Hi all,
I found a way to reliably crash my host system:
1) Boot guest VM with init=/bin/bash
2) In guest VM: echo b >/proc/sysrq-trigger
3) Try to reboot the guest -> crashes the host during kernel initialization
When I checked the logs I first thought it would be a KSM issue:
Jul 10 15:33:37 fsdevel7 kernel: [ 507.995602] br0: port 3(tap2) entered disabled state
Jul 10 15:33:37 fsdevel7 kernel: [ 508.043454] BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
Jul 10 15:33:37 fsdevel7 kernel: [ 508.043487] IP: [<ffffffff811825b9>] get_ksm_page+0x39/0x130
and
Jul 10 15:34:49 fsdevel7 kernel: [ 580.274709] RIP: 0010:[<ffffffff8116d694>] [<ffffffff8116d694>] anon_vma_clone+0x94/0x1a0
Jul 10 15:34:49 fsdevel7 kernel: [ 580.274710] RSP: 0018:ffff880406495cf0 EFLAGS: 00010286
Jul 10 15:34:49 fsdevel7 kernel: [ 580.274721] Call Trace:
Jul 10 15:34:49 fsdevel7 kernel: [ 580.274724] [<ffffffff8116d868>] anon_vma_fork+0x38/0x130
Jul 10 15:34:49 fsdevel7 kernel: [ 580.274728] [<ffffffff8105770f>] dup_mmap+0x1bf/0x420
But then I simply disabled KSM in rc.local
(echo 0 > /sys/kernel/mm/ksm/run) before starting the VMs. Now the
system still crashes, but now without any logs message.
At least sysrq-b still works, but I don' see any
"SysRq : Emergency Sync" messages in log files. So log messages are not
written properly anymore. Unfortunately I don't have a serial console on
my desktop system.
I don't have the time now, but the next step is probably to get a
crash-dump and to see if that has something useful. And I'm also going
to run the VM from a tty without X, maybe it prints something to the
console.
Anything else you might want? Or already any idea?
Crashes do not happen with 3.8-ubuntu, but very reliably with 3.9.9 or
3.10.1 (host).
Here's my kvm command line:
qemu-system-x86_64 \
-m 8192 \
-machine type=pc,accel=kvm,kernel_irqchip=on \
-netdev type=tap,script=${kvm_ifup},downscript=${kvm_ifdown},ifname=$iface,vhost=on,id=guest0 \
-device virtio-net-pci,netdev=guest0,mac=52:54:00:12:34:11 \
-boot c \
-drive file=${FILE},if=${DISKIF},cache=unsafe \
-drive file=${META},if=${DISKIF},cache=writeback \
-drive file=${STORAGE},if=${DISKIF},cache=writeback \
-enable-kvm \
-vga vmware \
-cpu host \
-smp 4 \
"$@"
Thanks,
Bernd
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