linux-kernel - Re: [PATCH 2/3] drm/scheduler: Don't call wait_event

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Date:   Wed, 25 Apr 2018 15:05:22 +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 2/3] drm/scheduler: Don't call wait_event_killable for
 signaled process.

On 04/24, Andrey Grodzovsky wrote:
>
> --- a/drivers/gpu/drm/scheduler/gpu_scheduler.c
> +++ b/drivers/gpu/drm/scheduler/gpu_scheduler.c
> @@ -227,9 +227,10 @@ void drm_sched_entity_do_release(struct drm_gpu_scheduler *sched,
>  		return;
>  	/**
>  	 * The client will not queue more IBs during this fini, consume existing
> -	 * queued IBs or discard them on SIGKILL
> +	 * queued IBs or discard them when in death signal state since
> +	 * wait_event_killable can't receive signals in that state.
>  	*/
> -	if ((current->flags & PF_SIGNALED) && current->exit_code == SIGKILL)
> +	if (current->flags & PF_SIGNALED)

please do not use PF_SIGNALED, it must die. Besides you can't rely on this flag
in multi-threaded case. current->exit_code doesn't look right too.

>  		entity->fini_status = -ERESTARTSYS;
>  	else
>  		entity->fini_status = wait_event_killable(sched->job_scheduled,

So afaics the problem is that fatal_signal_pending() is not necessarily true
after SIGKILL was already dequeued and thus wait_event_killable(), right?

This was already discussed, but it is not clear what we can/should do. We can
probably change get_signal() to not dequeue SIGKILL or do something else to keep
fatal_signal_pending() == T for the exiting killed thread.

But in this case we probably also want to discriminate the "real" SIGKILL's from
group_exit/exec/coredump.

Oleg.