[PATCH 1/2] drm/ttm: Fix a deadlock if the target BO is not idle during swap

[Christian König]

Am 03.09.21 um 08:49 schrieb Pan, Xinhui:
> The ret value might be -EBUSY, caller will think lru lock is still
> locked but actually NOT. So return -ENOSPC instead. Otherwise we hit
> list corruption.
>
> ttm_bo_cleanup_refs might fail too if BO is not idle. If we return 0,
> caller(ttm_tt_populate -> ttm_global_swapout ->ttm_device_swapout) will
> be stuck as we actually did not free any BO memory. This usually happens
> when the fence is not signaled for a long time.
>
> Signed-off-by: xinhui pan <xinhui.pan at amd.com>

Good catch, wanted to rework this for a very long time because of 
potential bugs like those.

Reviewed-by: Christian König <christian.koenig at amd.com>

> ---
>   drivers/gpu/drm/ttm/ttm_bo.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> index 1fedd0eb67ba..f1367107925b 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> @@ -1159,9 +1159,9 @@ int ttm_bo_swapout(struct ttm_buffer_object *bo, struct ttm_operation_ctx *ctx,
>   	}
>   
>   	if (bo->deleted) {
> -		ttm_bo_cleanup_refs(bo, false, false, locked);
> +		ret = ttm_bo_cleanup_refs(bo, false, false, locked);
>   		ttm_bo_put(bo);
> -		return 0;
> +		return ret == -EBUSY ? -ENOSPC : ret;
>   	}
>   
>   	ttm_bo_move_to_pinned(bo);
> @@ -1215,7 +1215,7 @@ int ttm_bo_swapout(struct ttm_buffer_object *bo, struct ttm_operation_ctx *ctx,
>   	if (locked)
>   		dma_resv_unlock(bo->base.resv);
>   	ttm_bo_put(bo);
> -	return ret;
> +	return ret == -EBUSY ? -ENOSPC : ret;
>   }
>   
>   void ttm_bo_tt_destroy(struct ttm_buffer_object *bo)