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

[Andrey Grodzovsky]

Will do.

Andrey

On 2/17/21 4:37 PM, Christian König wrote:
>
>
> Am 17.02.21 um 22:36 schrieb Andrey Grodzovsky:
>>
>> On 2/17/21 4:32 PM, Christian König wrote:
>>> Am 16.02.21 um 18:07 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.
>>>>
>>>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky at amd.com>
>>>> ---
>>>>   drivers/gpu/drm/scheduler/sched_main.c | 31 +++++++++++++++++++++++++++++++
>>>>   1 file changed, 31 insertions(+)
>>>>
>>>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c 
>>>> b/drivers/gpu/drm/scheduler/sched_main.c
>>>> index 908b0b5..11abf5d 100644
>>>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>>>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>>>> @@ -897,9 +897,40 @@ EXPORT_SYMBOL(drm_sched_init);
>>>>    */
>>>>   void drm_sched_fini(struct drm_gpu_scheduler *sched)
>>>>   {
>>>> +    int i;
>>>> +    struct drm_sched_entity *s_entity;
>>>>       if (sched->thread)
>>>>           kthread_stop(sched->thread);
>>>>   +    /* Detach all sched_entites from this scheduler once it's stopped */
>>>> +    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;
>>>> +
>>>> +        /* Loop this way because rq->lock is taken in 
>>>> drm_sched_rq_remove_entity */
>>>> +        spin_lock(&rq->lock);
>>>> +        while ((s_entity = list_first_entry_or_null(&rq->entities,
>>>> +                                struct drm_sched_entity,
>>>> +                                list))) {
>>>> +            spin_unlock(&rq->lock);
>>>> +            drm_sched_rq_remove_entity(rq, s_entity);
>>>> +
>>>> +            /* Mark as stopped to reject adding to any new rq */
>>>> +            spin_lock(&s_entity->rq_lock);
>>>> +            s_entity->stopped = true;
>>>
>>> Why not marking it as stopped and then removing it?
>>>
>>> Regards,
>>> Christian.
>>
>>
>> You mean just reverse the order of operations here to prevent a race where 
>> someone adding it again to rq before marking it as stopped ?
>
> Exactly that, yeah.
>
> Christian.
>
>>
>> Andrey
>>
>>
>>>
>>>> + spin_unlock(&s_entity->rq_lock);
>>>> +
>>>> +            spin_lock(&rq->lock);
>>>> +        }
>>>> +        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);
>>>
>