linux-kernel - Re: [PATCH v2] ptrace: fix ptrace vs tasklist_lock race on PREEMPT

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Message-ID: <20220405102849.GA2708@redhat.com>
Date:   Tue, 5 Apr 2022 12:29:03 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        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>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH v2] ptrace: fix ptrace vs tasklist_lock race on
 PREEMPT_RT.

On 04/05, Peter Zijlstra wrote:
>
> As is, I think we can write task_is_stopped() like:
>
> #define task_is_stopped(task)	((task)->jobctl & JOBCTL_STOP_PENDING)
>
> Because jobctl is in fact the canonical state.

Not really. JOBCTL_STOP_PENDING means that the task should stop.

And this flag is cleared right before set_special_state(TASK_STOPPED)
in do_signal_stop(), see task_participate_group_stop().

Oleg.