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@xxxxxxxxxxxxxxxx>
---
Need this for the scan stuff I'm doing next, but this has the side
effect of allowing you to call ieee80211_iterate_active_interfaces()
from mac80211's workqueue, which might be interesting. Ivo, that's
the reason you got a copy of this.
net/mac80211/ieee80211_i.h | 2 ++
net/mac80211/iface.c | 31 +++++++++++++++++++++++++++++++
net/mac80211/main.c | 3 +++
net/mac80211/util.c | 4 ++--
4 files changed, 38 insertions(+), 2 deletions(-)
--- wireless-testing.orig/net/mac80211/ieee80211_i.h 2009-01-21 12:48:12.000000000 +0100
+++ wireless-testing/net/mac80211/ieee80211_i.h 2009-01-21 13:57:49.000000000 +0100
@@ -643,7 +643,9 @@ struct ieee80211_local {
struct crypto_blkcipher *wep_rx_tfm;
u32 wep_iv;
+ /* see iface.c */
struct list_head interfaces;
+ struct mutex iflist_mtx;
/*
* Key lock, protects sdata's key_list and sta_info's
--- wireless-testing.orig/net/mac80211/iface.c 2009-01-21 12:48:12.000000000 +0100
+++ wireless-testing/net/mac80211/iface.c 2009-01-21 13:57:49.000000000 +0100
@@ -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 @@ int ieee80211_if_add(struct ieee80211_lo
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 @@ void ieee80211_if_remove(struct ieee8021
{
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 @@ void ieee80211_remove_interfaces(struct
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);
}
}
--- wireless-testing.orig/net/mac80211/main.c 2009-01-21 12:48:21.000000000 +0100
+++ wireless-testing/net/mac80211/main.c 2009-01-21 13:57:50.000000000 +0100
@@ -718,6 +718,7 @@ struct ieee80211_hw *ieee80211_alloc_hw(
local->hw.conf.radio_enabled = true;
INIT_LIST_HEAD(&local->interfaces);
+ mutex_init(&local->iflist_mtx);
spin_lock_init(&local->key_lock);
@@ -968,6 +969,8 @@ void ieee80211_free_hw(struct ieee80211_
{
struct ieee80211_local *local = hw_to_local(hw);
+ mutex_destroy(&local->iflist_mtx);
+
wiphy_free(local->hw.wiphy);
}
EXPORT_SYMBOL(ieee80211_free_hw);
--- wireless-testing.orig/net/mac80211/util.c 2009-01-21 12:48:12.000000000 +0100
+++ wireless-testing/net/mac80211/util.c 2009-01-21 12:48:21.000000000 +0100
@@ -459,7 +459,7 @@ void ieee80211_iterate_active_interfaces
struct ieee80211_local *local = hw_to_local(hw);
struct ieee80211_sub_if_data *sdata;
- rtnl_lock();
+ mutex_lock(&local->iflist_mtx);
list_for_each_entry(sdata, &local->interfaces, list) {
switch (sdata->vif.type) {
@@ -480,7 +480,7 @@ void ieee80211_iterate_active_interfaces
&sdata->vif);
}
- rtnl_unlock();
+ mutex_unlock(&local->iflist_mtx);
}
EXPORT_SYMBOL_GPL(ieee80211_iterate_active_interfaces);
--
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