When removing an interface with nl80211, cfg80211 will
deadlock in the netdev notifier because we're already
holding rdev->mtx and try to acquire it again to verify
the scan has been done.
This bug was introduced by my patch
"cfg80211: check for and abort dangling scan requests".
To fix this, move the dangling scan request check into
wiphy_unregister(). This will not be able to catch all
cases right away, but if the scan problem happens with
a manual ifdown or so it will be possible to remedy it
by removing the module/device.
Additionally, add comments about the deadlock scenario.
Reported-by: Christian Lamparter <chunkeey@xxxxxx>
Signed-off-by: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
---
v2: don't move flush_work under cfg80211_mutex locked section
net/wireless/core.c | 30 ++++++++++++++++++------------
1 file changed, 18 insertions(+), 12 deletions(-)
--- wireless-testing.orig/net/wireless/core.c 2009-08-16 13:35:51.000000000 +0200
+++ wireless-testing/net/wireless/core.c 2009-08-17 12:22:50.000000000 +0200
@@ -586,9 +586,14 @@ void wiphy_unregister(struct wiphy *wiph
* get to lock contention here if userspace issues a command
* that identified the hardware by wiphy index.
*/
- mutex_lock(&rdev->mtx);
- /* unlock again before freeing */
- mutex_unlock(&rdev->mtx);
+ cfg80211_lock_rdev(rdev);
+
+ if (WARN_ON(rdev->scan_req)) {
+ rdev->scan_req->aborted = true;
+ ___cfg80211_scan_done(rdev);
+ }
+
+ cfg80211_unlock_rdev(rdev);
cfg80211_debugfs_rdev_del(rdev);
@@ -605,7 +610,6 @@ void wiphy_unregister(struct wiphy *wiph
flush_work(&rdev->scan_done_wk);
cancel_work_sync(&rdev->conn_work);
- kfree(rdev->scan_req);
flush_work(&rdev->event_work);
}
EXPORT_SYMBOL(wiphy_unregister);
@@ -653,6 +657,11 @@ static int cfg80211_netdev_notifier_call
switch (state) {
case NETDEV_REGISTER:
+ /*
+ * NB: cannot take rdev->mtx here because this may be
+ * called within code protected by it when interfaces
+ * are added with nl80211.
+ */
mutex_init(&wdev->mtx);
INIT_LIST_HEAD(&wdev->event_list);
spin_lock_init(&wdev->event_lock);
@@ -730,13 +739,11 @@ static int cfg80211_netdev_notifier_call
#endif
break;
case NETDEV_UNREGISTER:
- cfg80211_lock_rdev(rdev);
-
- if (WARN_ON(rdev->scan_req && rdev->scan_req->dev == dev)) {
- rdev->scan_req->aborted = true;
- ___cfg80211_scan_done(rdev);
- }
-
+ /*
+ * NB: cannot take rdev->mtx here because this may be
+ * called within code protected by it when interfaces
+ * are removed with nl80211.
+ */
mutex_lock(&rdev->devlist_mtx);
/*
* It is possible to get NETDEV_UNREGISTER
@@ -755,7 +762,6 @@ static int cfg80211_netdev_notifier_call
#endif
}
mutex_unlock(&rdev->devlist_mtx);
- cfg80211_unlock_rdev(rdev);
break;
case NETDEV_PRE_UP:
if (!(wdev->wiphy->interface_modes & BIT(wdev->iftype)))
--
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