Recently I've been trying to get a stable baseline for my DAX testing using
various filesystems, and in doing so I noticed a pair of tests that were
behaving badly when run on XFS without DAX.  These test failures happen in
both v4.2 and v4.3-rc3, though the signatures may vary a bit.

My testing setup is a kvm virtual machine with 8 GiB of its 16GiB of memory
reserved for PMEM using the mmap parameter (memmap=8G!8G) and with the
CONFIG_X86_PMEM_LEGACY config option enabled.  I've attached my full kernel
config to this mail.

The first test failure is generic/299, which consistently deadlocks in the XFS
code in both v4.2 and v4.3-rc3.  The stack traces presented in dmesg via "echo
w > /proc/sysrq-trigger" are consistent between these two kernel versions, and
can be found in the "generic_299.deadlock" attachment.

The second test failure is xfs/083, which in v4.2 seems to fail with an XFS
assertion (I have XFS_DEBUG turned on):

XFS: Assertion failed: fs_is_ok, file: fs/xfs/libxfs/xfs_dir2_data.c, line: 168

In v4.3, though, this same test seems to create some random memory corruption
in XFS.  I've hit at least two failure signatures that look nothing alike
except they both look like somebody corrupted memory.

I've attached logs of all three of these failures to this mail.

Because of all the attachments I decided not to spam the fsdevel or
linux-kernel mailing lists - please let me know if this was correct, or if
there is a better way of sending along logs with bug reports.

Thanks,
- Ross