netdev - Re: [PATCH] net: Revert tx queue length on partial failure in dev_qdisc_change_tx_queue

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Message-ID: <CANn89iKwrp0j1bYQ8yGsbj_B1+eEv8BaWavHAuWpYdQVg-dqsA@mail.gmail.com>
Date: Wed, 23 Jul 2025 11:36:31 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Suchit K <suchitkarunakaran@...il.com>
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, horms@...nel.org, 
	jhs@...atatu.com, xiyou.wangcong@...il.com, jiri@...nulli.us, sdf@...ichev.me, 
	kuniyu@...gle.com, aleksander.lobakin@...el.com, netdev@...r.kernel.org, 
	skhan@...uxfoundation.org, linux-kernel-mentees@...ts.linux.dev, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: Revert tx queue length on partial failure in dev_qdisc_change_tx_queue_len()

On Wed, Jul 23, 2025 at 11:17 AM Suchit K <suchitkarunakaran@...il.com> wrote:
>
> >
> > WRITE_ONCE() is missing.
> >
> > > +               while (i >= 0) {
> > > +                       qdisc_change_tx_queue_len(dev, &dev->_tx[i]);
> >
> > What happens if one of these calls fails ?
> >
> > I think a fix will be more complicated...
>
> Hi Eric,
> Given that pfifo_fast_change_tx_queue_len is currently the only
> implementation of change_tx_queue_len, would it be reasonable to
> handle partial failures solely within pfifo_fast_change_tx_queue_len
> (which in turn leads to skb_array_resize_multiple_bh)? In other words,
> is it sufficient to modify only the underlying low level
> implementation of pfifo_fast_change_tx_queue_len for partial failures,
> given that it's the sole implementation of change_tx_queue_len?

A generic solution will involve two phases...
Lots of core changes, for a very narrow case.

Most of us do not use pfifo_fast anyway.