Re: [PATCH v2] fix qemu-kvm sigsegv at exit

[Avi Kivity <avi@redhat.com>]

On 10/27/2009 05:33 PM, Marcelo Tosatti wrote:
> Michael reported a qemu-kvm SIGSEGV at shutdown:
>
> 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
>
> Problem is kvm_main_loop_wait(env, 0) can process the stop request
> (signalling iothread that vcpu is stopped, so its OK to exit) and
> continue to kvm_cpu_exec.
>
> Reorder kvm_main_loop_wait and kvm_cpu_exec, as suggested by Gleb.
>
> Signed-off-by: Marcelo Tosatti<mtosatti@redhat.com>
> Reported-by: "Michael S. Tsirkin"<mst@redhat.com>
>
> diff --git a/qemu-kvm.c b/qemu-kvm.c
> index 4c13628..809fd65 100644
> --- a/qemu-kvm.c
> +++ b/qemu-kvm.c
> @@ -1867,8 +1867,8 @@ static int kvm_main_loop_cpu(CPUState *env)
>               run_cpu = !env->halted;
>           }
>           if (run_cpu) {
> -            kvm_main_loop_wait(env, 0);
>               kvm_cpu_exec(env);
> +            kvm_main_loop_wait(env, 0);
>           } else {
>               kvm_main_loop_wait(env, 1000);
>           }
>    

This will miss an event at the very beginning of the loop (powerdown 
requested before we had a chance to spin up?).  I think it should be 
fine since there will be a pending signal which will break us out of 
kvm_cpu_exec() before it has a chance to do anything (i.e. spin in the 
guest).

So, I think it's fine, but please double check the above.

-- 
error compiling committee.c: too many arguments to function