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

["Christian König" <christian.koenig@amd.com>]

Am 09.09.24 um 19:19 schrieb Tvrtko Ursulin:
> From: Tvrtko Ursulin <tvrtko.ursulin@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@igalia.com>
> Fixes: b37aced31eb0 ("drm/scheduler: implement a function to modify sched list")
> Cc: Christian König <christian.koenig@amd.com>
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: Luben Tuikov <ltuikov89@gmail.com>
> Cc: Matthew Brost <matthew.brost@intel.com>
> Cc: David Airlie <airlied@gmail.com>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Cc: Philipp Stanner <pstanner@redhat.com>
> Cc: dri-devel@lists.freedesktop.org
> Cc: <stable@vger.kernel.org> # v5.7+
> ---
>   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 ae8be30472cd..76e422548d40 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;

The rq variable is now not needed any more except for getting the 
scheduler, isn't it? If yes I would ditch that as well.

Either way Reviewed-by: Christian König <christian.koenig@amd.com> to 
this patch.

Regards,
Christian.

> +
> +		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, entity);
> +		drm_sched_wakeup(sched, entity);
>   	}
>   }
>   EXPORT_SYMBOL(drm_sched_entity_push_job);