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Message-ID: <CAHp75VcTyubQFXyKA1RoYkpWowfKYwA1N_zZtmvGTeCmDG89Ow@mail.gmail.com> Date: Wed, 3 Aug 2022 18:50:13 +0200 From: Andy Shevchenko <andy.shevchenko@...il.com> To: Sebastian Würl <sebastian.wuerl@...ratech.com> Cc: Wolfgang Grandegger <wg@...ndegger.com>, Marc Kleine-Budde <mkl@...gutronix.de>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Vincent Mailhol <mailhol.vincent@...adoo.fr>, Stefan Mätje <stefan.maetje@....eu>, Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Oliver Hartkopp <socketcan@...tkopp.net>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Uwe Kleine-König <u.kleine-koenig@...gutronix.de>, linux-can@...r.kernel.org, netdev <netdev@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] drivers/net/can/spi/mcp251x.c: Fix race condition on receive interrupt On Wed, Aug 3, 2022 at 6:48 PM Andy Shevchenko <andy.shevchenko@...il.com> wrote: > > On Wed, Aug 3, 2022 at 5:36 PM Sebastian Würl > <sebastian.wuerl@...ratech.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 checks > > 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 until > > 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 pair > > Fixes tag? Also fix the Subject prefix (you may see the most used ones by running `git log --no-merges --oneline -- drivers/net/can/spi/mcp251x.c`). -- With Best Regards, Andy Shevchenko
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