[libvirt] [PATCH v2 3/3] qemu: agent: take monitor lock in qemuAgentNotifyEvent

Nikolay Shirokovskiy nshirokovskiy at virtuozzo.com
Mon Dec 12 09:13:44 UTC 2016

qemuAgentNotifyEvent accesses monitor structure and is called on qemu
reset/shutdown/suspend events under domain lock. Other monitor
functions on the other hand take monitor lock and don't hold domain lock.
Thus it is possible to have risky simultaneous access to the structure
from 2 threads. Let's take monitor lock here to make access exclusive.

John, I decided to formulate patch purpuse this way as I doubt we
can have actual signalling race here becase shutdown/suspend functions
first set await_event and then send message to agent which in turn causes
the event that qemuAgentNotifyEvent handles.

 src/qemu/qemu_agent.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/qemu/qemu_agent.c b/src/qemu/qemu_agent.c
index c50f760..46cad53 100644
--- a/src/qemu/qemu_agent.c
+++ b/src/qemu/qemu_agent.c
@@ -1248,6 +1248,8 @@ qemuAgentMakeStringsArray(const char **strings, unsigned int len)
 void qemuAgentNotifyEvent(qemuAgentPtr mon,
                           qemuAgentEvent event)
+    virObjectLock(mon);
     VIR_DEBUG("mon=%p event=%d await_event=%d", mon, event, mon->await_event);
     if (mon->await_event == event) {
         mon->await_event = QEMU_AGENT_EVENT_NONE;
@@ -1257,6 +1259,8 @@ void qemuAgentNotifyEvent(qemuAgentPtr mon,
+    virObjectUnlock(mon);

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