btrfs: zoned: disable metadata overcommit for zoned

The metadata overcommit makes the space reservation flexible but it is also
harmful to active zone tracking. Since we cannot finish a block group from
the metadata allocation context, we might not activate a new block group
and might not be able to actually write out the overcommit reservations.

So, disable metadata overcommit for zoned filesystems. We will ensure
the reservations are under active_total_bytes in the following patches.

CC: stable@vger.kernel.org # 5.16+
Fixes: afba2bc ("btrfs: zoned: implement active zone tracking")
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: naota

fs/btrfs/space-info.c

@@ -399,7 +399,10 @@ int btrfs_can_overcommit(struct btrfs_fs_info *fs_info,
 		return 0;
 
 	used = btrfs_space_info_used(space_info, true);
-	avail = calc_available_free_space(fs_info, space_info, flush);
+	if (btrfs_is_zoned(fs_info) && (space_info->flags & BTRFS_BLOCK_GROUP_METADATA))
+		avail = 0;
+	else
+		avail = calc_available_free_space(fs_info, space_info, flush);
 
 	if (used + bytes < writable_total_bytes(fs_info, space_info) + avail)
 		return 1;