drm/sched: Fix bounds limiting when given a malformed entity

If we're given a malformed entity in drm_sched_entity_init()--shouldn't
happen, but we verify--with out-of-bounds priority value, we set it to an
allowed value. Fix the expression which sets this limit.
Signed-off-by: Luben Tuikov <ltuikov89@gmail.com>
Fixes: 56e44960 ("drm/sched: Convert the GPU scheduler to variable number of run-queues")
Link: https://patchwork.freedesktop.org/patch/msgid/20231123122422.167832-2-ltuikov89@gmail.comReviewed-by: Christian König <christian.koenig@amd.com>
Link: https://lore.kernel.org/r/dbb91dbe-ef77-4d79-aaf9-2adb171c1d7a@amd.com

drivers/gpu/drm/scheduler/sched_entity.c

@@ -81,12 +81,15 @@ int drm_sched_entity_init(struct drm_sched_entity *entity,
 		 */
 		pr_warn("%s: called with uninitialized scheduler\n", __func__);
 	} else if (num_sched_list) {
-		/* The "priority" of an entity cannot exceed the number
-		 * of run-queues of a scheduler.
+		/* The "priority" of an entity cannot exceed the number of run-queues of a
+		 * scheduler. Protect against num_rqs being 0, by converting to signed.
 		 */
-		if (entity->priority >= sched_list[0]->num_rqs)
-			entity->priority = max_t(u32, sched_list[0]->num_rqs,
-						 DRM_SCHED_PRIORITY_MIN);
+		if (entity->priority >= sched_list[0]->num_rqs) {
+			drm_err(sched_list[0], "entity with out-of-bounds priority:%u num_rqs:%u\n",
+				entity->priority, sched_list[0]->num_rqs);
+			entity->priority = max_t(s32, (s32) sched_list[0]->num_rqs - 1,
+						 (s32) DRM_SCHED_PRIORITY_MIN);
+		}
 		entity->rq = sched_list[0]->sched_rq[entity->priority];
 	}