Commit Graph

1774 Commits

Author SHA1 Message Date
Frederic Weisbecker
e75bcd48e2 rcu/nocb: Unify timers
Now that ->nocb_timer and ->nocb_bypass_timer have become quite similar,
this commit merges them together.  A new RCU_NOCB_WAKE_BYPASS wake level
is introduced.  As a result, timers perform all kinds of deferred wake
ups but other deferred wakeup callsites only handle non-bypass wakeups
in order not to wake up rcuo too early.

The timer also unconditionally executes a full barrier so as to order
timer_pending() and callback enqueue although the path performing
RCU_NOCB_WAKE_FORCE that makes use of it is debatable. It should also
test against the rdp leader instead of the current rdp.

This unconditional full barrier shouldn't bring visible overhead since
these timers almost never fire.

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>
2021-05-12 12:10:23 -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
Frederic Weisbecker
f9fc166b79 rcu/nocb: Only cancel nocb timer if not polling
This commit refrains deleting the ->nocb_timer if rcu_nocb is polling
because it should not ever have been queued in the polling case.

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>
2021-05-12 12:10:23 -07:00
Frederic Weisbecker
3b2348e2fd rcu/nocb: Delete bypass_timer upon nocb_gp wakeup
A NOCB-gp wake p can safely delete the ->nocb_bypass_timer because
nocb_gp_wait() will recheck again the bypass state and rearm the bypass
timer if necessary.  This commit therefore deletes this timer.

Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
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>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-05-12 12:10:23 -07:00
Frederic Weisbecker
b6e2c4ed35 rcu/nocb: Cancel nocb_timer upon nocb_gp wakeup
When waking up in nocb_gp_wait(), there is no need to keep the nocb_timer
around because this function will traverse the whole rdp list. Any
update performed before the timer was armed will now be visible after
the ->nocb_gp_lock acquire.

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>
2021-05-12 12:10:23 -07:00
Frederic Weisbecker
552cac80e6 rcu/nocb: Allow de-offloading rdp leader
The only thing that prevented an rdp leader from being de-offloaded was
the nocb_bypass_timer that used to lock the nocb_lock of the rdp leader.

If an rdp gets de-offloaded, it will subtlely ignore rcu_nocb_lock()
calls and do its job in the timer unsafely.  Worse yet:  If it gets
re-offloaded in the middle of the timer, rcu_nocb_unlock() would try to
unlock, leaving it imbalanced.

Now that the nocb_bypass_timer doesn't use the nocb_lock anymore,
de-offloading the rdp leader is now safe.  This commit therefore allows
the rdp leader to be de-offloaded.

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>
2021-05-12 12:10:23 -07:00
Frederic Weisbecker
c7ef7500a8 rcu/nocb: Directly call __wake_nocb_gp() from bypass timer
The bypass timer calls __call_rcu_nocb_wake() instead of directly
calling __wake_nocb_gp().  The only difference here is that
rdp->qlen_last_fqs_check gets overridden.  But resetting the deferred
force quiescent state base shouldn't be relevant for that timer.  In fact
the bypass queue in question can be for any rdp from the group and not
necessarily the rdp leader on which the bypass timer is attached.

This commit therefore calls __wake_nocb_gp() directly.  This way we
don't even need to lock the ->nocb_lock.

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>
2021-05-12 12:10:08 -07:00
Frederic Weisbecker
d76e0926d8 rcu/nocb: Use the rcuog CPU's ->nocb_timer
Currently each CPU has its own ->nocb_timer queued when the nocb_gp
wakeup must be deferred.  This approach has many drawbacks, compared to
a solution based on a single timer per NOCB group:

* There are a lot of timers to maintain.

* The per-rdp ->nocb_lock must be held to queue and cancel the timer
  and this lock can already be heavily contended.

* One timer firing doesn't cancel the other timers in the same group:
  - These other timers can thus cause spurious wakeups
  - Each rdp that queued a timer must lock both ->nocb_lock and then
    ->nocb_gp_lock upon exit from the kernel to idle/user/guest mode.

