Commit graph

842 commits

Author SHA1 Message Date
Paul E. McKenney
88ee23ef1c rcu: Eliminate rcu_implicit_dynticks_qs() local variable rnhqp
The rcu_implicit_dynticks_qs() function's local variable rnhqp references
the ->rcu_need_heavy_qs field in the rcu_data structure referenced by
the function parameter rdp, with a rather odd method for computing
the pointer to this field.  This commit therefore simplifies things
and saves a few lines of code by replacing each instance of rnhqp with
&rdp->need_heavy_qs.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-09-13 16:32:45 -07:00
Paul E. McKenney
2431774f04 rcu: Mark accesses to rcu_state.n_force_qs
This commit marks accesses to the rcu_state.n_force_qs.  These data
races are hard to make happen, but syzkaller was equal to the task.

Reported-by: syzbot+e08a83a1940ec3846cd5@syzkaller.appspotmail.com
Acked-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-09-13 16:32:45 -07:00
Paul E. McKenney
b770efc460 Merge branches 'doc.2021.07.20c', 'fixes.2021.08.06a', 'nocb.2021.07.20c', 'nolibc.2021.07.20c', 'tasks.2021.07.20c', 'torture.2021.07.27a' and 'torturescript.2021.07.27a' into HEAD
doc.2021.07.20c: Documentation updates.
fixes.2021.08.06a: Miscellaneous fixes.
nocb.2021.07.20c: Callback-offloading (NOCB CPU) updates.
nolibc.2021.07.20c: Tiny userspace library updates.
tasks.2021.07.20c: Tasks RCU updates.
torture.2021.07.27a: In-kernel torture-test updates.
torturescript.2021.07.27a: Torture-test scripting updates.
2021-08-10 11:00:53 -07:00
Sebastian Andrzej Siewior
d3dd95a885 rcu: Replace deprecated CPU-hotplug functions
The functions get_online_cpus() and put_online_cpus() have been
deprecated during the CPU hotplug rework. They map directly to
cpus_read_lock() and cpus_read_unlock().

Replace deprecated CPU-hotplug functions with the official version.
The behavior remains unchanged.

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: rcu@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-08-10 10:47:32 -07:00
Liu Song
8211e922de rcu: Use per_cpu_ptr to get the pointer of per_cpu variable
There are a few remaining locations in kernel/rcu that still use
"&per_cpu()".  This commit replaces them with "per_cpu_ptr(&)", and does
not introduce any functional change.

Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Liu Song <liu.song11@zte.com.cn>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-08-06 13:41:49 -07:00
Liu Song
eb880949ef rcu: Remove useless "ret" update in rcu_gp_fqs_loop()
Within rcu_gp_fqs_loop(), the "ret" local variable is set to the
return value from swait_event_idle_timeout_exclusive(), but "ret" is
unconditionally overwritten later in the code.  This commit therefore
removes this useless assignment.

Signed-off-by: Liu Song <liu.song11@zte.com.cn>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-08-06 13:41:48 -07:00
Paul E. McKenney
f74126dcbc rcu: Make rcu_gp_init() and rcu_gp_fqs_loop noinline to conserve stack
The kbuild test project found an oversized stack frame in rcu_gp_kthread()
for some kernel configurations.  This oversizing was due to a very large
amount of inlining, which is unnecessary due to the fact that this code
executes infrequently.  This commit therefore marks rcu_gp_init() and
rcu_gp_fqs_loop noinline_for_stack to conserve stack space.

Reported-by: kernel test robot <lkp@intel.com>
Tested-by: Rong Chen <rong.a.chen@intel.com>
[ paulmck: noinline_for_stack per Nathan Chancellor. ]
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-08-06 13:41:48 -07:00
Paul E. McKenney
2be57f7328 rcu: Weaken ->dynticks accesses and updates
Accesses to the rcu_data structure's ->dynticks field have always been
fully ordered because it was not possible to prove that weaker ordering
was safe.  However, with the removal of the rcu_eqs_special_set() function
and the advent of the Linux-kernel memory model, it is now easy to show
that two of the four original full memory barriers can be weakened to
acquire and release operations.  The remaining pair must remain full
memory barriers.  This change makes the memory ordering requirements
more evident, and it might well also speed up the to-idle and from-idle
fastpaths on some architectures.

The following litmus test, adapted from one supplied off-list by Frederic
Weisbecker, models the RCU grace-period kthread detecting an idle CPU
that is concurrently transitioning to non-idle:

	C dynticks-from-idle

	{
		DYNTICKS=0; (* Initially idle. *)
	}

	P0(int *X, int *DYNTICKS)
	{
		int dynticks;
		int x;

		// Idle.
		dynticks = READ_ONCE(*DYNTICKS);
		smp_store_release(DYNTICKS, dynticks + 1);
		smp_mb();
		// Now non-idle
		x = READ_ONCE(*X);
	}

	P1(int *X, int *DYNTICKS)
	{
		int dynticks;

		WRITE_ONCE(*X, 1);
		smp_mb();
		dynticks = smp_load_acquire(DYNTICKS);
	}

	exists (1:dynticks=0 /\ 0:x=1)

Running "herd7 -conf linux-kernel.cfg dynticks-from-idle.litmus" verifies
this transition, namely, showing that if the RCU grace-period kthread (P1)
sees another CPU as idle (P0), then any memory access prior to the start
of the grace period (P1's write to X) will be seen by any RCU read-side
critical section following the to-non-idle transition (P0's read from X).
This is a straightforward use of full memory barriers to force ordering
in a store-buffering (SB) litmus test.

