btrfs: properly report 0 avail for very full file systems

A user reported some issues with smaller file systems that get very
full.  While investigating this issue I noticed that df wasn't showing
100% full, despite having 0 chunk space and having < 1MiB of available
metadata space.

This turns out to be an overflow issue, we're doing:

  total_available_metadata_space - SZ_4M < global_block_rsv_size

to determine if there's not enough space to make metadata allocations,
which overflows if total_available_metadata_space is < 4M.  Fix this by
checking to see if our available space is greater than the 4M threshold.
This makes df properly report 100% usage on the file system.

CC: stable@vger.kernel.org # 4.14+
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Josef Bacik 2023-09-18 10:34:51 -04:00 committed by David Sterba
parent 8ec0a4a577
commit 58bfe2ccec

View File

@ -2117,7 +2117,7 @@ static int btrfs_statfs(struct dentry *dentry, struct kstatfs *buf)
* calculated f_bavail.
*/
if (!mixed && block_rsv->space_info->full &&
total_free_meta - thresh < block_rsv->size)
(total_free_meta < thresh || total_free_meta - thresh < block_rsv->size))
buf->f_bavail = 0;
buf->f_type = BTRFS_SUPER_MAGIC;