nodedev: fix race in API usage vs initial device enumeration

During startup the udev node device driver impl uses a background thread
to populate the list of devices to avoid blocking the daemon startup
entirely. There is no synchronization to the public APIs, so it is
possible for an application to start calling APIs before the device
initialization is complete.

This was not a problem in the old approach where libvirtd was started
on boot, as initialization would easily complete before any APIs were
called.

With the use of socket activation, however, APIs are invoked from the
very moment the daemon starts. This is easily seen by doing a

  'virsh -c nodedev:///system list'

the first time it runs it will only show one or two devices. The second
time it runs it will show all devices. The solution is to introduce a
flag and condition variable for APIs to synchronize against before
returning any data.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

src/conf/virnodedeviceobj.h

@@ -36,6 +36,8 @@ typedef struct _virNodeDeviceDriverState virNodeDeviceDriverState;
 typedef virNodeDeviceDriverState *virNodeDeviceDriverStatePtr;
 struct _virNodeDeviceDriverState {
     virMutex lock;
+    virCond initCond;
+    bool initialized;
 
     /* pid file FD, ensures two copies of the driver can't use the same root */
     int lockFD;

src/node_device/node_device_driver.c

@@ -156,6 +156,22 @@ nodeDeviceUnlock(void)
 }
 
 
+static int
+nodeDeviceWaitInit(void)
+{
+    nodeDeviceLock();
+    while (!driver->initialized) {
+        if (virCondWait(&driver->initCond, &driver->lock) < 0) {
+            virReportSystemError(errno, "%s",
+                                 _("failed to wait on condition"));
+            nodeDeviceUnlock();
+            return -1;
+        }
+    }
+    nodeDeviceUnlock();
+    return 0;
+}
+
 int
 nodeNumOfDevices(virConnectPtr conn,
                  const char *cap,
@@ -166,6 +182,9 @@ nodeNumOfDevices(virConnectPtr conn,
 
     virCheckFlags(0, -1);
 
+    if (nodeDeviceWaitInit() < 0)
+        return -1;
+
     return virNodeDeviceObjListNumOfDevices(driver->devs, conn, cap,
                                             virNodeNumOfDevicesCheckACL);
 }
@@ -183,6 +202,9 @@ nodeListDevices(virConnectPtr conn,
 
     virCheckFlags(0, -1);
 
+    if (nodeDeviceWaitInit() < 0)
+        return -1;
+
     return virNodeDeviceObjListGetNames(driver->devs, conn,
                                         virNodeListDevicesCheckACL,
                                         cap, names, maxnames);
@@ -199,6 +221,9 @@ nodeConnectListAllNodeDevices(virConnectPtr conn,
     if (virConnectListAllNodeDevicesEnsureACL(conn) < 0)
         return -1;
 
+    if (nodeDeviceWaitInit() < 0)
+        return -1;
+
     return virNodeDeviceObjListExport(conn, driver->devs, devices,
                                       virConnectListAllNodeDevicesCheckACL,
                                       flags);
@@ -228,6 +253,9 @@ nodeDeviceLookupByName(virConnectPtr conn,
     virNodeDeviceDefPtr def;
     virNodeDevicePtr device = NULL;
 
+    if (nodeDeviceWaitInit() < 0)
+        return NULL;
+
     if (!(obj = nodeDeviceObjFindByName(name)))
         return NULL;
     def = virNodeDeviceObjGetDef(obj);
@@ -256,6 +284,9 @@ nodeDeviceLookupSCSIHostByWWN(virConnectPtr conn,
 
     virCheckFlags(0, NULL);
 
+    if (nodeDeviceWaitInit() < 0)
+        return NULL;
+
     if (!(obj = virNodeDeviceObjListFindSCSIHostByWWNs(driver->devs,
                                                        wwnn, wwpn)))
         return NULL;
@@ -470,6 +501,10 @@ nodeDeviceCreateXML(virConnectPtr conn,
     const char *virt_type = NULL;
 
     virCheckFlags(0, NULL);
+
+    if (nodeDeviceWaitInit() < 0)
+        return NULL;
+
     virt_type  = virConnectGetType(conn);
 
     if (!(def = virNodeDeviceDefParseString(xmlDesc, CREATE_DEVICE, virt_type)))
@@ -512,6 +547,9 @@ nodeDeviceDestroy(virNodeDevicePtr device)
     g_autofree char *wwpn = NULL;
     unsigned int parent_host;
 
