netdev - Re: [Intel-wired-lan] [PATCH net-next 1/2] stmmac: xsk: fix underflow of budget in zerocopy mode

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Message-ID: <687f9d4cf0b14_2aa7cc29443@willemb.c.googlers.com.notmuch>
Date: Tue, 22 Jul 2025 10:16:44 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Jason Xing <kerneljasonxing@...il.com>, 
 Paul Menzel <pmenzel@...gen.mpg.de>
Cc: anthony.l.nguyen@...el.com, 
 przemyslaw.kitszel@...el.com, 
 andrew+netdev@...n.ch, 
 davem@...emloft.net, 
 edumazet@...gle.com, 
 kuba@...nel.org, 
 pabeni@...hat.com, 
 bjorn@...nel.org, 
 magnus.karlsson@...el.com, 
 maciej.fijalkowski@...el.com, 
 jonathan.lemon@...il.com, 
 sdf@...ichev.me, 
 ast@...nel.org, 
 daniel@...earbox.net, 
 hawk@...nel.org, 
 john.fastabend@...il.com, 
 mcoquelin.stm32@...il.com, 
 alexandre.torgue@...s.st.com, 
 linux-stm32@...md-mailman.stormreply.com, 
 bpf@...r.kernel.org, 
 intel-wired-lan@...ts.osuosl.org, 
 netdev@...r.kernel.org, 
 Jason Xing <kernelxing@...cent.com>
Subject: Re: [Intel-wired-lan] [PATCH net-next 1/2] stmmac: xsk: fix underflow
 of budget in zerocopy mode

Jason Xing wrote:
> Hi Paul,
> 
> On Mon, Jul 21, 2025 at 4:56 PM Paul Menzel <pmenzel@...gen.mpg.de> wrote:
> >
> > Dear Jason,
> >
> >
> > Thank you for your patch.
> 
> Thanks for your quick response and review :)
> 
> >
> > Am 21.07.25 um 10:33 schrieb Jason Xing:
> > > From: Jason Xing <kernelxing@...cent.com>
> > >
> > > The issue can happen when the budget number of descs are consumed. As
> >
> > Instead of “The issue”, I’d use “An underflow …”.
> 
> Will change it.
> 
> >
> > > long as the budget is decreased to zero, it will again go into
> > > while (budget-- > 0) statement and get decreased by one, so the
> > > underflow issue can happen. It will lead to returning true whereas the
> > > expected value should be false.
> >
> > What is “it”?
> 
> It means 'underflow of budget' behavior.

A technicality, but this is (negative) overflow.

Underflow is a computation that results in a value that is too small
to be represented by the given type.