* We can't cancel all of them if we detect an unflushed bypass in
  nocb_gp_wait(). In fact currently we only ever cancel the ->nocb_timer
  of the leader group.

* The leader group's nocb_timer is cancelled without locking ->nocb_lock
  in nocb_gp_wait().  This currently appears to be safe but is an
  accident waiting to happen.

* Since the timer acquires ->nocb_lock, it requires extra care in the
  NOCB (de-)offloading process, requiring that it be either enabled or
  disabled and then flushed.

This commit instead uses the rcuog kthread's CPU's ->nocb_timer instead.
It is protected by nocb_gp_lock, which is _way_ less contended and
remains so even after this change.  As a matter of fact, the nocb_timer
almost never fires and the deferred wakeup is mostly carried out upon
idle/user/guest entry.  Now the early check performed at this point in
do_nocb_deferred_wakeup() is done on rdp_gp->nocb_defer_wakeup, which
is of course racy.  However, this raciness is harmless because we only
need the guarantee that the timer is queued if we were the last one to
queue it.  Any other situation (another CPU has queued it and we either
see it or not) is fine.

This solves all the issues listed above.

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>
2021-05-10 16:02:44 -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
7ac3fdf099 rcutorture: Test start_poll_synchronize_rcu() and poll_state_synchronize_rcu()
This commit causes rcutorture to test the new start_poll_synchronize_rcu()
and poll_state_synchronize_rcu() functions.  Because of the difficulty of
determining the nature of a synchronous RCU grace (expedited or not),
the test that insisted that poll_state_synchronize_rcu() detect an
intervening synchronize_rcu() had to be dropped.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-24 17:17:38 -07:00
Paul E. McKenney
0909fc2b2c rcu: Provide polling interfaces for Tiny 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: Revert cond_synchronize_rcu() to might_sleep() per Frederic Weisbecker feedback. ]
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-24 17:16:15 -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
e02691b7ef rcu/nocb: Move trace_rcu_nocb_wake() calls outside nocb_lock when possible
Those tracing calls don't need to be under ->nocb_lock.  This commit
therefore moves them outside of that lock.

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>
2021-03-15 13:54:55 -07:00
Frederic Weisbecker
0efdf14a9f rcu/nocb: Remove stale comment above rcu_segcblist_offload()
This commit removes a stale comment claiming that the cblist must be
empty before changing the offloading state.  This claim was correct back
when the offloaded state was defined exclusively at boot.

Reported-by: Paul E. McKenney <paulmck@kernel.org>
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>
2021-03-15 13:54:54 -07:00
Frederic Weisbecker
76d00b494d rcu/nocb: Disable bypass when CPU isn't completely offloaded
Currently, the bypass is flushed at the very last moment in the
deoffloading procedure.  However, this approach leads to a larger state
space than would be preferred.  This commit therefore disables the
bypass at soon as the deoffloading procedure begins, then flushes it.
This guarantees that the bypass remains empty and thus out of the way
of the deoffloading procedure.

Symmetrically, this commit waits to enable the bypass until the offloading
procedure has completed.

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>
2021-03-15 13:54:54 -07:00
Frederic Weisbecker
b2fcf21020 rcu/nocb: Fix missed nocb_timer requeue
This sequence of events can lead to a failure to requeue a CPU's
->nocb_timer:

1.	There are no callbacks queued for any CPU covered by CPU 0-2's
	->nocb_gp_kthread.  Note that ->nocb_gp_kthread is associated
	with CPU 0.

2.	CPU 1 enqueues its first callback with interrupts disabled, and
	thus must defer awakening its ->nocb_gp_kthread.  It therefore
	queues its rcu_data structure's ->nocb_timer.  At this point,
	CPU 1's rdp->nocb_defer_wakeup is RCU_NOCB_WAKE.

