi: Convert to sched_set_fifo*()
sched,mmc: Convert to sched_set_fifo*()
sched,ivtv: Convert to sched_set_fifo*()
sched,drm/scheduler: Convert to sched_set_fifo*()
sched,msm: Convert to sched_set_fifo*()
sched,psci: Convert to sched_set_fifo*()
sched,drbd: Convert to sched_set_fifo*()
...
- LKMM updates: mostly documentation changes, but also some new litmus tests for atomic ops.
- KCSAN updates: the most important change is that GCC 11 now has all fixes in place
to support KCSAN, so GCC support can be enabled again. Also more annotations.
- futex updates: minor cleanups and simplifications
- seqlock updates: merge preparatory changes/cleanups for the 'associated locks' facilities.
- lockdep updates:
- simplify IRQ trace event handling
- add various new debug checks
- simplify header dependencies, split out <linux/lockdep_types.h>, decouple
lockdep from other low level headers some more
- fix NMI handling
- misc cleanups and smaller fixes
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'locking-core-2020-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Ingo Molnar:
- LKMM updates: mostly documentation changes, but also some new litmus
tests for atomic ops.
- KCSAN updates: the most important change is that GCC 11 now has all
fixes in place to support KCSAN, so GCC support can be enabled again.
Also more annotations.
- futex updates: minor cleanups and simplifications
- seqlock updates: merge preparatory changes/cleanups for the
'associated locks' facilities.
- lockdep updates:
- simplify IRQ trace event handling
- add various new debug checks
- simplify header dependencies, split out <linux/lockdep_types.h>,
decouple lockdep from other low level headers some more
- fix NMI handling
- misc cleanups and smaller fixes
* tag 'locking-core-2020-08-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (60 commits)
kcsan: Improve IRQ state trace reporting
lockdep: Refactor IRQ trace events fields into struct
seqlock: lockdep assert non-preemptibility on seqcount_t write
lockdep: Add preemption enabled/disabled assertion APIs
seqlock: Implement raw_seqcount_begin() in terms of raw_read_seqcount()
seqlock: Add kernel-doc for seqcount_t and seqlock_t APIs
seqlock: Reorder seqcount_t and seqlock_t API definitions
seqlock: seqcount_t latch: End read sections with read_seqcount_retry()
seqlock: Properly format kernel-doc code samples
Documentation: locking: Describe seqlock design and usage
locking/qspinlock: Do not include atomic.h from qspinlock_types.h
locking/atomic: Move ATOMIC_INIT into linux/types.h
lockdep: Move list.h inclusion into lockdep.h
locking/lockdep: Fix TRACE_IRQFLAGS vs. NMIs
futex: Remove unused or redundant includes
futex: Consistently use fshared as boolean
futex: Remove needless goto's
futex: Remove put_futex_key()
rwsem: fix commas in initialisation
docs: locking: Replace HTTP links with HTTPS ones
...
Pull v5.9 KCSAN bits from Paul E. McKenney.
Perhaps the most important change is that GCC 11 now has all fixes in place
to support KCSAN, so GCC support can be enabled again.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Refactor the IRQ trace events fields, used for printing information
about the IRQ trace events, into a separate struct 'irqtrace_events'.
This improves readability by separating the information only used in
reporting, as well as enables (simplified) storing/restoring of
irqtrace_events snapshots.
No functional change intended.
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200729110916.3920464-1-elver@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Prior to commit:
859d069ee1 ("lockdep: Prepare for NMI IRQ state tracking")
IRQ state tracking was disabled in NMIs due to nmi_enter()
doing lockdep_off() -- with the obvious requirement that NMI entry
call nmi_enter() before trace_hardirqs_off().
[ AFAICT, PowerPC and SH violate this order on their NMI entry ]
However, that commit explicitly changed lockdep_hardirqs_*() to ignore
lockdep_off() and breaks every architecture that has irq-tracing in
it's NMI entry that hasn't been fixed up (x86 being the only fixed one
at this point).
The reason for this change is that by ignoring lockdep_off() we can:
- get rid of 'current->lockdep_recursion' in lockdep_assert_irqs*()
which was going to to give header-recursion issues with the
seqlock rework.
- allow these lockdep_assert_*() macros to function in NMI context.
Restore the previous state of things and allow an architecture to
opt-in to the NMI IRQ tracking support, however instead of relying on
lockdep_off(), rely on in_nmi(), both are part of nmi_enter() and so
over-all entry ordering doesn't need to change.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200727124852.GK119549@hirez.programming.kicks-ass.net
Though the number of lock-acquisitions is tracked as unsigned long, this
is passed as the divisor to div_s64() which interprets it as a s32,
giving nonsense values with more than 2 billion acquisitons. E.g.
acquisitions holdtime-min holdtime-max holdtime-total holdtime-avg
-------------------------------------------------------------------------
2350439395 0.07 353.38 649647067.36 0.-32
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20200725185110.11588-1-chris@chris-wilson.co.uk
Using uninitialized_var() is dangerous as it papers over real bugs[1]
(or can in the future), and suppresses unrelated compiler warnings
(e.g. "unused variable"). If the compiler thinks it is uninitialized,
either simply initialize the variable or make compiler changes.
