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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Duoming Zhou <duoming@zju.edu.cn>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.15 169/247] drivers: staging: rtl8723bs: Fix deadlock in rtw_surveydone_event_callback()
Date:   Mon, 13 Jun 2022 12:11:11 +0200
Message-Id: <20220613094928.083747391@linuxfoundation.org>
In-Reply-To: <20220613094922.843438024@linuxfoundation.org>
References: <20220613094922.843438024@linuxfoundation.org>
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From: Duoming Zhou <duoming@zju.edu.cn>

[ Upstream commit cc7ad0d77b51c872d629bcd98aea463a3c4109e7 ]

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>
Link: https://lore.kernel.org/r/20220409061836.60529-1-duoming@zju.edu.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 cf79bec916c5..2c20bf26b10e 100644
--- a/drivers/staging/rtl8723bs/core/rtw_mlme.c
+++ b/drivers/staging/rtl8723bs/core/rtw_mlme.c
@@ -749,7 +749,9 @@ 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);
 	}
 
@@ -1584,11 +1586,11 @@ 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);
 }
-- 
2.35.1