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qemu-system-x86_64 run VM (nested) doesn't reboot occasionally

From: Anoop Karollil
Subject: qemu-system-x86_64 run VM (nested) doesn't reboot occasionally
Date: Tue, 2 Jun 2020 12:50:44 -0700



QEMU VM (run within another KVM) doesn't reboot occasionally when a
kernel panic is induced, with either the kernel configured to reboot
on panics, or when a watchdog is configured. The VM kernel log (set to
be printed to console) doesn't show anything after the kernel panic,
and qemu-system-x86_64 is still running, but the VM doesn't reboot.
Any suggestions to debug this would be appreciated!


A test runs a Linux OS (Yocto based, with 4.14.157 kernel) in a QEMU
VM, with the test itself running in a KVM. The OS uses systemd, which
is configured to use any watchdog available to reboot the VM if the
watchdog isn't tickled for more than 10 seconds (using
RuntimeWatchdogSec=10s). The VM has been setup to use the i6300esb
watchdog. This is the command used to start the VM:

qemu-system-x86_64 -global isa-fdc.driveA= -boot c -bios ovmf/ovmf.fd
-nographic -cpu core2duo -m 1000 -net nic,model=virtio -net
user,hostfwd=tcp::22221-:22 -boot c -drive
file=image.hddirect.qcow2,if=virtio -watchdog i6300esb -enable-kvm
-global virtio-pci.disable-modern=on

The test induces a kernel panic with `echo c > /proc/sysrq-trigger`.
This results in the VM being rebooted by the watchdog most of the
time, but occasionally the reboot doesn't happen though the watchdog
does seem to trigger every time (I tested this by setting the watchdog
action to debug). Also when I removed the watchdog from the VM (by
removing -watchdog parameter) and enabled configuration to reboot on
kernel panic, then too the VM doesn't reboot occasionally.


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