Re: [PATCH net v3] igb: cope with large MAX_SKB_FRAGS.

[Eric Dumazet]

On Thu, Jul 18, 2024 at 10:56 AM Corinna Vinschen <vinschen@xxxxxxxxxx> wrote:
>
> From: Paolo Abeni <pabeni@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> Reported-by: Jirka Hladky <jhladky@xxxxxxxxxx>
> Reported-by: Sabrina Dubroca <sd@xxxxxxxxxxxxxxx>
> Tested-by: Sabrina Dubroca <sd@xxxxxxxxxxxxxxx>
> Tested-by: Corinna Vinschen <vinschen@xxxxxxxxxx>
> Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>

Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>