Re: Flaky test: generic/085

["Theodore Ts'o" <tytso@mit.edu>]

On Wed, Jun 12, 2024 at 01:25:07PM +0200, Christian Brauner wrote:
> I've been trying to reproduce this with pmem yesterday and wasn't able to.
> 
> What's the kernel config and test config that's used?
>

The kernel config can be found here:

https://github.com/tytso/xfstests-bld/blob/master/kernel-build/kernel-configs/config-6.1

Drop it into .config in the build directory of any kernel sources
newer than 6.1, and then run "make olddefconfig".  This is all
automated in the install-kconfig script which I use:

https://github.com/tytso/xfstests-bld/blob/master/kernel-build/install-kconfig

The VM has 4 CPU's, and 26GiB of memory, and kernel is booted with the
boot command line options "memmap=4G!9G memmap=9G!14G", which sets up
fake /dev/pmem0 and /dev/pmem1 devices backed by RAM.  This is my poor
engineer's way of testing DAX without needing to get access to
expensive VM's with pmem.  :-)

I'm assuming this is a timing-dependant bug which is easiest to
trigger on fast devices, so a ramdisk might also work.  FWIW, I also
can see failures relatively frequently using the ext4/nojournal
configuration on a SSD-backed cloud block device (GCE's Persistent
Disk SSD product).

As a result, if you grab my xfstests-bld repo from github, and then
run "qemu-xfstests -c ext4/nojournal C 20 generic/085" it should
also reproduce.  See the Documentation/kvm-quickstart.md for more details.

						- Ted