btrfs: regression in 3.16 with renaming of directory in between two snapshots

[Colin Ian King]

SRU Justification: (Utopic)

[Impact]
If between two snapshots we rename an existing directory named X to Y and
make it a child (direct or not) of a new inode named X, we were delaying
the move/rename of the former directory unnecessarily, which would result
in attempting to rename the new directory from its orphan name to name X
prematurely.

[Fix]
upstream commit bf8e8ca6fd4ac6e8edc58b92cffb2ffd51933138
"Btrfs: send, don't delay dir move if there's a new parent inode"

this is a simple one-liner, risk is low to zero.

[Testcase]
As from the commit:

        $ mkfs.btrfs -f /dev/vdd
        $ mount /dev/vdd /mnt
        $ mkdir -p /mnt/merlin/RC/OSD/Source

        $ btrfs subvolume snapshot -r /mnt /mnt/mysnap1

        $ mkdir /mnt/OSD
        $ mv /mnt/merlin/RC/OSD /mnt/OSD/OSD-Plane_788
        $ mv /mnt/OSD /mnt/merlin/RC

        $ btrfs subvolume snapshot -r /mnt /mnt/mysnap2

        $ btrfs send /mnt/mysnap1 -f /tmp/1.snap
        $ btrfs send -p /mnt/mysnap1 /mnt/mysnap2 -f /tmp/2.snap

        $ mkfs.btrfs -f /dev/vdc
        $ mount /dev/vdc /mnt2

        $ btrfs receive /mnt2 -f /tmp/1.snap
        $ btrfs receive /mnt2 -f /tmp/2.snap

    The second receive (from an incremental send) failed with the following
    error message: "rename o261-7-0 -> merlin/RC/OSD failed".
    This is a regression introduced in the 3.16 kernel.

[Brad Figg (brad-figg)]

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-utopic' to 'verification-done-utopic'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

[Colin Ian King (colin-king)]

Tested and works OK with -proposed kernel:
uname -a
Linux ubuntu 3.16.0-34-generic #45-Ubuntu SMP Mon Mar 23 17:21:27 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux - 3.16.0-34.45

---------------
linux (3.16.0-34.45) utopic; urgency=low

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