netdev - Re: [Intel-wired-lan] [PATCH] igb: cope with large MAX_SKB

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Message-ID: <5d30a9df-224e-4285-94d1-53f6995d648a@molgen.mpg.de>
Date: Tue, 23 Apr 2024 13:52:26 +0200
From: Paul Menzel <pmenzel@...gen.mpg.de>
To: Corinna Vinschen <vinschen@...hat.com>
Cc: netdev@...r.kernel.org, intel-wired-lan@...ts.osuosl.org
Subject: Re: [Intel-wired-lan] [PATCH] igb: cope with large MAX_SKB_FRAGS.

Dear Corinna,


Thank you for the patch.


Am 23.04.24 um 12:24 schrieb Corinna Vinschen:
> From: Paolo Abeni <pabeni@...hat.com>

It’d be great if you removed the trailing dot/period in the commit 
message summary.

> 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.
> 
> 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.

If you have a reproducer for this, it’d be great if you could document 
it in the commit message.

> Fixes: 3948b05950fd ("net: introduce a config option to tweak MAX_SKB_FRAG")
> 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>
> ---
>   drivers/net/ethernet/intel/igb/igb_main.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
> index a3f100769e39..22fb2c322bca 100644
> --- a/drivers/net/ethernet/intel/igb/igb_main.c
> +++ b/drivers/net/ethernet/intel/igb/igb_main.c
> @@ -4833,6 +4833,7 @@ static void igb_set_rx_buffer_len(struct igb_adapter *adapter,
>   
>   #if (PAGE_SIZE < 8192)
>   	if (adapter->max_frame_size > IGB_MAX_FRAME_BUILD_SKB ||
> +	    SKB_HEAD_ALIGN(adapter->max_frame_size) > (PAGE_SIZE / 2) ||
>   	    rd32(E1000_RCTL) & E1000_RCTL_SBP)
>   		set_ring_uses_large_buffer(rx_ring);
>   #endif


Kind regards,

Paul