Please delay review, I plan to provide better patch.
On 08.09.2017 10:16, Nikolay Shirokovskiy wrote:
> Patch aeda1b8c needs some enhancement.
>
> 1. Shutdown event is delivired on reboot too and we don't want
> to set willhangup flag is this case.
>
> 2. There is a next race condition.
>
> - EOF is delivered in event loop thread
> - qemuMonitorSend is called on client behalf and waits for notification
> on message response or monitor close
> - EOF handler tries to accquire job condition and fail on timeout as
> it is grabbed by the request above
>
> Now qemuMonitorSend hangs.
>
> Previously if qemuMonitorSend is called after EOF then it failed
> immediately due to lastError is set. Now we need to check willhangup too.
>
> ---
>
> Race is easy to trigger with patch [1]. One need to query domain
> frequently enough in a loop and do a shutdown.
>
> [1] Patch to trigger race condition.
>
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index b782451..4445f88 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -4742,6 +4742,9 @@ static void qemuProcessEventHandler(void *data, void *opaque)
>
> VIR_DEBUG("vm=%p, event=%d", vm, processEvent->eventType);
>
> + if (processEvent->eventType == QEMU_PROCESS_EVENT_MONITOR_EOF)
> + sleep(3);
> +
> virObjectLock(vm);
>
> switch (processEvent->eventType) {
>
>
>
>
> src/qemu/qemu_monitor.c | 16 +++++++++++++++-
> src/qemu/qemu_monitor.h | 2 ++
> src/qemu/qemu_process.c | 1 +
> 3 files changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
> index 19082d8..6270191 100644
> --- a/src/qemu/qemu_monitor.c
> +++ b/src/qemu/qemu_monitor.c
> @@ -315,6 +315,15 @@ qemuMonitorEscapeNonPrintable(const char *text)
> #endif
>
>
> +void
> +qemuMonitorShutdown(qemuMonitorPtr mon)
> +{
> + virObjectLock(mon);
> + mon->willhangup = 1;
> + virObjectUnlock(mon);
> +}
> +
> +
> static void
> qemuMonitorDispose(void *obj)
> {
> @@ -1055,6 +1064,12 @@ qemuMonitorSend(qemuMonitorPtr mon,
> return -1;
> }
>
> + if (mon->willhangup) {
> + virReportError(VIR_ERR_OPERATION_INVALID, "%s",
> + _("Domain is shutting down."));
> + return -1;
> + }
> +
> mon->msg = msg;
> qemuMonitorUpdateWatch(mon);
>
> @@ -1336,7 +1351,6 @@ qemuMonitorEmitShutdown(qemuMonitorPtr mon, virTristateBool guest)
> {
> int ret = -1;
> VIR_DEBUG("mon=%p guest=%u", mon, guest);
> - mon->willhangup = 1;
>
> QEMU_MONITOR_CALLBACK(mon, ret, domainShutdown, mon->vm, guest);
> return ret;
> diff --git a/src/qemu/qemu_monitor.h b/src/qemu/qemu_monitor.h
> index 9805a33..30533ef 100644
> --- a/src/qemu/qemu_monitor.h
> +++ b/src/qemu/qemu_monitor.h
> @@ -303,6 +303,8 @@ void qemuMonitorUnregister(qemuMonitorPtr mon)
> ATTRIBUTE_NONNULL(1);
> void qemuMonitorClose(qemuMonitorPtr mon);
>
> +void qemuMonitorShutdown(qemuMonitorPtr mon);
> +
> virErrorPtr qemuMonitorLastError(qemuMonitorPtr mon);
>
> int qemuMonitorSetCapabilities(qemuMonitorPtr mon);
> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
> index ab81d65..824be86 100644
> --- a/src/qemu/qemu_process.c
> +++ b/src/qemu/qemu_process.c
> @@ -618,6 +618,7 @@ qemuProcessShutdownOrReboot(virQEMUDriverPtr driver,
> virObjectUnref(vm);
> }
> } else {
> + qemuMonitorShutdown(priv->mon);
> ignore_value(qemuProcessKill(vm, VIR_QEMU_PROCESS_KILL_NOWAIT));
> }
> }
>
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