+    if (nodeDeviceWaitInit() < 0)
+        return -1;
+
     if (!(obj = nodeDeviceObjFindByName(device->name)))
         return -1;
     def = virNodeDeviceObjGetDef(obj);
@@ -564,6 +602,9 @@ nodeConnectNodeDeviceEventRegisterAny(virConnectPtr conn,
     if (virConnectNodeDeviceEventRegisterAnyEnsureACL(conn) < 0)
         return -1;
 
+    if (nodeDeviceWaitInit() < 0)
+        return -1;
+
     if (virNodeDeviceEventStateRegisterID(conn, driver->nodeDeviceEventState,
                                           device, eventID, callback,
                                           opaque, freecb, &callbackID) < 0)
@@ -580,6 +621,9 @@ nodeConnectNodeDeviceEventDeregisterAny(virConnectPtr conn,
     if (virConnectNodeDeviceEventDeregisterAnyEnsureACL(conn) < 0)
         return -1;
 
+    if (nodeDeviceWaitInit() < 0)
+        return -1;
+
     if (virObjectEventStateDeregisterID(conn,
                                         driver->nodeDeviceEventState,
                                         callbackID, true) < 0)

src/node_device/node_device_hal.c

@@ -611,6 +611,15 @@ nodeStateInitialize(bool privileged G_GNUC_UNUSED,
         VIR_FREE(driver);
         return VIR_DRV_STATE_INIT_ERROR;
     }
+
+    if (virCondInit(&driver->initCond) < 0) {
+        virReportSystemError(errno, "%s",
+                             _("Unable to initialize condition variable"));
+        virMutexDestroy(&driver->lock);
+        VIR_FREE(driver);
+        return VIR_DRV_STATE_INIT_ERROR;
+    }
+
     nodeDeviceLock();
 
     if (privileged) {
@@ -701,6 +710,11 @@ nodeStateInitialize(bool privileged G_GNUC_UNUSED,
     }
     VIR_FREE(udi);
 
+    nodeDeviceLock();
+    driver->initialized = true;
+    nodeDeviceUnlock();
+    virCondBroadcast(&driver->initCond);
+
     return VIR_DRV_STATE_INIT_COMPLETE;
 
  failure:
@@ -733,6 +747,7 @@ nodeStateCleanup(void)
 
         VIR_FREE(driver->stateDir);
         nodeDeviceUnlock();
+        virCondDestroy(&driver->initCond);
         virMutexDestroy(&driver->lock);
         VIR_FREE(driver);
         return 0;

src/node_device/node_device_udev.c

@@ -1477,6 +1477,7 @@ nodeStateCleanup(void)
         virPidFileRelease(driver->stateDir, "driver", driver->lockFD);
 
     VIR_FREE(driver->stateDir);
+    virCondDestroy(&driver->initCond);
     virMutexDestroy(&driver->lock);
     VIR_FREE(driver);
 
@@ -1744,6 +1745,11 @@ nodeStateInitializeEnumerate(void *opaque)
     if (udevEnumerateDevices(udev) != 0)
         goto error;
 
+    nodeDeviceLock();
+    driver->initialized = true;
+    nodeDeviceUnlock();
+    virCondBroadcast(&driver->initCond);
+
     return;
 
  error:
@@ -1806,6 +1812,13 @@ nodeStateInitialize(bool privileged,
         VIR_FREE(driver);
         return VIR_DRV_STATE_INIT_ERROR;
     }
+    if (virCondInit(&driver->initCond) < 0) {
+        virReportSystemError(errno, "%s",
+                             _("Unable to initialize condition variable"));
+        virMutexDestroy(&driver->lock);
+        VIR_FREE(driver);
+        return VIR_DRV_STATE_INIT_ERROR;
+    }
 
     driver->privileged = privileged;