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

[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 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;
+
+		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);
-- 
2.46.0