cfg80211: fix BSS double-unlinking (continued)

This patch adds to the fix "fix BSS double-unlinking"
(commit 3207390a) by Johannes Berg.

It turns out, that the double-unlinking scenario can also occur if expired
BSS elements are removed whilst an interface is performing association.

To work around that, replace list_del with list_del_init also in the
"cfg80211_bss_expire" function, so that the check for whether the BSS still is
in the list works correctly in cfg80211_unlink_bss.
Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/wireless/scan.c

@@ -123,6 +123,15 @@ void cfg80211_bss_age(struct cfg80211_registered_device *dev,
 	}
 }
 
+/* must hold dev->bss_lock! */
+static void __cfg80211_unlink_bss(struct cfg80211_registered_device *dev,
+				  struct cfg80211_internal_bss *bss)
+{
+	list_del_init(&bss->list);
+	rb_erase(&bss->rbn, &dev->bss_tree);
+	kref_put(&bss->ref, bss_release);
+}
+
 /* must hold dev->bss_lock! */
 void cfg80211_bss_expire(struct cfg80211_registered_device *dev)
 {
@@ -134,9 +143,7 @@ void cfg80211_bss_expire(struct cfg80211_registered_device *dev)
 			continue;
 		if (!time_after(jiffies, bss->ts + IEEE80211_SCAN_RESULT_EXPIRE))
 			continue;
-		list_del(&bss->list);
-		rb_erase(&bss->rbn, &dev->bss_tree);
-		kref_put(&bss->ref, bss_release);
+		__cfg80211_unlink_bss(dev, bss);
 		expired = true;
 	}
 
@@ -669,11 +676,8 @@ void cfg80211_unlink_bss(struct wiphy *wiphy, struct cfg80211_bss *pub)
 
 	spin_lock_bh(&dev->bss_lock);
 	if (!list_empty(&bss->list)) {
-		list_del_init(&bss->list);
+		__cfg80211_unlink_bss(dev, bss);
 		dev->bss_generation++;
-		rb_erase(&bss->rbn, &dev->bss_tree);
-
-		kref_put(&bss->ref, bss_release);
 	}
 	spin_unlock_bh(&dev->bss_lock);
 }