drivers: staging: rtl8192e: Fix deadlock in rtllib_beacons_stop()

stonezdm · gregkh · commit 9b6bdbd9337d · 2022-04-20T18:47:24.000+02:00
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@zju.edu.cn> Link: https://lore.kernel.org/r/20220417141641.124388-1-duoming@zju.edu.cn Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/staging/rtl8192e/rtllib_softmac.c b/drivers/staging/rtl8192e/rtllib_softmac.c
@@ -651,9 +651,9 @@ 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);
 
 }
 

Original file line number	Diff line number	Diff line change
`@@ -651,9 +651,9 @@ static void rtllib_beacons_stop(struct rtllib_device *ieee)`
`651`	`651`	`spin_lock_irqsave(&ieee->beacon_lock, flags);`
`652`	`652`
`653`	`653`	`ieee->beacon_txing = 0;`
`654`		`- del_timer_sync(&ieee->beacon_timer);`
`655`	`654`
`656`	`655`	`spin_unlock_irqrestore(&ieee->beacon_lock, flags);`
	`656`	`+ del_timer_sync(&ieee->beacon_timer);`
`657`	`657`
`658`	`658`	`}`
`659`	`659`