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

[Christian König]

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 at amd.com>
>>> Reviewed-by: Christian König <christian.koenig at amd.com>
>>> ---
>>>   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);
>>