linux-kernel - Re: [PATCH] drm/amdgpu: Initialize value of r in amdgpu_fill

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Date:   Mon, 21 Feb 2022 08:06:15 +0100
From:   Christian König <christian.koenig@....com>
To:     Souptick Joarder <jrdr.linux@...il.com>, alexander.deucher@....com,
        Xinhui.Pan@....com, airlied@...ux.ie, daniel@...ll.ch,
        nathan@...nel.org, desaulniers@...gle.com, Felix.Kuehling@....com,
        Oak.Zeng@....com, nirmoy.das@....com, jonathan.kim@....com,
        kevin1.wang@....com, tzimmermann@...e.de, Philip.Yang@....com
Cc:     amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] drm/amdgpu: Initialize value of r in amdgpu_fill_buffer()

Am 18.02.22 um 19:53 schrieb Souptick Joarder:
> From: "Souptick Joarder (HPE)" <jrdr.linux@...il.com>
>
> Kernel test robot reported warning ->
> drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c:2129:2: warning: Undefined
> or garbage value returned to caller [clang-analyzer-core.
> uninitialized.UndefReturn]

Good catch, but that fix is usually seen as bad practice.

The warning is a false positive because the code path which would lead 
to returning an undefined value can never happen. There is just no way 
the compiler could know that.

I suggest to better initialize the return value directly before the 
error handling to indicate that when we have reached this point we can 
return success safely.

Regards,
Christian.

>
> Initialize r inside amdgpu_fill_buffer().
>
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Souptick Joarder (HPE) <jrdr.linux@...il.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index 414a22dddc78..5fafb223177f 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -2089,7 +2089,7 @@ int amdgpu_fill_buffer(struct amdgpu_bo *bo,
>   	struct amdgpu_ring *ring = adev->mman.buffer_funcs_ring;
>   	struct dma_fence *fence = NULL;
>   	struct amdgpu_res_cursor dst;
> -	int r;
> +	int r = 0;
>   
>   	if (!adev->mman.buffer_funcs_enabled) {
>   		DRM_ERROR("Trying to clear memory with ring turned off.\n");