Re: [PATCH net] net: 8139cp: close race between NAPI completion and Rx unmask

[Geert Uytterhoeven]

On Thu, 22 Oct 2026 at 01:12, Colton Pawielski via B4 Relay
<devnull+colton.pawielski.gmail.com@xxxxxxxxxx> wrote:
> From: Colton Pawielski <colton.pawielski@xxxxxxxxx>
>
> cp_rx_poll() calls napi_complete_done() and only then takes cp->lock
> with interrupts disabled to unmask the Rx interrupts.  An interrupt
> that is not masked while polling (TxOK, TxErr, ...) can arrive in
> between.  cp_interrupt() then sees the Rx status bits, which are still
> set, finds NAPI no longer scheduled, masks Rx and schedules NAPI again.
> cp_rx_poll() then carries on and unmasks Rx anyway.
>
> From that point Rx interrupts are enabled while NAPI is scheduled:
> cp_interrupt() leaves the Rx bits for the poll routine, does not mask
> them because napi_schedule_prep() fails, and the level-triggered
> interrupt fires again as soon as it returns.  On an SH7751 LANDISK
> under combined Tx/Rx load this interrupt storm was captured with a RAM
> trace right before the board locked up hard.
>
> Do the completion and the unmask under the lock, as 8139too does.
>
> Fixes: ab1e7e1d2666 ("8139cp: use napi_complete_done()")
> Signed-off-by: Colton Pawielski <colton.pawielski@xxxxxxxxx>

Seems to improve nfsroot on Landisk/USL-5P: no lock-ups seen anymore.
Tested-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds