I started having a host freeze randomly when running a 4.18 kernel. The
host was stable when running 4.17.12.
At first, it appeared that it was only IO that was frozen since I could
run common commands that were likely cached in RAM and that did not
touch storage. Anything that did touch storage would freeze and I would
not be able to ctrl-c it.
I noticed today, when it happened with kernel 4.19.2, that backups were
still running and that the backup app could still read from the backup
snapshot subvol. It's possible that the backups are still able to
proceed because the accesses are all read-only and the snapshot was
mounted with noatime so the backup process never triggers a write.
There never are any errors output to the console when this happens and
nothing is logged. When I first encountered this back in Sept. I managed
to record a few sysrq dumps and attached them to a redhat ticket. See
links below.
https://bugzilla.redhat.com/show_bug.cgi?id=1627288
https://bugzilla.redhat.com/attachment.cgi?id=1482177
I do have several VMs running that have their image files nocow'd.
Interestingly, all the VMs, except 1, seem to be able to write just
fine. The one that can't has frozen completely and is the one that
regularly generates the most IO.
Any ideas on how to debug this further?
--Larkin
