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From:   Mike Looijmans <mike.looijmans@topic.nl>
To:     linux-can@vger.kernel.org
CC:     Mike Looijmans <mike.looijmans@topic.nl>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
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        Marc Kleine-Budde <mkl@pengutronix.de>,
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        Thomas Kopp <thomas.kopp@microchip.com>,
        Wolfgang Grandegger <wg@grandegger.com>,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org
Subject: [PATCH] can: mcp251xfd: Always stop on BUS_OFF and call netif_stop_queue
Date:   Tue, 11 Jul 2023 17:26:47 +0200
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When there's an error attempting to store the BER counter, don't abort
but continue shutting down the chip as required.

After disabling communications, also stop the TX queue with a call to
netif_stop_queue. When the interface restarts, mcp251xfd_set_mode will
call netif_wake_queue and resume.

This fixes a hangup in either send() or poll() from userspace. To
reproduce: I ran "cansequence can0 -p" to flood the system with packets.
While running that, I shorted the CAN signals, causing a bus error.
Usually communications would resume after the CAN bus restarted, but
sometimes the system got stuck and refused to send any more packets.
The sending process would be in either poll() or send(), waiting for
the queue to resume. To "unstuck" the process from send() it was
sufficient to send any packet on the can interface from another
process. To get it out of the poll() hang, only bringing the can
interface down (and up) would work.

After adding the netif_stop_queue call, I was unable to reproduce the
problem.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>

---

 drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c b/drivers/net/c=
an/spi/mcp251xfd/mcp251xfd-core.c
index 68df6d4641b5..854e0644764c 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c
@@ -1084,10 +1084,11 @@ static int mcp251xfd_handle_cerrif(struct mcp251xfd=
_priv *priv)
 		 */
 		err =3D __mcp251xfd_get_berr_counter(priv->ndev, &priv->bec);
 		if (err)
-			return err;
+			netdev_err(priv->ndev, "Failed to store BER counter\n");
=20
 		mcp251xfd_chip_stop(priv, CAN_STATE_BUS_OFF);
 		can_bus_off(priv->ndev);
+		netif_stop_queue(priv->ndev);
 	}
=20
 	if (!skb)
--=20
2.17.1


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