Commit graph

653 commits

Author SHA1 Message Date
Lai Jiangshan
c130d2dc93 rcu: Rename some instance of CONFIG_PREEMPTION to CONFIG_PREEMPT_RCU
CONFIG_PREEMPTION and CONFIG_PREEMPT_RCU are always identical,
but some code depends on CONFIG_PREEMPTION to access to
rcu_preempt functionality. This patch changes CONFIG_PREEMPTION
to CONFIG_PREEMPT_RCU in these cases.

Signed-off-by: Lai Jiangshan <jiangshanlai@gmail.com>
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-01-24 10:26:28 -08:00
Sebastian Andrzej Siewior
90326f0521 rcu: Use CONFIG_PREEMPTION where appropriate
The config option `CONFIG_PREEMPT' is used for the preemption model
"Low-Latency Desktop". The config option `CONFIG_PREEMPTION' is enabled
when kernel preemption is enabled which is true for the preemption model
`CONFIG_PREEMPT' and `CONFIG_PREEMPT_RT'.

Use `CONFIG_PREEMPTION' if it applies to both preemption models and not
just to `CONFIG_PREEMPT'.

Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: rcu@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2019-12-09 12:37:51 -08:00
Paul E. McKenney
8dcdfb7096 Merge branches 'doc.2019.10.29a', 'fixes.2019.10.30a', 'nohz.2019.10.28a', 'replace.2019.10.30a', 'torture.2019.10.05a' and 'lkmm.2019.10.05a' into HEAD
doc.2019.10.29a: RCU documentation updates.
fixes.2019.10.30a: RCU miscellaneous fixes.
nohz.2019.10.28a: RCU NO_HZ and NO_HZ_FULL updates.
replace.2019.10.30a: Replace rcu_swap_protected() with rcu_replace().
torture.2019.10.05a: RCU torture-test updates.

lkmm.2019.10.05a: Linux kernel memory model updates.
2019-10-30 08:47:13 -07:00
Joel Fernandes (Google)
05ef9e9eb3 rcu: Ensure that ->rcu_urgent_qs is set before resched IPI
The RCU-specific resched_cpu() function sends a resched IPI to the
specified CPU, which can be used to force the tick on for a given
nohz_full CPU.  This is needed when this nohz_full CPU is looping in the
kernel while blocking the current grace period.  However, for the tick
to actually be forced on in all cases, that CPU's rcu_data structure's
->rcu_urgent_qs flag must be set beforehand.  This commit therefore
causes rcu_implicit_dynticks_qs() to set this flag prior to invoking
resched_cpu() on a holdout nohz_full CPU.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2019-10-30 08:34:35 -07:00
Paul E. McKenney
dd7dafd1ad rcu: Make kernel-mode nohz_full CPUs invoke the RCU core processing
If a nohz_full CPU is idle or executing in userspace, it makes good sense
to keep it out of RCU core processing.  After all, the RCU grace-period
kthread can see its quiescent states and all of its callbacks are
offloaded, so there is nothing for RCU core processing to do.

However, if a nohz_full CPU is executing in kernel space, the RCU
grace-period kthread cannot do anything for it, so such a CPU must report
its own quiescent states.  This commit therefore makes nohz_full CPUs
skip RCU core processing only if the scheduler-clock interrupt caught
them in idle or in userspace.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2019-10-28 07:02:21 -07:00
Paul E. McKenney
ed93dfc6bc rcu: Confine ->core_needs_qs accesses to the corresponding CPU
Commit 671a63517c ("rcu: Avoid unnecessary softirq when system
is idle") fixed a bug that could result in an indefinite number of
unnecessary invocations of the RCU_SOFTIRQ handler at the trailing edge
of a scheduler-clock interrupt.  However, the fix introduced off-CPU
stores to ->core_needs_qs.  These writes did not conflict with the
on-CPU stores because the CPU's leaf rcu_node structure's ->lock was
held across all such stores.  However, the loads from ->core_needs_qs
were not promoted to READ_ONCE() and, worse yet, the code loading from
->core_needs_qs was written assuming that it was only ever updated by
the corresponding CPU.  So operation has been robust, but only by luck.
This situation is therefore an accident waiting to happen.

This commit therefore takes a different approach.  Instead of clearing
->core_needs_qs from the grace-period kthread's force-quiescent-state
processing, it modifies the rcu_pending() function to suppress the
rcu_sched_clock_irq() function's call to invoke_rcu_core() if there is no
grace period in progress.  This avoids the infinite needless RCU_SOFTIRQ
handlers while still keeping all accesses to ->core_needs_qs local to
the corresponding CPU.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2019-10-28 07:02:21 -07:00
Joel Fernandes (Google)
516e5ae0c9 rcu: Reset CPU hints when reporting a quiescent state
In some cases, tracing shows that need_heavy_qs is still set even though
urgent_qs was cleared upon reporting of a quiescent state.  One such
case is when the softirq reports that a CPU has passed quiescent state.

Commit 671a63517c ("rcu: Avoid unnecessary softirq when system is
idle") fixed a bug where core_needs_qs was not being cleared.  In order
to avoid running into similar situations with the urgent-grace-period
flags, this commit causes rcu_disable_urgency_upon_qs(), previously
rcu_disable_tick_upon_qs(), to clear the urgency hints, ->rcu_urgent_qs
and ->rcu_need_heavy_qs.  Note that it is possible for CPUs to go
offline with these urgency hints still set.  This is handled because
rcu_disable_urgency_upon_qs() is also invoked during the online process.

Because these hints can be cleared both by the corresponding CPU and by
the grace-period kthread, this commit also adds a number of READ_ONCE()
and WRITE_ONCE() calls.

Tested overnight with rcutorture running for 60 minutes on all
configurations of RCU.

Signed-off-by: "Joel Fernandes (Google)" <joel@joelfernandes.org>
[ paulmck: Clear urgency flags in rcu_disable_urgency_upon_qs(). ]
[ paulmck: Remove ->core_needs_qs from the set cleared at quiescent state. ]
[ paulmck: Make rcu_disable_urgency_upon_qs static per kbuild test robot. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2019-10-28 07:02:21 -07:00
Paul E. McKenney
b200a04895 rcu: Force nohz_full tick on upon irq enter instead of exit
There is interrupt-exit code that forces on the tick for nohz_full CPUs
failing to respond to the current grace period in a timely fashion.
However, this code must compare ->dynticks_nmi_nesting to the value 2
in the interrupt-exit fastpath.  This commit therefore moves this code
to the interrupt-entry fastpath, where a lighter-weight comparison to
zero may be used.

Reported-by: Joel Fernandes <joel@joelfernandes.org>
[ paulmck: Apply Joel Fernandes TICK_DEP_MASK_RCU->TICK_DEP_BIT_RCU fix. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2019-10-28 07:02:21 -07:00
Paul E. McKenney
66e4c33b51 rcu: Force tick on for nohz_full CPUs not reaching quiescent states
CPUs running for long time periods in the kernel in nohz_full mode
might leave the scheduling-clock interrupt disabled for then full
duration of their in-kernel execution.  This can (among other things)
delay grace periods.  This commit therefore forces the tick back on
for any nohz_full CPU that is failing to pass through a quiescent state
upon return from interrupt, which the resched_cpu() will induce.

Reported-by: Joel Fernandes <joel@joelfernandes.org>
[ paulmck: Clear ->rcu_forced_tick as reported by Joel Fernandes testing. ]
[ paulmck: Apply Joel Fernandes TICK_DEP_MASK_RCU->TICK_DEP_BIT_RCU fix. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2019-10-28 07:02:21 -07:00
Paul E. McKenney
79ba7ff5a9 rcutorture: Emulate dyntick aspect of userspace nohz_full sojourn
During an actual call_rcu() flood, there would be frequent trips to
userspace (in-kernel call_rcu() floods must be otherwise housebroken).
Userspace execution on nohz_full CPUs implies an RCU dyntick idle/not-idle
transition pair, so this commit adds emulation of that pair.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2019-10-05 10:46:05 -07:00
Paul E. McKenney
96926686de rcu: Make CPU-hotplug removal operations enable tick
CPU-hotplug removal operations run the multi_cpu_stop() function, which
relies on the scheduler to gain control from whatever is running on the
various online CPUs, including any nohz_full CPUs running long loops in
kernel-mode code.  Lack of the scheduler-clock interrupt on such CPUs
can delay multi_cpu_stop() for several minutes and can also result in
RCU CPU stall warnings.  This commit therefore causes CPU-hotplug removal
operations to enable the scheduler-clock interrupt on all online CPUs.

[ paulmck: Apply Joel Fernandes TICK_DEP_MASK_RCU->TICK_DEP_BIT_RCU fix. ]
[ paulmck: Apply simplifications suggested by Frederic Weisbecker. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2019-10-05 10:46:05 -07:00
Paul E. McKenney
366237e7b0 stop_machine: Provide RCU quiescent state in multi_cpu_stop()
When multi_cpu_stop() loops waiting for other tasks, it can trigger an RCU
CPU stall warning.  This can be misleading because what is instead needed
is information on whatever task is blocking multi_cpu_stop().  This commit
therefore inserts an RCU quiescent state into the multi_cpu_stop()
function's waitloop.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2019-10-05 10:46:05 -07:00
Paul E. McKenney
6a949b7af8 rcu: Force on tick when invoking lots of callbacks
Callback invocation can run for a significant time period, and within
CONFIG_NO_HZ_FULL=y kernels, this period will be devoid of scheduler-clock
interrupts.  In-kernel execution without such interrupts can cause all
manner of malfunction, with RCU CPU stall warnings being but one result.

This commit therefore forces scheduling-clock interrupts on whenever more
than a few RCU callbacks are invoked.  Because offloaded callback invocation
can be preempted, this forcing is withdrawn on each context switch.  This
in turn requires that the loop invoking RCU callbacks reiterate the forcing
periodically.

[ paulmck: Apply Joel Fernandes TICK_DEP_MASK_RCU->TICK_DEP_BIT_RCU fix. ]
[ paulmck: Remove NO_HZ_FULL check per Frederic Weisbecker feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2019-10-05 10:46:04 -07:00
Linus Torvalds
7e67a85999 Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler updates from Ingo Molnar:

 - MAINTAINERS: Add Mark Rutland as perf submaintainer, Juri Lelli and
   Vincent Guittot as scheduler submaintainers. Add Dietmar Eggemann,
   Steven Rostedt, Ben Segall and Mel Gorman as scheduler reviewers.

