qemu-kvm: sigsegv at exit

["Michael S. Tsirkin" <mst@redhat.com>]

Hi!
I'm sometimes getting segfaults when I kill qemu.
This time I caught it when qemu was under gdb:


Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x411d0940 (LWP 14446)]
0x000000000040afb4 in qemu_mod_timer (ts=0x19f0fd0, expire_time=62275467335)
    at /home/mst/scm/qemu-kvm/vl.c:1009
1009            if ((alarm_timer->flags & ALARM_FLAG_EXPIRED) == 0) {
(gdb) l
1004        ts->next = *pt;
1005        *pt = ts;
1006
1007        /* Rearm if necessary  */
1008        if (pt == &active_timers[ts->clock->type]) {
1009            if ((alarm_timer->flags & ALARM_FLAG_EXPIRED) == 0) {
1010                qemu_rearm_alarm_timer(alarm_timer);
1011            }
1012            /* Interrupt execution to force deadline recalculation.  */
1013            if (use_icount)
(gdb) p alarm_timer
$1 = (struct qemu_alarm_timer *) 0x0
(gdb) where
#0  0x000000000040afb4 in qemu_mod_timer (ts=0x19f0fd0, expire_time=62275467335)
    at /home/mst/scm/qemu-kvm/vl.c:1009
#1  0x000000000041aadf in virtio_net_handle_tx (vdev=<value optimized out>, vq=0x19f5af0)
    at /home/mst/scm/qemu-kvm/hw/virtio-net.c:696
#2  0x0000000000421669 in kvm_run (vcpu=0x19d46a0, env=0x19c2250) at /home/mst/scm/qemu-kvm/qemu-kvm.c:797
#3  0x00000000004216d6 in kvm_cpu_exec (env=0x83d0f8) at /home/mst/scm/qemu-kvm/qemu-kvm.c:1714
#4  0x0000000000422981 in ap_main_loop (_env=<value optimized out>) at /home/mst/scm/qemu-kvm/qemu-kvm.c:1969
#5  0x000000377dc06367 in start_thread () from /lib64/libpthread.so.0
#6  0x000000377d0d30ad in clone () from /lib64/libc.so.6
(gdb)

So this probably means that we have already run quit_timers:

static void quit_timers(void)
{
    alarm_timer->stop(alarm_timer);
    alarm_timer = NULL;
}

but kvm vcpu thread is still running.


Not sure what the right fix is here: should we stop
kvm after main loop has exited?

-- 
MST