xfstests failures with xfs, dax and v4.4-rc3

[Eric Sandeen]

On 12/2/15 12:34 PM, Ross Zwisler wrote:
> I'm hitting a few more test failures in my testing setup with v4.4-rc3, xfs
> and DAX.  My test setup is a pair of 4GiB PMEM partitions in a KVM virtual
> machine.  Here are the failures:

...

> generic/274 7s ... [failed, exit status 1] - output mismatch (see /root/xfstests/results//generic/274.out.bad)
>     --- tests/generic/274.out	2015-10-02 10:19:36.808795907 -0600
>     +++ /root/xfstests/results//generic/274.out.bad	2015-12-02 11:22:37.656868990 -0700
>     @@ -2,4 +2,5 @@
>      ------------------------------
>      preallocation test
>      ------------------------------
>     -done
>     +failed to write to test file
>     +(see /root/xfstests/results//generic/274.full for details)
>     ...
>     (Run 'diff -u tests/generic/274.out /root/xfstests/results//generic/274.out.bad'  to see the entire diff)

I looked at this one a bit last night, and talked to Dave about it; its' different
handling with DAX w.r.t. preallocation; we go down a path which actually tries to
re-reserve the disk blocks it'll be writing to, even though they're already allocated.

If the disk isn't full, I guess it doesn't matter, but this test explicitly tests ENOSPC.

Working on better understanding this path to see if I can fix it (unless Dave beats me
to it ...)

-Eric