netdev - RE: [Intel-wired-lan] [PATCH net v3] igb: cope with large MAX_SKB

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Message-ID: <CYYPR11MB8429498A55692627ECB2B10FBDBF2@CYYPR11MB8429.namprd11.prod.outlook.com>
Date: Tue, 6 Aug 2024 15:13:36 +0000
From: "Pucha, HimasekharX Reddy" <himasekharx.reddy.pucha@...el.com>
To: "Vinschen, Corinna" <vinschen@...hat.com>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>, "intel-wired-lan@...ts.osuosl.org"
	<intel-wired-lan@...ts.osuosl.org>, Eric Dumazet <edumazet@...gle.com>
CC: Jason Xing <kerneljasonxing@...il.com>, Nikolay Aleksandrov
	<razor@...ckwall.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Nguyen, Anthony L"
	<anthony.l.nguyen@...el.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, "David S . Miller" <davem@...emloft.net>
Subject: RE: [Intel-wired-lan] [PATCH net v3] igb: cope with large
 MAX_SKB_FRAGS.

> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces@...osl.org> On Behalf Of Corinna Vinschen
> Sent: Thursday, July 18, 2024 2:27 PM
> To: netdev@...r.kernel.org; intel-wired-lan@...ts.osuosl.org; Eric Dumazet <edumazet@...gle.com>
> Cc: Jason Xing <kerneljasonxing@...il.com>; Nikolay Aleksandrov <razor@...ckwall.org>; linux-kernel@...r.kernel.org; Nguyen, Anthony L <anthony.l.nguyen@...el.com>; Jakub Kicinski <kuba@...nel.org>; Paolo Abeni <pabeni@...hat.com>; David S . Miller <davem@...emloft.net>
> Subject: [Intel-wired-lan] [PATCH net v3] igb: cope with large MAX_SKB_FRAGS.
>
> 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>
> ---
> v2: fix subject, add a simple reproducer
> v3: fix Fixes, tested with all MTUs from 1200 to 1280 per Eric's suggestion
>
>  drivers/net/ethernet/intel/igb/igb_main.c | 1 +
>  1 file changed, 1 insertion(+)
>

Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@...el.com> (A Contingent worker at Intel)