linux-kernel - Re: [PATCH 1/2] kthread: don't use to_live_kthread() in kthread

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Message-ID: <alpine.DEB.2.20.1611090857280.3501@nanos>
Date:   Wed, 9 Nov 2016 08:58:36 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Oleg Nesterov <oleg@...hat.com>
cc:     Andy Lutomirski <luto@...capital.net>,
        Roman Pen <roman.penyaev@...fitbricks.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Tejun Heo <tj@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Chunming Zhou <David1.Zhou@....com>,
        Alex Deucher <alexander.deucher@....com>
Subject: Re: [PATCH 1/2] kthread: don't use to_live_kthread() in
 kthread_stop()



On Mon, 31 Oct 2016, Oleg Nesterov wrote:

> kthread_stop() had to use to_live_kthread() simply because it was not
> possible to access kthread->exited after the exiting kthread clears
> task_struct->vfork_done. Now that to_kthread() is always valid we can
> do wake_up_process() + wait_for_completion() unconditionally, we don't
> care if it has already passed complete_vfork_done() or even dead.
> 
> The exiting kthread can get the spurious wakeup after mm_release() but
> this is possible without this change too and this is fine, do_task_dead()
> ensures that this can't make any harm.
> 
> Note: we can even change this function to use task_work_add() and avoid
> ->vfork_done altogether, probably we will do this later.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>