4.19-stable review patch. If anyone has any objections, please let me know.
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From: Marc Kleine-Budde mkl@pengutronix.de
[ Upstream commit 6841cab8c4504835e4011689cbdb3351dec693fd ]
This race condition was discovered while updating the at91_can driver to use can_bus_off(). The following scenario describes how the converted at91_can driver would behave.
When a CAN device goes into BUS-OFF state, the driver usually stops/resets the CAN device and calls can_bus_off().
This function sets the netif carrier to off, and (if configured by user space) schedules a delayed work that calls can_restart() to restart the CAN device.
The can_restart() function first checks if the carrier is off and triggers an error message if the carrier is OK.
Then it calls the driver's do_set_mode() function to restart the device, then it sets the netif carrier to on. There is a race window between these two calls.
The at91 CAN controller (observed on the sama5d3, a single core 32 bit ARM CPU) has a hardware limitation. If the device goes into bus-off while sending a CAN frame, there is no way to abort the sending of this frame. After the controller is enabled again, another attempt is made to send it.
If the bus is still faulty, the device immediately goes back to the bus-off state. The driver calls can_bus_off(), the netif carrier is switched off and another can_restart is scheduled. This occurs within the race window before the original can_restart() handler marks the netif carrier as OK. This would cause the 2nd can_restart() to be called with an OK netif carrier, resulting in an error message.
The flow of the 1st can_restart() looks like this:
can_restart() // bail out if netif_carrier is OK
netif_carrier_ok(dev) priv->do_set_mode(dev, CAN_MODE_START) // enable CAN controller // sama5d3 restarts sending old message
// CAN devices goes into BUS_OFF, triggers IRQ
// IRQ handler start at91_irq() at91_irq_err_line() can_bus_off() netif_carrier_off() schedule_delayed_work() // IRQ handler end
netif_carrier_on()
The 2nd can_restart() will be called with an OK netif carrier and the error message will be printed.
To close the race window, first set the netif carrier to on, then restart the controller. In case the restart fails with an error code, roll back the netif carrier to off.
Fixes: 39549eef3587 ("can: CAN Network device driver and Netlink interface") Link: https://lore.kernel.org/all/20231005-can-dev-fix-can-restart-v2-2-91b5c1fd92... Reviewed-by: Vincent Mailhol mailhol.vincent@wanadoo.fr Signed-off-by: Marc Kleine-Budde mkl@pengutronix.de Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/can/dev/dev.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/drivers/net/can/dev/dev.c b/drivers/net/can/dev/dev.c index 487cb9acdd456..3797d4de254dd 100644 --- a/drivers/net/can/dev/dev.c +++ b/drivers/net/can/dev/dev.c @@ -590,11 +590,12 @@ static void can_restart(struct net_device *dev) priv->can_stats.restarts++;
/* Now restart the device */ - err = priv->do_set_mode(dev, CAN_MODE_START); - netif_carrier_on(dev); - if (err) + err = priv->do_set_mode(dev, CAN_MODE_START); + if (err) { netdev_err(dev, "Error %d during restart", err); + netif_carrier_off(dev); + } }
static void can_restart_work(struct work_struct *work)