Re: [PATCH net] can: mcp251xfd: flush RX offload queue during long IRQs

[Marc Kleine-Budde]

On 22.09.2026 00:01:06, Chris Strong via B4 Relay wrote:
> From: Chris Strong <chris.strong@xxxxxxxxxxxxxxx>
>
> Under sustained receive traffic, the threaded interrupt handler can
> continue draining the controller indefinitely. Received SKBs accumulate
> in skb_irq_queue, but can_rx_offload_threaded_irq_finish() only splices
> them into the NAPI-visible skb_queue when the handler finishes.
>
> The RX-offload overflow checks inspect skb_queue rather than
> skb_irq_queue. If the handler does not return, the IRQ-local queue can
> therefore grow without bound while NAPI remains unscheduled. This can
> exhaust memory and prevent received frames from reaching the networking
> stack.
>
> Add a small RX-offload predicate that reports when the IRQ-local queue
> has reached the NAPI weight. Use it to stop the dedicated RX interrupt
> loop, process TEF and the other pending interrupt sources, and then
> publish the batch. Publish additional batches from the main interrupt
> loop while the controller remains busy. Since one RX pass can enqueue a
> complete hardware ring, this keeps each splice near the NAPI weight
> rather than enforcing a strict limit.
>
> Keep this policy in mcp251xfd because its controller-draining loops are
> the source of the unbounded handler. Accounting for skb_irq_queue in the
> generic overflow check would cap memory use by dropping frames, but
> would still leave NAPI unscheduled.
>
> Publishing smaller batches narrows the timestamp sorting window.
> Ordering across batches is already best-effort; RX and TEF events from
> each controller-status pass are processed before the batch is published.
>
> Fixes: c757096ea103 ("can: rx-offload: add skb queue for use during ISR")
> Assisted-by: LLM
> Signed-off-by: Chris Strong <chris.strong@xxxxxxxxxxxxxxx>
> ---
> Hi all,
>
> This is my first upstream Linux kernel patch submission, so feedback on both
> the implementation and the submission format would be appreciated.

You're using b4, this is a good choice and the best tool for this job.

Please split the changes into 2 patches, first add the rx-offload
helper, then the mcp251xfd changes.

The changes look pretty good to me! Good Work!

If you want to improve you can shorten the patch description. The
subject already states what you do, the patch description should explain
in more detail (if needed) and why. Finish with describing your changes
in imperative mood. See [1] for details.

[1] https://github.com/torvalds/linux/blob/master/Documentation/process/submitting-patches.rst#describe-your-changes

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde          |
Embedded Linux                   | https://www.pengutronix.de |
Vertretung Nürnberg              | Phone: +49-5121-206917-129 |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-9   |

Attachment: signature.asc
Description: PGP signature