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

[Andrey Grodzovsky]

On 04/24/2018 03:44 PM, Daniel Vetter wrote:
> On Tue, Apr 24, 2018 at 05:46:52PM +0200, Michel DÃnzer 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@xxxxxxx>
> > > ---
> > >   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.

I rely on current->flags & PF_SIGNALED because this being set from 
within get_signal,
meaning I am within signal processing in which case I want to avoid any 
signal based wait for that task,
From what i see in the code, task_struct.pending.signal is being set 
for other threads in same
group (zap_other_threads) or for other scenarios, those task are still 
able to receive signals
so calling wait_event_killable there will not have problem.
> > >   		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.

Even when wait_event_interruptible is called as following - 
...->do_signal->get_signal->....->wait_event_interruptible ?
I haven't tried it but wait_event_interruptible is very much alike to 
wait_event_killable so I would assume it will also
not be interrupted if called like that. (Will give it a try just out of 
curiosity anyway)

Andrey

> I think this should be fixed in core code, not papered over in some
> subsystem.
> -Daniel
>
> > --
> > Earthling Michel DÃnzer               |               http://www.amd.com
> > Libre software enthusiast             |             Mesa and X developer
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