I assume that this is the only code change and no locks are taken in
drm_sched_entity_push_job -
What happens if process A runs drm_sched_entity_push_job after this code
was executed from the (dying) process B and there
are still jobs in the queue (the wait_event terminated prematurely), the
entity already removed from rq , but bool 'first' in
drm_sched_entity_push_job
will return false and so the entity will not be reinserted back into rq
entity list and no wake up trigger will happen for process A pushing a
new job.
Another issue bellow -
Andrey
On 08/14/2018 03:05 AM, Christian König wrote:
I would rather like to avoid taking the lock in the hot path.
How about this:
/* For killed process disable any more IBs enqueue right now */
last_user = cmpxchg(&entity->last_user, current->group_leader, NULL);
if ((!last_user || last_user == current->group_leader) &&
(current->flags & PF_EXITING) && (current->exit_code ==
SIGKILL)) {
grab_lock();
drm_sched_rq_remove_entity(entity->rq, entity);
if (READ_ONCE(&entity->last_user) != NULL)
This condition is true because just exactly now process A did
drm_sched_entity_push_job->WRITE_ONCE(entity->last_user,
current->group_leader);
and so the line bellow executed and entity reinserted into rq. Let's say
also that the entity job queue is empty now. For process A bool 'first'
will be true
and hence also
drm_sched_entity_push_job->drm_sched_rq_add_entity(entity->rq, entity)
will take place causing double insertion of the entity queue into rq list.
Andrey
drm_sched_rq_add_entity(entity->rq, entity);
drop_lock();
}
Christian.
Am 13.08.2018 um 18:43 schrieb Andrey Grodzovsky:
Attached.
If the general idea in the patch is OK I can think of a test (and
maybe add to libdrm amdgpu tests) to actually simulate this scenario
with 2 forked
concurrent processes working on same entity's job queue when one is
dying while the other keeps pushing to the same queue. For now I only
tested it
with normal boot and ruining multiple glxgears concurrently - which
doesn't really test this code path since i think each of them works
on it's own FD.
Andrey
On 08/10/2018 09:27 AM, Christian König wrote:
Crap, yeah indeed that needs to be protected by some lock.
Going to prepare a patch for that,
Christian.
Am 09.08.2018 um 21:49 schrieb Andrey Grodzovsky:
Reviewed-by: Andrey Grodzovsky <andrey.grodzov...@amd.com>
But I still have questions about entity->last_user (didn't notice
this before) -
Looks to me there is a race condition with it's current usage,
let's say process A was preempted after doing
drm_sched_entity_flush->cmpxchg(...)
now process B working on same entity (forked) is inside
drm_sched_entity_push_job, he writes his PID to entity->last_user
and also
executes drm_sched_rq_add_entity. Now process A runs again and
execute drm_sched_rq_remove_entity inadvertently causing process B
removal
from it's scheduler rq.
Looks to me like instead we should lock together entity->last_user
accesses and adds/removals of entity to the rq.
Andrey
On 08/06/2018 10:18 AM, Nayan Deshmukh wrote:
I forgot about this since we started discussing possible scenarios
of processes and threads.
In any case, this check is redundant. Acked-by: Nayan Deshmukh
<nayan26deshm...@gmail.com <mailto:nayan26deshm...@gmail.com>>
Nayan
On Mon, Aug 6, 2018 at 7:43 PM Christian König
<ckoenig.leichtzumer...@gmail.com
<mailto:ckoenig.leichtzumer...@gmail.com>> wrote:
Ping. Any objections to that?
Christian.
Am 03.08.2018 um 13:08 schrieb Christian König:
> That is superflous now.
>
> Signed-off-by: Christian König <christian.koe...@amd.com
<mailto:christian.koe...@amd.com>>
> ---
> drivers/gpu/drm/scheduler/gpu_scheduler.c | 5 -----
> 1 file changed, 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/scheduler/gpu_scheduler.c
b/drivers/gpu/drm/scheduler/gpu_scheduler.c
> index 85908c7f913e..65078dd3c82c 100644
> --- a/drivers/gpu/drm/scheduler/gpu_scheduler.c
> +++ b/drivers/gpu/drm/scheduler/gpu_scheduler.c
> @@ -590,11 +590,6 @@ void drm_sched_entity_push_job(struct
drm_sched_job *sched_job,
> if (first) {
> /* Add the entity to the run queue */
> spin_lock(&entity->rq_lock);
> - if (!entity->rq) {
> - DRM_ERROR("Trying to push to a killed
entity\n");
> - spin_unlock(&entity->rq_lock);
> - return;
> - }
> drm_sched_rq_add_entity(entity->rq, entity);
> spin_unlock(&entity->rq_lock);
> drm_sched_wakeup(entity->rq->sched);
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