linux-kernel - Re: [tip: sched/core] sched/tracing: Don't re-read p->state when emitting sched

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Date:   Tue, 8 Mar 2022 19:10:57 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Qais Yousef <qais.yousef@....com>
Cc:     linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
        Abhijeet Dharmapurikar <adharmap@...cinc.com>,
        Valentin Schneider <valentin.schneider@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        "Steven Rostedt (Google)" <rostedt@...dmis.org>, x86@...nel.org,
        stable@...r.kernel.org
Subject: Re: [tip: sched/core] sched/tracing: Don't re-read p->state when
 emitting sched_switch event

On Tue, Mar 08, 2022 at 06:02:40PM +0000, Qais Yousef wrote:
> +CC stable
> 
> On 03/01/22 15:24, tip-bot2 for Valentin Schneider wrote:
> > The following commit has been merged into the sched/core branch of tip:
> > 
> > Commit-ID:     fa2c3254d7cfff5f7a916ab928a562d1165f17bb
> > Gitweb:        https://git.kernel.org/tip/fa2c3254d7cfff5f7a916ab928a562d1165f17bb
> > Author:        Valentin Schneider <valentin.schneider@....com>
> > AuthorDate:    Thu, 20 Jan 2022 16:25:19 
> > Committer:     Peter Zijlstra <peterz@...radead.org>
> > CommitterDate: Tue, 01 Mar 2022 16:18:39 +01:00
> > 
> > sched/tracing: Don't re-read p->state when emitting sched_switch event
> > 
> > As of commit
> > 
> >   c6e7bd7afaeb ("sched/core: Optimize ttwu() spinning on p->on_cpu")
> > 
> > the following sequence becomes possible:
> > 
> > 		      p->__state = TASK_INTERRUPTIBLE;
> > 		      __schedule()
> > 			deactivate_task(p);
> >   ttwu()
> >     READ !p->on_rq
> >     p->__state=TASK_WAKING
> > 			trace_sched_switch()
> > 			  __trace_sched_switch_state()
> > 			    task_state_index()
> > 			      return 0;
> > 
> > TASK_WAKING isn't in TASK_REPORT, so the task appears as TASK_RUNNING in
> > the trace event.
> > 
> > Prevent this by pushing the value read from __schedule() down the trace
> > event.
> > 
> > Reported-by: Abhijeet Dharmapurikar <adharmap@...cinc.com>
> > Signed-off-by: Valentin Schneider <valentin.schneider@....com>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> > Link: https://lore.kernel.org/r/20220120162520.570782-2-valentin.schneider@arm.com
> 
> Any objection to picking this for stable? I'm interested in this one for some
> Android users but prefer if it can be taken by stable rather than backport it
> individually.
> 
> I think it makes sense to pick the next one in the series too.

What commit does this fix in Linus's tree?

Once it hits Linus's tree, let stable@...r.kernel.org know what the git
commit id is in Linus's tree.

thanks,

greg k-h