Re: [PATCH] btrfs: handle errors while updating refcounts in update_ref_for_cow

[Edmund Nadolski <enadolski@suse.de>]

On 11/21/2017 11:58 AM, jeffm@suse.com wrote:
> From: Jeff Mahoney <jeffm@suse.com>
> 
> Since commit fb235dc06fa (btrfs: qgroup: Move half of the qgroup
> accounting time out of commit trans) the assumption that
> btrfs_add_delayed_{data,tree}_ref can only return 0 or -ENOMEM has
> been false.  The qgroup operations call into btrfs_search_slot
> and friends and can now return the full spectrum of error codes.
> 
> Fortunately, the fix here is easy since update_ref_for_cow failing
> is already handled so we just need to bail early with the error
> code.
> 
> Fixes: fb235dc06fa (btrfs: qgroup: Move half of the qgroup accounting ...)
> Cc: <stable@vger.kernel.org> # v4.11+
> Signed-off-by: Jeff Mahoney <jeffm@suse.com>

Reviewed-by: Edmund Nadolski <enadolski@suse.com>

> ---
>  fs/btrfs/ctree.c | 18 ++++++++++++------
>  1 file changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
> index 531e0a8645b0..1e74cf826532 100644
> --- a/fs/btrfs/ctree.c
> +++ b/fs/btrfs/ctree.c
> @@ -1032,14 +1032,17 @@ static noinline int update_ref_for_cow(struct btrfs_trans_handle *trans,
>  		     root->root_key.objectid == BTRFS_TREE_RELOC_OBJECTID) &&
>  		    !(flags & BTRFS_BLOCK_FLAG_FULL_BACKREF)) {
>  			ret = btrfs_inc_ref(trans, root, buf, 1);
> -			BUG_ON(ret); /* -ENOMEM */
> +			if (ret)
> +				return ret;
>  
>  			if (root->root_key.objectid ==
>  			    BTRFS_TREE_RELOC_OBJECTID) {
>  				ret = btrfs_dec_ref(trans, root, buf, 0);
> -				BUG_ON(ret); /* -ENOMEM */
> +				if (ret)
> +					return ret;
>  				ret = btrfs_inc_ref(trans, root, cow, 1);
> -				BUG_ON(ret); /* -ENOMEM */
> +				if (ret)
> +					return ret;
>  			}
>  			new_flags |= BTRFS_BLOCK_FLAG_FULL_BACKREF;
>  		} else {
> @@ -1049,7 +1052,8 @@ static noinline int update_ref_for_cow(struct btrfs_trans_handle *trans,
>  				ret = btrfs_inc_ref(trans, root, cow, 1);
>  			else
>  				ret = btrfs_inc_ref(trans, root, cow, 0);
> -			BUG_ON(ret); /* -ENOMEM */
> +			if (ret)
> +				return ret;
>  		}
>  		if (new_flags != 0) {
>  			int level = btrfs_header_level(buf);
> @@ -1068,9 +1072,11 @@ static noinline int update_ref_for_cow(struct btrfs_trans_handle *trans,
>  				ret = btrfs_inc_ref(trans, root, cow, 1);
>  			else
>  				ret = btrfs_inc_ref(trans, root, cow, 0);
> -			BUG_ON(ret); /* -ENOMEM */
> +			if (ret)
> +				return ret;
>  			ret = btrfs_dec_ref(trans, root, buf, 1);
> -			BUG_ON(ret); /* -ENOMEM */
> +			if (ret)
> +				return ret;
>  		}
>  		clean_tree_block(fs_info, buf);
>  		*last_ref = 1;
>