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From: Peter Zijlstra <peterz@infradead.org>
To: Josh Don <joshdon@google.com>
Cc: Joel Fernandes <joel@joelfernandes.org>,
	"Hyser,Chris" <chris.hyser@oracle.com>,
	Ingo Molnar <mingo@kernel.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Mel Gorman <mgorman@suse.de>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 04/19] sched: Prepare for Core-wide rq->lock
Date: Mon, 26 Apr 2021 10:31:34 +0200
Message-ID: <YIZ6ZpkrMGQ9A9x2@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CABk29Ntop2nX+z1bV7giG8ToR_w3f_+GYGAw+hFQ6g9rCZunmw@mail.gmail.com>

On Fri, Apr 23, 2021 at 06:22:52PM -0700, Josh Don wrote:
> Hi Peter,
> 
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -186,12 +186,37 @@ int sysctl_sched_rt_runtime = 950000;
> >
> >  void raw_spin_rq_lock_nested(struct rq *rq, int subclass)
> >  {
> > -       raw_spin_lock_nested(rq_lockp(rq), subclass);
> > +       raw_spinlock_t *lock;
> > +
> > +       if (sched_core_disabled()) {
> 
> Nothing to stop sched_core from being enabled right here? Leading to
> us potentially taking the wrong lock.
> 
> > +               raw_spin_lock_nested(&rq->__lock, subclass);
> > +               return;
> > +       }
> > +
> > +       for (;;) {
> > +               lock = rq_lockp(rq);
> > +               raw_spin_lock_nested(lock, subclass);
> > +               if (likely(lock == rq_lockp(rq)))
> > +                       return;
> > +               raw_spin_unlock(lock);
> > +       }
> >  }

Very good; something like the below seems to be the best I can make of
it..

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f732642e3e09..1a81e9cc9e5d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -290,6 +290,10 @@ static void sched_core_assert_empty(void)
 static void __sched_core_enable(void)
 {
 	static_branch_enable(&__sched_core_enabled);
+	/*
+	 * Ensure raw_spin_rq_*lock*() have completed before flipping.
+	 */
+	synchronize_sched();
 	__sched_core_flip(true);
 	sched_core_assert_empty();
 }
@@ -449,16 +453,22 @@ void raw_spin_rq_lock_nested(struct rq *rq, int subclass)
 {
 	raw_spinlock_t *lock;
 
+	preempt_disable();
 	if (sched_core_disabled()) {
 		raw_spin_lock_nested(&rq->__lock, subclass);
+		/* preempt *MUST* still be disabled here */
+		preempt_enable_no_resched();
 		return;
 	}
 
 	for (;;) {
 		lock = __rq_lockp(rq);
 		raw_spin_lock_nested(lock, subclass);
-		if (likely(lock == __rq_lockp(rq)))
+		if (likely(lock == __rq_lockp(rq))) {
+			/* preempt *MUST* still be disabled here */
+			preempt_enable_no_resched();
 			return;
+		}
 		raw_spin_unlock(lock);
 	}
 }
@@ -468,14 +478,20 @@ bool raw_spin_rq_trylock(struct rq *rq)
 	raw_spinlock_t *lock;
 	bool ret;
 
-	if (sched_core_disabled())
-		return raw_spin_trylock(&rq->__lock);
+	preempt_disable();
+	if (sched_core_disabled()) {
+		ret = raw_spin_trylock(&rq->__lock);
+		preempt_enable();
+		return ret;
+	}
 
 	for (;;) {
 		lock = __rq_lockp(rq);
 		ret = raw_spin_trylock(lock);
-		if (!ret || (likely(lock == __rq_lockp(rq))))
+		if (!ret || (likely(lock == __rq_lockp(rq)))) {
+			preempt_enable();
 			return ret;
+		}
 		raw_spin_unlock(lock);
 	}
 }

