Re: [PATCH v3 01/20] drm/sched: entity->rq selection cannot fail

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Am 08.07.21 um 19:37 schrieb Daniel Vetter:
If it does, someone managed to set up a sched_entity without
schedulers, which is just a driver bug.

NAK, it is perfectly valid for rq selection to fail.

See drm_sched_pick_best():

                if (!sched->ready) {
                        DRM_WARN("scheduler %s is not ready, skipping",
                                 sched->name);
                        continue;
                }

This can happen when a device reset fails for some engine.

Regards,
Christian.


We BUG_ON() here because in the next patch drm_sched_job_init() will
be split up, with drm_sched_job_arm() never failing. And that's the
part where the rq selection will end up in.

Note that if having an empty sched_list set on an entity is indeed a
valid use-case, we can keep that check in job_init even after the split
into job_init/arm.

Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
Cc: "Christian König" <christian.koenig@xxxxxxx>
Cc: Luben Tuikov <luben.tuikov@xxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: Steven Price <steven.price@xxxxxxx>
Cc: Andrey Grodzovsky <andrey.grodzovsky@xxxxxxx>
Cc: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
Cc: Jack Zhang <Jack.Zhang1@xxxxxxx>
---
  drivers/gpu/drm/scheduler/sched_entity.c | 2 +-
  drivers/gpu/drm/scheduler/sched_main.c   | 3 +--
  2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
index 79554aa4dbb1..6fc116ee7302 100644
--- a/drivers/gpu/drm/scheduler/sched_entity.c
+++ b/drivers/gpu/drm/scheduler/sched_entity.c
@@ -45,7 +45,7 @@
   * @guilty: atomic_t set to 1 when a job on this queue
   *          is found to be guilty causing a timeout
   *
- * Note: the sched_list should have at least one element to schedule
+ * Note: the sched_list must have at least one element to schedule
   *       the entity
   *
   * Returns 0 on success or a negative error code on failure.
diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
index 33c414d55fab..01dd47154181 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -586,8 +586,7 @@ int drm_sched_job_init(struct drm_sched_job *job,
  	struct drm_gpu_scheduler *sched;
drm_sched_entity_select_rq(entity);
-	if (!entity->rq)
-		return -ENOENT;
+	BUG_ON(!entity->rq);
sched = entity->rq->sched;




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