linux-kernel - [PATCH 06/11] drivers: staging: rtl8192e: Fix deadlock in rtw_joinbss_event

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Date:   Thu,  7 Apr 2022 14:36:25 +0800
From:   Duoming Zhou <duoming@....edu.cn>
To:     linux-kernel@...r.kernel.org
Cc:     chris@...kel.net, jcmvbkbc@...il.com, mustafa.ismail@...el.com,
        shiraz.saleem@...el.com, jgg@...pe.ca, wg@...ndegger.com,
        mkl@...gutronix.de, davem@...emloft.net, kuba@...nel.org,
        pabeni@...hat.com, jes@...ined-monkey.org,
        gregkh@...uxfoundation.org, jirislaby@...nel.org,
        alexander.deucher@....com, linux-xtensa@...ux-xtensa.org,
        linux-rdma@...r.kernel.org, linux-can@...r.kernel.org,
        netdev@...r.kernel.org, linux-hippi@...site.dk,
        linux-staging@...ts.linux.dev, linux-serial@...r.kernel.org,
        linux-usb@...r.kernel.org, Duoming Zhou <duoming@....edu.cn>
Subject: [PATCH 06/11] drivers: staging: rtl8192e: 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()
 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.

Signed-off-by: Duoming Zhou <duoming@....edu.cn>
---
 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 d559eefe633..5030556929d 100644
--- a/drivers/staging/rtl8723bs/core/rtw_mlme.c
+++ b/drivers/staging/rtl8723bs/core/rtw_mlme.c
@@ -1240,8 +1240,10 @@ void rtw_joinbss_event_prehandle(struct adapter *adapter, u8 *pbuf)
 
 			spin_unlock_bh(&pmlmepriv->scanned_queue.lock);
 
+			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));
 		}
-- 
2.17.1