mac80211: use freezable workqueue for restart work

Requesting hw restart during suspend might result
in the restart work being executed after mac80211
and the hw are suspended.

Solve the race by simply scheduling the restart
work on a freezable workqueue.

Note that there can be some cases of reconfiguration
on resume (besides the hardware restart):

* wowlan is not configured -
    All the interfaces removed were removed on suspend,
    and drv_stop() was called. At this point the driver
    shouldn't expect for hw_restart anyway, so we can
    simply cancel it (on resume).

* wowlan is configured, drv_resume() == 1
    There is no definitive expected behavior in this case,
    as each driver might have different expectations (e.g.
    setting some flags on suspend/restart vs. not handling
    spurious recovery).
    For now, simply let the hw_restart work run again after
    resume, and hope the driver will handle it well (or at
    least initiate another hw restart).

Signed-off-by: Eliad Peller <[email protected]>
Signed-off-by: Emmanuel Grumbach <[email protected]>
Signed-off-by: Johannes Berg <[email protected]>

net/mac80211/main.c

@@ -281,7 +281,7 @@ void ieee80211_restart_hw(struct ieee80211_hw *hw)
 	local->in_reconfig = true;
 	barrier();
 
-	schedule_work(&local->restart_work);
+	queue_work(system_freezable_wq, &local->restart_work);
 }
 EXPORT_SYMBOL(ieee80211_restart_hw);
 

net/mac80211/util.c

@@ -4,6 +4,7 @@
  * Copyright 2006-2007	Jiri Benc <[email protected]>
  * Copyright 2007	Johannes Berg <[email protected]>
  * Copyright 2013-2014  Intel Mobile Communications GmbH
+ * Copyright (C) 2015	Intel Deutschland GmbH
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
@@ -1753,6 +1754,16 @@ int ieee80211_reconfig(struct ieee80211_local *local)
 	}
 #endif
 
+	/*
+	 * In case of hw_restart during suspend (without wowlan),
+	 * cancel restart work, as we are reconfiguring the device
+	 * anyway.
+	 * Note that restart_work is scheduled on a frozen workqueue,
+	 * so we can't deadlock in this case.
+	 */
+	if (suspended && local->in_reconfig && !reconfig_due_to_wowlan)
+		cancel_work_sync(&local->restart_work);
+
 	/*
 	 * Upon resume hardware can sometimes be goofy due to
 	 * various platform / driver / bus issues, so restarting