Description of problem: libvirt 3.9 on CentOS Linux release 7.4.1708 (kernel 3.10.0-693.21.1.el7.x86_64) on Qemu version 2.10.0 I’m currently facing a strange situation. Sometimes my vm is shown by ‘virsh list’ as in state “in shutdown” but there is no qemu-kvm process linked to it. Libvirt log when “in shutdown” state occur is as follows: “d470c3b284425b9bacb34d3b5f3845fe” is vm’s name, remoteDispatchDomainMemoryStats API is called by ‘collectd’, which is used to collect some vm running states and host information once every 30’s. 2019-07-25 14:23:58.706+0000: 15818: warning : qemuMonitorJSONIOProcessEvent:235 : type: POWERDOWN, vm: d470c3b284425b9bacb34d3b5f3845fe, cost 1.413 secs 2019-07-25 14:23:59.601+0000: 15818: warning : qemuMonitorJSONIOProcessEvent:235 : type: SHUTDOWN, vm: d470c3b284425b9bacb34d3b5f3845fe, cost 1.202 secs 2019-07-25 14:23:59.601+0000: 15818: warning : qemuMonitorJSONIOProcessEvent:235 : type: STOP, vm: d470c3b284425b9bacb34d3b5f3845fe, cost 1.203 secs 2019-07-25 14:23:59.601+0000: 15818: warning : qemuMonitorJSONIOProcessEvent:235 : type: SHUTDOWN, vm: d470c3b284425b9bacb34d3b5f3845fe, cost 1.203 secs 2019-07-25 14:23:59.629+0000: 15818: error : qemuMonitorIORead:597 : Unable to read from monitor: Connection reset by peer 2019-07-25 14:23:59.629+0000: 121081: warning : qemuProcessEventHandler:4840 : vm: d470c3b284425b9bacb34d3b5f3845fe, event: 6 locked 2019-07-25 14:23:59.629+0000: 15822: error : qemuMonitorJSONCommandWithFd:364 : internal error: Missing monitor reply object 2019-07-25 14:24:29.483+0000: 15821: warning : qemuGetProcessInfo:1468 : cannot parse process status data 2019-07-25 14:24:29.829+0000: 15823: warning : qemuDomainObjBeginJobInternal:4391 : Cannot start job (modify, none) for domain d470c3b284425b9bacb34d3b5f3845fe; current job is (query, none) owned by (15822 remoteDispatchDomainMemoryStats, 0 <null>) for (30s, 0s) 2019-07-25 14:24:29.829+0000: 15823: error : qemuDomainObjBeginJobInternal:4403 : Timed out during operation: cannot acquire state change lock (held by remoteDispatchDomainMemoryStats) 2019-07-25 14:24:29.829+0000: 121081: warning : qemuDomainObjBeginJobInternal:4391 : Cannot start job (destroy, none) for domain d470c3b284425b9bacb34d3b5f3845fe; current job is (query, none) owned by (15822 remoteDispatchDomainMemoryStats, 0 <null>) for (30s, 0s) 2019-07-25 14:24:29.829+0000: 121081: error : qemuDomainObjBeginJobInternal:4403 : Timed out during operation: cannot acquire state change lock (held by remoteDispatchDomainMemoryStats) 2019-07-25 14:24:29.829+0000: 121081: warning : qemuProcessEventHandler:4875 : vm: d470c3b284425b9bacb34d3b5f3845fe, event: 6, cost 31.459 secs I’ve tried to find out how did this problem happened. I analyzed the execution process of the job and speculated that the problem occurred as follows: step one: libvirt send command 'system_powerdown' to qemu. step two: libvirt receive qemu monitor close event, and then deal EOF event. step three: remoteDispatchDomainMemoryStats job start on the same vm. step four: work thread dealing stop job is waited on job.cond, the timeout is 30s. It seems that the remoteDispatchDomainMemoryStats job is too slow to let the stop job wait timeout. Then I tried to reproduce this process. The step is as follows: First step: add a sleep on ‘qemuProcessEventHandler' by using pthread_cond_timedwait. So can execute 'virsh dommemstat active’ command at this time interval. Second step: start a vm to test Third step: execute 'virsh shutdown active’ to shutdown the vm Fourth step: execute 'virsh dommemstat active’ when stop job is sleep. Then it works. The test vm state became to 'in shutdown’, and the libvirt log is as follows: “active” is my test vm’s name. 2019-08-05 08:39:57.001+0000: 25889: warning : qemuDomainObjBeginJobInternal:4308 : Starting job: modify (vm=0x7f7bbc145fe0 name=active, current job=none async=none) 2019-08-05 08:39:57.003+0000: 25889: warning : qemuDomainObjEndJob:4522 : Stopping job: modify (async=none vm=0x7f7bbc145fe0 name=active) 2019-08-05 08:39:57.003+0000: 25881: warning : qemuMonitorJSONIOProcessEvent:235 : type: POWERDOWN, vm: active, cost 0.008 secs 2019-08-05 08:39:57.854+0000: 25881: warning : qemuMonitorJSONIOProcessEvent:235 : type: SHUTDOWN, vm: active, cost 1.709 secs 2019-08-05 08:39:57.875+0000: 25881: warning : qemuMonitorJSONIOProcessEvent:235 : type: STOP, vm: active, cost 1.751 secs 2019-08-05 08:39:57.875+0000: 25881: warning : qemuMonitorJSONIOProcessEvent:235 : type: SHUTDOWN, vm: active, cost 1.751 secs 2019-08-05 08:39:57.915+0000: 25881: warning : qemuMonitorIO:756 : Error on monitor <null> 2019-08-05 08:39:57.915+0000: 25881: warning : qemuMonitorIO:777 : Triggering EOF callback 2019-08-05 08:39:57.915+0000: 26915: warning : qemuProcessEventHandler:4822 : usleep 20s 2019-08-05 08:40:01.004+0000: 25886: warning : qemuDomainObjBeginJobInternal:4308 : Starting job: query (vm=0x7f7bbc145fe0 name=active, current job=none async=none) ^@2019-08-05 08:40:17.915+0000: 26915: warning : qemuProcessEventHandler:4845 : vm=0x7f7bbc145fe0, event=6 2019-08-05 08:40:17.915+0000: 26915: warning : qemuProcessEventHandler:4851 : vm: active, event: 6 locked 2019-08-05 08:40:17.915+0000: 26915: warning : qemuDomainObjBeginJobInternal:4308 : Starting job: destroy (vm=0x7f7bbc145fe0 name=active, current job=query async=none) 2019-08-05 08:40:17.915+0000: 26915: warning : qemuDomainObjBeginJobInternal:4344 : Waiting for job (vm=0x7f7bbc145fe0 name=active), job 26915 qemuProcessEventHandler, owned by 25886 remoteDispatchDomainMemoryStats ^@^@^@2019-08-05 08:40:47.915+0000: 26915: warning : qemuDomainObjBeginJobInternal:4405 : Cannot start job (destroy, none) for domain active; current job is (query, none) owned by (25886 remoteDispatchDomainMemoryStats, 0 <null>) for (46s, 0s) 2019-08-05 08:40:47.915+0000: 26915: error : qemuDomainObjBeginJobInternal:4417 : 操作超时：cannot acquire state change lock (held by remoteDispatchDomainMemoryStats) 2019-08-05 08:40:47.915+0000: 26915: warning : qemuProcessEventHandler:4886 : vm: active, event: 6, cost 31.830 secs The threads backtraces is as follows: [Switching to thread 17 (Thread 0x7f12fddf5700 (LWP 32580))] #2 0x00007f12eb26df21 in qemuMonitorSend (mon=mon@entry=0x7f12d0013af0, msg=msg@entry=0x7f12fddf46e0) at qemu/qemu_monitor.c:1075 1075 if (virCondWait(&mon->notify, &mon->parent.lock) < 0) { (gdb) l 1070 PROBE(QEMU_MONITOR_SEND_MSG, 1071 "mon=%p msg=%s fd=%d", 1072 mon, mon->msg->txBuffer, mon->msg->txFD); 1073 1074 while (mon && mon->msg && !mon->msg->finished) { 1075 if (virCondWait(&mon->notify, &mon->parent.lock) < 0) { 1076 