On Wed, Jul 10, 2013 at 04:16:46PM +0200, Bernd Schubert wrote:
> 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
>
What 3 means? 2 already reboots it.
>
> 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).
>
What is your host cpu? cat /proc/cpuinfo.
> 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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--
Gleb.
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