drm/sched: Always wake up correct scheduler in drm_sched_entity_push_job

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: b37aced ("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+
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240924101914.2713-3-tursulin@igalia.com
Signed-off-by: Christian König <christian.koenig@amd.com>

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);