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Date: Tue, 30 Aug 2011 10:40:41 +0200
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Subject: Re: [Qemu-devel] [PATCH 1/5] Support for vm_stop from the migration
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To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Umesh Deshpande <udeshpan@redhat.com>, qemu-devel@nongnu.org, kvm@vger.kernel.org

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