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 18:02:40 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     linux-kernel@...r.kernel.org
Cc:     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

+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.

Thanks!

--
Qais Yousef