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

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.grodzovsky@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 <nayan26deshmukh@gmail.com>

Nayan

On Mon, Aug 6, 2018 at 7:43 PM Christian König <ckoenig.leichtzumerken@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.koenig@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);