linux-kernel - Re: [PATCH 2/3] drm/scheduler: Don't call wait_event_killable for signaled process.

Open Source and information security mailing list archives

Date:   Tue, 24 Apr 2018 21:44:18 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Michel Dänzer <michel@...nzer.net>
Cc:     Andrey Grodzovsky <andrey.grodzovsky@....com>,
        linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, David.Panariti@....com,
        oleg@...hat.com, ebiederm@...ssion.com, Alexander.Deucher@....com,
        akpm@...ux-foundation.org, Christian.Koenig@....com
Subject: Re: [PATCH 2/3] drm/scheduler: Don't call wait_event_killable for
 signaled process.

On Tue, Apr 24, 2018 at 05:46:52PM +0200, Michel Dänzer wrote:
> 
> Adding the dri-devel list, since this is driver independent code.
> 
> 
> On 2018-04-24 05:30 PM, Andrey Grodzovsky wrote:
> > Avoid calling wait_event_killable when you are possibly being called
> > from get_signal routine since in that case you end up in a deadlock
> > where you are alreay blocked in singla processing any trying to wait
> 
> Multiple typos here, "[...] already blocked in signal processing and [...]"?
> 
> 
> > on a new signal.
> > 
> > Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@....com>
> > ---
> >  drivers/gpu/drm/scheduler/gpu_scheduler.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/scheduler/gpu_scheduler.c b/drivers/gpu/drm/scheduler/gpu_scheduler.c
> > index 088ff2b..09fd258 100644
> > --- 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)

You want fatal_signal_pending() here, instead of inventing your own broken
version.
> >  		entity->fini_status = -ERESTARTSYS;
> >  	else
> >  		entity->fini_status = wait_event_killable(sched->job_scheduled,

But really this smells like a bug in wait_event_killable, since
wait_event_interruptible does not suffer from the same bug. It will return
immediately when there's a signal pending.

I think this should be fixed in core code, not papered over in some
subsystem.
-Daniel

> > 
> 
> 
> -- 
> Earthling Michel Dänzer               |               http://www.amd.com
> Libre software enthusiast             |             Mesa and X developer
> _______________________________________________
> dri-devel mailing list
> dri-devel@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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