The following litmus test, also adapted from the one supplied off-list
by Frederic Weisbecker, models the RCU grace-period kthread detecting
a non-idle CPU that is concurrently transitioning to idle:

	C dynticks-into-idle

	{
		DYNTICKS=1; (* Initially non-idle. *)
	}

	P0(int *X, int *DYNTICKS)
	{
		int dynticks;

		// Non-idle.
		WRITE_ONCE(*X, 1);
		dynticks = READ_ONCE(*DYNTICKS);
		smp_store_release(DYNTICKS, dynticks + 1);
		smp_mb();
		// Now idle.
	}

	P1(int *X, int *DYNTICKS)
	{
		int x;
		int dynticks;

		smp_mb();
		dynticks = smp_load_acquire(DYNTICKS);
		x = READ_ONCE(*X);
	}

	exists (1:dynticks=2 /\ 1:x=0)

Running "herd7 -conf linux-kernel.cfg dynticks-into-idle.litmus" verifies
this transition, namely, showing that if the RCU grace-period kthread
(P1) sees another CPU as newly idle (P0), then any pre-idle memory access
(P0's write to X) will be seen by any code following the grace period
(P1's read from X).  This is a simple release-acquire pair forcing
ordering in a message-passing (MP) litmus test.

Of course, if the grace-period kthread detects the CPU as non-idle,
it will refrain from reporting a quiescent state on behalf of that CPU,
so there are no ordering requirements from the grace-period kthread in
that case.  However, other subsystems call rcu_is_idle_cpu() to check
for CPUs being non-idle from an RCU perspective.  That case is also
verified by the above litmus tests with the proviso that the sense of
the low-order bit of the DYNTICKS counter be inverted.

Unfortunately, on x86 smp_mb() is as expensive as a cache-local atomic
increment.  This commit therefore weakens only the read from ->dynticks.
However, the updates are abstracted into a rcu_dynticks_inc() function
to ease any future changes that might be needed.

[ paulmck: Apply Linus Torvalds feedback. ]

Link: https://lore.kernel.org/lkml/20210721202127.2129660-4-paulmck@kernel.org/
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-08-06 13:41:48 -07:00
Joel Fernandes (Google)
a86baa69c2 rcu: Remove special bit at the bottom of the ->dynticks counter
Commit b8c17e6664 ("rcu: Maintain special bits at bottom of ->dynticks
counter") reserved a bit at the bottom of the ->dynticks counter to defer
flushing of TLBs, but this facility never has been used.  This commit
therefore removes this capability along with the rcu_eqs_special_set()
function used to trigger it.

Link: https://lore.kernel.org/linux-doc/CALCETrWNPOOdTrFabTDd=H7+wc6xJ9rJceg6OL1S0rTV5pfSsA@mail.gmail.com/
Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: "Joel Fernandes (Google)" <joel@joelfernandes.org>
[ paulmck: Forward-port to v5.13-rc1. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-08-06 13:41:48 -07:00
Frederic Weisbecker
cba712beeb rcu/nocb: Remove NOCB deferred wakeup from rcutree_dead_cpu()
At CPU offline time, we must handle any pending wakeup for the nocb_gp
kthread linked to the outgoing CPU.

Now we are making sure of that twice:

1) From rcu_report_dead() when the outgoing CPU makes the very last
   local cleanups by itself before switching offline.

2) From rcutree_dead_cpu(). Here the offlining CPU has gone and is truly
   now offline. Another CPU takes care of post-portem cleaning up and
   check if the offline CPU had pending wakeup.

Both ways are fine but we have to choose one or the other because we
don't need to repeat that action. Simply benefit from cache locality
and keep only the first solution.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-07-20 13:41:51 -07:00
Frederic Weisbecker
dfcb275402 rcu/nocb: Start moving nocb code to its own plugin file
The kernel/rcu/tree_plugin.h file contains not only the plugins for
preemptible RCU, but also many other features including rcu_nocbs
callback offloading.  This offloading has become large and complex,
so it is time to put it in its own file.

This commit starts that process.

Suggested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
[ paulmck: Rename to tree_nocb.h, add Frederic as author. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-07-20 13:41:51 -07:00
Linus Torvalds
28e92f9903 Merge branch 'core-rcu-2021.07.04' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu
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
  ...
2021-07-04 12:58:33 -07:00
Andy Shevchenko
f39650de68 kernel.h: split out panic and oops helpers
kernel.h is being used as a dump for all kinds of stuff for a long time.
Here is the attempt to start cleaning it up by splitting out panic and
oops helpers.

There are several purposes of doing this:
- dropping dependency in bug.h
- dropping a loop by moving out panic_notifier.h
- unload kernel.h from something which has its own domain

At the same time convert users tree-wide to use new headers, although for
the time being include new header back to kernel.h to avoid twisted
indirected includes for existing users.

