[PATCH] mac80211: fix scheduled scan rtnl deadlock

[PATCH] mac80211: fix scheduled scan rtnl deadlock

[Johannes Berg]

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

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.

Cc: stable@vger.kernel.org
Fixes: 5fe231e87372 ("cfg80211: vastly simplify locking")
Reported-and-tested-by: Eliad Peller <eliadx.peller@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.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 21d5d44..e765f77 100644
--- a/net/mac80211/main.c
+++ b/net/mac80211/main.c
@@ -1047,6 +1047,7 @@ 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 a0b78b1..01fdf20 100644
--- a/net/mac80211/scan.c
+++ b/net/mac80211/scan.c
@@ -1069,6 +1069,6 @@ 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);
-- 
1.8.4.rc3

Re: [PATCH] mac80211: fix scheduled scan rtnl deadlock

[Johannes Berg]

On Wed, 2013-11-06 at 10:43 +0100, Johannes Berg wrote:
> From: Johannes Berg <johannes.berg@intel.com>
> 
> 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.

Applied.

johannes