linux-kernel - Re: [PATCH v3 2/2] sched/tracing: Report TASK_RTLOCK_WAIT tasks as TASK

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Date:   Sun, 10 Apr 2022 08:14:03 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Qais Yousef <qais.yousef@....com>
Cc:     stable@...r.kernel.org, linux-kernel@...r.kernel.org,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Abhijeet Dharmapurikar <adharmap@...cinc.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Juri Lelli <juri.lelli@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Alexey Gladkov <legion@...nel.org>,
        "Kenta.Tada@...y.com" <Kenta.Tada@...y.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Ed Tsai <ed.tsai@...iatek.com>,
        Valentin Schneider <valentin.schneider@....com>
Subject: Re: [PATCH v3 2/2] sched/tracing: Report TASK_RTLOCK_WAIT tasks as
 TASK_UNINTERRUPTIBLE

On Sun, Apr 10, 2022 at 12:42:24AM +0100, Qais Yousef wrote:
> +CC stable
> 
> On 01/20/22 16:25, Valentin Schneider wrote:
> > TASK_RTLOCK_WAIT currently isn't part of TASK_REPORT, thus a task blocking
> > on an rtlock will appear as having a task state == 0, IOW TASK_RUNNING.
> > 
> > The actual state is saved in p->saved_state, but reading it after reading
> > p->__state has a few issues:
> > o that could still be TASK_RUNNING in the case of e.g. rt_spin_lock
> > o ttwu_state_match() might have changed that to TASK_RUNNING
> > 
> > As pointed out by Eric, adding TASK_RTLOCK_WAIT to TASK_REPORT implies
> > exposing a new state to userspace tools which way not know what to do with
> > them. The only information that needs to be conveyed here is that a task is
> > waiting on an rt_mutex, which matches TASK_UNINTERRUPTIBLE - there's no
> > need for a new state.
> > 
> > Reported-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> > Signed-off-by: Valentin Schneider <valentin.schneider@....com>
> 
> Any objection for this to be picked up by stable? We care about Patch 1 only in
> this series for stable, but it seems sensible to pick this one too, no strong
> feeling if it is omitted though.
> 
> AFAICT it seems the problem dates back since commit:
> 
> 	1593baab910d ("sched/debug: Implement consistent task-state printing")
> 
> or even before. I think v4.14+ is good enough.


<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>