netdev - Re: [PATCH net-next] net: fix GRO skb truesize update

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Message-ID: <5d4fb1de-7cef-b1fd-7513-27da5793f99@linux.intel.com>
Date:   Wed, 4 Aug 2021 12:29:20 -0700 (PDT)
From:   Mat Martineau <mathew.j.martineau@...ux.intel.com>
To:     Paolo Abeni <pabeni@...hat.com>
cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH net-next] net: fix GRO skb truesize update

On Wed, 4 Aug 2021, Paolo Abeni wrote:

> commit 5e10da5385d2 ("skbuff: allow 'slow_gro' for skb carring sock
> reference") introduces a serious regression at the GRO layer setting
> the wrong truesize for stolen-head skbs.
>
> Restore the correct truesize: SKB_DATA_ALIGN(...) instead of
> SKB_TRUESIZE(...)
>
> Reported-by: Mat Martineau <mathew.j.martineau@...ux.intel.com>
> Fixes: 5e10da5385d2 ("skbuff: allow 'slow_gro' for skb carring sock reference")
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>

With this patch I'm no longer seeing the WARN_ON_ONCE() fire in 
skb_try_coalesce(). Thanks Paolo!

Tested-by: Mat Martineau <mathew.j.martineau@...ux.intel.com>

> ---
> net/core/skbuff.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 97ed77a86bb0..02a603556408 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -4375,7 +4375,7 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb)
> 		memcpy(frag + 1, skbinfo->frags, sizeof(*frag) * skbinfo->nr_frags);
> 		/* We dont need to clear skbinfo->nr_frags here */
>
> -		new_truesize = SKB_TRUESIZE(sizeof(struct sk_buff));
> +		new_truesize = SKB_DATA_ALIGN(sizeof(struct sk_buff));
> 		delta_truesize = skb->truesize - new_truesize;
> 		skb->truesize = new_truesize;
> 		NAPI_GRO_CB(skb)->free = NAPI_GRO_FREE_STOLEN_HEAD;
> --

--
Mat Martineau
Intel