When doing an incremental send it is possible that when processing the new
references for an inode we end up issuing rename or link operations that
have an invalid path, which contains the orphanized name of a directory
before we actually orphanized it, causing the receiver to fail.
The following reproducer triggers such scenario:
$ cat reproducer.sh
#!/bin/bash
mkfs.btrfs -f /dev/sdi >/dev/null
mount /dev/sdi /mnt/sdi
touch /mnt/sdi/a
touch /mnt/sdi/b
mkdir /mnt/sdi/testdir
# We want "a" to have a lower inode number then "testdir" (257 vs 259).
mv /mnt/sdi/a /mnt/sdi/testdir/a
# Filesystem looks like:
#
# . (ino 256)
# |----- testdir/ (ino 259)
# | |----- a (ino 257)
# |
# |----- b (ino 258)
btrfs subvolume snapshot -r /mnt/sdi /mnt/sdi/snap1
btrfs send -f /tmp/snap1.send /mnt/sdi/snap1
# Now rename 259 to "testdir_2", then change the name of 257 to
# "testdir" and make it a direct descendant of the root inode (256).
# Also create a new link for inode 257 with the old name of inode 258.
# By swapping the names and location of several inodes and create a
# nasty dependency chain of rename and link operations.
mv /mnt/sdi/testdir/a /mnt/sdi/a2
touch /mnt/sdi/testdir/a
mv /mnt/sdi/b /mnt/sdi/b2
ln /mnt/sdi/a2 /mnt/sdi/b
mv /mnt/sdi/testdir /mnt/sdi/testdir_2
mv /mnt/sdi/a2 /mnt/sdi/testdir
# Filesystem now looks like:
#
# . (ino 256)
# |----- testdir_2/ (ino 259)
# | |----- a (ino 260)
# |
# |----- testdir (ino 257)
# |----- b (ino 257)
# |----- b2 (ino 258)
btrfs subvolume snapshot -r /mnt/sdi /mnt/sdi/snap2
btrfs send -f /tmp/snap2.send -p /mnt/sdi/snap1 /mnt/sdi/snap2
mkfs.btrfs -f /dev/sdj >/dev/null
mount /dev/sdj /mnt/sdj
btrfs receive -f /tmp/snap1.send /mnt/sdj
btrfs receive -f /tmp/snap2.send /mnt/sdj
umount /mnt/sdi
umount /mnt/sdj
When running the reproducer, the receive of the incremental send stream
fails:
$ ./reproducer.sh
Create a readonly snapshot of '/mnt/sdi' in '/mnt/sdi/snap1'
At subvol /mnt/sdi/snap1
Create a readonly snapshot of '/mnt/sdi' in '/mnt/sdi/snap2'
At subvol /mnt/sdi/snap2
At subvol snap1
At snapshot snap2
ERROR: link b -> o259-6-0/a failed: No such file or directory
The problem happens because of the following:
1) Before we start iterating the list of new references for inode 257,
we generate its current path and store it at @valid_path, done at
the very beginning of process_recorded_refs(). The generated path
is "o259-6-0/a", containing the orphanized name for inode 259;
2) Then we iterate over the list of new references, which has the
references "b" and "testdir" in that specific order;
3) We process reference "b" first, because it is in the list before
reference "testdir". We then issue a link operation to create
the new reference "b" using a target path corresponding to the
content at @valid_path, which corresponds to "o259-6-0/a".
However we haven't yet orphanized inode 259, its name is still
"testdir", and not "o259-6-0". The orphanization of 259 did not
happen yet because we will process the reference named "testdir"
for inode 257 only in the next iteration of the loop that goes
over the list of new references.
Fix the issue by having a preliminar iteration over all the new references
at process_recorded_refs(). This iteration is responsible only for doing
the orphanization of other inodes that have and old reference that
conflicts with one of the new references of the inode we are currently
processing. The emission of rename and link operations happen now in the
next iteration of the new references.
A test case for fstests will follow soon.
CC: stable@vger.kernel.org # 4.4+
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
98272bb77b