[Bug 60642] New: guest uses 100% and completely hangs

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=60642

            Bug ID: 60642
           Summary: guest uses 100% and completely hangs
           Product: Virtualization
           Version: unspecified
    Kernel Version: guest: 3.10, host: 3.10
          Hardware: x86-64
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: kvm
          Assignee: virtualization_kvm@kernel-bugs.osdl.org
          Reporter: folkert@vanheusden.com
        Regression: No

Situation:
pc with 3 vms running.
2 run fine, 1 jumps to 100% cpu and completely hangs minutes after start
this vm has a virtual serial port connected to /dev/ttyUMTS0 which is an umts
stick.
as soon as wvdial successfully started a ppp session, the guest hangs
The last thing top shows in the guest is:
    3 root      20   0     0    0    0 R  40.2  0.0   0:00.86 ksoftirqd/0
 2320 root      20   0 21476 1648 1260 R  36.0  0.7   0:02.14 tincd
  132 root      20   0     0    0    0 R  27.7  0.0   0:01.18 kworker/0:2

strace on the kvm process in the host gives me:
[pid  9418] write(5, "`", 1)            = -1 EAGAIN (Resource temporarily
unavailable)
[pid  9418] write(5, "`", 1)            = -1 EAGAIN (Resource temporarily
unavailable)
[pid  9418] write(5, "`", 1)            = -1 EAGAIN (Resource temporarily
unavailable)
[pid  9418] write(5, "`", 1)            = -1 EAGAIN (Resource temporarily
unavailable)
[pid  9418] write(5, "`", 1)            = -1 EAGAIN (Resource temporarily
unavailable)

fd 5 is the /dev/ttyUMTS0 device.

gdb says:
#0  __lll_lock_wait () at
../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:135
#1  0x00007f69ced73f3c in _L_lock_974 () from
/lib/x86_64-linux-gnu/libpthread.so.0
#2  0x00007f69ced73d8b in __GI___pthread_mutex_lock (mutex=0x7f69d3acfa80
<qemu_global_mutex>) at pthread_mutex_lock.c:64
#3  0x00007f69d2daedc9 in ?? ()
#4  0x00007f69d2d83c98 in ?? ()
#5  0x00007f69d2c93973 in main ()

There's absolutely _no_ logging regarding this issue in dmesg on the host.

I did some googling and tried replacing utc-clock by local clock, I also tried
adding clocksource=acpi_pm but none of those helped.

versions:
root@neo:/sys/bus/usb/devices# dpkg --list | grep -e qemu -e kvm | awk '{ print
$1"\t"$2"\t"$3"\t"$4; }'
ii      ipxe-qemu       1.0.0+git-20120202.f6840ba-3    all
ii      kvm     1:1.1.2+dfsg-6  amd64
ii      qemu    1.1.2+dfsg-6a   amd64
ii      qemu-keymaps    1.1.2+dfsg-6a   all
ii      qemu-kvm        1.1.2+dfsg-6    amd64
ii      qemu-system     1.1.2+dfsg-6a   amd64
ii      qemu-user       1.1.2+dfsg-6a   amd64
ii      qemu-utils      1.1.2+dfsg-6a   amd64

After a restart of the vm, the exact same problem happens after 10 seconds so
it is 100% reproducible here.

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