  reply index

Thread overview: 92+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-22 12:04 [PATCH 00/19] sched: Core Scheduling Peter Zijlstra
2021-04-22 12:05 ` [PATCH 01/19] sched/fair: Add a few assertions Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-05-13  8:56     ` Ning, Hongyu
2021-04-22 12:05 ` [PATCH 02/19] sched: Provide raw_spin_rq_*lock*() helpers Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 03/19] sched: Wrap rq::lock access Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 04/19] sched: Prepare for Core-wide rq->lock Peter Zijlstra
2021-04-24  1:22   ` Josh Don
2021-04-26  8:31     ` Peter Zijlstra [this message]
2021-04-26 22:21       ` Josh Don
2021-04-27 17:10         ` Don Hiatt
2021-04-27 23:35           ` Josh Don
2021-04-28  1:03             ` Aubrey Li
2021-04-28  6:05               ` Aubrey Li
2021-04-28 10:57                 ` Aubrey Li
2021-04-28 16:41                   ` Don Hiatt
2021-04-29 20:48                     ` Josh Don
2021-04-29 21:09                       ` Don Hiatt
2021-04-29 23:22                         ` Josh Don
2021-04-30 16:18                           ` Don Hiatt
2021-04-30  8:26                         ` Aubrey Li
2021-04-28 16:04             ` Don Hiatt
2021-04-27 23:30         ` Josh Don
2021-04-28  9:13           ` Peter Zijlstra
2021-04-28 10:35             ` Aubrey Li
2021-04-28 11:03               ` Peter Zijlstra
2021-04-28 14:18                 ` Paul E. McKenney
2021-04-29 20:11             ` Josh Don
2021-05-03 19:17               ` Peter Zijlstra
2021-04-28  7:13         ` Peter Zijlstra
2021-04-28  6:02   ` Aubrey Li
2021-04-29  8:03   ` Aubrey Li
2021-04-29 20:39     ` Josh Don
2021-04-30  8:20       ` Aubrey Li
2021-04-30  8:48         ` Josh Don
2021-04-30 14:15           ` Aubrey Li
2021-05-04  7:38       ` Peter Zijlstra
2021-05-05 16:20         ` Don Hiatt
2021-05-06 10:25           ` Peter Zijlstra
2021-05-07  9:50   ` [PATCH v2 " Peter Zijlstra
2021-05-08  8:07     ` Aubrey Li
2021-05-12  9:07       ` Peter Zijlstra
2021-04-22 12:05 ` [PATCH 05/19] sched: " Peter Zijlstra
2021-05-07  9:50   ` [PATCH v2 " Peter Zijlstra
2021-05-12 10:28     ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 06/19] sched: Optimize rq_lockp() usage Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 07/19] sched: Allow sched_core_put() from atomic context Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 08/19] sched: Introduce sched_class::pick_task() Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 09/19] sched: Basic tracking of matching tasks Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 10/19] sched: Add core wide task selection and scheduling Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 11/19] sched/fair: Fix forced idle sibling starvation corner case Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Vineeth Pillai
2021-04-22 12:05 ` [PATCH 12/19] sched: Fix priority inversion of cookied task with sibling Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Joel Fernandes (Google)
2021-04-22 12:05 ` [PATCH 13/19] sched/fair: Snapshot the min_vruntime of CPUs on force idle Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Joel Fernandes (Google)
2021-04-22 12:05 ` [PATCH 14/19] sched: Trivial forced-newidle balancer Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 15/19] sched: Migration changes for core scheduling Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Aubrey Li
2021-04-22 12:05 ` [PATCH 16/19] sched: Trivial core scheduling cookie management Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 17/19] sched: Inherit task cookie on fork() Peter Zijlstra
2021-05-10 16:06   ` Joel Fernandes
2021-05-10 16:22     ` Chris Hyser
2021-05-10 20:47       ` Joel Fernandes
2021-05-10 21:38         ` Chris Hyser
2021-05-12  9:05           ` Peter Zijlstra
2021-05-12 20:20             ` Josh Don
2021-05-12 21:07               ` Don Hiatt
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 18/19] sched: prctl() core-scheduling interface Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Chris Hyser
2021-06-14 23:36   ` [PATCH 18/19] " Josh Don
2021-06-15 11:31     ` Joel Fernandes
2021-04-22 12:05 ` [PATCH 19/19] kselftest: Add test for core sched prctl interface Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Chris Hyser
2021-04-22 16:43 ` [PATCH 00/19] sched: Core Scheduling Don Hiatt
2021-04-22 17:29   ` Peter Zijlstra
2021-04-30  6:47 ` Ning, Hongyu
2021-05-06 10:29   ` Peter Zijlstra
2021-05-06 12:53     ` Ning, Hongyu
2021-05-07 18:02 ` Joel Fernandes
2021-05-10 16:16 ` Vincent Guittot
2021-05-11  7:00   ` Vincent Guittot

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