generic/232 test failures on 4.14-rc1

[Eric Whitney <enwlinux@gmail.com>]

I'm seeing generic/232 fail from time to time when running a 4.14-rc1 kernel
on xfstest-bld's most recent kvm-xfstests test appliance.  In one set of
trials, it failed in the same manner 4 out of 10 times when running the 4k test
configuration for ext4.

The failure bisects to "quota: Do not acquire dqio_sem for dquot overwrites in
v2 format" (ab2b86360f6e).  When this patch was reverted in a 4.14-rc1 kernel,
the failure did not reoccur in a series of 20 trials.

Example output from the failed test:

QA output created by 232

Testing fsstress

seed = S
Comparing user usage
218a219
> #3740     --       4       0       0              1     0     0       
245a247
> #45       --       0       0       0              1     0     0     

Note:  I'm also seeing a similar failure for generic/233, but the patch
containing the root cause likely comes somewhere after ab2b86360f6e.  I'll post
another bug report once I locate it.

Thanks,
Eric