qemu: use systemd's TerminateMachine to kill all processes

If we don't properly clean up all processes in the
machine-<vmname>.scope systemd won't remove the cgroup and subsequent vm
starts fail with

  'CreateMachine: File exists'

Additional processes can e.g. be added via

  echo $PID > /sys/fs/cgroup/systemd/machine.slice/machine-${VMNAME}.scope/tasks

but there are other cases like

  http://bugs.debian.org/761521

Invoke TerminateMachine to be on the safe side since systemd tracks the
cgroup anyway. This is a noop if all processes have terminated already.

src/libvirt_private.syms

@@ -1118,6 +1118,7 @@ virCgroupSetMemorySoftLimit;
 virCgroupSetMemSwapHardLimit;
 virCgroupSetOwner;
 virCgroupSupportsCpuBW;
+virCgroupTerminateMachine;
 
 
 # util/virclosecallbacks.h

src/qemu/qemu_cgroup.c

@@ -1206,13 +1206,22 @@ qemuSetupCgroupForIOThreads(virDomainObjPtr vm)
 }
 
 int
-qemuRemoveCgroup(virDomainObjPtr vm)
+qemuRemoveCgroup(virQEMUDriverPtr driver,
+                 virDomainObjPtr vm)
 {
     qemuDomainObjPrivatePtr priv = vm->privateData;
+    virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
 
     if (priv->cgroup == NULL)
         return 0; /* Not supported, so claim success */
 
+    if (virCgroupTerminateMachine(vm->def->name,
+                                  "qemu",
+                                  cfg->privileged) < 0) {
+        if (!virCgroupNewIgnoreError())
+            VIR_DEBUG("Failed to terminate cgroup for %s", vm->def->name);
+    }
+
     return virCgroupRemove(priv->cgroup);
 }
 

src/qemu/qemu_cgroup.h

@@ -66,7 +66,7 @@ int qemuSetupCgroupForIOThreads(virDomainObjPtr vm);
 int qemuSetupCgroupForEmulator(virQEMUDriverPtr driver,
                                virDomainObjPtr vm,
                                virBitmapPtr nodemask);
-int qemuRemoveCgroup(virDomainObjPtr vm);
+int qemuRemoveCgroup(virQEMUDriverPtr driver, virDomainObjPtr vm);
 int qemuAddToCgroup(virDomainObjPtr vm);
 
 #endif /* __QEMU_CGROUP_H__ */

src/qemu/qemu_process.c

@@ -4143,7 +4143,7 @@ int qemuProcessStart(virConnectPtr conn,
     /* Ensure no historical cgroup for this VM is lying around bogus
      * settings */
     VIR_DEBUG("Ensuring no historical cgroup is lying around");
-    qemuRemoveCgroup(vm);
+    qemuRemoveCgroup(driver, vm);
 
     for (i = 0; i < vm->def->ngraphics; ++i) {
         virDomainGraphicsDefPtr graphics = vm->def->graphics[i];
@@ -4921,7 +4921,7 @@ void qemuProcessStop(virQEMUDriverPtr driver,
     }
 
  retry:
-    if ((ret = qemuRemoveCgroup(vm)) < 0) {
+    if ((ret = qemuRemoveCgroup(driver, vm)) < 0) {
         if (ret == -EBUSY && (retries++ < 5)) {
             usleep(200*1000);
             goto retry;

src/util/vircgroup.c

@@ -1680,6 +1680,17 @@ virCgroupNewMachineSystemd(const char *name,
 }
 
 
+/*
+ * Returns 0 on success, -1 on fatal error
+ */
+int virCgroupTerminateMachine(const char *name,
+                              const char *drivername,
+                              bool privileged)
+{
+    return virSystemdTerminateMachine(name, drivername, privileged);
+}
+
+
 static int
 virCgroupNewMachineManual(const char *name,
                           const char *drivername,

src/util/vircgroup.h

@@ -106,6 +106,11 @@ int virCgroupNewMachine(const char *name,
     ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2)
     ATTRIBUTE_NONNULL(4);
 
+int virCgroupTerminateMachine(const char *name,
+                              const char *drivername,
+                              bool privileged)
+    ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2);
+
 bool virCgroupNewIgnoreError(void);
 
 void virCgroupFree(virCgroupPtr *group);