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Date:   Wed, 3 Aug 2022 21:08:04 +0200
From:   Marc Kleine-Budde <mkl@pengutronix.de>
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
Cc:     Sebastian =?utf-8?B?V8O8cmw=?= <sebastian.wuerl@ororatech.com>,
        Wolfgang Grandegger <wg@grandegger.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Vincent Mailhol <mailhol.vincent@wanadoo.fr>,
        Stefan =?utf-8?B?TcOkdGpl?= <stefan.maetje@esd.eu>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Oliver Hartkopp <socketcan@hartkopp.net>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= 
        <u.kleine-koenig@pengutronix.de>, linux-can@vger.kernel.org,
        netdev <netdev@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] drivers/net/can/spi/mcp251x.c: Fix race condition on
 receive interrupt
Message-ID: <20220803190804.b3p4iugcz3yp6mtc@pengutronix.de>
References: <20220803153300.58732-1-sebastian.wuerl@ororatech.com>
 <CAHp75VdCH2tJQq3v_-iNP27oWFGF7EtKc-w299tLhDV85WbroQ@mail.gmail.com>
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On 03.08.2022 18:48:57, Andy Shevchenko wrote:
> On Wed, Aug 3, 2022 at 5:36 PM Sebastian W=C3=BCrl
> <sebastian.wuerl@ororatech.com> wrote:
> >
> > The mcp251x driver uses both receiving mailboxes of the can controller
>=20
> CAN
>=20
> > chips. For retrieving the CAN frames from the controller via SPI, it ch=
ecks
> > once per interrupt which mailboxes have been filled, an will retrieve t=
he
> > messages accordingly.
> >
> > This introduces a race condition, as another CAN frame can enter mailbo=
x 1
> > while mailbox 0 is emptied. If now another CAN frame enters mailbox 0 u=
ntil
> > the interrupt handler is called next, mailbox 0 is emptied before
> > mailbox 1, leading to out-of-order CAN frames in the network device.
> >
> > This is fixed by checking the interrupt flags once again after freeing
> > mailbox 0, to correctly also empty mailbox 1 before leaving the handler.
> >
> > For reproducing the bug I created the following setup:
> >  - Two CAN devices, one Raspberry Pi with MCP2515, the other can be any.
> >  - Setup CAN to 1 MHz
> >  - Spam bursts of 5 CAN-messages with increasing CAN-ids
> >  - Continue sending the bursts while sleeping a second between the burs=
ts
> >  - Check on the RPi whether the received messages have increasing CAN-i=
ds
> >  - Without this patch, every burst of messages will contain a flipped p=
air
>=20
> Fixes tag?

Should be:
Fixes: bf66f3736a94 ("can: mcp251x: Move to threaded interrupts instead of =
workqueues.")

Marc

--=20
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |

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