linux-kernel - [PATCH V2 06/11] drivers: staging: rtl8192bs: Fix deadlock in rtw_joinbss_event

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Date:   Sat,  9 Apr 2022 14:49:53 +0800
From:   Duoming Zhou <duoming@....edu.cn>
To:     linux-kernel@...r.kernel.org
Cc:     linux-staging@...ts.linux.dev, alexander.deucher@....com,
        davem@...emloft.net, gregkh@...uxfoundation.org,
        Duoming Zhou <duoming@....edu.cn>
Subject: [PATCH V2 06/11] drivers: staging: rtl8192bs: 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. 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>
---
Changes in V2:
  - Change spin_lock_bh() to spin_lock_irq() in
    _rtw_join_timeout_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 62f140985e3..24d6af886f7 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));
 		}
@@ -1547,7 +1549,7 @@ void _rtw_join_timeout_handler(struct timer_list *t)
 	if (adapter->bDriverStopped || adapter->bSurpriseRemoved)
 		return;
 
-	spin_lock_bh(&pmlmepriv->lock);
+	spin_lock_irq(&pmlmepriv->lock);
 
 	if (rtw_to_roam(adapter) > 0) { /* join timeout caused by roaming */
 		while (1) {
@@ -1575,7 +1577,7 @@ void _rtw_join_timeout_handler(struct timer_list *t)
 
 	}
 
-	spin_unlock_bh(&pmlmepriv->lock);
+	spin_unlock_irq(&pmlmepriv->lock);
 }
 
 /*
-- 
2.17.1