linux-kernel - Re: [Intel-wired-lan] [PATCH net v4 1/1] i40e: xsk: advance next_to

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Message-ID: <aR3sLeEpPGK0iP+3@boxer>
Date: Wed, 19 Nov 2025 17:11:25 +0100
From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To: Alessandro Decina <alessandro.d@...il.com>
CC: "Loktionov, Aleksandr" <aleksandr.loktionov@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>, "David S. Miller"
	<davem@...emloft.net>, Alexei Starovoitov <ast@...nel.org>, Andrew Lunn
	<andrew+netdev@...n.ch>, Daniel Borkmann <daniel@...earbox.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, "Jesper Dangaard
 Brouer" <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>, "Paolo
 Abeni" <pabeni@...hat.com>, "Kitszel, Przemyslaw"
	<przemyslaw.kitszel@...el.com>, Stanislav Fomichev <sdf@...ichev.me>,
	"Sarkar, Tirthendu" <tirthendu.sarkar@...el.com>, "Nguyen, Anthony L"
	<anthony.l.nguyen@...el.com>, "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
	"intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Intel-wired-lan] [PATCH net v4 1/1] i40e: xsk: advance
 next_to_clean on status descriptors

On Wed, Nov 19, 2025 at 11:49:44AM +1100, Alessandro Decina wrote:
> On Tue, Nov 18, 2025 at 07:45:24PM +0100, Maciej Fijalkowski wrote:
> > Repro steps would be nice to have, rest would be rather redundant to me.
> 
> Yeah unfortunately I don't really know how to _manually_ reproduce.
> 
> I don't know why I'm getting these status descriptors, but I'm getting
> them reproducibly every few minutes on ubuntu 24.04 across 3 machines

Might be a HW quirk, I don't remember. Other example I have handy is HW
that is served by ice driver can sometimes produce 0-length descriptors
for jumbo frames and we do handle this in driver.

Describing your setup in commit message would be enough, if you ask me.

> where I've hit this bug/tested the fix. The machines are doing ~300Mbps
> of UDP traffic, some of which is done using AF_XDP. The AF_XDP code is
> TX only, so it's executing the build-skb-in-zc-path all the time as all
> the ingress traffic goes to sockets. 
> 
> If you have any idea on how to reliably produce the descriptors I'm
> happy to give it a try.