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cfg80211: fix deadlock

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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@web.de>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Tested-by: Christian Lamparter <chunkeey@web.de>
Tested-by: Kalle Valo <kalle.valo@iki.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
This commit is contained in:
Johannes Berg 2009-08-17 12:25:37 +02:00 committed by John W. Linville
parent 96909e9771
commit 0ff6ce7b36
1 changed files with 18 additions and 12 deletions
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30
net/wireless/core.c
View file

@ -586,9 +586,14 @@ void wiphy_unregister(struct wiphy *wiphy)
* 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 *wiphy)
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(struct notifier_block * nb,
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(struct notifier_block * nb,
#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(struct notifier_block * nb,
#endif
}
mutex_unlock(&rdev->devlist_mtx);
cfg80211_unlock_rdev(rdev);
break;
case NETDEV_PRE_UP:
if (!(wdev->wiphy->interface_modes & BIT(wdev->iftype)))