netdev - Re: [PATCH net] net: don't let netpoll invoke NAPI if in xmit context

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Date:   Fri, 31 Mar 2023 05:34:29 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, pabeni@...hat.com,
        Roman Gushchin <roman.gushchin@...ux.dev>, leitao@...ian.org,
        shemminger@...ux.foundation.org
Subject: Re: [PATCH net] net: don't let netpoll invoke NAPI if in xmit context

On Fri, Mar 31, 2023 at 5:23 AM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Fri, 31 Mar 2023 04:41:23 +0200 Eric Dumazet wrote:
> > Note that we update WRITE_ONCE(txq->xmit_lock_owner, cpu) _after_
> > spin_lock(&txq->_xmit_lock);
> >
> > So there is a tiny window I think, for missing that we got the
> > spinlock, but I do not see how to avoid it without excessive cost.
>
> Ugh, true. Hopefully the chances of taking an IRQ which tries to print
> something between those two instructions are fairly low.
>
> I was considering using dev_recursion_level() but AFAICT we don't
> currently bump it when dequeuing from the qdisc..

SGTM, thanks.

Reviewed-by: Eric Dumazet <edumazet@...gle.com>