[akpm@linux-foundation.org: thread_info.h needs limits.h]
[andriy.shevchenko@linux.intel.com: ia64 fix]
  Link: https://lkml.kernel.org/r/20210520130557.55277-1-andriy.shevchenko@linux.intel.com

Link: https://lkml.kernel.org/r/20210511074137.33666-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Co-developed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Mike Rapoport <rppt@linux.ibm.com>
Acked-by: Corey Minyard <cminyard@mvista.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Wei Liu <wei.liu@kernel.org>
Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Sebastian Reichel <sre@kernel.org>
Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Acked-by: Helge Deller <deller@gmx.de> # parisc
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-07-01 11:06:04 -07:00
Paul E. McKenney
641faf1b90 Merge branches 'bitmaprange.2021.05.10c', 'doc.2021.05.10c', 'fixes.2021.05.13a', 'kvfree_rcu.2021.05.10c', 'mmdumpobj.2021.05.10c', 'nocb.2021.05.12a', 'srcu.2021.05.12a', 'tasks.2021.05.18a' and 'torture.2021.05.10c' into HEAD
bitmaprange.2021.05.10c: Allow "all" for bitmap ranges.
doc.2021.05.10c: Documentation updates.
fixes.2021.05.13a: Miscellaneous fixes.
kvfree_rcu.2021.05.10c: kvfree_rcu() updates.
mmdumpobj.2021.05.10c: mem_dump_obj() updates.
nocb.2021.05.12a: RCU NOCB CPU updates, including limited deoffloading.
srcu.2021.05.12a: SRCU updates.
tasks.2021.05.18a: Tasks-RCU updates.
torture.2021.05.10c: Torture-test updates.
2021-05-18 10:56:19 -07:00
Paul E. McKenney
cf868c2af2 rcu-tasks: Make ksoftirqd provide RCU Tasks quiescent states
Heavy networking load can cause a CPU to execute continuously and
indefinitely within ksoftirqd, in which case there will be no voluntary
task switches and thus no RCU-tasks quiescent states.  This commit
therefore causes the exiting rcu_softirq_qs() to provide an RCU-tasks
quiescent state.

This of course means that __do_softirq() and its callers cannot be
invoked from within a tracing trampoline.

Reported-by: Toke Høiland-Jørgensen <toke@redhat.com>
Tested-by: Toke Høiland-Jørgensen <toke@redhat.com>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
2021-05-18 10:54:51 -07:00
Paul E. McKenney
1893afd634 rcu: Improve comments describing RCU read-side critical sections
There are a number of places that call out the fact that preempt-disable
regions of code now act as RCU read-side critical sections, where
preempt-disable regions of code include irq-disable regions of code,
bh-disable regions of code, hardirq handlers, and NMI handlers.  However,
someone relying solely on (for example) the call_rcu() header comment
might well have no idea that preempt-disable regions of code have RCU
semantics.

This commit therefore updates the header comments for
call_rcu(), synchronize_rcu(), rcu_dereference_bh_check(), and
rcu_dereference_sched_check() to call out these new(ish) forms of RCU
readers.

Reported-by: Michel Lespinasse <michel@lespinasse.org>
[ paulmck: Apply Matthew Wilcox and Michel Lespinasse feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-05-13 09:13:23 -07:00
Ingo Molnar
a616aec9aa rcu: Fix various typos in comments
Fix ~12 single-word typos in RCU code comments.

[ paulmck: Apply feedback from Randy Dunlap. ]
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-05-12 12:11:05 -07:00
Frederic Weisbecker
870905169d rcu/nocb: Prepare for fine-grained deferred wakeup
Tuning the deferred wakeup level must be done from a safe wakeup
point. Currently those sites are:

* ->nocb_timer
* user/idle/guest entry
* CPU down
* softirq/rcuc

All of these sites perform the wake up for both RCU_NOCB_WAKE and
RCU_NOCB_WAKE_FORCE.

In order to merge ->nocb_timer and ->nocb_bypass_timer together, we plan
to add a new RCU_NOCB_WAKE_BYPASS that really should be deferred until
a timer fires so that we don't wake up the NOCB-gp kthread too early.

To prepare for that, this commit specifies the per-callsite wakeup
level/limit.

Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
[ paulmck: Fix non-NOCB rcu_nocb_need_deferred_wakeup() definition. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-05-12 12:10:23 -07:00
Paul E. McKenney
3d3a0d1b50 rcu: Point to documentation of ordering guarantees
Add comments to synchronize_rcu() and friends that point to
Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-05-10 16:22:54 -07:00
Paul E. McKenney
2f20de99a6 rcu: Make rcu_gp_cleanup() be noinline for tracing
Although there are trace events for RCU grace periods, these are only
enabled in CONFIG_RCU_TRACE=y kernels.  This commit therefore marks
rcu_gp_cleanup() noinline in order to provide a function that can be
traced that is invoked near the end of each grace period.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-05-10 16:22:54 -07:00
Paul E. McKenney
3ef5a1c382 rcu: Make RCU priority boosting work on single-CPU rcu_node structures
When any CPU comes online, it checks to see if an RCU-boost kthread has
already been created for that CPU's leaf rcu_node structure, and if
not, it creates one.  Unfortunately, it also verifies that this leaf
rcu_node structure actually has at least one online CPU, and if not,
it declines to create the kthread.  Although this behavior makes sense
during early boot, especially on systems that claim far more CPUs than
they actually have, it makes no sense for the first CPU to come online
for a given rcu_node structure.  There is no point in checking because
we know there is a CPU on its way in.

The problem is that timing differences can cause this incoming CPU to not
yet be reflected in the various bit masks even at rcutree_online_cpu()
time, and there is no chance at rcutree_prepare_cpu() time.  Plus it
would be better to create the RCU-boost kthread at rcutree_prepare_cpu()
to handle the case where the CPU is involved in an RCU priority inversion
very shortly after it comes online.

This commit therefore moves the checking to rcu_prepare_kthreads(), which
is called only at early boot, when the check is appropriate.  In addition,
it makes rcutree_prepare_cpu() invoke rcu_spawn_one_boost_kthread(), which
no longer does any checking for online CPUs.

With this change, RCU priority boosting tests now pass for short rcutorture
runs, even with single-CPU leaf rcu_node structures.

Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Scott Wood <swood@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-05-10 16:22:54 -07:00
Paul E. McKenney
8e4b1d2bc1 rcu: Invoke rcu_spawn_core_kthreads() from rcu_spawn_gp_kthread()
Currently, rcu_spawn_core_kthreads() is invoked via an early_initcall(),
which works, except that rcu_spawn_gp_kthread() is also invoked via an
early_initcall() and rcu_spawn_core_kthreads() relies on adjustments to
kthread_prio that are carried out by rcu_spawn_gp_kthread().  There is
no guaranttee of ordering among early_initcall() handlers, and thus no
guarantee that kthread_prio will be properly checked and range-limited
at the time that rcu_spawn_core_kthreads() needs it.

In most cases, this bug is harmless.  After all, the only reason that
rcu_spawn_gp_kthread() adjusts the value of kthread_prio is if the user
specified a nonsensical value for this boot parameter, which experience
indicates is rare.

Nevertheless, a bug is a bug.  This commit therefore causes the
rcu_spawn_core_kthreads() function to be invoked directly from
rcu_spawn_gp_kthread() after any needed adjustments to kthread_prio have
been carried out.

Fixes: 48d07c04b4 ("rcu: Enable elimination of Tree-RCU softirq processing")
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-05-10 16:22:54 -07:00
Zhouyi Zhou
277ffe1b70 rcu: Improve tree.c comments and add code cleanups
This commit cleans up some comments and code in kernel/rcu/tree.c.

Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-05-10 16:22:53 -07:00
Paul E. McKenney
ce7c169dee rcu: Remove the unused rcu_irq_exit_preempt() function
Commit 9ee01e0f69 ("x86/entry: Clean up idtentry_enter/exit()
leftovers") left the rcu_irq_exit_preempt() in place in order to avoid
conflicts with the -rcu tree.  Now that this change has long since hit
mainline, this commit removes the no-longer-used rcu_irq_exit_preempt()
function.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-05-10 16:22:53 -07:00
Frederic Weisbecker
b5befe842e srcu: Fix broken node geometry after early ssp init
An srcu_struct structure that is initialized before rcu_init_geometry()
will have its srcu_node hierarchy based on CONFIG_NR_CPUS.  Once
rcu_init_geometry() is called, this hierarchy is compressed as needed
for the actual maximum number of CPUs for this system.

Later on, that srcu_struct structure is confused, sometimes referring
to its initial CONFIG_NR_CPUS-based hierarchy, and sometimes instead
to the new num_possible_cpus() hierarchy.  For example, each of its
->mynode fields continues to reference the original leaf rcu_node
structures, some of which might no longer exist.  On the other hand,
srcu_for_each_node_breadth_first() traverses to the new node hierarchy.

There are at least two bad possible outcomes to this:

1) a) A callback enqueued early on an srcu_data structure (call it
      *sdp) is recorded pending on sdp->mynode->srcu_data_have_cbs in
      srcu_funnel_gp_start() with sdp->mynode pointing to a deep leaf
      (say 3 levels).

   b) The grace period ends after rcu_init_geometry() shrinks the
      nodes level to a single one.  srcu_gp_end() walks through the new
      srcu_node hierarchy without ever reaching the old leaves so the
      callback is never executed.

   This is easily reproduced on an 8 CPUs machine with CONFIG_NR_CPUS >= 32
   and "rcupdate.rcu_self_test=1". The srcu_barrier() after early tests
   verification never completes and the boot hangs:

	[ 5413.141029] INFO: task swapper/0:1 blocked for more than 4915 seconds.
	[ 5413.147564]       Not tainted 5.12.0-rc4+ #28
	[ 5413.151927] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
	[ 5413.159753] task:swapper/0       state:D stack:    0 pid:    1 ppid:     0 flags:0x00004000
	[ 5413.168099] Call Trace:
	[ 5413.170555]  __schedule+0x36c/0x930
	[ 5413.174057]  ? wait_for_completion+0x88/0x110
	[ 5413.178423]  schedule+0x46/0xf0
	[ 5413.181575]  schedule_timeout+0x284/0x380
	[ 5413.185591]  ? wait_for_completion+0x88/0x110
	[ 5413.189957]  ? mark_held_locks+0x61/0x80
	[ 5413.193882]  ? mark_held_locks+0x61/0x80
	[ 5413.197809]  ? _raw_spin_unlock_irq+0x24/0x50
	[ 5413.202173]  ? wait_for_completion+0x88/0x110
	[ 5413.206535]  wait_for_completion+0xb4/0x110
	[ 5413.210724]  ? srcu_torture_stats_print+0x110/0x110
	[ 5413.215610]  srcu_barrier+0x187/0x200
	[ 5413.219277]  ? rcu_tasks_verify_self_tests+0x50/0x50
	[ 5413.224244]  ? rdinit_setup+0x2b/0x2b
	[ 5413.227907]  rcu_verify_early_boot_tests+0x2d/0x40
	[ 5413.232700]  do_one_initcall+0x63/0x310
	[ 5413.236541]  ? rdinit_setup+0x2b/0x2b
	[ 5413.240207]  ? rcu_read_lock_sched_held+0x52/0x80
	[ 5413.244912]  kernel_init_freeable+0x253/0x28f
	[ 5413.249273]  ? rest_init+0x250/0x250
	[ 5413.252846]  kernel_init+0xa/0x110
	[ 5413.256257]  ret_from_fork+0x22/0x30

2) An srcu_struct structure that is initialized before rcu_init_geometry()
   and used afterward will always have stale rdp->mynode references,
   resulting in callbacks to be missed in srcu_gp_end(), just like in
   the previous scenario.

This commit therefore causes init_srcu_struct_nodes to initialize the
geometry, if needed.  This ensures that the srcu_node hierarchy is
properly built and distributed from the get-go.

