[PATCH 3.11 122/208] mac80211: fix scheduled scan rtnl deadlock

[Luis Henriques]

3.11.10.2 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Johannes Berg <johannes.berg at intel.com>

commit 18db594a1005d908d995a2fc8f5a7bf4286fdca0 upstream.

When changing cfg80211 to use RTNL locking, this caused a
deadlock in mac80211 as it calls cfg80211_sched_scan_stopped()
from a work item that's on a workqueue that is flushed with
the RTNL held.

Fix this by simply using schedule_work(), the work only needs
to finish running before the wiphy is unregistered, no other
synchronisation (e.g. with suspend) is really required since
for suspend userspace is already blocked anyway when we flush
the workqueue so will only pick up the event after resume.

Fixes: 5fe231e87372 ("cfg80211: vastly simplify locking")
Reported-and-tested-by: Eliad Peller <eliadx.peller at intel.com>
Signed-off-by: Johannes Berg <johannes.berg at intel.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/mac80211/main.c | 1 +
 net/mac80211/scan.c | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/mac80211/main.c b/net/mac80211/main.c
index 091088a..ec53369 100644
--- a/net/mac80211/main.c
+++ b/net/mac80211/main.c
@@ -1059,6 +1059,7 @@ void ieee80211_unregister_hw(struct ieee80211_hw *hw)
 
 	cancel_work_sync(&local->restart_work);
 	cancel_work_sync(&local->reconfig_filter);
+	flush_work(&local->sched_scan_stopped_work);
 
 	ieee80211_clear_tx_pending(local);
 	rate_control_deinitialize(local);
diff --git a/net/mac80211/scan.c b/net/mac80211/scan.c
index 7aafa54..89fb87b 100644
--- a/net/mac80211/scan.c
+++ b/net/mac80211/scan.c
@@ -1033,6 +1033,6 @@ void ieee80211_sched_scan_stopped(struct ieee80211_hw *hw)
 
 	trace_api_sched_scan_stopped(local);
 
-	ieee80211_queue_work(&local->hw, &local->sched_scan_stopped_work);
+	schedule_work(&local->sched_scan_stopped_work);
 }
 EXPORT_SYMBOL(ieee80211_sched_scan_stopped);
-- 
1.8.3.2