In preparation for removing[2] the[3] macro[4], remove all remaining
needless uses with the following script:
git grep '\buninitialized_var\b' | cut -d: -f1 | sort -u | \
xargs perl -pi -e \
's/\buninitialized_var\(([^\)]+)\)/\1/g;
s:\s*/\* (GCC be quiet|to make compiler happy) \*/$::g;'
drivers/video/fbdev/riva/riva_hw.c was manually tweaked to avoid
pathological white-space.
No outstanding warnings were found building allmodconfig with GCC 9.3.0
for x86_64, i386, arm64, arm, powerpc, powerpc64le, s390x, mips, sparc64,
alpha, and m68k.
[1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/
[2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/
[3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/
[4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/
Reviewed-by: Leon Romanovsky <leonro@mellanox.com> # drivers/infiniband and mlx4/mlx5
Acked-by: Jason Gunthorpe <jgg@mellanox.com> # IB
Acked-by: Kalle Valo <kvalo@codeaurora.org> # wireless drivers
Reviewed-by: Chao Yu <yuchao0@huawei.com> # erofs
Signed-off-by: Kees Cook <keescook@chromium.org>
Currently all IRQ-tracking state is in task_struct, this means that
task_struct needs to be defined before we use it.
Especially for lockdep_assert_irq*() this can lead to header-hell.
Move the hardirq state into per-cpu variables to avoid the task_struct
dependency.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200623083721.512673481@infradead.org
There is no reason not to always, accurately, track IRQ state.
This change also makes IRQ state tracking ignore lockdep_off().
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200623083721.155449112@infradead.org
There are cases where a guest tries to switch spinlocks to bare metal
behavior (e.g. by setting "xen_nopvspin" on XEN platform and
"hv_nopvspin" on HYPER_V).
That feature is missed on KVM, add a new parameter "nopvspin" to disable
PV spinlocks for KVM guest.
The new 'nopvspin' parameter will also replace Xen and Hyper-V specific
parameters in future patches.
Define variable nopvsin as global because it will be used in future
patches as above.
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krcmar <rkrcmar@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Jim Mattson <jmattson@google.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
The prev->next pointer can be accessed concurrently as noticed by KCSAN:
write (marked) to 0xffff9d3370dbbe40 of 8 bytes by task 3294 on cpu 107:
osq_lock+0x25f/0x350
osq_wait_next at kernel/locking/osq_lock.c:79
(inlined by) osq_lock at kernel/locking/osq_lock.c:185
rwsem_optimistic_spin
<snip>
read to 0xffff9d3370dbbe40 of 8 bytes by task 3398 on cpu 100:
osq_lock+0x196/0x350
osq_lock at kernel/locking/osq_lock.c:157
rwsem_optimistic_spin
<snip>
Since the write only stores NULL to prev->next and the read tests if
prev->next equals to this_cpu_ptr(&osq_node). Even if the value is
shattered, the code is still working correctly. Thus, mark it as an
intentional data race using the data_race() macro.
Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit fixes the following coccicheck warnings:
kernel/locking/locktorture.c:689:6-10: WARNING: Assignment of 0/1 to bool variable
kernel/locking/locktorture.c:907:2-20: WARNING: Assignment of 0/1 to bool variable
kernel/locking/locktorture.c:938:3-20: WARNING: Assignment of 0/1 to bool variable
kernel/locking/locktorture.c:668:2-19: WARNING: Assignment of 0/1 to bool variable
kernel/locking/locktorture.c:674:2-19: WARNING: Assignment of 0/1 to bool variable
kernel/locking/locktorture.c:634:2-20: WARNING: Assignment of 0/1 to bool variable
kernel/locking/locktorture.c:640:2-20: WARNING: Assignment of 0/1 to bool variable
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zou Wei <zou_wei@huawei.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Currently, lockdep_rcu_suspicious() complains twice about RCU read-side
critical sections being invoked from within extended quiescent states,
for example:
RCU used illegally from idle CPU!
rcu_scheduler_active = 2, debug_locks = 1
RCU used illegally from extended quiescent state!
This commit therefore saves a couple lines of code and one line of
console-log output by eliminating the first of these two complaints.
Link: https://lore.kernel.org/lkml/87wo4wnpzb.fsf@nanos.tec.linutronix.de
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Maarten Lankhorst