netdev - Re: [PATCH net v5] aquantia: Remove the build

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Message-ID: <20201124110202.38dc6d5b@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Tue, 24 Nov 2020 11:02:02 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     "Ramsay, Lincoln" <Lincoln.Ramsay@...i.com>
Cc:     Florian Westphal <fw@...len.de>,
        Igor Russkikh <irusskikh@...vell.com>,
        "David S. Miller" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Dmitry Bogdanov <dbogdanov@...vell.com>
Subject: Re: [PATCH net v5] aquantia: Remove the build_skb path

On Mon, 23 Nov 2020 21:40:43 +0000 Ramsay, Lincoln wrote:
> From: Lincoln Ramsay <lincoln.ramsay@...ngear.com>
> 
> When performing IPv6 forwarding, there is an expectation that SKBs
> will have some headroom. When forwarding a packet from the aquantia
> driver, this does not always happen, triggering a kernel warning.
> 
> aq_ring.c has this code (edited slightly for brevity):
> 
> if (buff->is_eop && buff->len <= AQ_CFG_RX_FRAME_MAX - AQ_SKB_ALIGN) {
>     skb = build_skb(aq_buf_vaddr(&buff->rxdata), AQ_CFG_RX_FRAME_MAX);
> } else {
>     skb = napi_alloc_skb(napi, AQ_CFG_RX_HDR_SIZE);
> 
> There is a significant difference between the SKB produced by these
> 2 code paths. When napi_alloc_skb creates an SKB, there is a certain
> amount of headroom reserved. However, this is not done in the
> build_skb codepath.
> 
> As the hardware buffer that build_skb is built around does not
> handle the presence of the SKB header, this code path is being
> removed and the napi_alloc_skb path will always be used. This code
> path does have to copy the packet header into the SKB, but it adds
> the packet data as a frag.
> 
> Fixes: 018423e90bee ("net: ethernet: aquantia: Add ring support code")
> Signed-off-by: Lincoln Ramsay <lincoln.ramsay@...ngear.com>

Applied, queued of stable.

Thanks!