linux-kernel - [PATCH] drivers: staging: rtl8192eu: Fix deadlock in rtw_joinbss_event

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Message-Id: <20220409072135.74248-1-duoming@zju.edu.cn>
Date:   Sat,  9 Apr 2022 15:21:35 +0800
From:   Duoming Zhou <duoming@....edu.cn>
To:     linux-kernel@...r.kernel.org
Cc:     linux-staging@...ts.linux.dev, alexander.deucher@....com,
        kuba@...nel.org, broonie@...nel.org, davem@...emloft.net,
        gregkh@...uxfoundation.org, phil@...lpotter.co.uk,
        Larry.Finger@...inger.net, Duoming Zhou <duoming@....edu.cn>
Subject: [PATCH] drivers: staging: rtl8192eu: Fix deadlock in rtw_joinbss_event_prehandle

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

   (Thread 1)                |      (Thread 2)
                             | _set_timer()
rtw_joinbss_event_prehandle()|  mod_timer()
 spin_lock_bh() //(1)        |  (wait a time)
 ...                         | rtw_join_timeout_handler()
                             |  _rtw_join_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_joinbss_event_prehandle() 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() to
spin_lock_irq() in _rtw_join_timeout_handler() in order to
prevent deadlock.

Signed-off-by: Duoming Zhou <duoming@....edu.cn>
---
 drivers/staging/r8188eu/core/rtw_mlme.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/r8188eu/core/rtw_mlme.c b/drivers/staging/r8188eu/core/rtw_mlme.c
index 6f0bff18647..76cf6a69bf0 100644
--- a/drivers/staging/r8188eu/core/rtw_mlme.c
+++ b/drivers/staging/r8188eu/core/rtw_mlme.c
@@ -1071,8 +1071,10 @@ void rtw_joinbss_event_prehandle(struct adapter *adapter, u8 *pbuf)
 				rtw_indicate_connect(adapter);
 			}
 
+			spin_unlock_bh(&pmlmepriv->lock);
 			/* s5. Cancel assoc_timer */
 			del_timer_sync(&pmlmepriv->assoc_timer);
+			spin_lock_bh(&pmlmepriv->lock);
 		} else {
 			spin_unlock_bh(&pmlmepriv->scanned_queue.lock);
 			goto ignore_joinbss_callback;
@@ -1310,7 +1312,7 @@ void _rtw_join_timeout_handler (struct adapter *adapter)
 	if (adapter->bDriverStopped || adapter->bSurpriseRemoved)
 		return;
 
-	spin_lock_bh(&pmlmepriv->lock);
+	spin_lock_irq(&pmlmepriv->lock);
 
 	if (rtw_to_roaming(adapter) > 0) { /* join timeout caused by roaming */
 		while (1) {
@@ -1329,7 +1331,7 @@ void _rtw_join_timeout_handler (struct adapter *adapter)
 		rtw_indicate_disconnect(adapter);
 		free_scanqueue(pmlmepriv);/*  */
 	}
-	spin_unlock_bh(&pmlmepriv->lock);
+	spin_unlock_irq(&pmlmepriv->lock);
 
 }
 
-- 
2.17.1