mac80211: fix some key comments and code

The key documentation is slightly out of date, fix
that. Also, the list entry in the key struct is no
longer used that way, so list_del_init() isn't
necessary any more there.

Finally, ieee80211_key_link() is no longer invoked
under RCU read lock, but rather with an appropriate
station lock held.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/key.c

@@ -30,19 +30,20 @@
  * keys and per-station keys. Since each station belongs to an interface,
  * each station key also belongs to that interface.
  *
- * Hardware acceleration is done on a best-effort basis, for each key
- * that is eligible the hardware is asked to enable that key but if
- * it cannot do that they key is simply kept for software encryption.
- * There is currently no way of knowing this except by looking into
- * debugfs.
+ * Hardware acceleration is done on a best-effort basis for algorithms
+ * that are implemented in software,  for each key the hardware is asked
+ * to enable that key for offloading but if it cannot do that the key is
+ * simply kept for software encryption (unless it is for an algorithm
+ * that isn't implemented in software).
+ * There is currently no way of knowing whether a key is handled in SW
+ * or HW except by looking into debugfs.
  *
- * All key operations are protected internally.
- *
- * Within mac80211, key references are, just as STA structure references,
- * protected by RCU. Note, however, that some things are unprotected,
- * namely the key->sta dereferences within the hardware acceleration
- * functions. This means that sta_info_destroy() must remove the key
- * which waits for an RCU grace period.
+ * All key management is internally protected by a mutex. Within all
+ * other parts of mac80211, key references are, just as STA structure
+ * references, protected by RCU. Note, however, that some things are
+ * unprotected, namely the key->sta dereferences within the hardware
+ * acceleration functions. This means that sta_info_destroy() must
+ * remove the key which waits for an RCU grace period.
  */
 
 static const u8 bcast_addr[ETH_ALEN] = { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF };
@@ -279,13 +280,8 @@ static void __ieee80211_key_replace(struct ieee80211_sub_if_data *sdata,
 							 new->conf.keyidx);
 	}
 
-	if (old) {
-		/*
-		 * We'll use an empty list to indicate that the key
-		 * has already been removed.
-		 */
-		list_del_init(&old->list);
-	}
+	if (old)
+		list_del(&old->list);
 }
 
 struct ieee80211_key *ieee80211_key_alloc(u32 cipher, int idx, size_t key_len,
@@ -420,8 +416,8 @@ int ieee80211_key_link(struct ieee80211_key *key,
 			struct sta_info *ap;
 
 			/*
-			 * We're getting a sta pointer in,
-			 * so must be under RCU read lock.
+			 * We're getting a sta pointer in, so must be under
+			 * appropriate locking for sta_info_get().
 			 */
 
 			/* same here, the AP could be using QoS */