On 2/18/21 10:15 AM, Christian König wrote:
Am 18.02.21 um 16:05 schrieb Andrey Grodzovsky:
On 2/18/21 3:07 AM, Christian König wrote:
Am 17.02.21 um 22:59 schrieb Andrey Grodzovsky:
Problem: If scheduler is already stopped by the time sched_entity
is released and entity's job_queue not empty I encountred
a hang in drm_sched_entity_flush. This is because drm_sched_entity_is_idle
never becomes false.
Fix: In drm_sched_fini detach all sched_entities from the
scheduler's run queues. This will satisfy drm_sched_entity_is_idle.
Also wakeup all those processes stuck in sched_entity flushing
as the scheduler main thread which wakes them up is stopped by now.
v2:
Reverse order of drm_sched_rq_remove_entity and marking
s_entity as stopped to prevent reinserion back to rq due
to race.
Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@xxxxxxx>
---
drivers/gpu/drm/scheduler/sched_main.c | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)
diff --git a/drivers/gpu/drm/scheduler/sched_main.c
b/drivers/gpu/drm/scheduler/sched_main.c
index 908b0b5..c6b7947 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -897,9 +897,40 @@ EXPORT_SYMBOL(drm_sched_init);
*/
void drm_sched_fini(struct drm_gpu_scheduler *sched)
{
+ int i;
+ struct drm_sched_entity *s_entity;
BTW: Please order that so that i is declared last.
if (sched->thread)
kthread_stop(sched->thread);
+ /* Detach all sched_entites from this scheduler once it's stopped */
+ for (i = DRM_SCHED_PRIORITY_COUNT - 1; i >= DRM_SCHED_PRIORITY_MIN;
i--) {
+ struct drm_sched_rq *rq = &sched->sched_rq[i];
+
+ if (!rq)
+ continue;
+
+ /* Loop this way because rq->lock is taken in
drm_sched_rq_remove_entity */
+ spin_lock(&rq->lock);
+ while ((s_entity = list_first_entry_or_null(&rq->entities,
+ struct drm_sched_entity,
+ list))) {
+ spin_unlock(&rq->lock);
+
+ /* Prevent reinsertion and remove */
+ spin_lock(&s_entity->rq_lock);
+ s_entity->stopped = true;
+ drm_sched_rq_remove_entity(rq, s_entity);
+ spin_unlock(&s_entity->rq_lock);
Well this spin_unlock/lock dance here doesn't look correct at all now.
Christian.
In what way ? It's in the same same order as in other call sites (see
drm_sched_entity_push_job and drm_sched_entity_flush).
If i just locked rq->lock and did list_for_each_entry_safe while manually
deleting entity->list instead of calling
drm_sched_rq_remove_entity this still would not be possible as the order of
lock acquisition between s_entity->rq_lock
and rq->lock would be reverse compared to the call sites mentioned above.
Ah, now I understand. You need this because drm_sched_rq_remove_entity() will
grab the rq lock again!
Problem is now what prevents the entity from being destroyed while you remove it?
Christian.
Right, well, since (unfortunately) sched_entity is part of amdgpu_ctx_entity and
amdgpu_ctx_entity is refcounted
there is a problem here that we don't increment amdgpu_ctx.refcount when
assigning sched_entity
to new rq (e.g. before drm_sched_rq_add_entity) and not decrement before
removing. We do it for
amdgpu_cs_parser.entity for example (in amdgpu_cs_parser_init and
amdgpu_cs_parser_fini by
calling amdgpu_ctx_get and amdgpu_ctx_put). But this seems a bit tricky due to
all the drm_sched_entity_select_rq
logic.
Another, kind of a band aid fix, would probably be just locking
amdgpu_ctx_mgr.lock around drm_sched_fini
when finalizing the fence driver and around idr iteration in amdgpu_ctx_mgr_fini
(which should be lock protected
anyway as I see from other idr usages in the code) ... This should prevent this
use after free.
Andrey
Andrey
+
+ spin_lock(&rq->lock);
+ }
+ spin_unlock(&rq->lock);
+
+ }
+
+ /* Wakeup everyone stuck in drm_sched_entity_flush for this scheduler */
+ wake_up_all(&sched->job_scheduled);
+
/* Confirm no work left behind accessing device structures */
cancel_delayed_work_sync(&sched->work_tdr);
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