data=journal regressions in 3.16-rc1

[Eric Whitney <enwlinux@gmail.com>]

My regression test results for 3.16-rc1 on x86_64 show three new xfstests
failures since 3.15 final when running on an ext4 filesystem mounted with the
data=journal and block_validity mount options (xfstests-bld's data_journal
scenario). These are generic/075, /112, and /231.  All three tests fail
consistently.

These failures bisect to this kernel patch:
7fc34a62ca  mm/msync.c: sync only the requested range in msync()

These failures also appear when running on 3.16-rc2, and disappear if the
aforementioned patch is reverted.  I've not seen the failures in any of the
other test scenarios I've run on 3.16-rc1 (4k, ext3, nojournal, etc.).

No error messages appear in the kernel log, and not a lot useful is reported
when a test fails.  Just for reference, here's the result of a generic/075
failure:

generic/075 62s ...	[15:33:07] [15:33:09] [failed, exit status 1] - output mismatch (see /root/xfstests/results//generic/075.out.bad)
    --- tests/generic/075.out	2014-06-16 13:14:27.233891460 -0400
    +++ /root/xfstests/results//generic/075.out.bad	2014-06-23 15:33:09.654212783 -0400
    @@ -4,15 +4,5 @@
     -----------------------------------------------
     fsx.0 : -d -N numops -S 0
     -----------------------------------------------
    -
    ------------------------------------------------
    -fsx.1 : -d -N numops -S 0 -x
    ------------------------------------------------
    ...
    (Run 'diff -u tests/generic/075.out /root/xfstests/results//generic/075.out.bad'  to see the entire diff)
Ran: generic/075
Failures: generic/075
Failed 1 of 1 tests


And the contents of xfstests/results/generic/075.out.bad:


QA output created by 075
brevity is wit...

-----------------------------------------------
fsx.0 : -d -N numops -S 0
-----------------------------------------------
    fsx (-d -N 1000 -S 0) failed, 0 - compare /root/xfstests/results//generic/075.0.{good,bad,fsxlog}
od: /root/xfstests/results//generic/075.0.fsxgood: No such file or directory


Additional test configuration info:

e2fsprogs master branch:  bb9cca2ca9
xfstests master branch:  45d1fac130

Perhaps data=journal has an unexpected dependency on the old msync behavior,
given the patch comment?

Thanks,
Eric