linux-kernel - [PATCH AUTOSEL 4.19 06/27] drivers: staging: rtl8192e: Fix deadlock in rtllib_beacons

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Message-Id: <20220607180133.481701-6-sashal@kernel.org>
Date:   Tue,  7 Jun 2022 14:01:10 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Duoming Zhou <duoming@....edu.cn>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sasha Levin <sashal@...nel.org>, baihaowen@...zu.com,
        dan.carpenter@...cle.com, paskripkin@...il.com, wjsota@...il.com,
        dave@...olabs.net, edumazet@...gle.com, yangyingliang@...wei.com,
        linux-staging@...ts.linux.dev
Subject: [PATCH AUTOSEL 4.19 06/27] drivers: staging: rtl8192e: Fix deadlock in rtllib_beacons_stop()

From: Duoming Zhou <duoming@....edu.cn>

[ Upstream commit 9b6bdbd9337de3917945847bde262a34a87a6303 ]

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

   (Thread 1)              |      (Thread 2)
                           | rtllib_send_beacon()
rtllib_beacons_stop()      |  mod_timer()
 spin_lock_irqsave() //(1) |  (wait a time)
 ...                       | rtllib_send_beacon_cb()
 del_timer_sync()          |  spin_lock_irqsave() //(2)
 (wait timer to stop)      |  ...

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

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

Signed-off-by: Duoming Zhou <duoming@....edu.cn>
Link: https://lore.kernel.org/r/20220417141641.124388-1-duoming@zju.edu.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/staging/rtl8192e/rtllib_softmac.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/staging/rtl8192e/rtllib_softmac.c b/drivers/staging/rtl8192e/rtllib_softmac.c
index 919231fec09c..5f1dd4e2d12e 100644
--- a/drivers/staging/rtl8192e/rtllib_softmac.c
+++ b/drivers/staging/rtl8192e/rtllib_softmac.c
@@ -654,9 +654,9 @@ static void rtllib_beacons_stop(struct rtllib_device *ieee)
 	spin_lock_irqsave(&ieee->beacon_lock, flags);
 
 	ieee->beacon_txing = 0;
-	del_timer_sync(&ieee->beacon_timer);
 
 	spin_unlock_irqrestore(&ieee->beacon_lock, flags);
+	del_timer_sync(&ieee->beacon_timer);
 
 }
 
-- 
2.35.1