Suggested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Uladzislau Rezki <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-05-10 16:03:35 -07:00
Frederic Weisbecker
8e9c01c717 srcu: Initialize SRCU after timers
Once srcu_init() is called, the SRCU core will make use of delayed
workqueues, which rely on timers.  However init_timers() is called
several steps after rcu_init().  This means that a call_srcu() after
rcu_init() but before init_timers() would find itself within a dangerously
uninitialized timer core.

This commit therefore creates a separate call to srcu_init() after
init_timer() completes, which ensures that we stay in early SRCU mode
until timers are safe(r).

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Uladzislau Rezki <urezki@gmail.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-05-10 16:03:35 -07:00
Uladzislau Rezki (Sony)
a78d4a2a10 kvfree_rcu: Refactor kfree_rcu_monitor()
Currently we have three functions which depend on each other.
Two of them are quite tiny and the last one where the most
work is done. All of them are related to queuing RCU batches
to reclaim objects after a GP.

1. kfree_rcu_monitor(). It consist of few lines. It acquires a spin-lock
   and calls kfree_rcu_drain_unlock().

2. kfree_rcu_drain_unlock(). It also consists of few lines of code. It
   calls queue_kfree_rcu_work() to queue the batch.  If this fails,
   it rearms the monitor work to try again later.

3. queue_kfree_rcu_work(). This provides the bulk of the functionality,
   attempting to start a new batch to free objects after a GP.

Since there are no external users of functions [2] and [3], both
can eliminated by moving all logic directly into [1], which both
shrinks and simplifies the code.

Also replace comments which start with "/*" to "//" format to make it
unified across the file.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-05-10 16:00:48 -07:00
Uladzislau Rezki (Sony)
d8628f35ba kvfree_rcu: Fix comments according to current code
The kvfree_rcu() function now defers allocations in the common
case due to the fact that there is no lockless access to the
memory-allocator caches/pools.  In addition, in CONFIG_PREEMPT_NONE=y
and in CONFIG_PREEMPT_VOLUNTARY=y kernels, there is no reliable way to
determine if spinlocks are held.  As a result, allocation is deferred in
the common case, and the two-argument form of kvfree_rcu() thus uses the
"channel 3" queue through all the rcu_head structures.  This channel
is called referred to as the emergency case in comments, and these
comments are now obsolete.

This commit therefore updates these comments to reflect the new
common-case nature of such emergencies.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-05-10 16:00:48 -07:00
Uladzislau Rezki (Sony)
7fe1da33f6 kvfree_rcu: Use kfree_rcu_monitor() instead of open-coded variant
Replace an open-coded version of the kfree_rcu_monitor() function body
with a call to that function.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-05-10 16:00:48 -07:00
Uladzislau Rezki (Sony)
dd28c9f057 kvfree_rcu: Update "monitor_todo" once a batch is started
Before attempting to start a new batch the "monitor_todo" variable is
set to "false" and set back to "true" when a previous RCU batch is still
in progress.  This is at best confusing.

Thus change this variable to "false" only when a new batch has been
successfully queued, otherwise, just leave it be.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-05-10 16:00:48 -07:00
Uladzislau Rezki (Sony)
d434c00fa3 kvfree_rcu: Add a bulk-list check when a scheduler is run
The rcu_scheduler_active flag is set to RCU_SCHEDULER_RUNNING once the
scheduler is up and running.  That signal is used in order to check
and queue a "monitor work" to reclaim freed objects (if there are any)
during early boot.  This flag is used by kvfree_rcu() to determine when
work can safely be queued, at which point memory passed to earlier
invocations of kvfree_rcu() can be processed.

However, only "krcp->head" is checked for objects that need to be
released, and there are now two more, namely, "krcp->bkvhead[0]" and
"krcp->bkvhead[1]".  Therefore, check these two additional channels.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-05-10 16:00:48 -07:00
Uladzislau Rezki (Sony)
ac7625ebd5 kvfree_rcu: Use [READ/WRITE]_ONCE() macros to access to nr_bkv_objs
nr_bkv_objs is a count of the objects in the kvfree_rcu page cache.
Accessing it requires holding the ->lock.  Switch to READ_ONCE() and
WRITE_ONCE() macros to provide lockless access to this counter.
This lockless access is used for the shrinker.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-05-10 16:00:48 -07:00
Zhang Qiang
d0bfa8b3c4 kvfree_rcu: Release a page cache under memory pressure
Add a drain_page_cache() function to drain a per-cpu page cache.
The reason behind of it is a system can run into a low memory
condition, in that case a page shrinker can ask for its users
to free their caches in order to get extra memory available for
other needs in a system.

When a system hits such condition, a page cache is drained for
all CPUs in a system. By default a page cache work is delayed
with 5 seconds interval until a memory pressure disappears, if
needed it can be changed. See a rcu_delay_page_cache_fill_msec
module parameter.

