[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>

1 files changed, 15 insertions, 4 deletions

diff --git a/net/wireless/core.c b/net/wireless/core.c
index 24a21add0ba6..7eabd55417a5 100644
--- a/net/wireless/core.c
+++ b/net/wireless/core.c
@@ -91,7 +91,6 @@ int wiphy_register(struct wiphy *wiphy)
 
         mutex_lock(&cfg80211_drv_mutex);
 
-
         res = device_add(&drv->wiphy.dev);
         if (res)
                 goto out_unlock;
@@ -114,14 +113,26 @@ void wiphy_unregister(struct wiphy *wiphy)
 {
         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);