From: Will Deacon <will@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>,
Mel Gorman <mgorman@techsingularity.net>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] sched: Fix data-race in wakeup
Date: Tue, 17 Nov 2020 10:36:23 +0000 [thread overview]
Message-ID: <20201117103622.GA32035@willie-the-truck> (raw)
In-Reply-To: <20201117094621.GE3121429@hirez.programming.kicks-ass.net>
On Tue, Nov 17, 2020 at 10:46:21AM +0100, Peter Zijlstra wrote:
> On Tue, Nov 17, 2020 at 10:29:36AM +0100, Peter Zijlstra wrote:
> > On Tue, Nov 17, 2020 at 09:15:46AM +0000, Will Deacon wrote:
> > > On Tue, Nov 17, 2020 at 09:30:16AM +0100, Peter Zijlstra wrote:
> > > > /* Unserialized, strictly 'current' */
> > > >
> > > > + /*
> > > > + * p->in_iowait = 1; ttwu()
> > > > + * schedule() if (p->on_rq && ..) // false
> > > > + * smp_mb__after_spinlock(); if (smp_load_acquire(&p->on_cpu) && //true
> > > > + * deactivate_task() ttwu_queue_wakelist())
> > > > + * p->on_rq = 0; p->sched_remote_wakeup = X;
> > > > + *
> > > > + * Guarantees all stores of 'current' are visible before
> > > > + * ->sched_remote_wakeup gets used.
> > >
> > > I'm still not sure this is particularly clear -- don't we want to highlight
> > > that the store of p->on_rq is unordered wrt the update to
> > > p->sched_contributes_to_load() in deactivate_task()?
>
> How's this then? It still doesn't explicitly call out the specific race,
> but does mention the more fundamental issue that wakelist queueing
> doesn't respect the regular rules anymore.
>
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -775,7 +775,6 @@ struct task_struct {
> unsigned sched_reset_on_fork:1;
> unsigned sched_contributes_to_load:1;
> unsigned sched_migrated:1;
> - unsigned sched_remote_wakeup:1;
> #ifdef CONFIG_PSI
> unsigned sched_psi_wake_requeue:1;
> #endif
> @@ -785,6 +784,21 @@ struct task_struct {
>
> /* Unserialized, strictly 'current' */
>
> + /*
> + * This field must not be in the scheduler word above due to wakelist
> + * queueing no longer being serialized by p->on_cpu. However:
> + *
> + * p->XXX = X; ttwu()
> + * schedule() if (p->on_rq && ..) // false
> + * smp_mb__after_spinlock(); if (smp_load_acquire(&p->on_cpu) && //true
> + * deactivate_task() ttwu_queue_wakelist())
> + * p->on_rq = 0; p->sched_remote_wakeup = Y;
> + *
> + * guarantees all stores of 'current' are visible before
> + * ->sched_remote_wakeup gets used, so it can be in this word.
> + */
> + unsigned sched_remote_wakeup:1;
Much better, thanks!
Will
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-11-17 10:37 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-16 9:10 Loadavg accounting error on arm64 Mel Gorman
2020-11-16 11:49 ` Mel Gorman
2020-11-16 12:00 ` Mel Gorman
2020-11-16 12:53 ` Peter Zijlstra
2020-11-16 12:58 ` Peter Zijlstra
2020-11-16 15:29 ` Mel Gorman
2020-11-16 16:42 ` Mel Gorman
2020-11-16 16:49 ` Peter Zijlstra
2020-11-16 17:24 ` Mel Gorman
2020-11-16 17:41 ` Will Deacon
2020-11-16 12:46 ` Peter Zijlstra
2020-11-16 12:58 ` Mel Gorman
2020-11-16 13:11 ` Will Deacon
2020-11-16 13:37 ` Mel Gorman
2020-11-16 14:20 ` Peter Zijlstra
2020-11-16 15:52 ` Mel Gorman
2020-11-16 16:54 ` Peter Zijlstra
2020-11-16 17:16 ` Mel Gorman
2020-11-16 19:31 ` Mel Gorman
2020-11-17 8:30 ` [PATCH] sched: Fix data-race in wakeup Peter Zijlstra
2020-11-17 9:15 ` Will Deacon
2020-11-17 9:29 ` Peter Zijlstra
2020-11-17 9:46 ` Peter Zijlstra
2020-11-17 10:36 ` Will Deacon [this message]
2020-11-17 12:52 ` Valentin Schneider
2020-11-17 15:37 ` Valentin Schneider
2020-11-17 16:13 ` Peter Zijlstra
2020-11-17 19:32 ` Valentin Schneider
2020-11-18 8:05 ` Peter Zijlstra
2020-11-18 9:51 ` Valentin Schneider
2020-11-18 13:33 ` Marco Elver
2020-11-17 9:38 ` [PATCH] sched: Fix rq->nr_iowait ordering Peter Zijlstra
2020-11-17 11:43 ` Mel Gorman
2020-11-17 12:40 ` [PATCH] sched: Fix data-race in wakeup Mel Gorman
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20201117103622.GA32035@willie-the-truck \
--to=will@kernel.org \
--cc=dave@stgolabs.net \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mgorman@techsingularity.net \
--cc=peterz@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox