drm_sched_fence_create() assigns a sequence number to the fence it creates.
Now drm_sched_fence_create() is called by drm_sched_job_init() to
initialize the jobs we want to push on the scheduler queue.
When you now call drm_sched_entity_push_job() without a protecting lock
it can happen that you push two (or even more) job with reversed
sequence numbers.
Since the sequence numbers are used to determine job completion order
reversing them can seriously mess things up.
So the spin lock should be superfluous, if it isn't we have a much
larger bug we need to fix.
Christian.
Am 16.05.2018 um 13:15 schrieb Andrey Grodzovsky:
Can you please elaborate more, maybe give an example - I don't
understand yet the problematic scenario.
Andrey
On 05/16/2018 02:50 AM, Christian König wrote:
No, that spinlock is indeed incorrect. I
See even when we protect the spsc queue with a spinlock that doesn't
make it correct. It can happen that the jobs pushed to the queue are
reversed in their sequence order and that can cause severe problems
in the memory management.
Christian.
Am 16.05.2018 um 05:33 schrieb Grodzovsky, Andrey:
Yeah, that what I am not sure about... It's lockless in a sense of
single producer single consumer but not for multiple concurrent
producers... So now I think this spinlock should stay there... It
just looked useless to me at first sight...
Andrey
________________________________________
From: Zhou, David(ChunMing)
Sent: 15 May 2018 23:04:44
To: Grodzovsky, Andrey; amd-gfx@xxxxxxxxxxxxxxxxxxxxx;
dri-devel@xxxxxxxxxxxxxxxxxxxxx
Cc: Koenig, Christian
Subject: Re: [PATCH 2/2] drm/scheduler: Remove obsolete spinlock.
On 2018年05月16日 03:31, Andrey Grodzovsky wrote:
Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@xxxxxxx>
---
drivers/gpu/drm/scheduler/gpu_scheduler.c | 4 ----
include/drm/gpu_scheduler.h | 1 -
2 files changed, 5 deletions(-)
diff --git a/drivers/gpu/drm/scheduler/gpu_scheduler.c
b/drivers/gpu/drm/scheduler/gpu_scheduler.c
index 1f1dd70..2569a63 100644
--- a/drivers/gpu/drm/scheduler/gpu_scheduler.c
+++ b/drivers/gpu/drm/scheduler/gpu_scheduler.c
@@ -140,7 +140,6 @@ int drm_sched_entity_init(struct
drm_gpu_scheduler *sched,
entity->last_scheduled = NULL;
spin_lock_init(&entity->rq_lock);
- spin_lock_init(&entity->queue_lock);
spsc_queue_init(&entity->job_queue);
atomic_set(&entity->fence_seq, 0);
@@ -424,11 +423,8 @@ void drm_sched_entity_push_job(struct
drm_sched_job *sched_job,
trace_drm_sched_job(sched_job, entity);
- spin_lock(&entity->queue_lock);
first = spsc_queue_push(&entity->job_queue,
&sched_job->queue_node);
- spin_unlock(&entity->queue_lock);
Is your spsc safely to be added simultaneously?
Regards,
David Zhou
-
/* first job wakes up scheduler */
if (first) {
/* Add the entity to the run queue */
diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
index 350a62c..683eb65 100644
--- a/include/drm/gpu_scheduler.h
+++ b/include/drm/gpu_scheduler.h
@@ -56,7 +56,6 @@ struct drm_sched_entity {
spinlock_t rq_lock;
struct drm_gpu_scheduler *sched;
- spinlock_t queue_lock;
struct spsc_queue job_queue;
atomic_t fence_seq;
_______________________________________________
amd-gfx mailing list
amd-gfx@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/amd-gfx
_______________________________________________
dri-devel mailing list
dri-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/dri-devel
