cfg80211: fix deadlock with rfkill/sched_scan by adding new mutex

There was a deadlock when rfkill-blocking a wireless interface,
because we were locking the rdev mutex on NETDEV_GOING_DOWN to stop
sched_scans that were eventually running.  The rfkill block code was
already holding a mutex under rdev:

kernel: =======================================================
kernel: [ INFO: possible circular locking dependency detected ]
kernel: 3.0.0-rc1-00049-g1fa7b6a #57
kernel: -------------------------------------------------------
kernel: kworker/0:1/4525 is trying to acquire lock:
kernel: (&rdev->mtx){+.+.+.}, at: [<ffffffff8164c831>] cfg80211_netdev_notifier_call+0x131/0x5b0
kernel:
kernel: but task is already holding lock:
kernel: (&rdev->devlist_mtx){+.+.+.}, at: [<ffffffff8164dcef>] cfg80211_rfkill_set_block+0x4f/0xa0
kernel:
kernel: which lock already depends on the new lock.

To fix this, add a new mutex specifically for sched_scan, to protect
the sched_scan_req element in the rdev struct, instead of using the
global rdev mutex.

Reported-by: Duane Griffin <duaneg@dghda.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 5 insertions, 5 deletions

diff --git a/net/wireless/scan.c b/net/wireless/scan.c
index 7a6c67667d70..ae0c2256ba3b 100644
--- a/net/wireless/scan.c
+++ b/net/wireless/scan.c
@@ -100,14 +100,14 @@ void __cfg80211_sched_scan_results(struct work_struct *wk)
         rdev = container_of(wk, struct cfg80211_registered_device,
                             sched_scan_results_wk);
 
-        cfg80211_lock_rdev(rdev);
+        mutex_lock(&rdev->sched_scan_mtx);
 
         /* we don't have sched_scan_req anymore if the scan is stopping */
         if (rdev->sched_scan_req)
                 nl80211_send_sched_scan_results(rdev,
                                                 rdev->sched_scan_req->dev);
 
-        cfg80211_unlock_rdev(rdev);
+        mutex_unlock(&rdev->sched_scan_mtx);
 }
 
 void cfg80211_sched_scan_results(struct wiphy *wiphy)
@@ -123,9 +123,9 @@ void cfg80211_sched_scan_stopped(struct wiphy *wiphy)
 {
         struct cfg80211_registered_device *rdev = wiphy_to_dev(wiphy);
 
-        cfg80211_lock_rdev(rdev);
+        mutex_lock(&rdev->sched_scan_mtx);
         __cfg80211_stop_sched_scan(rdev, true);
-        cfg80211_unlock_rdev(rdev);
+        mutex_unlock(&rdev->sched_scan_mtx);
 }
 EXPORT_SYMBOL(cfg80211_sched_scan_stopped);
 
@@ -135,7 +135,7 @@ int __cfg80211_stop_sched_scan(struct cfg80211_registered_device *rdev,
         int err;
         struct net_device *dev;
 
-        ASSERT_RDEV_LOCK(rdev);
+        lockdep_assert_held(&rdev->sched_scan_mtx);
 
         if (!rdev->sched_scan_req)
                 return 0;