linux-kernel - Re: [RFC PATCH 2/2] sched/tracing: Add TASK_RTLOCK_WAIT to TASK

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Date:   Fri, 14 Jan 2022 11:11:08 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     linux-kernel@...r.kernel.org,
        Abhijeet Dharmapurikar <adharmap@...cinc.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        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>,
        Juri Lelli <juri.lelli@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 2/2] sched/tracing: Add TASK_RTLOCK_WAIT to
 TASK_REPORT

On 2021-11-29 12:36:01 [+0000], 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
> 
> Add TASK_RTLOCK_WAIT to TASK_REPORT.
> 
> Signed-off-by: Valentin Schneider <valentin.schneider@....com>

We used to have the D state which was used in the locked case and was
sufficient. With the rework to TASK_RTLOCK_WAIT (which made other things
easier) we lost that. It makes debuging/ looking into the system more
obvious or does not hide things so why not.

Reviewed-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

Sebastian