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

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Date:   Wed, 25 Apr 2018 15:36:40 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Andrey Grodzovsky <Andrey.Grodzovsky@....com>,
        Michel Dänzer <michel@...nzer.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        David.Panariti@....com, Eric Biederman <ebiederm@...ssion.com>,
        Alex Deucher <Alexander.Deucher@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian König <Christian.Koenig@....com>
Subject: Re: [PATCH 2/3] drm/scheduler: Don't call wait_event_killable for
 signaled process.

On Wed, Apr 25, 2018 at 3:22 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> On 04/24, Daniel Vetter wrote:
>>
>> wait_event_killabel doesn't check for fatal_signal_pending before calling
>> schedule, so definitely has a nice race there.
>
> This is fine. See the signal_pending_state() check in __schedule().
>
> And this doesn't differ from wait_event_interruptible(), it too doesn't
> check signal_pending(), we rely on schedule() which must not block if the
> caller is signalled/killed.
>
> The problem is that it is not clear what should fatal_signal_pending() or
> even signal_pending() mean after exit_signals().

Uh, I was totally thrown off in all the wait_event* macros and somehow
landed in the _locked variants, which all need to recheck before they
drop the lock, for efficiency reasons. See do_wait_intr().

Sorry for the confusion.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch