Re: [PATCH] drm/sched: Avoid killing entity last used by parent on child SIGKILL

["Christian König" <christian.koenig@amd.com>]

On 02.10.25 17:05, David Rosca wrote:
> drm_sched_entity_flush should only kill the entity if the current
> process is the last user of the entity. The last_user is only set
> when adding new job, so entities that had no jobs submitted to them
> have NULL last_user and would always be killed.
> Another issue is setting last_user to NULL from drm_sched_entity_flush,
> which causes subsequent calls to kill the entity.
> 
> Signed-off-by: David Rosca <david.rosca@amd.com>
> Fixes: 51564e9f06f0 ("drm/amdgpu: Avoid extra evict-restore process.")

Good catch, but in general please CC the relevant maintainers and mailing lists for scheduler patches.

> ---
>  drivers/gpu/drm/scheduler/sched_entity.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
> index 8867b95ab089..a325e4a59990 100644
> --- a/drivers/gpu/drm/scheduler/sched_entity.c
> +++ b/drivers/gpu/drm/scheduler/sched_entity.c
> @@ -70,6 +70,7 @@ int drm_sched_entity_init(struct drm_sched_entity *entity,
>  	entity->guilty = guilty;
>  	entity->num_sched_list = num_sched_list;
>  	entity->priority = priority;
> +	entity->last_user = current->group_leader;
>  	/*
>  	 * It's perfectly valid to initialize an entity without having a valid
>  	 * scheduler attached. It's just not valid to use the scheduler before it
> @@ -278,7 +279,6 @@ static void drm_sched_entity_kill(struct drm_sched_entity *entity)
>  long drm_sched_entity_flush(struct drm_sched_entity *entity, long timeout)
>  {
>  	struct drm_gpu_scheduler *sched;
> -	struct task_struct *last_user;
>  	long ret = timeout;
>  
>  	if (!entity->rq)
> @@ -301,8 +301,7 @@ long drm_sched_entity_flush(struct drm_sched_entity *entity, long timeout)
>  	}
>  
>  	/* 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) &&
> +	if (entity->last_user == current->group_leader &&

You still need the cmpxchg() here or otherwise drm_sched_entity_kill() would run multiple times.

Regards,
Christian.

>  	    (current->flags & PF_EXITING) && (current->exit_code == SIGKILL))
>  		drm_sched_entity_kill(entity);
>