linux-kernel - Re: [PATCH] drm/amdgpu: Replace rcu_assign_pointer() with RCU_INIT_POINTER()

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Date:	Mon, 2 May 2016 10:46:47 -0400
From:	Alex Deucher <alexdeucher@...il.com>
To:	Christian König <christian.koenig@....com>
Cc:	Muhammad Falak R Wani <falakreyaz@...il.com>,
	David Airlie <airlied@...ux.ie>,
	Alex Deucher <alexander.deucher@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Maling list - DRI developers 
	<dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH] drm/amdgpu: Replace rcu_assign_pointer() with RCU_INIT_POINTER()

On Sun, May 1, 2016 at 11:26 AM, Christian König
<christian.koenig@....com> wrote:
> Am 30.04.2016 um 21:00 schrieb Muhammad Falak R Wani:
>>
>> The rcu_assign_pointer() ensures that the initialization of a structure
>> is carried out before storing a pointer to that structre. It is always
>> safe to use RCU_INIT_POINTER() to NULL a pointer, instead of
>> rcu_assign_pointer().
>> This results in slightly smaller/faster code.
>
>
> Thanks for the detailed explanation, I was already wondering what the
> difference is between the two.
>
>>
>> The following semantic patch was used:
>> <smpl>
>>
>> @@
>> @@
>>
>> - rcu_assign_pointer
>> + RCU_INIT_POINTER
>>    (..., NULL)
>>
>> </smpl>
>>
>> Signed-off-by: Muhammad Falak R Wani <falakreyaz@...il.com>
>
>
> Reviewed-by: Christian König <christian.koenig@....com>

Applied.  thanks!

Alex

>
> Regards,
> Christian.
>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
>> index d81f1f4..4500ff1 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
>> @@ -198,7 +198,7 @@ void amdgpu_fence_process(struct amdgpu_ring *ring)
>>                 /* There is always exactly one thread signaling this fence
>> slot */
>>                 fence = rcu_dereference_protected(*ptr, 1);
>> -               rcu_assign_pointer(*ptr, NULL);
>> +               RCU_INIT_POINTER(*ptr, NULL);
>>                 BUG_ON(!fence);
>>
>
>
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> dri-devel@...ts.freedesktop.org
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