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From: Aubrey Li <aubrey.intel@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Don <joshdon@google.com>,
	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>,
	Don Hiatt <dhiatt@digitalocean.com>
Subject: Re: [PATCH 04/19] sched: Prepare for Core-wide rq->lock
Date: Wed, 28 Apr 2021 18:35:36 +0800	[thread overview]
Message-ID: <CAERHkrttLutB1yUHS=i_syQZjqWmttm8PfQeH4WkcCLQvaR64A@mail.gmail.com> (raw)
In-Reply-To: <YIknPXxwZvq0qmId@hirez.programming.kicks-ass.net>

On Wed, Apr 28, 2021 at 5:14 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Tue, Apr 27, 2021 at 04:30:02PM -0700, Josh Don wrote:
>
> > Also, did you mean to have a preempt_enable_no_resched() rather than
> > prempt_enable() in raw_spin_rq_trylock?
>
> No, trylock really needs to be preempt_enable(), because it can have
> failed, at which point it will not have incremented the preemption count
> and our decrement can hit 0, at which point we really should reschedule.
>
> > I went over the rq_lockp stuff again after Don's reported lockup. Most
> > uses are safe due to already holding an rq lock. However,
> > double_rq_unlock() is prone to race:
> >
> > double_rq_unlock(rq1, rq2):
> > /* Initial state: core sched enabled, and rq1 and rq2 are smt
> > siblings. So, double_rq_lock(rq1, rq2) only took a single rq lock */
> > raw_spin_rq_unlock(rq1);
> > /* now not holding any rq lock */
> > /* sched core disabled. Now __rq_lockp(rq1) != __rq_lockp(rq2), so we
> > falsely unlock rq2 */
> > if (__rq_lockp(rq1) != __rq_lockp(rq2))
> >         raw_spin_rq_unlock(rq2);
> > else
> >         __release(rq2->lock);
> >
> > Instead we can cache __rq_lockp(rq1) and __rq_lockp(rq2) before
> > releasing the lock, in order to prevent this. FWIW I think it is
> > likely that Don is seeing a different issue.
>
> Ah, indeed so.. rq_lockp() could do with an assertion, not sure how to
> sanely do that. Anyway, double_rq_unlock() is simple enough to fix, we
> can simply flip the unlock()s.
>
> ( I'm suffering a cold and am really quite slow atm )
>
> How's this then?
>
> ---
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index f732642e3e09..3a534c0c1c46 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();

synchronize_sched() seems no longer exist...

Thanks,
-Aubrey

  reply	other threads:[~2021-04-28 10:35 UTC|newest]

Thread overview: 103+ 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
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 [this message]
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
2021-08-05 16:53   ` Eugene Syromiatnikov
2021-08-05 17:00     ` Peter Zijlstra
2021-08-17 15:15   ` Eugene Syromiatnikov
2021-08-17 15:52     ` Peter Zijlstra
2021-08-17 23:17       ` Eugene Syromiatnikov
2021-08-19 11:09         ` [PATCH] sched: Fix Core-wide rq->lock for uninitialized CPUs Peter Zijlstra
2021-08-19 15:50           ` Tao Zhou
2021-08-19 16:19           ` Eugene Syromiatnikov
2021-08-20  0:18           ` Josh Don
2021-08-20 10:02             ` Peter Zijlstra
2021-08-23  9:07           ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
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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