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

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Message-ID: <afdb7011-5098-47dd-89af-5ed0096294d8@redhat.com>
Date: Tue, 23 Jul 2024 10:27:07 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Corinna Vinschen <vinschen@...hat.com>,
 Tony Nguyen <anthony.l.nguyen@...el.com>
Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
 intel-wired-lan@...ts.osuosl.org, Nikolay Aleksandrov <razor@...ckwall.org>,
 Jason Xing <kerneljasonxing@...il.com>, Jakub Kicinski <kuba@...nel.org>,
 "David S . Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jesse Brandeburg <jesse.brandeburg@...el.com>
Subject: Re: [PATCH net v3] igb: cope with large MAX_SKB_FRAGS.

On 7/18/24 10:56, Corinna Vinschen 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>

@Tony: would you like to take this one in your tree first, or we can 
merge it directly?

Thanks!

Paolo