[libvirt] [PATCH 2/5] Fix race condition in HAL driver startup

[Daniel P. Berrange]

There is a race condition in HAL driver startup where the callback
can get triggered before we have finished startup. This then causes
a deadlock in the driver.

* src/node_device/node_device_hal.c: RElease driver lock before
  registering DBus callbacks
---
 src/node_device/node_device_hal.c |   14 ++++++++++----
 1 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/src/node_device/node_device_hal.c b/src/node_device/node_device_hal.c
index 818c7d6..918a3a9 100644
--- a/src/node_device/node_device_hal.c
+++ b/src/node_device/node_device_hal.c
@@ -742,6 +742,16 @@ static int halDeviceMonitorStartup(int privileged ATTRIBUTE_UNUSED)
         goto failure;
     }
 
+    /* Populate with known devices */
+    driverState->privateData = hal_ctx;
+
+    /* We need to unlock state now, since setting these callbacks cause
+     * a dbus RPC call, and while this call is waiting for the reply,
+     * a signal may already arrive, triggering the callback and thus
+     * requiring the lock !
+     */
+    nodeDeviceUnlock(driverState);
+
     /* Register HAL event callbacks */
     if (!libhal_ctx_set_device_added(hal_ctx, device_added) ||
         !libhal_ctx_set_device_removed(hal_ctx, device_removed) ||
@@ -753,10 +763,6 @@ static int halDeviceMonitorStartup(int privileged ATTRIBUTE_UNUSED)
         goto failure;
     }
 
-    /* Populate with known devices */
-    driverState->privateData = hal_ctx;
-
-    nodeDeviceUnlock(driverState);
     udi = libhal_get_all_devices(hal_ctx, &num_devs, &err);
     if (udi == NULL) {
         VIR_ERROR0("libhal_get_all_devices failed\n");
-- 
1.6.2.5