Re: [Qemu-devel] [PATCH 1/5] Support for vm_stop from the migration thread

[Paolo Bonzini]

On 08/29/2011 06:56 PM, Marcelo Tosatti wrote:
> > >  diff --git a/cpus.c b/cpus.c
> > >  index de70e02..f35f683 100644
> > >  --- a/cpus.c
> > >  +++ b/cpus.c
> > >  @@ -122,8 +122,8 @@ static void do_vm_stop(int reason)
> > >    {
> > >        if (vm_running) {
> > >            cpu_disable_ticks();
> > >  -        vm_running = 0;
> > >            pause_all_vcpus();
> > >  +        vm_running = 0;
> > >            vm_state_notify(0, reason);
> > >            qemu_aio_flush();
> > >            bdrv_flush_all();
> Why this change?

Without it, you could have two threads calling into do_vm_stop and the 
second would not wait for all CPUs to be paused.  Still not perfect as 
you'd get double notifications, you would need a condition variable or 
QemuEvent (from the RCU series) for that.

Paolo