3.	CPU 2, which shares the same ->nocb_gp_kthread, also enqueues a
	callback, but with interrupts enabled, allowing it to directly
	awaken the ->nocb_gp_kthread.

4.	The newly awakened ->nocb_gp_kthread associates both CPU 1's
	and CPU 2's callbacks with a future grace period and arranges
	for that grace period to be started.

5.	This ->nocb_gp_kthread goes to sleep waiting for the end of this
	future grace period.

6.	This grace period elapses before the CPU 1's timer fires.
	This is normally improbably given that the timer is set for only
	one jiffy, but timers can be delayed.  Besides, it is possible
	that kernel was built with CONFIG_RCU_STRICT_GRACE_PERIOD=y.

7.	The grace period ends, so rcu_gp_kthread awakens the
	->nocb_gp_kthread, which in turn awakens both CPU 1's and
	CPU 2's ->nocb_cb_kthread.  Then ->nocb_gb_kthread sleeps
	waiting for more newly queued callbacks.

8.	CPU 1's ->nocb_cb_kthread invokes its callback, then sleeps
	waiting for more invocable callbacks.

9.	Note that neither kthread updated any ->nocb_timer state,
	so CPU 1's ->nocb_defer_wakeup is still set to RCU_NOCB_WAKE.

10.	CPU 1 enqueues its second callback, this time with interrupts
 	enabled so it can wake directly	->nocb_gp_kthread.
	It does so with calling wake_nocb_gp() which also cancels the
	pending timer that got queued in step 2. But that doesn't reset
	CPU 1's ->nocb_defer_wakeup which is still set to RCU_NOCB_WAKE.
	So CPU 1's ->nocb_defer_wakeup and its ->nocb_timer are now
	desynchronized.

11.	->nocb_gp_kthread associates the callback queued in 10 with a new
	grace period, arranges for that grace period to start and sleeps
	waiting for it to complete.

12.	The grace period ends, rcu_gp_kthread awakens ->nocb_gp_kthread,
	which in turn wakes up CPU 1's ->nocb_cb_kthread which then
	invokes the callback queued in 10.

13.	CPU 1 enqueues its third callback, this time with interrupts
	disabled so it must queue a timer for a deferred wakeup. However
	the value of its ->nocb_defer_wakeup is RCU_NOCB_WAKE which
	incorrectly indicates that a timer is already queued.  Instead,
	CPU 1's ->nocb_timer was cancelled in 10.  CPU 1 therefore fails
	to queue the ->nocb_timer.

14.	CPU 1 has its pending callback and it may go unnoticed until
	some other CPU ever wakes up ->nocb_gp_kthread or CPU 1 ever
	calls an explicit deferred wakeup, for example, during idle entry.

This commit fixes this bug by resetting rdp->nocb_defer_wakeup everytime
we delete the ->nocb_timer.

It is quite possible that there is a similar scenario involving
->nocb_bypass_timer and ->nocb_defer_wakeup.  However, despite some
effort from several people, a failure scenario has not yet been located.
However, that by no means guarantees that no such scenario exists.
Finding a failure scenario is left as an exercise for the reader, and the
"Fixes:" tag below relates to ->nocb_bypass_timer instead of ->nocb_timer.

Fixes: d1b222c6be (rcu/nocb: Add bypass callback queueing)
Cc: <stable@vger.kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-15 13:54:54 -07:00
Jiapeng Chong
9640dcab97 rcu: Make nocb_nobypass_lim_per_jiffy static
RCU triggerse the following sparse warning:

kernel/rcu/tree_plugin.h:1497:5: warning: symbol
'nocb_nobypass_lim_per_jiffy' was not declared. Should it be static?

This commit therefore makes this variable static.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Reported-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-15 13:54:42 -07:00
Sangmoon Kim
565cfb9e64 rcu/tree: Add a trace event for RCU CPU stall warnings
This commit adds a trace event which allows tracing the beginnings of RCU
CPU stall warnings on systems where sysctl_panic_on_rcu_stall is disabled.

