[libvirt] [PATCH] qemuProcessReconnect: ensure vm xml integrity when save status

[Wang King]

From: Dingzhong Weng <wengdingzhong at huawei.com>

libvirtd starts qemuProcessReconnect threads when libvirtd is starting
and there are live vm on the host. but as qemuProcessReconnect threads
are simply side job done by libvirtd upon start and are only called
for existing vm. these threads are not managed like that of worker
threads and event pool.

once libvirtd receives SIGTERM signal or any similar command right after
it starts, these qemuProcessReconnect threads might still be running and
libvirtd goes to clean up and frees qemu_driver and its components. In
this short window, qemuProcessReconnect threads might have a NULL
qemu_driver->xmlopt.format, skip this function, and only partial vm
status can be saved to disk. As a result, vm may fail to recover with
missing information.

this patch increases qemu_driver->xmlopt ref count during the lifecycle
of qemuProcessReconnect so that libvirtd will not release this resource
until qemuProcessReconnect threads finish using it. thus make sure all
of vm status information can be formatted and thus maintain its integrity
in virDomainSaveStatus.

no vm is killed in this patch.

Signed-off-by: Dingzhong Weng <wengdingzhong at huawei.com>
---
 src/qemu/qemu_process.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index 90466771cd..36b9b5fd03 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -8000,6 +8000,7 @@ qemuProcessReconnect(void *opaque)
     struct qemuProcessReconnectData *data = opaque;
     virQEMUDriverPtr driver = data->driver;
     virDomainObjPtr obj = data->obj;
+    virDomainXMLOptionPtr xmlopt = NULL;
     qemuDomainObjPrivatePtr priv;
     qemuDomainJobObj oldjob;
     int state;
@@ -8023,6 +8024,9 @@ qemuProcessReconnect(void *opaque)
     cfg = virQEMUDriverGetConfig(driver);
     priv = obj->privateData;
 
+    /* need xmlopt later to save status, do not free */
+    xmlopt = virObjectRef(driver->xmlopt);
+
     if (!(caps = virQEMUDriverGetCapabilities(driver, false)))
         goto error;
 
@@ -8218,7 +8222,7 @@ qemuProcessReconnect(void *opaque)
     }
 
     /* update domain state XML with possibly updated state in virDomainObj */
-    if (virDomainSaveStatus(driver->xmlopt, cfg->stateDir, obj, driver->caps) < 0)
+    if (virDomainSaveStatus(xmlopt, cfg->stateDir, obj, driver->caps) < 0)
         goto error;
 
     /* Run an hook to allow admins to do some magic */
@@ -8253,6 +8257,7 @@ qemuProcessReconnect(void *opaque)
     virDomainObjEndAPI(&obj);
     virObjectUnref(cfg);
     virObjectUnref(caps);
+    virObjectUnref(xmlopt);
     virNWFilterUnlockFilterUpdates();
     virIdentitySetCurrent(NULL);
     return;
-- 
2.18.0.windows.1