linux-kernel - Re: [patch 07/44] posix-cpu-timers: Simplify sighand locking in run_posix_cpu

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Message-ID: <20190821120912.GD16213@lenoir>
Date:   Wed, 21 Aug 2019 14:09:18 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        John Stultz <john.stultz@...aro.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Anna-Maria Behnsen <anna-maria@...utronix.de>
Subject: Re: [patch 07/44] posix-cpu-timers: Simplify sighand locking in
 run_posix_cpu_timers()

On Mon, Aug 19, 2019 at 04:31:48PM +0200, Thomas Gleixner wrote:
> run_posix_cpu_timers() is called from the timer interrupt. The posix timer
> expiry always affects the current task which got interrupted.
> 
> sighand locking is only racy when done on a foreign task, which must use
> lock_task_sighand(). But in case of run_posix_cpu_timers() that's
> pointless.
> 
> sighand of a task can only be dropped or changed by the task itself. Drop
> happens in do_exit()

Well, that's only in case of autoreap. Otherwise this is dropped by the reaper.

> changing sighand happens in execve().