mac80211: fix ibss race

When a scan completes, we call ieee80211_sta_find_ibss(),
which is also called from other places. When the scan was
done in software, there's no problem as both run from the
single-threaded mac80211 workqueue and are thus serialised
against each other, but with hardware scan the completion
can be in a different context and race against callers of
this function from the workqueue (e.g. due to beacon RX).
So instead of calling ieee80211_sta_find_ibss() directly,
just arm the timer and have it fire, scheduling the work,
which will invoke ieee80211_sta_find_ibss() (if that is
appropriate in the current state).
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/ibss.c

@@ -829,7 +829,7 @@ void ieee80211_ibss_notify_scan_completed(struct ieee80211_local *local)
 		if (!sdata->u.ibss.ssid_len)
 			continue;
 		sdata->u.ibss.last_scan_completed = jiffies;
-		ieee80211_sta_find_ibss(sdata);
+		mod_timer(&sdata->u.ibss.timer, 0);
 	}
 	mutex_unlock(&local->iflist_mtx);
 }