[WIRELESS] cfg80211: Clarify locking comment.
This patch clarifies the comment about locking in wiphy_unregister.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/wireless/core.c b/net/wireless/core.c
index 24a21add..7eabd55 100644
--- a/net/wireless/core.c
+++ b/net/wireless/core.c
@@ -91,7 +91,6 @@
mutex_lock(&cfg80211_drv_mutex);
-
res = device_add(&drv->wiphy.dev);
if (res)
goto out_unlock;
@@ -114,14 +113,26 @@
{
struct cfg80211_registered_device *drv = wiphy_to_dev(wiphy);
+ /* protect the device list */
mutex_lock(&cfg80211_drv_mutex);
- /* hold registered driver mutex during list removal as well
- * to make sure no commands are in progress at the moment */
+ BUG_ON(!list_empty(&drv->netdev_list));
+
+ /*
+ * Try to grab drv->mtx. If a command is still in progress,
+ * hopefully the driver will refuse it since it's tearing
+ * down the device already. We wait for this command to complete
+ * before unlinking the item from the list.
+ * Note: as codified by the BUG_ON above we cannot get here if
+ * a virtual interface is still associated. Hence, we can only
+ * get to lock contention here if userspace issues a command
+ * that identified the hardware by wiphy index.
+ */
mutex_lock(&drv->mtx);
- list_del(&drv->list);
+ /* unlock again before freeing */
mutex_unlock(&drv->mtx);
+ list_del(&drv->list);
device_del(&drv->wiphy.dev);
debugfs_remove(drv->wiphy.debugfsdir);