[PATCH] drm/amdgpu: Fix the dead lock issue.

[Christian König]

Am 10.09.2018 um 06:07 schrieb Emily Deng:
> It will ramdomly have the dead lock issue when test TDR:
> 1. amdgpu_device_handle_vram_lost gets the lock shadow_list_lock
> 2. amdgpu_bo_create locked the bo's resv lock
> 3. amdgpu_bo_create_shadow is waiting for the shadow_list_lock
> 4. amdgpu_device_recover_vram_from_shadow is waiting for the bo's resv
> lock.
>
> Signed-off-by: Emily Deng <Emily.Deng at amd.com>

Good catch, problem is the fix doesn't work like this because the lock 
won't be dropped at this point in most cases.

Instead you need to fix amdgpu_device_recover_vram_from_shadow to make a 
local copy of the list.

You can do this by grabbing a reference to each BO and moving it to a 
local list.

Regards,
Christian.

> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_object.c | 12 +++++++-----
>   1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> index de990bd..c75447d 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> @@ -557,12 +557,8 @@ static int amdgpu_bo_create_shadow(struct amdgpu_device *adev,
>   	bp.resv = bo->tbo.resv;
>   
>   	r = amdgpu_bo_do_create(adev, &bp, &bo->shadow);
> -	if (!r) {
> +	if (!r)
>   		bo->shadow->parent = amdgpu_bo_ref(bo);
> -		mutex_lock(&adev->shadow_list_lock);
> -		list_add_tail(&bo->shadow_list, &adev->shadow_list);
> -		mutex_unlock(&adev->shadow_list_lock);
> -	}
>   
>   	return r;
>   }
> @@ -603,6 +599,12 @@ int amdgpu_bo_create(struct amdgpu_device *adev,
>   		if (!bp->resv)
>   			reservation_object_unlock((*bo_ptr)->tbo.resv);
>   
> +		if (!r) {
> +			mutex_lock(&adev->shadow_list_lock);
> +			list_add_tail(&(*bo_ptr)->shadow_list, &adev->shadow_list);
> +			mutex_unlock(&adev->shadow_list_lock);
> +		}
> +
>   		if (r)
>   			amdgpu_bo_unref(bo_ptr);
>   	}