[libvirt] [PATCH V2 3/3] hold an extra reference while handling watchdog event

[Wen Congyang]

If the domain is not persistent, and qemu quited unexpectedly before
calling processWatchdogEvent(), vm will be freed and the function
processWatchdogEvent() will be dangerous.

---
 src/qemu/qemu_driver.c  |   12 ++++++++----
 src/qemu/qemu_process.c |    4 ++++
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 628cfe3..d02891c 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -2436,15 +2436,19 @@ static void processWatchdogEvent(void *data, void *opaque)
         }
         break;
     default:
-        goto cleanup;
+        qemuDriverLock(driver);
+        virDomainObjLock(wdEvent->vm);
+        goto unlock;
     }
 
 endjob:
-    if (qemuDomainObjEndJob(wdEvent->vm) == 0)
-        wdEvent->vm = NULL;
+    /* Safe to ignore value since ref count was incremented in
+     * qemuProcessHandleWatchdog().
+     */
+    ignore_value(qemuDomainObjEndJob(wdEvent->vm));
 
 unlock:
-    if (wdEvent->vm)
+    if (virDomainObjUnref(wdEvent->vm) > 0)
         virDomainObjUnlock(wdEvent->vm);
     qemuDriverUnlock(driver);
 
diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index 48ecd5c..321374c 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -426,6 +426,10 @@ qemuProcessHandleWatchdog(qemuMonitorPtr mon ATTRIBUTE_UNUSED,
         if (VIR_ALLOC(wdEvent) == 0) {
             wdEvent->action = VIR_DOMAIN_WATCHDOG_ACTION_DUMP;
             wdEvent->vm = vm;
+            /* Hold an extra reference because we can't allow 'vm' to be
+             * deleted before handling watchdog event is finished.
+             */
+            virDomainObjRef(vm);
             ignore_value(virThreadPoolSendJob(driver->workerPool, wdEvent));
         } else
             virReportOOMError();
-- 
1.7.1