[PATCH 04/11] drivers: staging: rtl8723bs: Fix deadlock in rtw_surveydone_event_callback()

[Duoming Zhou]

There is a deadlock in rtw_surveydone_event_callback(),
which is shown below:

   (Thread 1)                  |      (Thread 2)
                               | _set_timer()
rtw_surveydone_event_callback()|  mod_timer()
 spin_lock_bh() //(1)          |  (wait a time)
 ...                           | rtw_scan_timeout_handler()
 del_timer_sync()              |  spin_lock_bh() //(2)
 (wait timer to stop)          |  ...

We hold pmlmepriv->lock in position (1) of thread 1 and use
del_timer_sync() to wait timer to stop, but timer handler
also need pmlmepriv->lock in position (2) of thread 2.
As a result, rtw_surveydone_event_callback() will block forever.

This patch extracts del_timer_sync() from the protection of
spin_lock_bh(), which could let timer handler to obtain
the needed lock.

Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
---
 drivers/staging/rtl8723bs/core/rtw_mlme.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/staging/rtl8723bs/core/rtw_mlme.c b/drivers/staging/rtl8723bs/core/rtw_mlme.c
index ed2d3b7d44d..d559eefe633 100644
--- a/drivers/staging/rtl8723bs/core/rtw_mlme.c
+++ b/drivers/staging/rtl8723bs/core/rtw_mlme.c
@@ -751,7 +751,9 @@ void rtw_surveydone_event_callback(struct adapter	*adapter, u8 *pbuf)
 	}
 
 	if (check_fwstate(pmlmepriv, _FW_UNDER_SURVEY)) {
+		spin_unlock_bh(&pmlmepriv->lock);
 		del_timer_sync(&pmlmepriv->scan_to_timer);
+		spin_lock_bh(&pmlmepriv->lock);
 		_clr_fwstate_(pmlmepriv, _FW_UNDER_SURVEY);
 	}
 
-- 
2.17.1