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From: Duoming Zhou <duoming@zju.edu.cn>
To: linux-kernel@vger.kernel.org
Cc: wg@grandegger.com, mkl@pengutronix.de, davem@davemloft.net,
	kuba@kernel.org, pabeni@redhat.com, linux-can@vger.kernel.org,
	netdev@vger.kernel.org, Duoming Zhou <duoming@zju.edu.cn>
Subject: [PATCH net] drivers: net: can: Fix deadlock in grcan_close()
Date: Mon, 25 Apr 2022 12:24:00 +0800	[thread overview]
Message-ID: <20220425042400.66517-1-duoming@zju.edu.cn> (raw)

There are deadlocks caused by del_timer_sync(&priv->hang_timer)
and del_timer_sync(&priv->rr_timer) in grcan_close(), one of
the deadlocks are shown below:

   (Thread 1)              |      (Thread 2)
                           | grcan_reset_timer()
grcan_close()              |  mod_timer()
 spin_lock_irqsave() //(1) |  (wait a time)
 ...                       | grcan_initiate_running_reset()
 del_timer_sync()          |  spin_lock_irqsave() //(2)
 (wait timer to stop)      |  ...

We hold priv->lock in position (1) of thread 1 and use
del_timer_sync() to wait timer to stop, but timer handler
also need priv->lock in position (2) of thread 2.
As a result, grcan_close() 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>
---
 drivers/net/can/grcan.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/can/grcan.c b/drivers/net/can/grcan.c
index d0c5a7a60da..1189057b5d6 100644
--- a/drivers/net/can/grcan.c
+++ b/drivers/net/can/grcan.c
@@ -1102,8 +1102,10 @@ static int grcan_close(struct net_device *dev)
 
 	priv->closing = true;
 	if (priv->need_txbug_workaround) {
+		spin_unlock_irqrestore(&priv->lock, flags);
 		del_timer_sync(&priv->hang_timer);
 		del_timer_sync(&priv->rr_timer);
+		spin_lock_irqsave(&priv->lock, flags);
 	}
 	netif_stop_queue(dev);
 	grcan_stop_hardware(dev);
-- 
2.17.1


             reply	other threads:[~2022-04-25  4:24 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-25  4:24 Duoming Zhou [this message]
2022-04-26 19:12 ` Oliver Hartkopp
2022-04-27 12:47   ` Andreas Larsson
2022-04-27 16:25     ` Oliver Hartkopp

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