Re: [PATCH] drm/sched: avoid killing parent entity on child SIGKILL v3

[Philipp Stanner <phasta@mailbox.org>]

On Wed, 2025-10-15 at 16:01 +0200, Christian König wrote:
> From: David Rosca <david.rosca@amd.com>
> 
> The DRM scheduler tracks who last uses an entity and when that process
> is killed blocks all further submissions to that entity.
> 
> The problem is that we didn't track who initially created an entity, so
> when a process accidently leaked its file descriptor to a child and
> that child got killed, we killed the parent's entities.
> 
> Avoid that and instead initialize the entities last user on entity
> creation. This also allows to drop the extra NULL check.
> 
> v2: still use cmpxchg
> v3: improve the commit message
> 
> Signed-off-by: David Rosca <david.rosca@amd.com>
> Signed-off-by: Christian König <christian.koenig@amd.com>
> Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/4568
> Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
> CC: stable@vger.kernel.org

Acked-by: Philipp Stanner <phasta@kernel.org>


Fire at will, Christian. Maybe optionally with the commit message nits
twirked in we discussed before.


P.

> ---
>  drivers/gpu/drm/scheduler/sched_entity.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
> index 5a4697f636f2..3e2f83dc3f24 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
> @@ -302,7 +303,7 @@ long drm_sched_entity_flush(struct drm_sched_entity *entity, long timeout)
>  
>  	/* For a killed process disallow further enqueueing of jobs. */
>  	last_user = cmpxchg(&entity->last_user, current->group_leader, NULL);
> -	if ((!last_user || last_user == current->group_leader) &&
> +	if (last_user == current->group_leader &&
>  	    (current->flags & PF_EXITING) && (current->exit_code == SIGKILL))
>  		drm_sched_entity_kill(entity);
>