Co-developed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Zqiang <qiang.zhang@windriver.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-05-10 16:00:48 -07:00
Paul E. McKenney
ab6ad3dbdd Merge branches 'bitmaprange.2021.03.08a', 'fixes.2021.03.15a', 'kvfree_rcu.2021.03.08a', 'mmdumpobj.2021.03.08a', 'nocb.2021.03.15a', 'poll.2021.03.24a', 'rt.2021.03.08a', 'tasks.2021.03.08a', 'torture.2021.03.08a' and 'torturescript.2021.03.22a' into HEAD
bitmaprange.2021.03.08a:  Allow 3-N for bitmap ranges.
fixes.2021.03.15a:  Miscellaneous fixes.
kvfree_rcu.2021.03.08a:  kvfree_rcu() updates.
mmdumpobj.2021.03.08a:  mem_dump_obj() updates.
nocb.2021.03.15a:  RCU NOCB CPU updates, including limited deoffloading.
poll.2021.03.24a:  Polling grace-period interfaces for RCU.
rt.2021.03.08a:  Realtime-related RCU changes.
tasks.2021.03.08a:  Tasks-RCU updates.
torture.2021.03.08a:  Torture-test updates.
torturescript.2021.03.22a:  Torture-test scripting updates.
2021-03-24 17:20:18 -07:00
Paul E. McKenney
7abb18bd75 rcu: Provide polling interfaces for Tree RCU grace periods
There is a need for a non-blocking polling interface for RCU grace
periods, so this commit supplies start_poll_synchronize_rcu() and
poll_state_synchronize_rcu() for this purpose.  Note that the existing
get_state_synchronize_rcu() may be used if future grace periods are
inevitable (perhaps due to a later call_rcu() invocation).  The new
start_poll_synchronize_rcu() is to be used if future grace periods
might not otherwise happen.  Finally, poll_state_synchronize_rcu()
provides a lockless check for a grace period having elapsed since
the corresponding call to either of the get_state_synchronize_rcu()
or start_poll_synchronize_rcu().

As with get_state_synchronize_rcu(), the return value from either
get_state_synchronize_rcu() or start_poll_synchronize_rcu() is passed in
to a later call to either poll_state_synchronize_rcu() or the existing
(might_sleep) cond_synchronize_rcu().

[ paulmck: Remove redundant smp_mb() per Frederic Weisbecker feedback. ]
[ Update poll_state_synchronize_rcu() docbook per Frederic Weisbecker feedback. ]
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-22 08:23:48 -07:00
Frederic Weisbecker
ec711bc12c rcu/nocb: Only (re-)initialize segcblist when needed on CPU up
At the start of a CPU-hotplug operation, the incoming CPU's callback
list can be in a number of states:

1.	Disabled and empty.  This is the case when the boot CPU has
	not invoked call_rcu(), when a non-boot CPU first comes online,
	and when a non-offloaded CPU comes back online.  In this case,
	it is both necessary and permissible to initialize ->cblist.
	Because either the CPU is currently running with interrupts
	disabled (boot CPU) or is not yet running at all (other CPUs),
	it is not necessary to acquire ->nocb_lock.

	In this case, initialization is required.

2.	Disabled and non-empty.  This cannot occur, because early boot
	call_rcu() invocations enable the callback list before enqueuing
	their callback.

3.	Enabled, whether empty or not.	In this case, the callback
	list has already been initialized.  This case occurs when the
	boot CPU has executed an early boot call_rcu() and also when
	an offloaded CPU comes back online.  In both cases, there is
	no need to initialize the callback list: In the boot-CPU case,
	the CPU has not (yet) gone offline, and in the offloaded case,
	the rcuo kthreads are taking care of business.

	Because it is not necessary to initialize the callback list,
	it is also not necessary to acquire ->nocb_lock.

Therefore, checking if the segcblist is enabled suffices.  This commit
therefore initializes the callback list at rcutree_prepare_cpu() time
only if that list is disabled.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-08 14:20:22 -08:00
Frederic Weisbecker
64305db285 rcu/nocb: Forbid NOCB toggling on offline CPUs
It makes no sense to de-offload an offline CPU because that CPU will never
invoke any remaining callbacks.  It also makes little sense to offload an
offline CPU because any pending RCU callbacks were migrated when that CPU
went offline.  Yes, it is in theory possible to use a number of tricks
to permit offloading and deoffloading offline CPUs in certain cases, but
in practice it is far better to have the simple and deterministic rule
"Toggling the offload state of an offline CPU is forbidden".

For but one example, consider that an offloaded offline CPU might have
millions of callbacks queued.  Best to just say "no".

This commit therefore forbids toggling of the offloaded state of
offline CPUs.

Reported-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-08 14:20:21 -08:00
Frederic Weisbecker
3820b513a2 rcu/nocb: Detect unsafe checks for offloaded rdp
Provide CONFIG_PROVE_RCU sanity checks to ensure we are always reading
the offloaded state of an rdp in a safe and stable way and prevent from
its value to be changed under us. We must either hold the barrier mutex,
the cpu-hotplug lock (read or write) or the nocb lock.
Local non-preemptible reads are also safe. NOCB kthreads and timers have
their own means of synchronization against the offloaded state updaters.

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: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-08 14:20:20 -08:00
Uladzislau Rezki (Sony)
ee6ddf5847 kvfree_rcu: Use same set of GFP flags as does single-argument
Running an rcuscale stress-suite can lead to "Out of memory" of a
system. This can happen under high memory pressure with a small amount
of physical memory.

