Re: [PATCH] drm/xe: Check empty pinned BO list with lock held.

[Matthew Brost <matthew.brost@intel.com>]

On Tue, May 28, 2024 at 01:54:08PM +0200, Nirmoy Das wrote:
> Use lock that is meant to use for accessing the BO pin list.
> 
> Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>

Agree with this patch removing removing micro optimization of bypassing
&xe->pinned.lock, we should avoid thing like this.

Curious if this was an actual problem (i.e. was their a bug report which
lead to this change)?

Anyways the patch LGTM. With that:
Reviewed-by: Matthew Brost <matthew.brost@intel.com>

> ---
>  drivers/gpu/drm/xe/xe_bo.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
> index 03f7fe7acf8c..2bae01ce4e5b 100644
> --- a/drivers/gpu/drm/xe/xe_bo.c
> +++ b/drivers/gpu/drm/xe/xe_bo.c
> @@ -1758,11 +1758,10 @@ void xe_bo_unpin_external(struct xe_bo *bo)
>  	xe_assert(xe, xe_bo_is_pinned(bo));
>  	xe_assert(xe, xe_bo_is_user(bo));
>  
> -	if (bo->ttm.pin_count == 1 && !list_empty(&bo->pinned_link)) {
> -		spin_lock(&xe->pinned.lock);
> +	spin_lock(&xe->pinned.lock);
> +	if (bo->ttm.pin_count == 1 && !list_empty(&bo->pinned_link))
>  		list_del_init(&bo->pinned_link);
> -		spin_unlock(&xe->pinned.lock);
> -	}
> +	spin_unlock(&xe->pinned.lock);
>  
>  	ttm_bo_unpin(&bo->ttm);
>  
> @@ -1785,9 +1784,8 @@ void xe_bo_unpin(struct xe_bo *bo)
>  		struct ttm_place *place = &(bo->placements[0]);
>  
>  		if (mem_type_is_vram(place->mem_type)) {
> -			xe_assert(xe, !list_empty(&bo->pinned_link));
> -
>  			spin_lock(&xe->pinned.lock);
> +			xe_assert(xe, !list_empty(&bo->pinned_link));
>  			list_del_init(&bo->pinned_link);
>  			spin_unlock(&xe->pinned.lock);
>  		}
> -- 
> 2.42.0
>