   As perf and the scheduler is getting bigger and more complex,
   document the status quo of current responsibilities and interests,
   and spread the review pain^H^H^H^H fun via an increase in the Cc:
   linecount generated by scripts/get_maintainer.pl. :-)

 - Add another series of patches that brings the -rt (PREEMPT_RT) tree
   closer to mainline: split the monolithic CONFIG_PREEMPT dependencies
   into a new CONFIG_PREEMPTION category that will allow the eventual
   introduction of CONFIG_PREEMPT_RT. Still a few more hundred patches
   to go though.

 - Extend the CPU cgroup controller with uclamp.min and uclamp.max to
   allow the finer shaping of CPU bandwidth usage.

 - Micro-optimize energy-aware wake-ups from O(CPUS^2) to O(CPUS).

 - Improve the behavior of high CPU count, high thread count
   applications running under cpu.cfs_quota_us constraints.

 - Improve balancing with SCHED_IDLE (SCHED_BATCH) tasks present.

 - Improve CPU isolation housekeeping CPU allocation NUMA locality.

 - Fix deadline scheduler bandwidth calculations and logic when cpusets
   rebuilds the topology, or when it gets deadline-throttled while it's
   being offlined.

 - Convert the cpuset_mutex to percpu_rwsem, to allow it to be used from
   setscheduler() system calls without creating global serialization.
   Add new synchronization between cpuset topology-changing events and
   the deadline acceptance tests in setscheduler(), which were broken
   before.

 - Rework the active_mm state machine to be less confusing and more
   optimal.

 - Rework (simplify) the pick_next_task() slowpath.

 - Improve load-balancing on AMD EPYC systems.

 - ... and misc cleanups, smaller fixes and improvements - please see
   the Git log for more details.

* 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (53 commits)
  sched/psi: Correct overly pessimistic size calculation
  sched/fair: Speed-up energy-aware wake-ups
  sched/uclamp: Always use 'enum uclamp_id' for clamp_id values
  sched/uclamp: Update CPU's refcount on TG's clamp changes
  sched/uclamp: Use TG's clamps to restrict TASK's clamps
  sched/uclamp: Propagate system defaults to the root group
  sched/uclamp: Propagate parent clamps
  sched/uclamp: Extend CPU's cgroup controller
  sched/topology: Improve load balancing on AMD EPYC systems
  arch, ia64: Make NUMA select SMP
  sched, perf: MAINTAINERS update, add submaintainers and reviewers
  sched/fair: Use rq_lock/unlock in online_fair_sched_group
  cpufreq: schedutil: fix equation in comment
  sched: Rework pick_next_task() slow-path
  sched: Allow put_prev_task() to drop rq->lock
  sched/fair: Expose newidle_balance()
  sched: Add task_struct pointer to sched_class::set_curr_task
  sched: Rework CPU hotplug task selection
  sched/{rt,deadline}: Fix set_next_task vs pick_next_task
  sched: Fix kerneldoc comment for ia64_set_curr_task
  ...
2019-09-16 17:25:49 -07:00
Ingo Molnar
563c4f85f9 Merge branch 'sched/rt' into sched/core, to pick up -rt changes
Pick up the first couple of patches working towards PREEMPT_RT.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-09-16 14:05:04 +02:00
Eric Dumazet
cfcdef5e30 rcu: Allow rcu_do_batch() to dynamically adjust batch sizes
Bimodal behavior of rcu_do_batch() is not really suited to Google
applications like gfe servers.

When a process with millions of sockets exits, closing all files
queues two rcu callbacks per socket.

This eventually reaches the point where RCU enters an emergency
mode, where rcu_do_batch() do not return until whole queue is flushed.

Each rcu callback lasts at least 70 nsec, so with millions of
elements, we easily spend more than 100 msec without rescheduling.

Goal of this patch is to avoid the infamous message like following
"need_resched set for > 51999388 ns (52 ticks) without schedule"

We dynamically adjust the number of elements we process, instead
of 10 / INFINITE choices, we use a floor of ~1 % of current entries.

If the number is above 1000, we switch to a time based limit of 3 msec
per batch, adjustable with /sys/module/rcutree/parameters/rcu_resched_ns

Signed-off-by: Eric Dumazet <edumazet@google.com>
[ paulmck: Forward-port and remove debug statements. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-08-13 14:38:24 -07:00
Paul E. McKenney
23651d9b96 rcu/nocb: Advance CBs after merge in rcutree_migrate_callbacks()
The rcutree_migrate_callbacks() invokes rcu_advance_cbs() on both the
offlined CPU's ->cblist and that of the surviving CPU, then merges
them.  However, after the merge, and of the offlined CPU's callbacks
that were not ready to be invoked will no longer be associated with a
grace-period number.  This commit therefore invokes rcu_advance_cbs()
one more time on the merged ->cblist in order to assign a grace-period
number to these callbacks.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-08-13 14:38:24 -07:00
Paul E. McKenney
d1b222c6be rcu/nocb: Add bypass callback queueing
Use of the rcu_data structure's segmented ->cblist for no-CBs CPUs
takes advantage of unrelated grace periods, thus reducing the memory
footprint in the face of floods of call_rcu() invocations.  However,
the ->cblist field is a more-complex rcu_segcblist structure which must
be protected via locking.  Even though there are only three entities
which can acquire this lock (the CPU invoking call_rcu(), the no-CBs
grace-period kthread, and the no-CBs callbacks kthread), the contention
on this lock is excessive under heavy stress.

