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References: <20220803153300.58732-1-sebastian.wuerl@ororatech.com>
In-Reply-To: <20220803153300.58732-1-sebastian.wuerl@ororatech.com>
From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Wed, 3 Aug 2022 18:48:57 +0200
Message-ID: <CAHp75VdCH2tJQq3v_-iNP27oWFGF7EtKc-w299tLhDV85WbroQ@mail.gmail.com>
Subject: Re: [PATCH] drivers/net/can/spi/mcp251x.c: Fix race condition on
 receive interrupt
To:     =?UTF-8?Q?Sebastian_W=C3=BCrl?= <sebastian.wuerl@ororatech.com>
Cc:     Wolfgang Grandegger <wg@grandegger.com>,
        Marc Kleine-Budde <mkl@pengutronix.de>,
        "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>,
        =?UTF-8?Q?Stefan_M=C3=A4tje?= <stefan.maetje@esd.eu>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Oliver Hartkopp <socketcan@hartkopp.net>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        =?UTF-8?Q?Uwe_Kleine=2DK=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>
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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

CAN

> chips. For retrieving the CAN frames from the controller via SPI, it chec=
ks
> once per interrupt which mailboxes have been filled, an will retrieve the
> messages accordingly.
>
> 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.
>
> 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 bursts
>  - Check on the RPi whether the received messages have increasing CAN-ids
>  - Without this patch, every burst of messages will contain a flipped pai=
r

Fixes tag?

--=20
With Best Regards,
Andy Shevchenko