qemu: Grab a QUERY job when formatting domain XML

It may happen that, for instance after daemon restart, that one
thread is still in qemuProcessReconnect(), i.e. filling in
runtime information by talking to QEMU on monitor. If another
thread then tries to format domain XML (which is currently
guarded by plain mutex on virDomainObj) it'll produce incomplete
and misleading information (e.g. current size of virtio-mem).
This happens because the reconnecting thread talks to QEMU on
monitor and thus unlocks the domain object frequently allowing
the XML formatting thread to acquire the mutex meanwhile.

Resolves: https://issues.redhat.com/browse/RHEL-71042
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 09f7edda7dc63bcfa928dc9a947c4722022345fc..f1a633fdd3bcf25681516098caf51f2936c2fa3c 100644 (file)
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -6163,6 +6163,9 @@ static char
     if (virDomainGetXMLDescEnsureACL(dom->conn, vm->def, flags) < 0)
         goto cleanup;
 
+    if (virDomainObjBeginJob(vm, VIR_JOB_QUERY) < 0)
+        goto cleanup;
+
     qemuDomainUpdateCurrentMemorySize(vm);
 
     if ((flags & VIR_DOMAIN_XML_MIGRATABLE))
@@ -6177,6 +6180,8 @@ static char
 
     ret = qemuDomainFormatXML(driver, vm, flags);
 
+    virDomainObjEndJob(vm);
+
  cleanup:
     virDomainObjEndAPI(&vm);
     return ret;