[libvirt] [PATCH 2/2] qemu: Avoid deadlock in autodestroy

[Jiri Denemark]

Since closeCallbacks were turned into virObjectLockable, we can no
longer call virQEMUCloseCallbacks APIs from within a registered close
callback.
---
 src/qemu/qemu_conf.c    | 19 ++++---------------
 src/qemu/qemu_conf.h    |  4 ++++
 src/qemu/qemu_domain.h  |  1 +
 src/qemu/qemu_process.c | 10 +++++++++-
 4 files changed, 18 insertions(+), 16 deletions(-)

diff --git a/src/qemu/qemu_conf.c b/src/qemu/qemu_conf.c
index edadf36..fc8e152 100644
--- a/src/qemu/qemu_conf.c
+++ b/src/qemu/qemu_conf.c
@@ -825,8 +825,6 @@ virQEMUCloseCallbacksRunOne(void *payload,
 {
     struct virQEMUCloseCallbacksData *data = opaque;
     qemuDriverCloseDefPtr closeDef = payload;
-    unsigned char uuid[VIR_UUID_BUFLEN];
-    char uuidstr[VIR_UUID_STRING_BUFLEN];
     virDomainObjPtr dom;
 
     VIR_DEBUG("conn=%p, thisconn=%p, uuid=%s, cb=%p",
@@ -835,18 +833,9 @@ virQEMUCloseCallbacksRunOne(void *payload,
     if (data->conn != closeDef->conn || !closeDef->cb)
         return;
 
-    if (virUUIDParse(name, uuid) < 0) {
-        VIR_WARN("Failed to parse %s", (const char *)name);
-        return;
-    }
-    /* We need to reformat uuidstr, because closeDef->cb
-     * might cause the current hash entry to be removed,
-     * which means 'name' will have been free()d
-     */
-    virUUIDFormat(uuid, uuidstr);
-
-    if (!(dom = virDomainObjListFindByUUID(data->driver->domains, uuid))) {
-        VIR_DEBUG("No domain object with UUID %s", uuidstr);
+    if (!(dom = virDomainObjListFindByUUID(data->driver->domains, name))) {
+        VIR_DEBUG("No domain object with UUID %s",
+                  (const char *) name);
         return;
     }
 
@@ -854,7 +843,7 @@ virQEMUCloseCallbacksRunOne(void *payload,
     if (dom)
         virObjectUnlock(dom);
 
-    virHashRemoveEntry(data->list, uuidstr);
+    virHashRemoveEntry(data->list, name);
 }
 
 void
diff --git a/src/qemu/qemu_conf.h b/src/qemu/qemu_conf.h
index 72380dc..b5a3281 100644
--- a/src/qemu/qemu_conf.h
+++ b/src/qemu/qemu_conf.h
@@ -254,6 +254,10 @@ struct qemuDomainDiskInfo {
     int io_status;
 };
 
+/*
+ * To avoid a certain deadlock this callback must never call any
+ * virQEMUCloseCallbacks* API.
+ */
 typedef virDomainObjPtr (*virQEMUCloseCallback)(virQEMUDriverPtr driver,
                                                 virDomainObjPtr vm,
                                                 virConnectPtr conn);
diff --git a/src/qemu/qemu_domain.h b/src/qemu/qemu_domain.h
index 905b099..c9d5f8b 100644
--- a/src/qemu/qemu_domain.h
+++ b/src/qemu/qemu_domain.h
@@ -137,6 +137,7 @@ struct _qemuDomainObjPrivate {
 
     bool gotShutdown;
     bool beingDestroyed;
+    bool autoDestroyed;
     char *pidfile;
 
     int nvcpupids;
diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index f987618..74406a6 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -4263,7 +4263,8 @@ void qemuProcessStop(virQEMUDriverPtr driver,
     qemuDomainCleanupRun(driver, vm);
 
     /* Stop autodestroy in case guest is restarted */
-    qemuProcessAutoDestroyRemove(driver, vm);
+    if (!priv->autoDestroyed)
+        qemuProcessAutoDestroyRemove(driver, vm);
 
     /* now that we know it's stopped call the hook if present */
     if (virHookPresent(VIR_HOOK_DRIVER_QEMU)) {
@@ -4647,8 +4648,15 @@ qemuProcessAutoDestroy(virQEMUDriverPtr driver,
         goto cleanup;
 
     VIR_DEBUG("Killing domain");
+
+    /* We need to prevent qemuProcessStop from removing this function from
+     * closeCallbacks since that would cause a deadlock.
+     */
+    priv->autoDestroyed = true;
     qemuProcessStop(driver, dom, VIR_DOMAIN_SHUTOFF_DESTROYED,
                     VIR_QEMU_PROCESS_STOP_MIGRATED);
+    priv->autoDestroyed = false;
+
     virDomainAuditStop(dom, "destroyed");
     event = virDomainEventNewFromObj(dom,
                                      VIR_DOMAIN_EVENT_STOPPED,
-- 
1.8.1.2