netdev - Re: [PATCH v4] aquantia: Remove the build

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Message-ID: <20201121132324.72d79e94@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Sat, 21 Nov 2020 13:23:24 -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 v4] aquantia: Remove the build_skb path

On Sat, 21 Nov 2020 13:22:04 -0800 Jakub Kicinski wrote:
> On Thu, 19 Nov 2020 23:52:55 +0000 Ramsay, Lincoln wrote:
> > 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.
> > 
> > Signed-off-by: Lincoln Ramsay <lincoln.ramsay@...ngear.com>  
> 
> I was going to apply as a fix to net and stable but too many small nits
> here to pass. First of all please add a From: line at the beginning of
> the mail which matches the signoff (or use git-send-email, it'll get it
> right).

Ah, one more thing, this is the correct fixes tag, right?

Fixes: 018423e90bee ("net: ethernet: aquantia: Add ring support code")

Please add it right before the signoff line.