[PATCH 2/8] drm/sched: Always wake up correct scheduler in drm_sched_entity_push_job

[Tvrtko Ursulin]

On 24/09/2024 14:55, Christian König wrote:
> I've pushed the first to drm-misc-next, but that one here fails to apply 
> cleanly.

This appears due 440d52b370b0 ("drm/sched: Fix dynamic job-flow control 
race") in drm-misc-fixes.

In theory 1-3 from my series are fixes. Should they also go to 
drm-misc-fixes? I am not too familiar with the drm-misc flow.

Or the series now needs to wait for some backmerge?

Regards,

Tvrtko

> Am 24.09.24 um 12:19 schrieb Tvrtko Ursulin:
>> From: Tvrtko Ursulin <tvrtko.ursulin at igalia.com>
>>
>> Since drm_sched_entity_modify_sched() can modify the entities run queue,
>> lets make sure to only dereference the pointer once so both adding and
>> waking up are guaranteed to be consistent.
>>
>> Alternative of moving the spin_unlock to after the wake up would for now
>> be more problematic since the same lock is taken inside
>> drm_sched_rq_update_fifo().
>>
>> v2:
>>   * Improve commit message. (Philipp)
>>   * Cache the scheduler pointer directly. (Christian)
>>
>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at igalia.com>
>> Fixes: b37aced31eb0 ("drm/scheduler: implement a function to modify 
>> sched list")
>> Cc: Christian König <christian.koenig at amd.com>
>> Cc: Alex Deucher <alexander.deucher at amd.com>
>> Cc: Luben Tuikov <ltuikov89 at gmail.com>
>> Cc: Matthew Brost <matthew.brost at intel.com>
>> Cc: David Airlie <airlied at gmail.com>
>> Cc: Daniel Vetter <daniel at ffwll.ch>
>> Cc: Philipp Stanner <pstanner at redhat.com>
>> Cc: dri-devel at lists.freedesktop.org
>> Cc: <stable at vger.kernel.org> # v5.7+
>> Reviewed-by: Christian König <christian.koenig at amd.com>
>> ---
>>   drivers/gpu/drm/scheduler/sched_entity.c | 10 ++++++++--
>>   1 file changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/scheduler/sched_entity.c 
>> b/drivers/gpu/drm/scheduler/sched_entity.c
>> index 0e002c17fcb6..a75eede8bf8d 100644
>> --- a/drivers/gpu/drm/scheduler/sched_entity.c
>> +++ b/drivers/gpu/drm/scheduler/sched_entity.c
>> @@ -599,6 +599,9 @@ void drm_sched_entity_push_job(struct 
>> drm_sched_job *sched_job)
>>       /* first job wakes up scheduler */
>>       if (first) {
>> +        struct drm_gpu_scheduler *sched;
>> +        struct drm_sched_rq *rq;
>> +
>>           /* Add the entity to the run queue */
>>           spin_lock(&entity->rq_lock);
>>           if (entity->stopped) {
>> @@ -608,13 +611,16 @@ void drm_sched_entity_push_job(struct 
>> drm_sched_job *sched_job)
>>               return;
>>           }
>> -        drm_sched_rq_add_entity(entity->rq, entity);
>> +        rq = entity->rq;
>> +        sched = rq->sched;
>> +
>> +        drm_sched_rq_add_entity(rq, entity);
>>           spin_unlock(&entity->rq_lock);
>>           if (drm_sched_policy == DRM_SCHED_POLICY_FIFO)
>>               drm_sched_rq_update_fifo(entity, submit_ts);
>> -        drm_sched_wakeup(entity->rq->sched);
>> +        drm_sched_wakeup(sched);
>>       }
>>   }
>>   EXPORT_SYMBOL(drm_sched_entity_push_job);
>