mac80211: add interface list lock
Using only the RTNL has a number of problems, most notably that
ieee80211_iterate_active_interfaces() and other interface list
traversals cannot be done from the internal workqueue because it
needs to be flushed under the RTNL.
This patch introduces a new mutex that protects the interface list
against modifications. A more detailed explanation is part of the
code change.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/iface.c b/net/mac80211/iface.c
index 8dc2c21..00562a8 100644
--- a/net/mac80211/iface.c
+++ b/net/mac80211/iface.c
@@ -21,6 +21,23 @@
#include "mesh.h"
#include "led.h"
+/**
+ * DOC: Interface list locking
+ *
+ * The interface list in each struct ieee80211_local is protected
+ * three-fold:
+ *
+ * (1) modifications may only be done under the RTNL
+ * (2) modifications and readers are protected against each other by
+ * the iflist_mtx.
+ * (3) modifications are done in an RCU manner so atomic readers
+ * can traverse the list in RCU-safe blocks.
+ *
+ * As a consequence, reads (traversals) of the list can be protected
+ * by either the RTNL, the iflist_mtx or RCU.
+ */
+
+
static int ieee80211_change_mtu(struct net_device *dev, int new_mtu)
{
int meshhdrlen;
@@ -800,7 +817,9 @@
params->mesh_id_len,
params->mesh_id);
+ mutex_lock(&local->iflist_mtx);
list_add_tail_rcu(&sdata->list, &local->interfaces);
+ mutex_unlock(&local->iflist_mtx);
if (new_dev)
*new_dev = ndev;
@@ -816,7 +835,10 @@
{
ASSERT_RTNL();
+ mutex_lock(&sdata->local->iflist_mtx);
list_del_rcu(&sdata->list);
+ mutex_unlock(&sdata->local->iflist_mtx);
+
synchronize_rcu();
unregister_netdevice(sdata->dev);
}
@@ -832,7 +854,16 @@
ASSERT_RTNL();
list_for_each_entry_safe(sdata, tmp, &local->interfaces, list) {
+ /*
+ * we cannot hold the iflist_mtx across unregister_netdevice,
+ * but we only need to hold it for list modifications to lock
+ * out readers since we're under the RTNL here as all other
+ * writers.
+ */
+ mutex_lock(&local->iflist_mtx);
list_del(&sdata->list);
+ mutex_unlock(&local->iflist_mtx);
+
unregister_netdevice(sdata->dev);
}
}