Re: [PATCH 4/4] drm/scheduler: do not keep a copy of sched list

[Nirmoy <nirmodas@amd.com>]

On 12/10/19 2:00 PM, Christian König wrote:
> Am 10.12.19 um 13:53 schrieb Nirmoy Das:
>> entity should not keep copy and maintain sched list for
>> itself.
>>
>> Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
>> ---
>>   drivers/gpu/drm/scheduler/sched_entity.c | 10 +---------
>>   1 file changed, 1 insertion(+), 9 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/scheduler/sched_entity.c 
>> b/drivers/gpu/drm/scheduler/sched_entity.c
>> index f9b6ce29c58f..a5f729f421f8 100644
>> --- a/drivers/gpu/drm/scheduler/sched_entity.c
>> +++ b/drivers/gpu/drm/scheduler/sched_entity.c
>> @@ -67,17 +67,10 @@ int drm_sched_entity_init(struct drm_sched_entity 
>> *entity,
>>       entity->guilty = guilty;
>>       entity->num_sched_list = num_sched_list;
>>       entity->priority = priority;
>> -    entity->sched_list =  kcalloc(num_sched_list,
>> -                      sizeof(struct drm_gpu_scheduler *), GFP_KERNEL);
>> +    entity->sched_list =  sched_list;
>
> Maybe make this "num_sched_list > 1 ? sched_list : NULL" to avoid 
> accidentally dereferencing a stale pointer to the stack.
Do you mean "num_sched_list >= 1 ? sched_list : NULL"
>
>>   -    if(!entity->sched_list)
>> -        return -ENOMEM;
>>         init_completion(&entity->entity_idle);
>> -
>> -    for (i = 0; i < num_sched_list; i++)
>> -        entity->sched_list[i] = sched_list[i];
>> -
>>       if (num_sched_list)
>
> That check can actually be dropped as well. We return -EINVAL when the 
> num_sched_list is zero.

This  one took me some time to understand. So we don't really return 
-EINVAL if num_sched_list == 0

if (!(entity && sched_list && (num_sched_list == 0 || sched_list[0])))
                 return -EINVAL;

This is coming from below patch. Are we suppose to tolerate IPs with 
uninitialized sched so that ctx creation dosn't return error ?

commit 1decbf6bb0b4dc56c9da6c5e57b994ebfc2be3aa
Author: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Date:   Wed Jan 30 02:53:19 2019 +0100

     drm/sched: Fix entities with 0 rqs.

     Some blocks in amdgpu can have 0 rqs.

     Job creation already fails with -ENOENT when entity->rq is NULL,
     so jobs cannot be pushed. Without a rq there is no scheduler to
     pop jobs, and rq selection already does the right thing with a
     list of length 0.

     So the operations we need to fix are:
       - Creation, do not set rq to rq_list[0] if the list can have 
length 0.
       - Do not flush any jobs when there is no rq.
       - On entity destruction handle the rq = NULL case.
       - on set_priority, do not try to change the rq if it is NULL.

>
> Regards,
> Christian.
>
>>           entity->rq = 
>> &entity->sched_list[0]->sched_rq[entity->priority];
>>   @@ -312,7 +305,6 @@ void drm_sched_entity_fini(struct 
>> drm_sched_entity *entity)
>>         dma_fence_put(entity->last_scheduled);
>>       entity->last_scheduled = NULL;
>> -    kfree(entity->sched_list);
>>   }
>>   EXPORT_SYMBOL(drm_sched_entity_fini);
>
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