[PATCH] Btrfs: fix incremental send's decision to delay a dir move/rename

Filipe David Borba Manana
2014-03-16T15:24:00Z

It's possible to change the parent/child relationship between directories
in such a way that if a child directory has a higher inode number than
its parent, it doesn't necessarily means the child rename/move operation
can be performed immediately. The parent migth have its own rename/move
operation delayed, therefore in this case the child needs to have its
rename/move operation delayed too, and be performed after its new parent's
rename/move.

Steps to reproduce the issue:

$ umount /mnt
$ mkfs.btrfs -f /dev/sdd
$ mount /dev/sdd /mnt

$ mkdir /mnt/A
$ mkdir /mnt/B
$ mkdir /mnt/C
$ mv /mnt/C /mnt/A
$ mv /mnt/B /mnt/A/C
$ mkdir /mnt/A/C/D

$ btrfs subvolume snapshot -r /mnt /mnt/snap1
$ btrfs send /mnt/snap1 -f /tmp/base.send

$ mv /mnt/A/C/D /mnt/A/D2
$ mv /mnt/A/C/B /mnt/A/D2/B2
$ mv /mnt/A/C /mnt/A/D2/B2/C2

$ btrfs subvolume snapshot -r /mnt /mnt/snap2
$ btrfs send -p /mnt/snap1 /mnt/snap2 -f /tmp/incremental.send

The incremental send caused the kernel code to enter an infinite loop when
building the path string for directory C after its references are processed.

The necessary conditions here are that C has an inode number higher than both
A and B, and B as an higher inode number higher than A, and D has the highest
inode number, that is:
inode_number(A) < inode_number(B) < inode_number(C) < inode_number(D)

The same issue could happen if after the first snapshot there's any number
of intermediary parent directories between A2 and B2, and between B2 and C2.

A test case for xfstests follows, covering this simple case and more advanced
ones, with files and hard links created inside the directories.

Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
---
fs/btrfs/send.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 6463691..163c29a 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -3185,7 +3185,7 @@ static int wait_for_parent_move(struct send_ctx *sctx,
int len1, len2;

if (parent_ref->dir <= sctx->cur_ino)
- return 0;
+ return is_waiting_for_move(sctx, parent_ref->dir);

if (is_waiting_for_move(sctx, ino))
return 1;
--
1.7.10.4