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

[David Rosca <david.rosca@amd.com>]

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.")
---
 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 &&
 	    (current->flags & PF_EXITING) && (current->exit_code == SIGKILL))
 		drm_sched_entity_kill(entity);
 
-- 
2.43.0