On Tue, Apr 20, 2021 at 10:55:12AM +0100, fdman...@kernel.org wrote: > From: Filipe Manana <fdman...@suse.com> > > When creating a subvolume we allocate an extent buffer for its root node > after starting a transaction. We setup a root item for the subvolume that > points to that extent buffer and then attempt to insert the root item into > the root tree - however if that fails, due to -ENOMEM for example, we do > not free the extent buffer previously allocated and we do not abort the > transaction (as at that point we did nothing that can not be undone). > > This means that we effectively do not return the metadata extent back to > the free space cache/tree and we leave a delayed reference for it which > causes a metadata extent item to be added to the extent tree, in the next > transaction commit, without having backreferences. When this happens > 'btrfs check' reports the following: > > $ btrfs check /dev/sdi > Opening filesystem to check... > Checking filesystem on /dev/sdi > UUID: dce2cb9d-025f-4b05-a4bf-cee0ad3785eb > [1/7] checking root items > [2/7] checking extents > ref mismatch on [30425088 16384] extent item 1, found 0 > backref 30425088 root 256 not referenced back 0x564a91c23d70 > incorrect global backref count on 30425088 found 1 wanted 0 > backpointer mismatch on [30425088 16384] > owner ref check failed [30425088 16384] > ERROR: errors found in extent allocation tree or chunk allocation > [3/7] checking free space cache > [4/7] checking fs roots > [5/7] checking only csums items (without verifying data) > [6/7] checking root refs > [7/7] checking quota groups skipped (not enabled on this FS) > found 212992 bytes used, error(s) found > total csum bytes: 0 > total tree bytes: 131072 > total fs tree bytes: 32768 > total extent tree bytes: 16384 > btree space waste bytes: 124669 > file data blocks allocated: 65536 > referenced 65536 > > So fix this by freeing the metadata extent if btrfs_insert_root() returns > an error. > > Signed-off-by: Filipe Manana <fdman...@suse.com>
Added to misc-next, thanks.
