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

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

FYI

On 09.10.25 09:01, Christian König wrote:
> 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);
>>  
>