qemu hangs until a signal is delivered when running Fedora 14 i386 with -smp 2

[Hans de Goede <hdegoede@redhat.com>]

Hi All,

It took me a while to figure the below out, I hope it gives some clues
into the problem I'm seeing. I'm running qemu compiled from git
from the following repo:

http://cgit.freedesktop.org/spice/qemu/

 From the spice.v20 branch.

So this is basically qemu HEAD (not qemu-kvm but plain qemu), with spice
patches added. I can reproduce this without the use of the spice vga device
however!

When I start Fedora 14 i386 inside a qemu vm with the following cmdline:
qemu-system-x86_64 -enable-kvm -cpu host \
  -m 1024 -name F14 -smp 2 \
  -drive file=/mnt/rhel6_x86_64/images/f14-i386.qcow2,if=virtio,media=disk \
  -net nic,macaddr=52:54:00:7a:b4:7d,vlan=0,model=virtio,name=virtio.0 -net tap,vlan=0 \
  -monitor stdio

And then:
-wait till it has booted into gdm
-switch to tty2 using sendkey ctrl+alt+f2 from the monitor
-login as root
-run the following:
  while true; fortune; sleep 1; done;
-wait (10 minutes or so at a maximum at my machine)
-note qemu cpu load goes to 100% all of a sudden, monitor is dead,
  ctrl+alt+1 to go to serial console is dead, guest is dead
-attach a debugger, see it is executing guest instructions
  (doing kvm_ioctl), also if you let it hang long enough you
  will get BUG: soft lockup in dmesg (once you unstuck it)
-detach, hang is gone everything works again, entered
  monitor commands during the hang are executed, etc.

Alternatively sending SIGCHLD to the qemu process also unstucks qemu +
the guest.

Removing -smp 2 from the cmdline makes this go away.

So any ideas what this can be?

Thanks & Regards,

Hans

p.s.

Please keep me in the CC I'm not on the list.