linux-kernel - Re: [PATCH net v3] igb: cope with large MAX_SKB

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Message-ID: <CANn89iK60X=ugZysD3Njs2FUQth0-s3anEHUv50EKzqZvDm6jw@mail.gmail.com>
Date: Tue, 23 Jul 2024 10:28:17 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Corinna Vinschen <vinschen@...hat.com>
Cc: netdev@...r.kernel.org, intel-wired-lan@...ts.osuosl.org, 
	linux-kernel@...r.kernel.org, Nikolay Aleksandrov <razor@...ckwall.org>, 
	Jason Xing <kerneljasonxing@...il.com>, Paolo Abeni <pabeni@...hat.com>, 
	Jakub Kicinski <kuba@...nel.org>, "David S . Miller" <davem@...emloft.net>, 
	Tony Nguyen <anthony.l.nguyen@...el.com>, Jesse Brandeburg <jesse.brandeburg@...el.com>
Subject: Re: [PATCH net v3] igb: cope with large MAX_SKB_FRAGS.

On Thu, Jul 18, 2024 at 10:56 AM Corinna Vinschen <vinschen@...hat.com> wrote:
>
> From: Paolo Abeni <pabeni@...hat.com>
>
> Sabrina reports that the igb driver does not cope well with large
> MAX_SKB_FRAG values: setting MAX_SKB_FRAG to 45 causes payload
> corruption on TX.
>
> An easy reproducer is to run ssh to connect to the machine.  With
> MAX_SKB_FRAGS=17 it works, with MAX_SKB_FRAGS=45 it fails.
>
> The root cause of the issue is that the driver does not take into
> account properly the (possibly large) shared info size when selecting
> the ring layout, and will try to fit two packets inside the same 4K
> page even when the 1st fraglist will trump over the 2nd head.
>
> Address the issue forcing the driver to fit a single packet per page,
> leaving there enough room to store the (currently) largest possible
> skb_shared_info.
>
> Fixes: 3948b05950fd ("net: introduce a config option to tweak MAX_SKB_FRAGS")
> Reported-by: Jan Tluka <jtluka@...hat.com>
> Reported-by: Jirka Hladky <jhladky@...hat.com>
> Reported-by: Sabrina Dubroca <sd@...asysnail.net>
> Tested-by: Sabrina Dubroca <sd@...asysnail.net>
> Tested-by: Corinna Vinschen <vinschen@...hat.com>
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>

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