linux-kernel - Re: [PATCH] sched: Consider task_struct::saved_state in wait_task

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Message-ID: <Y/YaTojZ1stY2fAO@hirez.programming.kicks-ass.net>
Date:   Wed, 22 Feb 2023 14:36:14 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Mel Gorman <mgorman@...e.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Valentin Schneider <vschneid@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH] sched: Consider task_struct::saved_state in
 wait_task_inactive().

On Fri, Feb 17, 2023 at 03:53:02PM +0100, Sebastian Andrzej Siewior wrote:
> wait_task_inactive() waits for thread to unschedule in a certain task state.
> On PREEMPT_RT that state may be stored in task_struct::saved_state while the
> thread, that is being waited for, blocks on a sleeping lock and
> task_struct::__state is set to TASK_RTLOCK_WAIT.
> It is not possible to check only for TASK_RTLOCK_WAIT to be sure that the task
> is blocked on a sleeping lock because during wake up (after the sleeping lock
> has been acquired) the task state is set TASK_RUNNING. After the task in on CPU
> and acquired the pi_lock it will reset the state accordingly but until then
> TASK_RUNNING will be observed (with the desired state is saved in saved_state).
> 
> Check also for task_struct::saved_state if the desired match was not found in
> task_struct::__state on PREEMPT_RT. If the state was found in saved_state, wait
> until the task is idle and state is visible in task_struct::__state.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Reviewed-by: Valentin Schneider <vschneid@...hat.com>
> ---

Which if the very few wait_task_inactive() users requires this?