> On 27.09.2018 14:37, Wang Yechao wrote:
> > qemuAgentClose and qemuAgentIO have race condition,
> > as follows:
> >
> > main thread: second thread:
> > virEventPollRunOnce processSerialChangedEvent
> > virEventPollDispatchHandles
> > virMutexUnlock(&eventLoop.lock)
> > qemuAgentClose
> > virObjectLock(mon)
> > virEventRemoveHandle
> > VIR_FORCE_CLOSE(mon->fd)
> > virObjectUnlock(mon)
> > priv->agentError = false
> > qemuAgentIO
> > virObjectLock(mon)
> > mon->fd != fd --> error = true
> > qemuProcessHandleAgentError
> > priv->agentError = true
> > virObjectUnlock(mon)
> > virMutexLock(&eventLoop.lock)
> >
> > qemuAgentClose set the mon->fd to '-1', and then qemuAgentIO
> > check the mon->fd not equals to fd that registered before.
> > qemuProcessHandleAgentError will be called to set
> > priv->agentError to 'true', then the priv->agentError is
> > always 'true' except restart libvirtd or restart
> > qemu-guest-agent process in guest. We can't send any
> > qemu-agent-command anymore even if qemuConnectAgent return
> > success later.
> >
> > This is accidently occurs when hot-add-vcpu in windows2012.
> > virsh setvcpus ...
> > virsh qemu-agent-command $vm '{"execute":"guest-get-vcpus"}'
> >
> > Reset the priv->agentError to 'false' when qemuConnectAgent sucess
> > to fix this problem.
> >
> > Signed-off-by: Wang Yechao <wang.yechao255@xxxxxxxxxx>
> > ---
> > src/qemu/qemu_process.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
> > index 29b0ba1..4fbb955 100644
> > --- a/src/qemu/qemu_process.c
> > +++ b/src/qemu/qemu_process.c
> > @@ -269,6 +269,7 @@ qemuConnectAgent(virQEMUDriverPtr driver, virDomainObjPtr vm)
> > virResetLastError();
> > }
> >
> > + priv->agentError = false;
> > return 0;
> > }
> >
> >
>
> There was similar problem with qemu monitor:
>
> commit 89563efc0209b854d2b2e554423423d7602acdbd
> Author: Daniel P. Berrange <berrange@xxxxxxxxxx>
> Date: Fri Sep 28 15:27:39 2012 +0100
>
> Avoid bogus I/O event errors when closing the QEMU monitor
>
> After calling qemuMonitorClose(), it is still possible for
> the QEMU monitor I/O event callback to get invoked. This
> will trigger an error message because mon->fd has been set
> to -1 at this point. Silently ignore the case where mon->fd
> is -1, likewise for mon->watch being zero.
>
> Signed-off-by: Daniel P. Berrange <berrange@xxxxxxxxxx
>
> This approach has advantage it does not set agentError at all. So clients
> see agent state as disconnected (which is true) instead of error.
>
> Nikolay
Thanks Nikolay, this solution is better. I'll give another patch.
---
Best wishes
Wang Yechao--
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