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Date: Thu, 7 Mar 2024 21:40:33 +0100
From: Marc Kleine-Budde <mkl@pengutronix.de>
To: vitor <ivitro@gmail.com>
Cc: manivannan.sadhasivam@linaro.org, thomas.kopp@microchip.com, 
	wg@grandegger.com, linux-can@vger.kernel.org, linux-kernel@vger.kernel.org, 
	vitor.soares@toradex.com, stable@vger.kernel.org
Subject: Re: [PATCH] can: mcp251xfd: fix infinite loop when xmit fails
Message-ID: <20240307-sturdy-cringe-fa9b095b25ab-mkl@pengutronix.de>
References: <20240307120442.12262-1-ivitro@gmail.com>
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On 07.03.2024 16:54:13, vitor wrote:
> > On 07.03.2024 12:04:42, Vitor Soares wrote:
> > > From: Vitor Soares <vitor.soares@toradex.com>
> > >=20
> > > When the mcp251xfd_start_xmit() function fails, the driver stops
> > > processing messages, and the interrupt routine does not return,
> > > running indefinitely even after killing the running application.
> > >=20
> > > Error messages:
> > > [=C2=A0 441.298819] mcp251xfd spi2.0 can0: ERROR in
> > > mcp251xfd_start_xmit: -16
> > > [=C2=A0 441.306498] mcp251xfd spi2.0 can0: Transmit Event FIFO buffer
> > > not empty. (seq=3D0x000017c7, tef_tail=3D0x000017cf,
> > > tef_head=3D0x000017d0, tx_head=3D0x000017d3).
> > > ... and repeat forever.
> > >=20
> > > The issue can be triggered when multiple devices share the same
> > > SPI interface. And there is concurrent access to the bus.
> > >=20
> > > The problem occurs because tx_ring->head increments even if
> > > mcp251xfd_start_xmit() fails. Consequently, the driver skips one
> > > TX package while still expecting a response in
> > > mcp251xfd_handle_tefif_one().
> > >=20
> > > This patch resolves the issue by decreasing tx_ring->head if
> > > mcp251xfd_start_xmit() fails. With the fix, if we attempt to
> > > trigger
> > > the issue again, the driver prints an error and discard the
> > > message.
> >=20
> > What about returning NETDEV_TX_BUSY, then the networking stack will
> > retry.
>=20
> Do you mean when err =3D=3D -EBUSY?

ACK

> >=20
> > > Fixes: 55e5b97f003e ("can: mcp25xxfd: add driver for Microchip
> > > MCP25xxFD SPI CAN")
> > > Cc: stable@vger.kernel.org
> > > Signed-off-by: Vitor Soares <vitor.soares@toradex.com>
> > > ---
> > > =C2=A0drivers/net/can/spi/mcp251xfd/mcp251xfd-tx.c | 27 ++++++++++---=
---
> > > ----
> > > =C2=A01 file changed, 14 insertions(+), 13 deletions(-)
> > >=20
> > > diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-tx.c
> > > b/drivers/net/can/spi/mcp251xfd/mcp251xfd-tx.c
> > > index 160528d3cc26..a8eb941c1b95 100644
> > > --- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-tx.c
> > > +++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-tx.c
> > > @@ -181,25 +181,26 @@ netdev_tx_t mcp251xfd_start_xmit(struct
> > > sk_buff *skb,
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0tx_obj =3D mcp251xfd_=
get_tx_obj_next(tx_ring);
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0mcp251xfd_tx_obj_from=
_skb(priv, tx_obj, skb, tx_ring-
> > > >head);
> > > =C2=A0
> > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0/* Stop queue if we occupy=
 the complete TX FIFO */
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0tx_head =3D mcp251xfd=
_get_tx_head(tx_ring);
> > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0tx_ring->head++;
> > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (mcp251xfd_get_tx_free(=
tx_ring) =3D=3D 0)
> > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0netif_stop_queue(ndev);
> > > -
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0frame_len =3D can_skb=
_get_frame_len(skb);
> > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0err =3D can_put_echo_skb(s=
kb, ndev, tx_head, frame_len);
> > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (!err)
> > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0netdev_sent_queue(priv->ndev, frame_len);
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0can_put_echo_skb(skb, ndev=
, tx_head, frame_len);
> > > +
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0tx_ring->head++;
> > > =C2=A0
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0err =3D mcp251xfd_tx_=
obj_write(priv, tx_obj);
> > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (err)
> > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0goto out_err;
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (err) {
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0can_free_echo_skb(ndev, tx_head, NULL);
> > > =C2=A0
> > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0return NETDEV_TX_OK;
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0tx_ring->head--;
> > > +
>=20
> I'm testing returning here when err =3D -EBUSY, but can_put_echo_skb()
> should be invoked after mcp251xfd_tx_obj_write(). Otherwise, I get a
> Kernel NULL pointer dereference error.

I mean if mcp251xfd_tx_obj_write() returns -EBUSY don't print an error
message, on any other error it's ok to print the error.

> >=20
> > I'm not sure, if we want an error message for -EBUSY. We could add
> > proper ethtool statistics.
> >=20
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0netdev_err(priv->ndev, "ERROR in %s: %d\n",
> > > __func__, err);
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0} else {
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0/* Stop queue if we occupy the complete TX FIFO */
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0if (mcp251xfd_get_tx_free(tx_ring) =3D=3D 0)
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0net=
if_stop_queue(ndev);
> > > =C2=A0
> > > - out_err:
> > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0netdev_err(priv->ndev, "ER=
ROR in %s: %d\n", __func__, err);
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0netdev_sent_queue(priv->ndev, frame_len);
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0}
> > > =C2=A0
> > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0return NETDEV_TX_OK;
> > > =C2=A0}

Marc

--=20
Pengutronix e.K.                 | Marc Kleine-Budde          |
Embedded Linux                   | https://www.pengutronix.de |
Vertretung N=C3=BCrnberg              | Phone: +49-5121-206917-129 |
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