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Date:   Thu, 4 Aug 2022 10:28:01 +0200
From:   Marc Kleine-Budde <mkl@pengutronix.de>
To:     Sebastian =?utf-8?B?V8O8cmw=?= <sebastian.wuerl@ororatech.com>
Cc:     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>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Oliver Hartkopp <socketcan@hartkopp.net>,
        Stefan =?utf-8?B?TcOkdGpl?= <stefan.maetje@esd.eu>,
        Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= 
        <u.kleine-koenig@pengutronix.de>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Christian Pellegrin <chripell@fsfe.org>,
        linux-can@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4] can: mcp251x: Fix race condition on receive interrupt
Message-ID: <20220804082801.prjdwdindpe3alk3@pengutronix.de>
References: <20220804081411.68567-1-sebastian.wuerl@ororatech.com>
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On 04.08.2022 10:14:11, Sebastian W=C3=BCrl wrote:
> The mcp251x driver uses both receiving mailboxes of the CAN controller
> chips. For retrieving the CAN frames from the controller via SPI, it chec=
ks
> once per interrupt which mailboxes have been filled and will retrieve the
> messages accordingly.
>=20
> This introduces a race condition, as another CAN frame can enter mailbox 1
> while mailbox 0 is emptied. If now another CAN frame enters mailbox 0 unt=
il
> the interrupt handler is called next, mailbox 0 is emptied before
> mailbox 1, leading to out-of-order CAN frames in the network device.
>=20
> This is fixed by checking the interrupt flags once again after freeing
> mailbox 0, to correctly also empty mailbox 1 before leaving the handler.
>=20
> 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 bursts
>  - Check on the RPi whether the received messages have increasing CAN-ids
>  - Without this patch, every burst of messages will contain a flipped pair
>=20
> Fixes: bf66f3736a94 ("can: mcp251x: Move to threaded interrupts instead o=
f workqueues.")
> Signed-off-by: Sebastian W=C3=BCrl <sebastian.wuerl@ororatech.com>

I've reduced the scope of intf1, eflag1 while applying the patch to
can-next/master.

Thanks,
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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