drm/sched: Drain all entities in DRM sched run job worker

All entities must be drained in the DRM scheduler run job worker to
avoid the following case. An entity found that is ready, no job found
ready on entity, and run job worker goes idle with other entities + jobs
ready. Draining all ready entities (i.e. loop over all ready entities)
in the run job worker ensures all job that are ready will be scheduled.

Cc: Thorsten Leemhuis <regressions@leemhuis.info>
Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Closes: https://lore.kernel.org/all/CABXGCsM2VLs489CH-vF-1539-s3in37=bwuOWtoeeE+q26zE+Q@mail.gmail.com/Reported-and-tested-by: Mario Limonciello <mario.limonciello@amd.com>
Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3124
Link: https://lore.kernel.org/all/20240123021155.2775-1-mario.limonciello@amd.com/Reported-and-tested-by: Vlastimil Babka <vbabka@suse.cz>
Closes: https://lore.kernel.org/dri-devel/05ddb2da-b182-4791-8ef7-82179fd159a8@amd.com/T/#m0c31d4d1b9ae9995bb880974c4f1dbaddc33a48aSigned-off-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240124210811.1639040-1-matthew.brost@intel.com

drivers/gpu/drm/scheduler/sched_main.c

@@ -1178,21 +1178,20 @@ static void drm_sched_run_job_work(struct work_struct *w)
 	struct drm_sched_entity *entity;
 	struct dma_fence *fence;
 	struct drm_sched_fence *s_fence;
-	struct drm_sched_job *sched_job;
+	struct drm_sched_job *sched_job = NULL;
 	int r;
 
 	if (READ_ONCE(sched->pause_submit))
 		return;
 
-	entity = drm_sched_select_entity(sched);
+	/* Find entity with a ready job */
+	while (!sched_job && (entity = drm_sched_select_entity(sched))) {
+		sched_job = drm_sched_entity_pop_job(entity);
+		if (!sched_job)
+			complete_all(&entity->entity_idle);
+	}
 	if (!entity)
-		return;
-
-	sched_job = drm_sched_entity_pop_job(entity);
-	if (!sched_job) {
-		complete_all(&entity->entity_idle);
 		return;	/* No more work */
-	}
 
 	s_fence = sched_job->s_fence;