On Tue, Nov 28, 2017 at 2:45 PM, Theodore Ts'o <tytso@xxxxxxx> wrote: > On Tue, Nov 28, 2017 at 07:04:54AM -0600, Ashlie Martinez wrote: >> No biggie, part of the reason this was so hard for me to wrap my head >> around is I don't have a physical machine that I can reproduce this on >> (and I never got around to getting a GCE instance to test on). Not >> being able to poke around a reproducing system makes it a little bit >> harder for me to reason about :) > > This does reproduce easily using kvm-xfstests[1]; using gce-xfstests > was not necessary. That's actually how I debugged it, since kvm > starts up in under 5 seconds, while starting up a cloud VM takes a bit > longer. So if you want a quick edit/compile/debug cycle, or if you > attach a debugger to the running kernel, using kvm-xfstests is the > right tool to use. 99% of the command syntax and test appliance > implementation is the same between kvm-xfstests and gce-xfstests. Unfortunately this timing bug only reproduces on some machines. Xiao and I have been unable to reproduce this bug (I've tried kvm-xfstests, my own kvm VMs, VMs without kvm, VMs with/without virtio drivers, and another bare metal system). generic/456 basically sets up a race condition between a kernel flusher thread and triggering dm-flakey, so I think things like system load, core count, etc. might cause different test results. > > [1] https://github.com/tytso/xfstests-bld/blob/master/Documentation/kvm-quickstart.md > > I've been trying to promote the use of kvm-xfstests for researchers > who are interested in doing file system work. So if you can help > promote {kvm,gce}-xfstests amongst your fellow students and > professors, that would be great! > > > You can run the reproducer automatically via "kvm-xfstests -c 4k > generic/456". But you can also run "kvm-xfstests shell", and then run > the following commands; > > kvm-xfstests# export FSTESTSET=generic/456 > kvm-xfstests# ./runtests.sh > > You can then edit the test script to add debugging commands; it can be > found in /root/xfstests/tests/generic/456 and then rerun the tests > using the "./runtests.sh" script. > > Sorry, the only editor available is /bin/ed. If you want to use some > other editor, and are willing to build your own test-appliance VM > image instead of just downloading the rebuilt test applinace image, > you can add it to the xfstests-packages file in the > kvm-xfstests/test-appliance directory, and generate your own test > appliance. See [2] for more details. > > [2] https://github.com/tytso/xfstests-bld/blob/master/Documentation/building-rootfs.md > > This is actually how I figured out what was happening; I added > commands such as "debugfs -R 'stat <11>'" so I could see was going on > with the file system before the _flakey_drop_and_remount statement, > and then varied the number of operations in the fsx operations to > replay list. > > Regards, > > - Ted
