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

["Christian König" <christian.koenig@amd.com>]

Added a Fixes tag and pushed this to drm-misc-fixes.

It will take a while until it cycles back into the development branches, 
so feel free to push some version to amd-staging-drm-next as well. Just 
ping Alex when you do this.

Thanks,
Christian.

Am 07.09.21 um 06:08 schrieb xinhui pan:
> 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@amd.com>
> Reviewed-by: Christian König <christian.koenig@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 8d7fd65ccced..23f906941ac9 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> @@ -1152,9 +1152,9 @@ 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_del_from_lru(bo);
> @@ -1208,7 +1208,7 @@ 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)