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>

diff --git a/net/wireless/core.c b/net/wireless/core.c
index 20db902..d07f57c 100644 (file)
--- 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 2d6a6b9..c326a66 100644 (file)
--- 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 */