For example, a KVM test configuration with 64 CPUs and 512 megabytes
can result in OOM when running rcuscale with below parameters:

../kvm.sh --torture rcuscale --allcpus --duration 10 --kconfig CONFIG_NR_CPUS=64 \
--bootargs "rcuscale.kfree_rcu_test=1 rcuscale.kfree_nthreads=16 rcuscale.holdoff=20 \
  rcuscale.kfree_loops=10000 torture.disable_onoff_at_boot" --trust-make

<snip>
[   12.054448] kworker/1:1H invoked oom-killer: gfp_mask=0x2cc0(GFP_KERNEL|__GFP_NOWARN), order=0, oom_score_adj=0
[   12.055303] CPU: 1 PID: 377 Comm: kworker/1:1H Not tainted 5.11.0-rc3+ #510
[   12.055416] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.12.0-1 04/01/2014
[   12.056485] Workqueue: events_highpri fill_page_cache_func
[   12.056485] Call Trace:
[   12.056485]  dump_stack+0x57/0x6a
[   12.056485]  dump_header+0x4c/0x30a
[   12.056485]  ? del_timer_sync+0x20/0x30
[   12.056485]  out_of_memory.cold.47+0xa/0x7e
[   12.056485]  __alloc_pages_slowpath.constprop.123+0x82f/0xc00
[   12.056485]  __alloc_pages_nodemask+0x289/0x2c0
[   12.056485]  __get_free_pages+0x8/0x30
[   12.056485]  fill_page_cache_func+0x39/0xb0
[   12.056485]  process_one_work+0x1ed/0x3b0
[   12.056485]  ? process_one_work+0x3b0/0x3b0
[   12.060485]  worker_thread+0x28/0x3c0
[   12.060485]  ? process_one_work+0x3b0/0x3b0
[   12.060485]  kthread+0x138/0x160
[   12.060485]  ? kthread_park+0x80/0x80
[   12.060485]  ret_from_fork+0x22/0x30
[   12.062156] Mem-Info:
[   12.062350] active_anon:0 inactive_anon:0 isolated_anon:0
[   12.062350]  active_file:0 inactive_file:0 isolated_file:0
[   12.062350]  unevictable:0 dirty:0 writeback:0
[   12.062350]  slab_reclaimable:2797 slab_unreclaimable:80920
[   12.062350]  mapped:1 shmem:2 pagetables:8 bounce:0
[   12.062350]  free:10488 free_pcp:1227 free_cma:0
...
[   12.101610] Out of memory and no killable processes...
[   12.102042] Kernel panic - not syncing: System is deadlocked on memory
[   12.102583] CPU: 1 PID: 377 Comm: kworker/1:1H Not tainted 5.11.0-rc3+ #510
[   12.102600] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.12.0-1 04/01/2014
<snip>

Because kvfree_rcu() has a fallback path, memory allocation failure is
not the end of the world.  Furthermore, the added overhead of aggressive
GFP settings must be balanced against the overhead of the fallback path,
which is a cache miss for double-argument kvfree_rcu() and a call to
synchronize_rcu() for single-argument kvfree_rcu().  The current choice
of GFP_KERNEL|__GFP_NOWARN can result in longer latencies than a call
to synchronize_rcu(), so less-tenacious GFP flags would be helpful.

Here is the tradeoff that must be balanced:
    a) Minimize use of the fallback path,
    b) Avoid pushing the system into OOM,
    c) Bound allocation latency to that of synchronize_rcu(), and
    d) Leave the emergency reserves to use cases lacking fallbacks.

This commit therefore changes GFP flags from GFP_KERNEL|__GFP_NOWARN to
GFP_KERNEL|__GFP_NORETRY|__GFP_NOMEMALLOC|__GFP_NOWARN.  This combination
leaves the emergency reserves alone and can initiate reclaim, but will
not invoke the OOM killer.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-08 14:18:07 -08:00
Uladzislau Rezki (Sony)
3e7ce7a187 kvfree_rcu: Replace __GFP_RETRY_MAYFAIL by __GFP_NORETRY
__GFP_RETRY_MAYFAIL can spend quite a bit of time reclaiming, and this
can be wasted effort given that there is a fallback code path in case
memory allocation fails.

__GFP_NORETRY does perform some light-weight reclaim, but it will fail
under OOM conditions, allowing the fallback to be taken as an alternative
to hard-OOMing the system.

There is a four-way tradeoff that must be balanced:
    1) Minimize use of the fallback path;
    2) Avoid full-up OOM;
    3) Do a light-wait allocation request;
    4) Avoid dipping into the emergency reserves.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-08 14:18:07 -08:00
Paul E. McKenney
7ffc9ec8ea kvfree_rcu: Make krc_this_cpu_unlock() use raw_spin_unlock_irqrestore()
The krc_this_cpu_unlock() function does a raw_spin_unlock() immediately
followed by a local_irq_restore().  This commit saves a line of code by
merging them into a raw_spin_unlock_irqrestore().  This transformation
also reduces scheduling latency because raw_spin_unlock_irqrestore()
responds immediately to a reschedule request.  In contrast,
local_irq_restore() does a scheduling-oblivious enabling of interrupts.

Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-08 14:18:07 -08:00
Paul E. McKenney
b01b405092 kvfree_rcu: Use __GFP_NOMEMALLOC for single-argument kvfree_rcu()
This commit applies the __GFP_NOMEMALLOC gfp flag to memory allocations
carried out by the single-argument variant of kvfree_rcu(), thus avoiding
this can-sleep code path from dipping into the emergency reserves.

Acked-by: Michal Hocko <mhocko@suse.com>
Suggested-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-08 14:18:07 -08:00
Uladzislau Rezki (Sony)
148e3731d1 kvfree_rcu: Directly allocate page for single-argument case
Single-argument kvfree_rcu() must be invoked from sleepable contexts,
so we can directly allocate pages.  Furthermmore, the fallback in case
of page-allocation failure is the high-latency synchronize_rcu(), so it
makes sense to do these page allocations from the fastpath, and even to
permit limited sleeping within the allocator.

This commit therefore allocates if needed on the fastpath using
GFP_KERNEL|__GFP_RETRY_MAYFAIL.  This also has the beneficial effect
of leaving kvfree_rcu()'s per-CPU caches to the double-argument variant
of kvfree_rcu(), given that the double-argument variant cannot directly
invoke the allocator.

