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
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