Negative qgroup sizes

[Alin Dobre <alin.dobre@elastichosts.com>]

Hello,

I am having trouble with one of the btrfs subvolumes, as it shows
negative quota accounting values, like in the following output:

  # btrfs qgroup show -f /tmp/test
  qgroupid rfer                 excl
  -------- ----                 ----
  0/299    -1576960             -1511424

Running a "btrfs quota rescan -w /tmp/test" seems to fix it, but it
seems to come back pretty often (happened twice in the last couple of
days). I can't think of a possible reproduction of the problem, so I'm
just stuck. Here's the output of subvolume after the rescan, maybe it
also gives you some insight:

  # btrfs qgroup show -f /tmp/test
  qgroupid rfer       excl
  -------- ----       ----
  0/299    1065955328 1056542720

The kernel we are using is 3.14.1 (stable) and the btrfs-progs version
is 3.12.

Any idea on why this happens or if there's an obvious fix I missed?

Cheers,
Alin.