linux-kernel - Re: [PATCH] sched: add READ_ONCE to task_on_rq

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Message-ID: <20241114191419.GH471026@pauld.westford.csb>
Date: Thu, 14 Nov 2024 14:14:19 -0500
From: Phil Auld <pauld@...hat.com>
To: Jon Kohler <jon@...anix.com>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: add READ_ONCE to task_on_rq_queued

On Thu, Nov 14, 2024 at 06:59:14PM +0000 Jon Kohler wrote:
> 
> 
> > On Nov 14, 2024, at 1:52 PM, Phil Auld <pauld@...hat.com> wrote:
> > 
> > !-------------------------------------------------------------------|
> >  CAUTION: External Email
> > 
> > |-------------------------------------------------------------------!
> > 
> > On Thu, Nov 14, 2024 at 09:21:28AM -0700 Jon Kohler wrote:
> >> task_on_rq_queued read p->on_rq without READ_ONCE, though p->on_rq is
> >> set with WRITE_ONCE in {activate|deactivate}_task and smp_store_release
> >> in __block_task, and also read with READ_ONCE in task_on_rq_migrating.
> >> 
> >> Make all of these accesses pair together by adding READ_ONCE in the
> >> task_on_rq_queued.
> >> 
> >> Signed-off-by: Jon Kohler <jon@...anix.com>
> >> ---
> >> kernel/sched/sched.h | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >> 
> >> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> >> index c03b3d7b320e..dbbe5ce0dd96 100644
> >> --- a/kernel/sched/sched.h
> >> +++ b/kernel/sched/sched.h
> >> @@ -2277,7 +2277,7 @@ static inline int task_on_cpu(struct rq *rq, struct task_struct *p)
> >> 
> >> static inline int task_on_rq_queued(struct task_struct *p)
> >> {
> >> - return p->on_rq == TASK_ON_RQ_QUEUED;
> >> + return READ_ONCE(p->on_rq) == TASK_ON_RQ_QUEUED;
> >> }
> >> 
> >> static inline int task_on_rq_migrating(struct task_struct *p)
> >> -- 
> >> 2.43.0
> >> 
> >> 
> > 
> > That looks right especially when seen with task_on_rq_migrating()
> > right below it, as you said.
> > 
> > Reviewed-by: Phil Auld <pauld@...hat.com>
> > 
> 
> Thanks Phil - note, I’ve got a v2 coming shortly as I’ve bungled the
> author and codeveloped tag from our internal version of this patch.
> 
> I’ll get that out, but it will be the exact same code.
>

You can just put my reviewed by on that one when you send it then.


Cheers,
Phil



> > 
> > Cheers,
> > Phil
> > -- 
> > 
> 

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