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

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Message-ID: <5726203E.7060308@amd.com>
Date:	Sun, 1 May 2016 17:26:54 +0200
From:	Christian König <christian.koenig@....com>
To:	Muhammad Falak R Wani <falakreyaz@...il.com>,
	David Airlie <airlied@...ux.ie>
CC:	Chunming Zhou <David1.Zhou@....com>,
	Alex Deucher <alexander.deucher@....com>,
	<dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/amdgpu: Replace rcu_assign_pointer() with
 RCU_INIT_POINTER()

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>

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);
>