linux-kernel - Re: [PATCH 1/3] signals: Allow generation of SIGKILL to exiting task.

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Message-ID: <20180425131350.GB7592@redhat.com>
Date:   Wed, 25 Apr 2018 15:13:50 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Andrey Grodzovsky <andrey.grodzovsky@....com>
Cc:     linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
        Alexander.Deucher@....com, Christian.Koenig@....com,
        David.Panariti@....com, akpm@...ux-foundation.org,
        ebiederm@...ssion.com
Subject: Re: [PATCH 1/3] signals: Allow generation of SIGKILL to exiting task.

On 04/24, Andrey Grodzovsky wrote:
>
> Currently calling wait_event_killable as part of exiting process
> will stall forever since SIGKILL generation is suppresed by PF_EXITING.

See my reply to 2/3,

> In our partilaur case AMDGPU driver wants to flush all GPU jobs in
> flight before shutting down. But if some job hangs the pipe we still want to
> be able to kill it and avoid a process in D state.

this patch won't really help in multi-threaded case,

> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -886,10 +886,10 @@ static inline int wants_signal(int sig, struct task_struct *p)
>  {
>  	if (sigismember(&p->blocked, sig))
>  		return 0;
> -	if (p->flags & PF_EXITING)
> -		return 0;
>  	if (sig == SIGKILL)
>  		return 1;
> +	if (p->flags & PF_EXITING)
> +		return 0;

So you want to trigger signal_wake_up() at the end of complete_signal().

Unless you use tkill() you can wake another thread, not the thread blocked
in drm_sched_entity_fini().

And if the whole process is already dying complete_signal() will do nothing
else.

Oleg.