linux-kernel - Re: [PATCH 2/2] sched: Introduce set_special

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Message-ID: <20180501135924.GA12696@redhat.com>
Date:   Tue, 1 May 2018 15:59:24 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, tglx@...utronix.de, linux-kernel@...r.kernel.org,
        will.deacon@....com, mpe@...erman.id.au, bigeasy@...utronix.de,
        gkohli@...eaurora.org, neeraju@...eaurora.org
Subject: Re: [PATCH 2/2] sched: Introduce set_special_state()

On 05/01, Peter Zijlstra wrote:
>
> The only code I found that seems to care is ptrace_attach(), where we
> wait for JOBCTL_TRAPPING to get cleared. That same function has a
> comment about hiding the STOPPED -> RUNNING -> TRACED transition. So I'm
> assuming it needs to observe TRACED if it observes !TRAPPING.

Yes, exactly.

> But I don't think there's enough barriers on that end to guarantee this.
> Any ->state load after wait_on_bit() is, afact, free to have happened
> before the ->jobctl load.

do_wait() does set_current_state() before it checks ->state or anything else.

Oleg.