linux-kernel - [PATCH 4.14 62/78] can: grcan: grcan

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Message-Id: <20220510130734.367303060@linuxfoundation.org>
Date:   Tue, 10 May 2022 15:07:48 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Duoming Zhou <duoming@....edu.cn>,
        Andreas Larsson <andreas@...sler.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>
Subject: [PATCH 4.14 62/78] can: grcan: grcan_close(): fix deadlock

From: Duoming Zhou <duoming@....edu.cn>

commit 47f070a63e735bcc8d481de31be1b5a1aa62b31c upstream.

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.

Link: https://lore.kernel.org/all/20220425042400.66517-1-duoming@zju.edu.cn
Fixes: 6cec9b07fe6a ("can: grcan: Add device driver for GRCAN and GRHCAN cores")
Cc: stable@...r.kernel.org
Signed-off-by: Duoming Zhou <duoming@....edu.cn>
Reviewed-by: Andreas Larsson <andreas@...sler.com>
Signed-off-by: Marc Kleine-Budde <mkl@...gutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/net/can/grcan.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/net/can/grcan.c
+++ b/drivers/net/can/grcan.c
@@ -1117,8 +1117,10 @@ static int grcan_close(struct net_device
 
 	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);