Re: [PATCH v5 15/27] drm/scheduler: Fix hang when sched_entity released

[Christian König <ckoenig.leichtzumerken@xxxxxxxxx>]

Am 29.04.21 um 19:06 schrieb Andrey Grodzovsky:
> On 2021-04-29 3:18 a.m., Christian König wrote:
> > I need to take another look at this part when I don't have a massive 
> > headache any more.
> >
> > Maybe split the patch set up into different parts, something like:
> > 1. Adding general infrastructure.
> > 2. Making sure all memory is unpolated.
> > 3. Job and fence handling
>
> I am not sure you mean this patch here, maybe another one ?
> Also note you already RBed it.

No what I meant was to send out the patches before this one as #1 and #2.

That is the easier stuff which can easily go into the drm-misc-next or 
amd-staging-drm-next branch.

The scheduler stuff certainly need to go into drm-misc-next.

Christian.

> Andrey
>
> > Christian.
> >
> > Am 28.04.21 um 17:11 schrieb Andrey Grodzovsky:
> > > Problem: If scheduler is already stopped by the time sched_entity
> > > is released and entity's job_queue not empty I encountred
> > > a hang in drm_sched_entity_flush. This is because 
> > > drm_sched_entity_is_idle
> > > never becomes false.
> > >
> > > Fix: In drm_sched_fini detach all sched_entities from the
> > > scheduler's run queues. This will satisfy drm_sched_entity_is_idle.
> > > Also wakeup all those processes stuck in sched_entity flushing
> > > as the scheduler main thread which wakes them up is stopped by now.
> > >
> > > v2:
> > > Reverse order of drm_sched_rq_remove_entity and marking
> > > s_entity as stopped to prevent reinserion back to rq due
> > > to race.
> > >
> > > v3:
> > > Drop drm_sched_rq_remove_entity, only modify entity->stopped
> > > and check for it in drm_sched_entity_is_idle
> > >
> > > Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@xxxxxxx>
> > > Reviewed-by: Christian König <christian.koenig@xxxxxxx>
> > > ---
> > >   drivers/gpu/drm/scheduler/sched_entity.c |  3 ++-
> > >   drivers/gpu/drm/scheduler/sched_main.c   | 24 
> > > ++++++++++++++++++++++++
> > >   2 files changed, 26 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/gpu/drm/scheduler/sched_entity.c 
> > > b/drivers/gpu/drm/scheduler/sched_entity.c
> > > index f0790e9471d1..cb58f692dad9 100644
> > > --- a/drivers/gpu/drm/scheduler/sched_entity.c
> > > +++ b/drivers/gpu/drm/scheduler/sched_entity.c
> > > @@ -116,7 +116,8 @@ static bool drm_sched_entity_is_idle(struct 
> > > drm_sched_entity *entity)
> > >       rmb(); /* for list_empty to work without lock */
> > >       if (list_empty(&entity->list) ||
> > > -        spsc_queue_count(&entity->job_queue) == 0)
> > > +        spsc_queue_count(&entity->job_queue) == 0 ||
> > > +        entity->stopped)
> > >           return true;
> > >       return false;
> > > diff --git a/drivers/gpu/drm/scheduler/sched_main.c 
> > > b/drivers/gpu/drm/scheduler/sched_main.c
> > > index 908b0b56032d..ba087354d0a8 100644
> > > --- a/drivers/gpu/drm/scheduler/sched_main.c
> > > +++ b/drivers/gpu/drm/scheduler/sched_main.c
> > > @@ -897,9 +897,33 @@ EXPORT_SYMBOL(drm_sched_init);
> > >    */
> > >   void drm_sched_fini(struct drm_gpu_scheduler *sched)
> > >   {
> > > +    struct drm_sched_entity *s_entity;
> > > +    int i;
> > > +
> > >       if (sched->thread)
> > >           kthread_stop(sched->thread);
> > > +    for (i = DRM_SCHED_PRIORITY_COUNT - 1; i >= 
> > > DRM_SCHED_PRIORITY_MIN; i--) {
> > > +        struct drm_sched_rq *rq = &sched->sched_rq[i];
> > > +
> > > +        if (!rq)
> > > +            continue;
> > > +
> > > +        spin_lock(&rq->lock);
> > > +        list_for_each_entry(s_entity, &rq->entities, list)
> > > +            /*
> > > +             * Prevents reinsertion and marks job_queue as idle,
> > > +             * it will removed from rq in drm_sched_entity_fini
> > > +             * eventually
> > > +             */
> > > +            s_entity->stopped = true;
> > > +        spin_unlock(&rq->lock);
> > > +
> > > +    }
> > > +
> > > +    /* Wakeup everyone stuck in drm_sched_entity_flush for this 
> > > scheduler */
> > > +    wake_up_all(&sched->job_scheduled);
> > > +
> > >       /* Confirm no work left behind accessing device structures */
> > >       cancel_delayed_work_sync(&sched->work_tdr);