This commit therefore greatly reduces contention by provisioning
an rcu_cblist structure field named ->nocb_bypass within the
rcu_data structure.  Each no-CBs CPU is permitted only a limited
number of enqueues onto the ->cblist per jiffy, controlled by a new
nocb_nobypass_lim_per_jiffy kernel boot parameter that defaults to
about 16 enqueues per millisecond (16 * 1000 / HZ).  When that limit is
exceeded, the CPU instead enqueues onto the new ->nocb_bypass.

The ->nocb_bypass is flushed into the ->cblist every jiffy or when
the number of callbacks on ->nocb_bypass exceeds qhimark, whichever
happens first.  During call_rcu() floods, this flushing is carried out
by the CPU during the course of its call_rcu() invocations.  However,
a CPU could simply stop invoking call_rcu() at any time.  The no-CBs
grace-period kthread therefore carries out less-aggressive flushing
(every few jiffies or when the number of callbacks on ->nocb_bypass
exceeds (2 * qhimark), whichever comes first).  This means that the
no-CBs grace-period kthread cannot be permitted to do unbounded waits
while there are callbacks on ->nocb_bypass.  A ->nocb_bypass_timer is
used to provide the needed wakeups.

[ paulmck: Apply Coverity feedback reported by Colin Ian King. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-08-13 14:37:32 -07:00
Paul E. McKenney
6608c3a027 rcu/nocb: Reduce contention at no-CBs registry-time CB advancement
Currently, __call_rcu_nocb_wake() conditionally acquires the leaf rcu_node
structure's ->lock, and only afterwards does rcu_advance_cbs_nowake()
check to see if it is possible to advance callbacks without potentially
needing to awaken the grace-period kthread.  Given that the no-awaken
check can be done locklessly, this commit reverses the order, so that
rcu_advance_cbs_nowake() is invoked without holding the leaf rcu_node
structure's ->lock and rcu_advance_cbs_nowake() checks the grace-period
state before conditionally acquiring that lock, thus reducing the number
of needless acquistions of the leaf rcu_node structure's ->lock.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-08-13 14:35:49 -07:00
Paul E. McKenney
7f36ef82e5 rcu/nocb: Avoid needless wakeups of no-CBs grace-period kthread
Currently, the code provides an extra wakeup for the no-CBs grace-period
kthread if one of its CPUs is generating excessive numbers of callbacks.
But satisfying though it is to wake something up when things are going
south, unless the thing being awakened can actually help solve the
problem, that extra wakeup does nothing but consume additional CPU time,
which is exactly what you don't want during a call_rcu() flood.

This commit therefore avoids doing anything if the corresponding
no-CBs callback kthread is going full tilt.  Otherwise, if advancing
callbacks immediately might help and if the leaf rcu_node structure's
lock is immediately available, this commit invokes a new variant of
rcu_advance_cbs() that advances callbacks only if doing so won't require
awakening the grace-period kthread (not to be confused with any of the
no-CBs grace-period kthreads).

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-08-13 14:35:49 -07:00
Paul E. McKenney
921bb5fad1 rcu/nocb: Use build-time no-CBs check in rcu_pending()
Currently, rcu_pending() invokes rcu_segcblist_is_offloaded() even
in CONFIG_RCU_NOCB_CPU=n kernels, which cannot possibly be offloaded.
Given that rcu_pending() is on a fastpath, it makes sense to check for
CONFIG_RCU_NOCB_CPU=y before invoking rcu_segcblist_is_offloaded().
This commit therefore makes this change.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-08-13 14:35:49 -07:00
Paul E. McKenney
c1ab99d66e rcu/nocb: Use build-time no-CBs check in rcu_core()
Currently, rcu_core() invokes rcu_segcblist_is_offloaded() each time it
needs to know whether the current CPU is a no-CBs CPU.  Given that it is
not possible to change the no-CBs status of a CPU after boot, and given
that it is not possible to even have no-CBs CPUs in CONFIG_RCU_NOCB_CPU=n
kernels, this repeated runtime invocation wastes CPU.  This commit
therefore created a const on-stack variable to allow this check to be
done only once per rcu_core() invocation.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-08-13 14:35:49 -07:00
Paul E. McKenney
ec5ef87bac rcu/nocb: Use build-time no-CBs check in rcu_do_batch()
Currently, rcu_do_batch() invokes rcu_segcblist_is_offloaded() each time
it needs to know whether the current CPU is a no-CBs CPU.  Given that it
is not possible to change the no-CBs status of a CPU after boot, and given
that it is not possible to even have no-CBs CPUs in CONFIG_RCU_NOCB_CPU=n
kernels, this per-callback invocation wastes CPU.  This commit therefore
created a const on-stack variable to allow this check to be done only
once per rcu_do_batch() invocation.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-08-13 14:35:49 -07:00
Paul E. McKenney
c035280f17 rcu/nocb: Remove obsolete nocb_q_count and nocb_q_count_lazy fields
This commit removes the obsolete nocb_q_count and nocb_q_count_lazy
fields, also removing rcu_get_n_cbs_nocb_cpu(), adjusting
rcu_get_n_cbs_cpu(), and making rcutree_migrate_callbacks() once again
disable the ->cblist fields of offline CPUs.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-08-13 14:35:49 -07:00
Paul E. McKenney
5d6742b377 rcu/nocb: Use rcu_segcblist for no-CBs CPUs
Currently the RCU callbacks for no-CBs CPUs are queued on a series of
ad-hoc linked lists, which means that these callbacks cannot benefit
from "drive-by" grace periods, thus suffering needless delays prior
to invocation.  In addition, the no-CBs grace-period kthreads first
wait for callbacks to appear and later wait for a new grace period,
which means that callbacks appearing during a grace-period wait can
be delayed.  These delays increase memory footprint, and could even
result in an out-of-memory condition.

This commit therefore enqueues RCU callbacks from no-CBs CPUs on the
rcu_segcblist structure that is already used by non-no-CBs CPUs.  It also
restructures the no-CBs grace-period kthread to be checking for incoming
callbacks while waiting for grace periods.  Also, instead of waiting
for a new grace period, it waits for the closest grace period that will
cause some of the callbacks to be safe to invoke.  All of these changes
reduce callback latency and thus the number of outstanding callbacks,
in turn reducing the probability of an out-of-memory condition.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-08-13 14:35:49 -07:00
Paul E. McKenney
e83e73f5b0 rcu/nocb: Leave ->cblist enabled for no-CBs CPUs
As a first step towards making no-CBs CPUs use the ->cblist, this commit
leaves the ->cblist enabled for these CPUs.  The main reason to make
no-CBs CPUs use ->cblist is to take advantage of callback numbering,
which will reduce the effects of missed grace periods which in turn will
reduce forward-progress problems for no-CBs CPUs.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-08-13 14:35:49 -07:00
Paul E. McKenney
85f69b3212 rcu/nocb: Check for deferred nocb wakeups before nohz_full early exit
In theory, a timer is used to defer wakeups of no-CBs grace-period
kthreads when the wakeup cannot be done safely directly from the
call_rcu().  In practice, the one-jiffy delay is not always consistent
with timely callback invocation under heavy call_rcu() loads.  Therefore,
there are a number of checks for a pending deferred wakeup, including
from the scheduling-clock interrupt.  Unfortunately, this check follows
the rcu_nohz_full_cpu() early exit, which renders it useless on such CPUs.

This commit therefore moves the check for the pending deferred no-CB
wakeup to precede the rcu_nohz_full_cpu() early exit.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-08-13 14:35:49 -07:00
Paul E. McKenney
c00045be32 rcu/nocb: Make rcutree_migrate_callbacks() start at leaf rcu_node structure
Because rcutree_migrate_callbacks() is invoked infrequently and because
an exact snapshot of the grace-period state might save some callbacks a
second trip through a grace period, this function has used the root
rcu_node structure.  However, this safe-second-trip optimization
happens only if rcutree_migrate_callbacks() races with grace-period
initialization, so it is not worth the added mental load.  This commit
therefore makes rcutree_migrate_callbacks() start with the leaf rcu_node
structures, as is done elsewhere.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-08-13 14:35:49 -07:00
Paul E. McKenney
750d7f6a43 rcu/nocb: Add checks for offloaded callback processing
This commit is a preparatory patch for offloaded callbacks using the
same ->cblist structure used by non-offloaded callbacks.  It therefore
adds rcu_segcblist_is_offloaded() calls where they will be needed when
!rcu_segcblist_is_enabled() no longer flags the offloaded case.  It also
adds checks in rcu_do_batch() to ensure that there are no missed checks:
Currently, it should not be possible for offloaded execution to reach
rcu_do_batch(), though this will change later in this series.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-08-13 14:35:49 -07:00
Paul E. McKenney
ce5215c134 rcu/nocb: Use separate flag to indicate offloaded ->cblist
RCU callback processing currently uses rcu_is_nocb_cpu() to determine
whether or not the current CPU's callbacks are to be offloaded.
This works, but it is not so good for cache locality.  Plus use of
->cblist for offloaded callbacks will greatly increase the frequency
of these checks.  This commit therefore adds a ->offloaded flag to the
rcu_segcblist structure to provide a more flexible and cache-friendly
means of checking for callback offloading.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-08-13 14:35:49 -07:00
Peter Zijlstra
130d9c331b rcu/tree: Fix SCHED_FIFO params
A rather embarrasing mistake had us call sched_setscheduler() before
initializing the parameters passed to it.

Fixes: 1a763fd7c6 ("rcu/tree: Call setschedule() gp ktread to SCHED_FIFO outside of atomic region")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Paul E. McKenney <paulmck@linux.ibm.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
2019-08-08 09:09:30 +02:00
Thomas Gleixner
01b1d88b09 rcu: Use CONFIG_PREEMPTION
CONFIG_PREEMPTION is selected by CONFIG_PREEMPT and by
CONFIG_PREEMPT_RT. Both PREEMPT and PREEMPT_RT require the same
functionality which today depends on CONFIG_PREEMPT.

Switch the conditionals in RCU to use CONFIG_PREEMPTION.

That's the first step towards RCU on RT. The further tweaks are work in
progress. This neither touches the selftest bits which need a closer look
by Paul.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20190726212124.210156346@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-07-31 19:03:35 +02:00
Juri Lelli
1a763fd7c6 rcu/tree: Call setschedule() gp ktread to SCHED_FIFO outside of atomic region
sched_setscheduler() needs to acquire cpuset_rwsem, but it is currently
called from an invalid (atomic) context by rcu_spawn_gp_kthread().

