mac80211: fix debugfs lockup

When debugfs_create_dir fails, sta_info_debugfs_add_work will not
terminate because it will find the same station again and again.
This is possible whenever debugfs fails for whatever reason; one
reason is a race condition in mac80211, unfortunately we cannot
do much about it, so just document it, it just means some station
may be missing from debugfs.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Cc: Robin Holt <holt@sgi.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/net/mac80211/debugfs_sta.c b/net/mac80211/debugfs_sta.c
index b9902e425f09..189d0bafa91a 100644
--- a/net/mac80211/debugfs_sta.c
+++ b/net/mac80211/debugfs_sta.c
@@ -249,11 +249,22 @@ void ieee80211_sta_debugfs_add(struct sta_info *sta)
 	DECLARE_MAC_BUF(mbuf);
 	u8 *mac;
 
+	sta->debugfs.add_has_run = true;
+
 	if (!stations_dir)
 		return;
 
 	mac = print_mac(mbuf, sta->sta.addr);
 
+	/*
+	 * This might fail due to a race condition:
+	 * When mac80211 unlinks a station, the debugfs entries
+	 * remain, but it is already possible to link a new
+	 * station with the same address which triggers adding
+	 * it to debugfs; therefore, if the old station isn't
+	 * destroyed quickly enough the old station's debugfs
+	 * dir might still be around.
+	 */
 	sta->debugfs.dir = debugfs_create_dir(mac, stations_dir);
 	if (!sta->debugfs.dir)
 		return;