[libvirt] [PATCH] qemu: check for vm after starting a job

[Eric Blake]

https://bugzilla.redhat.com/show_bug.cgi?id=638285 - when migrating
a guest, it was very easy to provoke a race where an application
could query block information on a VM that had just been migrated
away.  Any time qemu code obtains a job lock, it must also check
that the VM was not taken down in the time where it was waiting
for the lock.

* src/qemu/qemu_driver.c (qemudDomainSetMemory)
(qemudDomainGetInfo, qemuDomainGetBlockInfo): Check that vm still
exists after obtaining job lock, before starting monitor action.
---
 src/qemu/qemu_driver.c |   25 ++++++++++++++++++++++---
 1 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index ae1d833..af5126d 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -463,7 +463,8 @@ static int ATTRIBUTE_RETURN_CHECK qemuDomainObjEndJob(virDomainObjPtr obj)
  * obj must be locked before calling, qemud_driver must be unlocked
  *
  * To be called immediately before any QEMU monitor API call
- * Must have alrady called qemuDomainObjBeginJob().
+ * Must have already called qemuDomainObjBeginJob(), and checked
+ * that the VM is still active.
  *
  * To be followed with qemuDomainObjExitMonitor() once complete
  */
@@ -504,7 +505,7 @@ static void qemuDomainObjExitMonitor(virDomainObjPtr obj)
  * obj must be locked before calling, qemud_driver must be locked
  *
  * To be called immediately before any QEMU monitor API call
- * Must have alrady called qemuDomainObjBeginJob().
+ * Must have already called qemuDomainObjBeginJob().
  *
  * To be followed with qemuDomainObjExitMonitorWithDriver() once complete
  */
@@ -522,7 +523,7 @@ static void qemuDomainObjEnterMonitorWithDriver(struct qemud_driver *driver, vir
 /* obj must NOT be locked before calling, qemud_driver must be unlocked,
  * and will be locked after returning
  *
- * Should be paired with an earlier  qemuDomainObjEnterMonitor() call
+ * Should be paired with an earlier  qemuDomainObjEnterMonitorWithDriver() call
  */
 static void qemuDomainObjExitMonitorWithDriver(struct qemud_driver *driver, virDomainObjPtr obj)
 {
@@ -4948,6 +4949,12 @@ static int qemudDomainSetMemory(virDomainPtr dom, unsigned long newmem) {
     if (qemuDomainObjBeginJob(vm) < 0)
         goto cleanup;

+    if (!virDomainObjIsActive(vm)) {
+        qemuReportError(VIR_ERR_OPERATION_INVALID,
+                        "%s", _("domain is not running"));
+        goto endjob;
+    }
+
     priv = vm->privateData;
     qemuDomainObjEnterMonitor(vm);
     r = qemuMonitorSetBalloon(priv->mon, newmem);
@@ -5014,11 +5021,17 @@ static int qemudDomainGetInfo(virDomainPtr dom,
         } else if (!priv->jobActive) {
             if (qemuDomainObjBeginJob(vm) < 0)
                 goto cleanup;
+            if (!virDomainObjIsActive(vm)) {
+                qemuReportError(VIR_ERR_OPERATION_INVALID,
+                                "%s", _("domain is not running"));
+                goto endjob;
+            }

             qemuDomainObjEnterMonitor(vm);
             err = qemuMonitorGetBalloonInfo(priv->mon, &balloon);
             qemuDomainObjExitMonitor(vm);
             if (err < 0) {
+            endjob:
                 if (qemuDomainObjEndJob(vm) == 0)
                     vm = NULL;
                 goto cleanup;
@@ -10343,6 +10356,11 @@ static int qemuDomainGetBlockInfo(virDomainPtr dom,
         qemuDomainObjPrivatePtr priv = vm->privateData;
         if (qemuDomainObjBeginJob(vm) < 0)
             goto cleanup;
+        if (!virDomainObjIsActive(vm)) {
+            qemuReportError(VIR_ERR_OPERATION_INVALID,
+                            "%s", _("domain is not running"));
+            goto endjob;
+        }

         qemuDomainObjEnterMonitor(vm);
         ret = qemuMonitorGetBlockExtent(priv->mon,
@@ -10350,6 +10368,7 @@ static int qemuDomainGetBlockInfo(virDomainPtr dom,
                                         &info->allocation);
         qemuDomainObjExitMonitor(vm);

+    endjob:
         if (qemuDomainObjEndJob(vm) == 0)
             vm = NULL;
     } else {
-- 
1.7.2.3