The first parameter is the name of RCU flavor like other trace events.
The second parameter indicates whether this is a stall of an expedited
grace period, a self-detected stall of a normal grace period, or a stall
of a normal grace period detected by some CPU other than the one that
is stalled.

RCU CPU stall warnings are often caused by external-to-RCU issues,
for example, in interrupt handling or task scheduling.  Therefore,
this event uses TRACE_EVENT, not TRACE_EVENT_RCU, to avoid requiring
those interested in tracing RCU CPU stalls to rebuild their kernels
with CONFIG_RCU_TRACE=y.

Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Sangmoon Kim <sangmoon.kim@samsung.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-15 13:53:24 -07:00
Paul E. McKenney
7e937220af rcu: Add explicit barrier() to __rcu_read_unlock()
Because preemptible RCU's __rcu_read_unlock() is an external function,
the rough equivalent of an implicit barrier() is inserted by the compiler.
Except that there is a direct call to __rcu_read_unlock() in that same
file, and compilers are getting to the point where they might choose to
inline the fastpath of the __rcu_read_unlock() function.

This commit therefore adds an explicit barrier() to the very beginning
of __rcu_read_unlock().

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-15 13:53:24 -07:00
Stephen Zhang
0a27fff30a rcutorture: Replace rcu_torture_stall string with %s
This commit replaces a hard-coded "rcu_torture_stall" string in a
pr_alert() format with "%s" and __func__.

Signed-off-by: Stephen Zhang <stephenzhangzsd@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-08 14:22:28 -08:00
Paul E. McKenney
a434dd10cd rcu-tasks: Add block comment laying out RCU Tasks Trace design
This commit adds a block comment that gives a high-level overview of
how RCU tasks trace grace periods progress.  It also adds a note about
how exiting tasks are handled, plus it gives an overview of the memory
ordering.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Reported-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
[ paulmck: Fix commit log per Mathieu Desnoyers feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-08 14:22:02 -08:00
Lukas Bulwahn
85b8699428 rcu-tasks: Rectify kernel-doc for struct rcu_tasks
The command 'find ./kernel/rcu/ | xargs ./scripts/kernel-doc -none'
reported an issue with the kernel-doc of struct rcu_tasks.

This commit rectifies the kernel-doc, such that no issues remain for
./kernel/rcu/.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-08 14:22:02 -08:00
Paul E. McKenney
7308e02404 rcu: Make rcu_read_unlock_special() expedite strict grace periods
In kernels built with CONFIG_RCU_STRICT_GRACE_PERIOD=y, every grace
period is an expedited grace period.  However, rcu_read_unlock_special()
does not treat them that way, instead allowing the deferred quiescent
state to be reported whenever.  This commit therefore adds a check of
this Kconfig option that causes rcu_read_unlock_special() to treat all
grace periods as expedited for CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-08 14:21:41 -08:00
Paul E. McKenney
5e59fba573 rcutorture: Fix testing of RCU priority boosting
Currently, rcutorture refuses to test RCU priority boosting in
CONFIG_HOTPLUG_CPU=y kernels, which are the only kind normally built on
x86 these days.  This commit therefore updates rcutorture's tests of RCU
priority boosting to make them safe for CPU hotplug.  However, these tests
will fail unless TIMER_SOFTIRQ runs at realtime priority, which does not
happen in current mainline.  This commit therefore also refuses to test
RCU priority boosting except in kernels built with CONFIG_PREEMPT_RT=y.

While in the area, this commt adds some debug output at boost-fail time
that helps diagnose the cause of the failure, for example, failing to
run TIMER_SOFTIRQ at realtime priority.

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>
2021-03-08 14:21:41 -08:00
Paul E. McKenney
39bbfc62cc rcu: Expedite deboost in case of deferred quiescent state
Historically, a task that has been subjected to RCU priority boosting is
deboosted at rcu_read_unlock() time.  However, with the advent of deferred
quiescent states, if the outermost rcu_read_unlock() was invoked with
either bottom halves, interrupts, or preemption disabled, the deboosting
will be delayed for some time.  During this time, a low-priority process
might be incorrectly running at a high real-time priority level.

