Re: [PATCH net 2/3] can: gs_usb: gs_can_open(): fix race dev->can.state condition

[Matthieu Baerts <matthieu.baerts@tessares.net>]

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Hello,

On 21/09/2022 10:36, Marc Kleine-Budde wrote:
> The dev->can.state is set to CAN_STATE_ERROR_ACTIVE, after the device
> has been started. On busy networks the CAN controller might receive
> CAN frame between and go into an error state before the dev->can.state
> is assigned.
> 
> Assign dev->can.state before starting the controller to close the race
> window.
> 
> Fixes: d08e973a77d1 ("can: gs_usb: Added support for the GS_USB CAN devices")
> Link: https://lore.kernel.org/all/20220920195216.232481-1-mkl@pengutronix.de
> Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

FYI, we got a small conflict when merging -net in net-next in the MPTCP
tree due to this patch applied in -net:

  5440428b3da6 ("can: gs_usb: gs_can_open(): fix race dev->can.state
condition")

and this one from net-next:

  45dfa45f52e6 ("can: gs_usb: add RX and TX hardware timestamp support")

The conflict has been resolved on our side[1] and the resolution we
suggest is attached to this email.

Cheers,
Matt

[1] https://github.com/multipath-tcp/mptcp_net-next/commit/671f1521b564
-- 
Tessares | Belgium | Hybrid Access Solutions
www.tessares.net

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diff --cc drivers/net/can/usb/gs_usb.c
index cc363f1935ce,c1ff3c046d62..5e0d280b0cd3
--- a/drivers/net/can/usb/gs_usb.c
+++ b/drivers/net/can/usb/gs_usb.c
@@@ -956,11 -823,8 +956,12 @@@ static int gs_can_open(struct net_devic
  	if (ctrlmode & CAN_CTRLMODE_3_SAMPLES)
  		flags |= GS_CAN_MODE_TRIPLE_SAMPLE;
  
 +	/* if hardware supports timestamps, enable it */
 +	if (dev->feature & GS_CAN_FEATURE_HW_TIMESTAMP)
 +		flags |= GS_CAN_MODE_HW_TIMESTAMP;
 +
  	/* finally start device */
+ 	dev->can.state = CAN_STATE_ERROR_ACTIVE;
  	dm->mode = cpu_to_le32(GS_CAN_MODE_START);
  	dm->flags = cpu_to_le32(flags);
  	rc = usb_control_msg(interface_to_usbdev(dev->iface),
@@@ -977,12 -842,6 +979,10 @@@
  
  	kfree(dm);
  
 +	/* start polling timestamp */
 +	if (dev->feature & GS_CAN_FEATURE_HW_TIMESTAMP)
 +		gs_usb_timestamp_init(dev);
 +
- 	dev->can.state = CAN_STATE_ERROR_ACTIVE;
- 
  	parent->active_channels++;
  	if (!(dev->can.ctrlmode & CAN_CTRLMODE_LISTENONLY))
  		netif_start_queue(netdev);