[ paulmck: Add add_ptr_to_bulk_krc_lock header comment per Michal Hocko. ]
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-08 14:18:07 -08:00
Zhouyi Zhou
6494ccb932 rcu: Remove spurious instrumentation_end() in rcu_nmi_enter()
In rcu_nmi_enter(), there is an erroneous instrumentation_end() in the
second branch of the "if" statement.  Oddly enough, "objtool check -f
vmlinux.o" fails to complain because it is unable to correctly cover
all cases.  Instead, objtool visits the third branch first, which marks
following trace_rcu_dyntick() as visited.  This commit therefore removes
the spurious instrumentation_end().

Fixes: 04b25a495b ("rcu: Mark rcu_nmi_enter() call to rcu_cleanup_after_idle() noinstr")
Reported-by Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-08 14:17:35 -08:00
Neeraj Upadhyay
47fcbc8dd6 rcu: Fix CPU-offline trace in rcutree_dying_cpu
The condition in the trace_rcu_grace_period() in rcutree_dying_cpu() is
backwards, so that it uses the string "cpuofl" when the offline CPU is
blocking the current grace period and "cpuofl-bgp" otherwise.  Given that
the "-bgp" stands for "blocking grace period", this is at best misleading.
This commit therefore switches these strings in order to correctly trace
whether the outgoing cpu blocks the current grace period.

Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-08 14:17:35 -08:00
Frederic Weisbecker
d3ad5bbc4d rcu: Remove superfluous rdp fetch
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar<mingo@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-08 14:17:35 -08:00
Linus Torvalds
657bd90c93 Scheduler updates for v5.12:
[ 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>
 -----BEGIN PGP SIGNATURE-----
 
 iQJFBAABCgAvFiEEBpT5eoXrXCwVQwEKEnMQ0APhK1gFAmAtHBsRHG1pbmdvQGtl
 cm5lbC5vcmcACgkQEnMQ0APhK1itgg/+NGed12pgPjYBzesdou60Lvx7LZLGjfOt
 M1F1EnmQGn/hEH2fCY6ZoqIZQTVltm7GIcBNabzYTzlaHZsdtyuDUJBZyj19vTlk
 zekcj7WVt+qvfjChaNwEJhQ9nnOM/eohMgEOHMAAJd9zlnQvve7NOLQ56UDM+kn/
 9taFJ5ZPvb4avP6C5p3KivvKex6Bjof/Tl0m3utpNyPpI/qK3FyGxwdgCxU0yepT
 ABWQX5ZQCufFvo1bgnBPfqyzab4MqhoM3bNKBsLQfuAlssG1xRv4KQOev4dRwrt9
 pXJikV5C9yez5d2lGe5p0ltH5IZS/l9x2yI/ZQj3OUDTFyV1ic6WfFAqJgDzVF8E
 i/vvA4NPQiI241Bkps+ErcCw4aVOgiY6TWli74cHjLUIX0+As6aHrFWXGSxUmiHB
 WR+B8KmdfzRTTlhOxMA+cvlpZcKCfxWkJJmXzr/lDZzIuKPqM3QCE2wD9sixkfVo
 JNICT0IvZghWOdbMEfZba8Psh/e2LVI9RzdpEiuYJz1ZrVlt1hO0M6jBxY0hMz9n
 k54z81xODw0a8P2FHMtpmB1vhAeqCmvwA6DO8z0Oxs0DFi+KM2bLf2efHsCKafI+
 Bm5v9YFaOk/55R76hJVh+aYLlyFgFkKd+P/niJTPDnxOk3SqJuXvTrql1HeGHkNr
 kYgQa23dsZk=
 =pyaG
 -----END PGP SIGNATURE-----

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()
  ...
2021-02-21 12:35:04 -08:00
Frederic Weisbecker
4ae7dc97f7 entry/kvm: Explicitly flush pending rcuog wakeup before last rescheduling point
Following the idle loop model, cleanly check for pending rcuog wakeup
before the last rescheduling point upon resuming to guest mode. This
way we can avoid to do it from rcu_user_enter() with the last resort
self-IPI hack that enforces rescheduling.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20210131230548.32970-6-frederic@kernel.org
2021-02-17 14:12:43 +01:00
Frederic Weisbecker
47b8ff194c entry: Explicitly flush pending rcuog wakeup before last rescheduling point
Following the idle loop model, cleanly check for pending rcuog wakeup
before the last rescheduling point on resuming to user mode. This
way we can avoid to do it from rcu_user_enter() with the last resort
self-IPI hack that enforces rescheduling.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20210131230548.32970-5-frederic@kernel.org
2021-02-17 14:12:43 +01:00
Frederic Weisbecker
f8bb5cae96 rcu/nocb: Trigger self-IPI on late deferred wake up before user resume
Entering RCU idle mode may cause a deferred wake up of an RCU NOCB_GP
kthread (rcuog) to be serviced.

Unfortunately the call to rcu_user_enter() is already past the last
rescheduling opportunity before we resume to userspace or to guest mode.
We may escape there with the woken task ignored.

The ultimate resort to fix every callsites is to trigger a self-IPI
(nohz_full depends on arch to implement arch_irq_work_raise()) that will
trigger a reschedule on IRQ tail or guest exit.

Eventually every site that want a saner treatment will need to carefully
place a call to rcu_nocb_flush_deferred_wakeup() before the last explicit
need_resched() check upon resume.

Fixes: 96d3fd0d31 (rcu: Break call_rcu() deadlock involving scheduler and perf)
Reported-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20210131230548.32970-4-frederic@kernel.org
2021-02-17 14:12:43 +01:00