Fix that by simply moving sched_setscheduler_nocheck() call outside of
the atomic region, as it doesn't actually require to be guarded by
rcu_node lock.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bristot@redhat.com
Cc: claudio@evidence.eu.com
Cc: lizefan@huawei.com
Cc: longman@redhat.com
Cc: luca.abeni@santannapisa.it
Cc: mathieu.poirier@linaro.org
Cc: rostedt@goodmis.org
Cc: tj@kernel.org
Cc: tommaso.cucinotta@santannapisa.it
Link: https://lkml.kernel.org/r/20190719140000.31694-8-juri.lelli@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-07-25 15:55:03 +02:00
Paul E. McKenney
11ca7a9d54 Merge branches 'consolidate.2019.05.28a', 'doc.2019.05.28a', 'fixes.2019.06.13a', 'srcu.2019.05.28a', 'sync.2019.05.28a' and 'torture.2019.05.28a' into HEAD
consolidate.2019.05.28a: RCU flavor consolidation cleanups and optmizations.
doc.2019.05.28a: Documentation updates.
fixes.2019.06.13a: Miscellaneous fixes.
srcu.2019.05.28a: SRCU updates.
sync.2019.05.28a: RCU-sync flavor consolidation.
torture.2019.05.28a: Torture-test updates.
2019-06-19 09:21:46 -07:00
Paul E. McKenney
d5a9a8c3bc rcu: Set a maximum limit for back-to-back callback invocation
Currently, if a CPU has more than 10,000 callbacks pending, it will
increase rdp->blimit to LONG_MAX.  If you are lucky, LONG_MAX is only
about two billion, but this is still a bit too many callbacks to invoke
back-to-back while otherwise ignoring the world.

This commit therefore sets a maximum limit of DEFAULT_MAX_RCU_BLIMIT,
which is set to 10,000, for rdp->blimit.

Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-05-28 09:02:57 -07:00
Joel Fernandes (Google)
eddded8012 rcu: Add checks for dynticks counters in rcu_is_cpu_rrupt_from_idle()
It would be good to combine the dynticks and dynticks_nesting counters
in order to simplify the code.  Unfortunately, there are concerns
about usermode upcalls appearing to RCU as half of an interrupt, as
Byungchul learned [1].  The "half" in "half interrupt" is due to an
unpaired rcu_irq_enter(): Normally, each rcu_irq_enter() has a later
call to rcu_irq_exit().

Out of an abundance of caution, Paul added warnings [2] in the RCU
code which if not fired by 2021 will be interpreted as meaning that
this half-interrupt scenario cannot happen any more, thus permitting
simplification of this code.

In the meantime, this commit makes the following changes:

(1) Combining these two counters requires that rcu_rrupt_from_idle()
    is invoked only from hard-interrupt contexts as discussed here [3].
    This commit therefore adds the required lockdep_assert_in_irq()
    to check this constraint.

(2) Furthermore, rcu_rrupt_from_idle() is not explicit about how it
    is using the counters which can lead to weird future bugs. This
    commit therefore adds comments indicating the meaning and use of
    each counter.

(3) Lastly, this commit checks for counter underflows as another check
    that half interrupts don't occur.  (Previously, the function would
    simply return true upon underflow.)

All these checks checks are NOOPs if PROVE_LOCKING (and thus PROVE_RCU)
are disabled.

[1] https://lore.kernel.org/patchwork/patch/952349/
[2] Commit e11ec65cc8 ("rcu: Add warning to detect half-interrupts")
[3] https://lore.kernel.org/lkml/20190312150514.GB249405@google.com/

Cc: byungchul.park@lge.com
Cc: kernel-team@android.com
Cc: rcu@vger.kernel.org
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-05-28 08:48:19 -07:00
Paul E. McKenney
43e903ad3e rcu: Inline invoke_rcu_callbacks() into its sole remaining caller
This commit saves a few lines of code by inlining invoke_rcu_callbacks()
into its sole remaining caller.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-05-25 14:50:49 -07:00
Sebastian Andrzej Siewior
48d07c04b4 rcu: Enable elimination of Tree-RCU softirq processing
Some workloads need to change kthread priority for RCU core processing
without affecting other softirq work.  This commit therefore introduces
the rcutree.use_softirq kernel boot parameter, which moves the RCU core
work from softirq to a per-CPU SCHED_OTHER kthread named rcuc.  Use of
SCHED_OTHER approach avoids the scalability problems that appeared
with the earlier attempt to move RCU core processing to from softirq
to kthreads.  That said, kernels built with RCU_BOOST=y will run the
rcuc kthreads at the RCU-boosting priority.

Note that rcutree.use_softirq=0 must be specified to move RCU core
processing to the rcuc kthreads: rcutree.use_softirq=1 is the default.

