[add Markus.Elfring in mail list ]Re:Re: [PATCH V4] amdgpu: reduce no need mutex_lock area

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From: "Christian KÃnig" <christian.koenig@xxxxxxx>
Date: 2020-04-21 15:41:27
To:  1587181464-114215-1-git-send-email-bernard@xxxxxxxx,Felix Kuehling <Felix.Kuehling@xxxxxxx>,Alex Deucher <alexander.deucher@xxxxxxx>,"David (ChunMing) Zhou" <David1.Zhou@xxxxxxx>,David Airlie <airlied@xxxxxxxx>,Daniel Vetter <daniel@xxxxxxxx>,amd-gfx@xxxxxxxxxxxxxxxxxxxxx,dri-devel@xxxxxxxxxxxxxxxxxxxxx,linux-kernel@xxxxxxxxxxxxxxx
Cc:  opensource.kernel@xxxxxxxx,Bernard Zhao <bernard@xxxxxxxx>
Subject: Re: [PATCH V4] amdgpu: reduce no need mutex_lock area>Am 21.04.20 um 09:36 schrieb Bernard Zhao:
>> Maybe we could reduce the mutex_lock(&mem->lock)`s protected code area,
>> and no need to protect pr_debug.
>
>Well that change looks rather superfluous to me.
>
>This is for freeing memory which by definition can only be done once and 
>so the should be exactly zero contention on the lock except in a case of 
>an error.
>
>Regards,
>Christian.
>
>>
>> Signed-off-by: Bernard Zhao <bernard@xxxxxxxx>
>>
>> Changes since V1:
>> *commit message improve
>>
>> Changes since V2:
>> *move comment along with the mutex_unlock
>>
>> Changes since V3:
>> *lock protect the if check, there is some possibility of multi-threaded
>>   racing modify.
>>
>> Link for V1:
>> *https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fpatchwork%2Fpatch%2F1226588%2F&amp;data=02%7C01%7Cchristian.koenig%40amd.com%7C9f2b2080f4174c421e4f08d7e5c6b899%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637230513976133424&amp;sdata=6wezM%2F%2FjM5uuLblJejS9XFlE9DjWQ5zSt5PsqrfvCVo%3D&amp;reserved=0
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>> index 327317c54f7c..549bdb429883 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
>> @@ -1289,9 +1289,9 @@ int amdgpu_amdkfd_gpuvm_free_memory_of_gpu(
>>   	mutex_lock(&mem->lock);
>>   
>>   	if (mem->mapped_to_gpu_memory > 0) {
>> +		mutex_unlock(&mem->lock);
>>   		pr_debug("BO VA 0x%llx size 0x%lx is still mapped.\n",
>>   				mem->va, bo_size);
>> -		mutex_unlock(&mem->lock);
>>   		return -EBUSY;
>>   	}
>>   
>

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Regards,
Bernard