Fortunately, rcu_read_unlock_special() already provides mechanisms for
forcing a minimal deferral of quiescent states, at least for kernels
built with CONFIG_IRQ_WORK=y.  These mechanisms are currently used
when expedited grace periods are pending that might be blocked by the
current task.  This commit therefore causes those mechanisms to also be
used in cases where the current task has been or might soon be subjected
to RCU priority boosting.  Note that this applies to all kernels built
with CONFIG_RCU_BOOST=y, regardless of whether or not they are also
built with CONFIG_PREEMPT_RT=y.

This approach assumes that kernels build for use with aggressive real-time
applications are built with CONFIG_IRQ_WORK=y.  It is likely to be far
simpler to enable CONFIG_IRQ_WORK=y than to implement a fast-deboosting
scheme that works correctly in its absence.

While in the area, alphabetize the rcu_preempt_deferred_qs_handler()
function's local variables.

Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Scott Wood <swood@redhat.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-08 14:21:40 -08:00
Frederic Weisbecker
55adc3e1c8 rcu/nocb: Rename nocb_gp_update_state to nocb_gp_update_state_deoffloading
The name nocb_gp_update_state() is unenlightening, so this commit changes
it to nocb_gp_update_state_deoffloading().  This function now does what
its name says, updates state and returns true if the CPU corresponding to
the specified rcu_data structure is in the process of being de-offloaded.

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 14:20:22 -08:00
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
8a682b3974 rcu/nocb: Avoid confusing double write of rdp->nocb_cb_sleep
The nocb_cb_wait() function first sets the rdp->nocb_cb_sleep flag to
true by after invoking the callbacks, and then sets it back to false if
it finds more callbacks that are ready to invoke.

This is confusing and will become unsafe if this flag is ever read
locklessly.  This commit therefore writes it only once, based on the
state after both callback invocation and checking.

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
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
5de2e5bb80 rcu/nocb: Comment the reason behind BH disablement on batch processing
This commit explains why softirqs need to be disabled while invoking
callbacks, even when callback processing has been offloaded.  After
all, invoking callbacks concurrently is one thing, but concurrently
invoking the same callback is quite another.

Reported-by: Boqun Feng <boqun.feng@gmail.com>
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 14:20:20 -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
Paul E. McKenney
0d3dd2c8ea rcutorture: Add crude tests for mem_dump_obj()
This commit adds a few crude tests for mem_dump_obj() to rcutorture
runs.  Just to prevent bitrot, you understand!

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-08 14:18:46 -08:00
Uladzislau Rezki (Sony)
686fe1bf6b rcuscale: Add kfree_rcu() single-argument scale test
The single-argument variant of kfree_rcu() is currently not
tested by any member of the rcutoture test suite.  This
commit therefore adds rcuscale code to test it.  This
testing is controlled by two new boolean module parameters,
kfree_rcu_test_single and kfree_rcu_test_double.  If one
is set and the other not, only the corresponding variant
is tested, otherwise both are tested, with the variant to
be tested determined randomly on each invocation.

Both of these module parameters are initialized to false,
so setting either to true will test only that variant.

Suggested-by: Paul E. McKenney <paulmck@kernel.org>
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)
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
Paul Gortmaker
3e70df91f9 rcu: deprecate "all" option to rcu_nocbs=
With the core bitmap support now accepting "N" as a placeholder for
the end of the bitmap, "all" can be represented as "0-N" and has the
advantage of not being specific to RCU (or any other subsystem).

So deprecate the use of "all" by removing documentation references
to it.  The support itself needs to remain for now, since we don't
know how many people out there are using it currently, but since it
is in an __init area anyway, it isn't worth losing sleep over.

