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>

1 files changed, 2 insertions, 0 deletions

diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index 927cbde8c19c..eaf3603862b7 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -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