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    SubjectRe: [tip: sched/core] sched/tracing: Don't re-read p->state when emitting sched_switch event
    On Sun, Apr 10, 2022 at 12:38:29AM +0100, Qais Yousef wrote:
    > On 03/08/22 18:51, Qais Yousef wrote:
    > > On 03/08/22 19:10, Greg KH wrote:
    > > > 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@arm.com>
    > > > > > AuthorDate: Thu, 20 Jan 2022 16:25:19
    > > > > > Committer: Peter Zijlstra <peterz@infradead.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@quicinc.com>
    > > > > > Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
    > > > > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    > > > > > Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.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?
    > >
    > > It should be this one: c6e7bd7afaeb ("sched/core: Optimize ttwu() spinning on p->on_cpu")
    >
    > Should this be okay to be picked up by stable now? I can see AUTOSEL has picked
    > it up for v5.15+, but it impacts v5.10 too.

    It does not apply to 5.10 at all, how did you test this?

    {sigh}

    Again, if you want this applied to any stable trees, please test that it
    works and send the properly backported patches.

    thanks,

    greg k-h

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