[PATCH] mac80211: Add RTNL warning for workqueue

[Ivo van Doorn <ivdoorn@gmail.com>]

The workqueue provided by mac80211 should not be used for
scheduled tasks that acquire the RTNL lock. This could be done
when the driver uses the function ieee80211_iterate_active_interfaces()
within the scheduled work. Such behavior will end in locking
dependencies problems when an interface is being removed.

This patch will add a notification about the RTNL locking and
the mac80211 workqueue to prevent driver developers from
blindly using it.

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
---
diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index 19f1e41..02c79e6 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -738,8 +738,11 @@ enum ieee80211_hw_flags {
  * @conf: &struct ieee80211_conf, device configuration, don't use.
  *
  * @workqueue: single threaded workqueue available for driver use,
- *	allocated by mac80211 on registration and flushed on
- *	unregistration.
+ *	allocated by mac80211 on registration and flushed when an
+ *	interface is removed.
+ *	NOTICE: All work performed on this workqueue should NEVER
+ *	acquire the RTNL lock (i.e. Don't use the function
+ *	ieee80211_iterate_active_interfaces())
  *
  * @priv: pointer to private area that was allocated for driver use
  *	along with this structure.