[PATCH] drm/amdgpu: add the checking to avoid NULL pointer dereference

[Koenig, Christian]

Am 23.11.18 um 14:27 schrieb Zhou, David(ChunMing):
>
> 在 2018/11/22 19:25, Christian König 写道:
>> Am 22.11.18 um 07:56 schrieb Sharma, Deepak:
>>> when returned fence is not valid mostly due to userspace ignored
>>> previous error causes NULL pointer dereference.
>> Again, this is clearly incorrect. The my other mails on the earlier
>> patch.
> Sorry for I didn't get your history, but looks from the patch itself, it
> is still a valid patch, isn't it?

No, the semantic of amdgpu_ctx_get_fence() is that we return NULL when 
the fence is already signaled.

So this patch could totally break userspace because it changes the 
behavior when we try to sync to an already signaled fence.

If that patch was applied then please revert it immediately.

Christian.

>
> -David
>> If you have already pushed the patch then please revert.
>>
>> Christian.
>>
>>> Signed-off-by: Deepak Sharma <Deepak.Sharma at amd.com>
>>> ---
>>>    drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c | 2 ++
>>>    1 file changed, 2 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
>>> index 024dfbd87f11..14166cd8a12f 100644
>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
>>> @@ -1403,6 +1403,8 @@ static struct dma_fence
>>> *amdgpu_cs_get_fence(struct amdgpu_device *adev,
>>>          fence = amdgpu_ctx_get_fence(ctx, entity, user->seq_no);
>>>        amdgpu_ctx_put(ctx);
>>> +    if(!fence)
>>> +        return ERR_PTR(-EINVAL);
>>>          return fence;
>>>    }