Re: [PATCH v2 2/6] reuse env stop and stopped states

[Gleb Natapov <gleb@redhat.com>]

On Tue, Jul 28, 2009 at 09:17:05AM +0300, Avi Kivity wrote:
> On 07/28/2009 03:48 AM, Glauber Costa wrote:
>> On Mon, Jul 27, 2009 at 06:43:47PM +0300, Avi Kivity wrote:
>>    
>>> On 07/22/2009 01:13 AM, Glauber Costa wrote:
>>>      
>>>> qemu CPUState already provides "stop" and "stopped" states. And they
>>>> mean exactly that. There is no need for us to provide our own.
>>>>
>>>>
>>>>        
>>> This patch (known as dd0e1c1a589 in qemu-kvm.git) breaks reboot.  My
>>> test case is FC6 i386 -smp 2, running the reboot command in rc.local.
>>> In about 15 minutes qemu hangs hard.  Please check what's gone wrong.
>>>      
>> I found out that doing kill -38<your_pid>  makes it run again, so we're likely
>> hanging somewhere while holding qemu_mutex. The state of the process is "D",
>> so we're holding qemu_mutex, and then calling something that can block.
>>    
>
> Sounds like we call a vcpu ioctl from the iothread (or from a different  
> vcpu thread).
>
>> It's hard for me to believe that this patch introduced it. At best, it might have
>> made it more likely. Also, I also verified that it sometimes takes a while until
>> it happen for the first time. Are you sure this is the first patch that makes it happen?
>>    
>
> I haven't been able to reproduce it before this patch.  Maybe this patch  
> doesn't introduce it, only exposes it.
>
What are backtraces of all threads when it happens?

--
			Gleb.