Cc: Yury Norov <yury.norov@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Acked-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-03-08 14:16:58 -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>
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Merge tag 'sched-core-2021-02-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler updates from Ingo Molnar:
 "Core scheduler updates:

   - Add CONFIG_PREEMPT_DYNAMIC: this in its current form adds the
     preempt=none/voluntary/full boot options (default: full), to allow
     distros to build a PREEMPT kernel but fall back to close to
     PREEMPT_VOLUNTARY (or PREEMPT_NONE) runtime scheduling behavior via
     a boot time selection.

     There's also the /debug/sched_debug switch to do this runtime.

     This feature is implemented via runtime patching (a new variant of
     static calls).

     The scope of the runtime patching can be best reviewed by looking
     at the sched_dynamic_update() function in kernel/sched/core.c.

     ( Note that the dynamic none/voluntary mode isn't 100% identical,
       for example preempt-RCU is available in all cases, plus the
       preempt count is maintained in all models, which has runtime
       overhead even with the code patching. )

     The PREEMPT_VOLUNTARY/PREEMPT_NONE models, used by the vast
     majority of distributions, are supposed to be unaffected.

   - Fix ignored rescheduling after rcu_eqs_enter(). This is a bug that
     was found via rcutorture triggering a hang. The bug is that
     rcu_idle_enter() may wake up a NOCB kthread, but this happens after
     the last generic need_resched() check. Some cpuidle drivers fix it
     by chance but many others don't.

     In true 2020 fashion the original bug fix has grown into a 5-patch
     scheduler/RCU fix series plus another 16 RCU patches to address the
     underlying issue of missed preemption events. These are the initial
     fixes that should fix current incarnations of the bug.

   - Clean up rbtree usage in the scheduler, by providing & using the
     following consistent set of rbtree APIs:

       partial-order; less() based:
         - rb_add(): add a new entry to the rbtree
         - rb_add_cached(): like rb_add(), but for a rb_root_cached

       total-order; cmp() based:
         - rb_find(): find an entry in an rbtree
         - rb_find_add(): find an entry, and add if not found

         - rb_find_first(): find the first (leftmost) matching entry
         - rb_next_match(): continue from rb_find_first()
         - rb_for_each(): iterate a sub-tree using the previous two

   - Improve the SMP/NUMA load-balancer: scan for an idle sibling in a
     single pass. This is a 4-commit series where each commit improves
     one aspect of the idle sibling scan logic.

   - Improve the cpufreq cooling driver by getting the effective CPU
     utilization metrics from the scheduler

   - Improve the fair scheduler's active load-balancing logic by
     reducing the number of active LB attempts & lengthen the
     load-balancing interval. This improves stress-ng mmapfork
     performance.

   - Fix CFS's estimated utilization (util_est) calculation bug that can
     result in too high utilization values

  Misc updates & fixes:

   - Fix the HRTICK reprogramming & optimization feature

   - Fix SCHED_SOFTIRQ raising race & warning in the CPU offlining code

   - Reduce dl_add_task_root_domain() overhead

   - Fix uprobes refcount bug

   - Process pending softirqs in flush_smp_call_function_from_idle()

   - Clean up task priority related defines, remove *USER_*PRIO and
     USER_PRIO()

   - Simplify the sched_init_numa() deduplication sort

   - Documentation updates

   - Fix EAS bug in update_misfit_status(), which degraded the quality
     of energy-balancing

   - Smaller cleanups"