Reported-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
[ paulmck: Adjust for invoke_rcu_callbacks() only ever being invoked
  from RCU core processing, in contrast to softirq->rcuc transition
  in old mainline RCU priority boosting. ]
[ paulmck: Avoid wakeups when scheduler might have invoked rcu_read_unlock()
  while holding rq or pi locks, also possibly fixing a pre-existing latent
  bug involving raise_softirq()-induced wakeups. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-05-25 14:50:46 -07:00
Linus Torvalds
d2d8b14604 The major changes in this tracing update includes:
- Removing of non-DYNAMIC_FTRACE from 32bit x86
 
  - Removing of mcount support from x86
 
  - Emulating a call from int3 on x86_64, fixes live kernel patching
 
  - Consolidated Tracing Error logs file
 
 Minor updates:
 
  - Removal of klp_check_compiler_support()
 
  - kdb ftrace dumping output changes
 
  - Accessing and creating ftrace instances from inside the kernel
 
  - Clean up of #define if macro
 
  - Introduction of TRACE_EVENT_NOP() to disable trace events based on config
    options
 
 And other minor fixes and clean ups
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Merge tag 'trace-v5.2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing updates from Steven Rostedt:
 "The major changes in this tracing update includes:

   - Removal of non-DYNAMIC_FTRACE from 32bit x86

   - Removal of mcount support from x86

   - Emulating a call from int3 on x86_64, fixes live kernel patching

   - Consolidated Tracing Error logs file

  Minor updates:

   - Removal of klp_check_compiler_support()

   - kdb ftrace dumping output changes

   - Accessing and creating ftrace instances from inside the kernel

   - Clean up of #define if macro

   - Introduction of TRACE_EVENT_NOP() to disable trace events based on
     config options

  And other minor fixes and clean ups"

* tag 'trace-v5.2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: (44 commits)
  x86: Hide the int3_emulate_call/jmp functions from UML
  livepatch: Remove klp_check_compiler_support()
  ftrace/x86: Remove mcount support
  ftrace/x86_32: Remove support for non DYNAMIC_FTRACE
  tracing: Simplify "if" macro code
  tracing: Fix documentation about disabling options using trace_options
  tracing: Replace kzalloc with kcalloc
  tracing: Fix partial reading of trace event's id file
  tracing: Allow RCU to run between postponed startup tests
  tracing: Fix white space issues in parse_pred() function
  tracing: Eliminate const char[] auto variables
  ring-buffer: Fix mispelling of Calculate
  tracing: probeevent: Fix to make the type of $comm string
  tracing: probeevent: Do not accumulate on ret variable
  tracing: uprobes: Re-enable $comm support for uprobe events
  ftrace/x86_64: Emulate call function while updating in breakpoint handler
  x86_64: Allow breakpoints to emulate call instructions
  x86_64: Add gap to int3 to allow for call emulation
  tracing: kdb: Allow ftdump to skip all but the last few entries
  tracing: Add trace_total_entries() / trace_total_entries_cpu()
  ...
2019-05-15 16:05:47 -07:00
Linus Torvalds
0968621917 Printk changes for 5.2
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Merge tag 'printk-for-5.2' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk

Pull printk updates from Petr Mladek:

 - Allow state reset of printk_once() calls.

 - Prevent crashes when dereferencing invalid pointers in vsprintf().
   Only the first byte is checked for simplicity.

 - Make vsprintf warnings consistent and inlined.

 - Treewide conversion of obsolete %pf, %pF to %ps, %pF printf
   modifiers.

 - Some clean up of vsprintf and test_printf code.

* tag 'printk-for-5.2' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk:
  lib/vsprintf: Make function pointer_string static
  vsprintf: Limit the length of inlined error messages
  vsprintf: Avoid confusion between invalid address and value
  vsprintf: Prevent crash when dereferencing invalid pointers
  vsprintf: Consolidate handling of unknown pointer specifiers
  vsprintf: Factor out %pO handler as kobject_string()
  vsprintf: Factor out %pV handler as va_format()
  vsprintf: Factor out %p[iI] handler as ip_addr_string()
  vsprintf: Do not check address of well-known strings
  vsprintf: Consistent %pK handling for kptr_restrict == 0
  vsprintf: Shuffle restricted_pointer()
  printk: Tie printk_once / printk_deferred_once into .data.once for reset
  treewide: Switch printk users from %pf and %pF to %ps and %pS, respectively
  lib/test_printf: Switch to bitmap_zalloc()
2019-05-07 09:18:12 -07:00
Paul E. McKenney
6cdbc07a5a Merge branches 'consolidate.2019.04.09a', 'doc.2019.03.26b', 'fixes.2019.03.26b', 'srcu.2019.03.26b', 'stall.2019.03.26b' and 'torture.2019.03.26b' into HEAD
consolidate.2019.04.09a: Lingering RCU flavor consolidation cleanups.
doc.2019.03.26b: Documentation updates.
fixes.2019.03.26b: Miscellaneous fixes.
srcu.2019.03.26b: SRCU updates.
stall.2019.03.26b: RCU CPU stall warning updates.
torture.2019.03.26b: Torture-test updates.
2019-04-09 08:08:13 -07:00
Sakari Ailus
d75f773c86 treewide: Switch printk users from %pf and %pF to %ps and %pS, respectively
%pF and %pf are functionally equivalent to %pS and %ps conversion
specifiers. The former are deprecated, therefore switch the current users
to use the preferred variant.

The changes have been produced by the following command:

	git grep -l '%p[fF]' | grep -v '^\(tools\|Documentation\)/' | \
	while read i; do perl -i -pe 's/%pf/%ps/g; s/%pF/%pS/g;' $i; done

And verifying the result.

