drm/sched: avoid killing parent entity on child SIGKILL

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.

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>
Link: https://lore.kernel.org/r/20251015140128.1470-1-christian.koenig@amd.com
Signed-off-by: Philipp Stanner <phasta@kernel.org>
Link: https://patch.msgid.link/20251015140128.1470-1-christian.koenig@amd.com

diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
index aa222166de580bb3b49503b62506d1b4f611ced3..c8e949f4a5687c135a323087c69fee9cc2edcf1e 100644 (file)
--- 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);