* tag 'sched-core-2021-02-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (51 commits)
  sched,x86: Allow !PREEMPT_DYNAMIC
  entry/kvm: Explicitly flush pending rcuog wakeup before last rescheduling point
  entry: Explicitly flush pending rcuog wakeup before last rescheduling point
  rcu/nocb: Trigger self-IPI on late deferred wake up before user resume
  rcu/nocb: Perform deferred wake up before last idle's need_resched() check
  rcu: Pull deferred rcuog wake up to rcu_eqs_enter() callers
  sched/features: Distinguish between NORMAL and DEADLINE hrtick
  sched/features: Fix hrtick reprogramming
  sched/deadline: Reduce rq lock contention in dl_add_task_root_domain()
  uprobes: (Re)add missing get_uprobe() in __find_uprobe()
  smp: Process pending softirqs in flush_smp_call_function_from_idle()
  sched: Harden PREEMPT_DYNAMIC
  static_call: Allow module use without exposing static_call_key
  sched: Add /debug/sched_preempt
  preempt/dynamic: Support dynamic preempt with preempt= boot option
  preempt/dynamic: Provide irqentry_exit_cond_resched() static call
  preempt/dynamic: Provide preempt_schedule[_notrace]() static calls
  preempt/dynamic: Provide cond_resched() and might_resched() static calls
  preempt: Introduce CONFIG_PREEMPT_DYNAMIC
  static_call: Provide DEFINE_STATIC_CALL_RET0()
  ...
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
Frederic Weisbecker
43789ef3f7 rcu/nocb: Perform deferred wake up before last idle's need_resched() check
Entering RCU idle mode may cause a deferred wake up of an RCU NOCB_GP
kthread (rcuog) to be serviced.

Usually a local wake up happening while running the idle task is handled
in one of the need_resched() checks carefully placed within the idle
loop that can break to the scheduler.

Unfortunately the call to rcu_idle_enter() is already beyond the last
generic need_resched() check and we may halt the CPU with a resched
request unhandled, leaving the task hanging.

Fix this with splitting the rcuog wakeup handling from rcu_idle_enter()
and place it before the last generic need_resched() check in the idle
loop. It is then assumed that no call to call_rcu() will be performed
after that in the idle loop until the CPU is put in low power mode.

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/20210131230548.32970-3-frederic@kernel.org
2021-02-17 14:12:43 +01:00
Frederic Weisbecker
54b7429eff rcu: Pull deferred rcuog wake up to rcu_eqs_enter() callers
Deferred wakeup of rcuog kthreads upon RCU idle mode entry is going to
be handled differently whether initiated by idle, user or guest. Prepare
with pulling that control up to rcu_eqs_enter() callers.

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/20210131230548.32970-2-frederic@kernel.org
2021-02-17 14:12:42 +01:00
Paul E. McKenney
0d2460ba61 Merge branches 'doc.2021.01.06a', 'fixes.2021.01.04b', 'kfree_rcu.2021.01.04a', 'mmdumpobj.2021.01.22a', 'nocb.2021.01.06a', 'rt.2021.01.04a', 'stall.2021.01.06a', 'torture.2021.01.12a' and 'tortureall.2021.01.06a' into HEAD
doc.2021.01.06a: Documentation updates.
fixes.2021.01.04b: Miscellaneous fixes.
kfree_rcu.2021.01.04a: kfree_rcu() updates.
mmdumpobj.2021.01.22a: Dump allocation point for memory blocks.
nocb.2021.01.06a: RCU callback offload updates and cblist segment lengths.
rt.2021.01.04a: Real-time updates.
stall.2021.01.06a: RCU CPU stall warning updates.
torture.2021.01.12a: Torture-test updates and polling SRCU grace-period API.
tortureall.2021.01.06a: Torture-test script updates.
2021-01-22 15:26:44 -08:00
Paul E. McKenney
b4b7914a6a rcu: Make call_rcu() print mem_dump_obj() info for double-freed callback
The debug-object double-free checks in __call_rcu() print out the
RCU callback function, which is usually sufficient to track down the
double free.  However, all uses of things like queue_rcu_work() will
have the same RCU callback function (rcu_work_rcufn() in this case),
so a diagnostic message for a double queue_rcu_work() needs more than
just the callback function.

This commit therefore calls mem_dump_obj() to dump out any additional
available information on the double-freed callback.

Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: <linux-mm@kvack.org>
Reported-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2021-01-22 15:24:16 -08:00