netdev - Re: [PATCH v2] net: usb: ax88179_178a: ax88179_rx

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Message-ID: <8cd9e84dabcf2efbf80f3bc43326bbea8bd21a98.camel@redhat.com>
Date:   Tue, 21 Jun 2022 11:03:57 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Jose Alonso <joalonsof@...il.com>,
        David Laight <David.Laight@...LAB.COM>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v2] net: usb: ax88179_178a: ax88179_rx_fixup corrections

On Mon, 2022-06-20 at 22:18 -0300, Jose Alonso wrote:
> On Mon, 2022-06-20 at 03:45 +0000, David Laight wrote:
> > 
> > > -                       ax_skb->truesize = pkt_len + sizeof(struct sk_buff);
> > 
> > You've 'lost' this lie.
> > IIRC the 'skb' are allocated with 64k buffer space.
> > I'm not at all sure how the buffer space of skb that are cloned
> > into multiple rx buffers are supposed to be accounted for.

I agree that correct memory accounting here is not trivial. I think you
should restore the 'truesize' assignment.

Possibly a slightly more accurate adjustment would be:

	/* for last skb */
	skb->truesize = SKB_TRUESIZE(pkt_len_buf);

	/* for other skbs */
	skb->truesize = pkt_len_buf + SKB_DATA_ALIGN(sizeof(struct sk_buff);

> 
Thanks!

Paolo