cfg80211: rcu-ify rdev and wdev

Future code will need to look up rdev and wdev
within atomic sections, but currently we need
to lock a mutex for such lookups. Change the
list handling for both to be RCU-safe so that
we can look them up in rcu sections instead in
the future.

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

2 files changed, 17 insertions, 12 deletions

diff --git a/net/wireless/core.c b/net/wireless/core.c
index 20db90246de5..d07f57c906db 100644
--- a/net/wireless/core.c
+++ b/net/wireless/core.c
@@ -1,7 +1,7 @@
 /*
  * This is the linux wireless configuration interface.
  *
- * Copyright 2006-2009          Johannes Berg <johannes@sipsolutions.net>
+ * Copyright 2006-2010          Johannes Berg <johannes@sipsolutions.net>
  */
 
 #include <linux/if.h>
@@ -31,15 +31,10 @@ MODULE_AUTHOR("Johannes Berg");
 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("wireless configuration support");
 
-/* RCU might be appropriate here since we usually
- * only read the list, and that can happen quite
- * often because we need to do it for each command */
+/* RCU-protected (and cfg80211_mutex for writers) */
 LIST_HEAD(cfg80211_rdev_list);
 int cfg80211_rdev_list_generation;
 
-/*
- * This is used to protect the cfg80211_rdev_list
- */
 DEFINE_MUTEX(cfg80211_mutex);
 
 /* for debugfs */
@@ -477,7 +472,7 @@ int wiphy_register(struct wiphy *wiphy)
         /* set up regulatory info */
         wiphy_update_regulatory(wiphy, NL80211_REGDOM_SET_BY_CORE);
 
-        list_add(&rdev->list, &cfg80211_rdev_list);
+        list_add_rcu(&rdev->list, &cfg80211_rdev_list);
         cfg80211_rdev_list_generation++;
 
         mutex_unlock(&cfg80211_mutex);
@@ -554,7 +549,8 @@ void wiphy_unregister(struct wiphy *wiphy)
          * it impossible to find from userspace.
          */
         debugfs_remove_recursive(rdev->wiphy.debugfsdir);
-        list_del(&rdev->list);
+        list_del_rcu(&rdev->list);
+        synchronize_rcu();
 
         /*
          * Try to grab rdev->mtx. If a command is still in progress,
@@ -670,7 +666,7 @@ static int cfg80211_netdev_notifier_call(struct notifier_block * nb,
                 INIT_LIST_HEAD(&wdev->event_list);
                 spin_lock_init(&wdev->event_lock);
                 mutex_lock(&rdev->devlist_mtx);
-                list_add(&wdev->list, &rdev->netdev_list);
+                list_add_rcu(&wdev->list, &rdev->netdev_list);
                 rdev->devlist_generation++;
                 /* can only change netns with wiphy */
                 dev->features |= NETIF_F_NETNS_LOCAL;
@@ -782,13 +778,21 @@ static int cfg80211_netdev_notifier_call(struct notifier_block * nb,
                  */
                 if (!list_empty(&wdev->list)) {
                         sysfs_remove_link(&dev->dev.kobj, "phy80211");
-                        list_del_init(&wdev->list);
+                        list_del_rcu(&wdev->list);
                         rdev->devlist_generation++;
 #ifdef CONFIG_CFG80211_WEXT
                         kfree(wdev->wext.keys);
 #endif
                 }
                 mutex_unlock(&rdev->devlist_mtx);
+                /*
+                 * synchronise (so that we won't find this netdev
+                 * from other code any more) and then clear the list
+                 * head so that the above code can safely check for
+                 * !list_empty() to avoid double-cleanup.
+                 */
+                synchronize_rcu();
+                INIT_LIST_HEAD(&wdev->list);
                 break;
         case NETDEV_PRE_UP:
                 if (!(wdev->wiphy->interface_modes & BIT(wdev->iftype)))
diff --git a/net/wireless/core.h b/net/wireless/core.h
index 2d6a6b9c0c43..c326a667022a 100644
--- a/net/wireless/core.h
+++ b/net/wireless/core.h
@@ -1,7 +1,7 @@
 /*
  * Wireless configuration interface internals.
  *
- * Copyright 2006-2009  Johannes Berg <johannes@sipsolutions.net>
+ * Copyright 2006-2010  Johannes Berg <johannes@sipsolutions.net>
  */
 #ifndef __NET_WIRELESS_CORE_H
 #define __NET_WIRELESS_CORE_H
@@ -48,6 +48,7 @@ struct cfg80211_registered_device {
 
         /* associate netdev list */
         struct mutex devlist_mtx;
+        /* protected by devlist_mtx or RCU */
         struct list_head netdev_list;
         int devlist_generation;
         int opencount; /* also protected by devlist_mtx */