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From:   Duoming Zhou <duoming@zju.edu.cn>
To:     linux-kernel@vger.kernel.org
Cc:     linux-staging@lists.linux.dev, alexander.deucher@amd.com,
        davem@davemloft.net, gregkh@linuxfoundation.org,
        Duoming Zhou <duoming@zju.edu.cn>
Subject: [PATCH V2 04/11] drivers: staging: rtl8723bs: Fix deadlock in rtw_surveydone_event_callback()
Date:   Sat,  9 Apr 2022 14:18:35 +0800
Message-Id: <20220409061836.60529-1-duoming@zju.edu.cn>
Precedence: bulk

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. What`s more, we change spin_lock_bh() in
rtw_scan_timeout_handler() to spin_lock_irq(). Otherwise,
spin_lock_bh() will also cause deadlock() in timer handler.

Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
---
Changes in V2:
  - Change spin_lock_bh() to spin_lock_irq() in timer handler.

 drivers/staging/rtl8723bs/core/rtw_mlme.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/rtl8723bs/core/rtw_mlme.c b/drivers/staging/rtl8723bs/core/rtw_mlme.c
index ed2d3b7d44d..62f140985e3 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);
 	}
 
@@ -1586,11 +1588,11 @@ void rtw_scan_timeout_handler(struct timer_list *t)
 						  mlmepriv.scan_to_timer);
 	struct	mlme_priv *pmlmepriv = &adapter->mlmepriv;
 
-	spin_lock_bh(&pmlmepriv->lock);
+	spin_lock_irq(&pmlmepriv->lock);
 
 	_clr_fwstate_(pmlmepriv, _FW_UNDER_SURVEY);
 
-	spin_unlock_bh(&pmlmepriv->lock);
+	spin_unlock_irq(&pmlmepriv->lock);
 
 	rtw_indicate_scan_done(adapter, true);
 }
-- 
2.17.1