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(a)zte.com.cn&gt; > --- > 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(a)redhat.com&gt; 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(a)redhat.com 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