virReportError(VIR_ERR_INTERNAL_ERROR, "%s", 1077 _("Unable to wait on monitor condition")); 1078 goto cleanup; 1079 } (gdb) p *msg $2 = {txFD = -1, txBuffer = 0x7f12b8000d50 "{\"execute\":\"qom-list\",\"arguments\":{\"path\":\"/machine/peripheral\"},\"id\":\"libvirt-17\"}\r\n", txOffset = 0, txLength = 85, rxBuffer = 0x0, rxLength = 0, rxObject = 0x0, finished = false, passwordHandler = 0x0, passwordOpaque = 0x0} (gdb) bt #0 pthread_cond_wait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185 #1 0x00007f130d738316 in virCondWait (c=c@entry=0x7f12d0013b28, m=m@entry=0x7f12d0013b00) at util/virthread.c:154 #2 0x00007f12eb26df21 in qemuMonitorSend (mon=mon@entry=0x7f12d0013af0, msg=msg@entry=0x7f12fddf46e0) at qemu/qemu_monitor.c:1075 #3 0x00007f12eb283b40 in qemuMonitorJSONCommandWithFd ( mon=mon@entry=0x7f12d0013af0, cmd=cmd@entry=0x7f12b80008c0, scm_fd=scm_fd@entry=-1, reply=reply@entry=0x7f12fddf4780) at qemu/qemu_monitor_json.c:355 #4 0x00007f12eb2904b9 in qemuMonitorJSONCommand (reply=0x7f12fddf4780, cmd=0x7f12b80008c0, mon=0x7f12d0013af0) at qemu/qemu_monitor_json.c:385 ... I found that on function ‘qemuMonitorUpdateWatch’, if mon->watch is zero, then event would’t be update. But 'qemuMonitorSend' would still wait on mon->notify. So the remoteDispatchDomainMemoryStats job is blocked, and then the stop job blocked too. 618 static void 619 qemuMonitorUpdateWatch(qemuMonitorPtr mon) 620 { 621 int events = 622 VIR_EVENT_HANDLE_HANGUP | 623 VIR_EVENT_HANDLE_ERROR; 624 625 if (!mon->watch) 626 return; 627 628 if (mon->lastError.code == VIR_ERR_OK) { 629 events |= VIR_EVENT_HANDLE_READABLE; 630 631 if ((mon->msg && mon->msg->txOffset < mon->msg->txLength) && 632 !mon->waitGreeting) 633 events |= VIR_EVENT_HANDLE_WRITABLE; 634 } 635 636 virEventUpdateHandle(mon->watch, events); 637 } I try to fix this bugs by add a judgment before qemuMonitorUpdateWatch, and it seem works. 1046 int 1047 qemuMonitorSend(qemuMonitorPtr mon, 1048 qemuMonitorMessagePtr msg) 1049 { 1050 int ret = -1; 1051 1052 /* Check whether qemu quit unexpectedly */ 1053 if (mon->lastError.code != VIR_ERR_OK) { 1054 VIR_DEBUG("Attempt to send command while error is set %s", 1055 NULLSTR(mon->lastError.message)); 1056 virSetError(&mon->lastError); 1057 return -1; 1058 } 1059 1060 if (!mon->watch) { 1061 VIR_WARN("Attempt to send command while mon->watch is zero"); 1062 virReportError(VIR_ERR_INTERNAL_ERROR, "%s", 1063 _("attempt to send command when the monitor is closing")); 1064 return -1; 1065 } 1066 1067 mon->msg = msg; 1068 qemuMonitorUpdateWatch(mon); 1069 1070 PROBE(QEMU_MONITOR_SEND_MSG, 1071 "mon=%p msg=%s fd=%d", 1072 mon, mon->msg->txBuffer, mon->msg->txFD); 1073 1074 while (mon && mon->msg && !mon->msg->finished) { 1075 if (virCondWait(&mon->notify, &mon->parent.lock) < 0) { 1076 virReportError(VIR_ERR_INTERNAL_ERROR, "%s", 1077 _("Unable to wait on monitor condition")); 1078 goto cleanup; 1079 } 1080 } 1081 1082 if (mon->lastError.code != VIR_ERR_OK) { 1083 VIR_DEBUG("Send command resulted in error %s", 1084 NULLSTR(mon->lastError.message)); 1085 virSetError(&mon->lastError); 1086 goto cleanup; 1087 } 1088 1089 ret = 0; 1090 1091 cleanup: 1092 mon->msg = NULL; 1093 qemuMonitorUpdateWatch(mon); 1094 1095 return ret; 1096 } I’m not really sure that this change will affect other process. Thanks! Ma haocong