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, 9 insertions, 3 deletions

diff --git a/net/wireless/core.c b/net/wireless/core.c
index c22ef3492ee6..880dbe2e6f94 100644
--- a/net/wireless/core.c
+++ b/net/wireless/core.c
@@ -366,6 +366,7 @@ struct wiphy *wiphy_new(const struct cfg80211_ops *ops, int sizeof_priv)
 
         mutex_init(&rdev->mtx);
         mutex_init(&rdev->devlist_mtx);
+        mutex_init(&rdev->sched_scan_mtx);
         INIT_LIST_HEAD(&rdev->netdev_list);
         spin_lock_init(&rdev->bss_lock);
         INIT_LIST_HEAD(&rdev->bss_list);
@@ -701,6 +702,7 @@ void cfg80211_dev_free(struct cfg80211_registered_device *rdev)
         rfkill_destroy(rdev->rfkill);
         mutex_destroy(&rdev->mtx);
         mutex_destroy(&rdev->devlist_mtx);
+        mutex_destroy(&rdev->sched_scan_mtx);
         list_for_each_entry_safe(scan, tmp, &rdev->bss_list, list)
                 cfg80211_put_bss(&scan->pub);
         cfg80211_rdev_free_wowlan(rdev);
@@ -737,12 +739,16 @@ static void wdev_cleanup_work(struct work_struct *work)
                 ___cfg80211_scan_done(rdev, true);
         }
 
+        cfg80211_unlock_rdev(rdev);
+
+        mutex_lock(&rdev->sched_scan_mtx);
+
         if (WARN_ON(rdev->sched_scan_req &&
                     rdev->sched_scan_req->dev == wdev->netdev)) {
                 __cfg80211_stop_sched_scan(rdev, false);
         }
 
-        cfg80211_unlock_rdev(rdev);
+        mutex_unlock(&rdev->sched_scan_mtx);
 
         mutex_lock(&rdev->devlist_mtx);
         rdev->opencount--;
@@ -830,9 +836,9 @@ static int cfg80211_netdev_notifier_call(struct notifier_block * nb,
                         break;
                 case NL80211_IFTYPE_P2P_CLIENT:
                 case NL80211_IFTYPE_STATION:
-                        cfg80211_lock_rdev(rdev);
+                        mutex_lock(&rdev->sched_scan_mtx);
                         __cfg80211_stop_sched_scan(rdev, false);
-                        cfg80211_unlock_rdev(rdev);
+                        mutex_unlock(&rdev->sched_scan_mtx);
 
                         wdev_lock(wdev);
 #ifdef CONFIG_CFG80211_WEXT