Re: [PATCH] drm/scheduler: add NULL pointer check for run queue

["Christian König" <christian.koenig-5C7GfCeVMHo@public.gmane.org>]

Am 16.07.2018 um 11:01 schrieb Zhang, Jerry (Junwei):
> On 07/16/2018 04:31 PM, Christian König wrote:
>> Am 16.07.2018 um 04:59 schrieb Junwei Zhang:
>>> To check rq pointer before adding entity into it.
>>> That avoids NULL pointer access in some case.
>>>
>>> Suggested-by: Christian König <christian.koenig@amd.com>
>>> Signed-off-by: Junwei Zhang <Jerry.Zhang@amd.com>
>>> ---
>>>   drivers/gpu/drm/scheduler/gpu_scheduler.c | 4 ++++
>>>   1 file changed, 4 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/scheduler/gpu_scheduler.c 
>>> b/drivers/gpu/drm/scheduler/gpu_scheduler.c
>>> index 16bf446..5e5268d 100644
>>> --- a/drivers/gpu/drm/scheduler/gpu_scheduler.c
>>> +++ b/drivers/gpu/drm/scheduler/gpu_scheduler.c
>>> @@ -91,6 +91,10 @@ static void drm_sched_rq_add_entity(struct 
>>> drm_sched_rq *rq,
>>>   {
>>>       if (!list_empty(&entity->list))
>>>           return;
>>> +    if (!rq) {
>>> +        DRM_ERROR("rq is NULL!\n");
>>> +        return;
>>> +    }
>>
>> Better put that into drm_sched_entity_push_job(), e.g. something like:
>
> Considered that as well.
> Just be afraid of someone else could call it in another place without 
> rq checking in the future.

Well that's exactly the reason why I wanted to have the check in 
drm_sched_rq_add_entity().

Calling drm_sched_rq_add_entity() will a NULL rq is illegal and that 
should be avoided in the caller instead of more or less silently dropped 
in the function.

Regards,
Christian.

>
> Regards,
> Jerry
>
>>
>> /* first job wakes up scheduler */
>> if (first) {
>>      /* Add the entity to the run queue */
>>      spin_lock(&entity->rq_lock);
>>      if (!entity->rq) {
>>          DRM_ERROR("Trying to push to killed entity!\n");
>> ....
>>
>> Regards,
>> Christian.
>>
>>>       spin_lock(&rq->lock);
>>>       list_add_tail(&entity->list, &rq->entities);
>>>       spin_unlock(&rq->lock);
>>

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