Link: http://lkml.kernel.org/r/20190325193229.23390-1-sakari.ailus@linux.intel.com
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: sparclinux@vger.kernel.org
Cc: linux-um@lists.infradead.org
Cc: xen-devel@lists.xenproject.org
Cc: linux-acpi@vger.kernel.org
Cc: linux-pm@vger.kernel.org
Cc: drbd-dev@lists.linbit.com
Cc: linux-block@vger.kernel.org
Cc: linux-mmc@vger.kernel.org
Cc: linux-nvdimm@lists.01.org
Cc: linux-pci@vger.kernel.org
Cc: linux-scsi@vger.kernel.org
Cc: linux-btrfs@vger.kernel.org
Cc: linux-f2fs-devel@lists.sourceforge.net
Cc: linux-mm@kvack.org
Cc: ceph-devel@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: David Sterba <dsterba@suse.com> (for btrfs)
Acked-by: Mike Rapoport <rppt@linux.ibm.com> (for mm/memblock.c)
Acked-by: Bjorn Helgaas <bhelgaas@google.com> (for drivers/pci)
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
2019-04-09 14:19:06 +02:00
Yafang Shao
4f5fbd78a7 rcu: validate arguments for rcu tracepoints
When CONFIG_RCU_TRACE is not set, all these tracepoints are defined as
do-nothing macro.
We'd better make those inline functions that take proper arguments.

As RCU_TRACE() is defined as do-nothing marco as well when
CONFIG_RCU_TRACE is not set, so we can clean it up.

Link: http://lkml.kernel.org/r/1553602391-11926-4-git-send-email-laoar.shao@gmail.com

Reviewed-by: Paul E. McKenney <paulmck@linux.ibm.com>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
2019-04-08 09:22:51 -04:00
Paul E. McKenney
b51bcbbf16 rcu: Move forward-progress checkers into tree_stall.h
This commit further consolidates stall-warning functionality by moving
forward-progress checkers into kernel/rcu/tree_stall.h, updating a
comment or two while in the area.  More specifically, this commit moves
show_rcu_gp_kthreads(), rcu_check_gp_start_stall(), rcu_fwd_progress_check(),
sysrq_rcu, sysrq_show_rcu(), sysrq_rcudump_op, and rcu_sysrq_init() from
kernel/rcu/tree.c to kernel/rcu/tree_stall.h.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-03-26 14:40:13 -07:00
Paul E. McKenney
7ac1907c9e rcu: Move irq-disabled stall-warning checking to tree_stall.h
The rcu_iw_handler() function's sole purpose in life is to indicate
whether a stalled CPU had interrupts disabled, so it belongs in
kernel/rcu/tree_stall.h.  This commit therefore makes that move,
clarifying its header comment while in the area.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-03-26 14:40:13 -07:00
Paul E. McKenney
32255d51b6 rcu: Move RCU CPU stall-warning code out of tree.c
This commit completes the process of consolidating the code for RCU CPU
stall warnings for normal grace periods by moving the remaining such
code from kernel/rcu/tree.c to kernel/rcu/tree_stall.h.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-03-26 14:40:13 -07:00
Paul E. McKenney
10462d6f58 rcu: Move RCU CPU stall-warning code out of update.c
The RCU CPU stall-warning code for normal grace periods is currently
scattered across three files, due to earlier Tiny RCU support for RCU
CPU stall warnings and for old Kconfig options that have long since
been retired.  Given that it is hard for the lead RCU maintainer to
find relevant stall-warning code, it would be good to consolidate it.
This commit starts this process by moving stall-warning code from
kernel/rcu/update.c to a new kernel/rcu/tree_stall.h file.

Note that the definitions of rcu_cpu_stall_suppress and
rcu_cpu_stall_timeout must remain in kernel/rcu/update.h to provide
compatibility for kernel boot parameter lists.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-03-26 14:40:13 -07:00
Zhouyi Zhou
5d8a752e31 rcu: Fix force_qs_rnp() header comment
Previously, threads blocked on offlining CPUS were migrated to the
root rcu_node structure, thus requiring RCU priority boosting on this
structure.  However, since commit d19fb8d1f3 ("rcu: Don't migrate
blocked tasks even if all corresponding CPUs offline"), RCU does not
migrate blocked tasks.  Consequently, RCU no longer does RCU priority
boosting on the root rcu_node structure as of commit 1be0085b51 ("rcu:
Don't initiate RCU priority boosting on root rcu_node").

This commit therefore brings comments for the force_qs_rnp() function's
header comment in line with this new no-root-boosting reality.

Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
[ paulmck: Also remove obsolete comment on suppressing new grace periods. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-03-26 14:38:38 -07:00
Paul E. McKenney
85f2b60c43 rcu: Update jiffies_to_sched_qs and adjust_jiffies_till_sched_qs() comments
This commit better documents the jiffies_to_sched_qs default-value
strategy used by adjust_jiffies_till_sched_qs()

Reported-by: Joel Fernandes <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-03-26 14:38:38 -07:00
Neeraj Upadhyay
6973032a60 rcu: Default jiffies_to_sched_qs to jiffies_till_sched_qs
The current code only calls adjust_jiffies_till_sched_qs() if
jiffies_till_sched_qs is left at its default value, so when the
jiffies_till_sched_qs kernel-boot parameter actually is specified,
jiffies_to_sched_qs will be left with the value zero, which
will result in useless slowdowns of cond_resched().  This commit
therefore changes rcu_init_geometry() to unconditionally invoke
adjust_jiffies_till_sched_qs(), which ensures that jiffies_to_sched_qs
will be initialized in all cases, thus maintaining good cond_resched()
performance.

Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-03-26 14:38:38 -07:00