[PATCH] cfg80211: rcu-ify rdev and wdev

Johannes Berg
2010-01-17T14:49:10Z

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>
---
net/wireless/core.c | 26 +++++++++++++++-----------
net/wireless/core.h | 3 ++-
2 files changed, 17 insertions(+), 12 deletions(-)

--- wireless-testing.orig/net/wireless/core.c 2010-01-17 01:58:02.000000000 +0100
+++ wireless-testing/net/wireless/core.c 2010-01-17 02:13:45.000000000 +0100
@@ -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 *wiph
* 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
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
*/
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)))
--- wireless-testing.orig/net/wireless/core.h 2010-01-17 01:58:02.000000000 +0100
+++ wireless-testing/net/wireless/core.h 2010-01-17 02:13:49.000000000 +0100
@@ -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 */