Re: [Bug #16626] Machine hangs with EIP at skb_copy_and_csum_dev

[Plamen Petrov]

ÐÐ 05.9.2010 Ð. 10:49, Eric Dumazet ÐÐÐÐÑÐ:
> Le samedi 04 septembre 2010 Ã 22:34 +0200, Jarek Poplawski a Ãcrit :
>
> > Hi again,
> >
> > Just had a second look, and unless I miss something...
> >
> > Plamen, could you test this patch, too? (Without removing the previous
> > one.)
> >
> > Thanks,
> > Jarek P.
> >
> > ------------------->
> >
> > [PATCH] gro: Re-fix different skb headrooms
> >
> > The patch: "gro: fix different skb headrooms" in its part:
> > "2) allocate a minimal skb for head of frag_list" is buggy. The copied
> > skb has p->data set at the ip header at the moment, and skb_gro_offset
> > is the length of ip + tcp headers. So, after the change the length of
> > mac header is skipped. Later skb_set_mac_header() sets it into the
> > NET_SKB_PAD area (if it's long enough) and ip header is misaligned at
> > NET_SKB_PAD + NET_IP_ALIGN offset. There is no reason to assume the
> > original skb was wrongly allocated, so let's copy it as it was.
> >
> > bugzilla : https://bugzilla.kernel.org/show_bug.cgi?id=16626
> > fixes commit: 3d3be4333fdf6faa080947b331a6a19bce1a4f57
> >
> > Reported-by: Plamen Petrov<pvp-lsts@xxxxxxxxxxxxxx>
> > Signed-off-by: Jarek Poplawski<jarkao2@xxxxxxxxx>
> > CC: Eric Dumazet<eric.dumazet@xxxxxxxxx>
> > ---
> >
> > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> > index 26396ff..c83b421 100644
> > --- a/net/core/skbuff.c
> > +++ b/net/core/skbuff.c
> > @@ -2706,7 +2706,7 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
> >   	} else if (skb_gro_len(p) != pinfo->gso_size)
> >   		return -E2BIG;
> >
> > -	headroom = NET_SKB_PAD + NET_IP_ALIGN;
> > +	headroom = skb_headroom(p);
> >   	nskb = alloc_skb(headroom + skb_gro_offset(p), GFP_ATOMIC);
> >   	if (unlikely(!nskb))
> >   		return -ENOMEM;
>
> You are right, thanks for reviewing this patch again :)
>
> By the way, NET_IP_ALIGN is now 0 on x86, so technically speaking, your
> patch un-aligns IP header on x86, but thats OK, since other arches might
> want it being aligned, while x86 doesnt care.
>
> Acked-by: Eric Dumazet<eric.dumazet@xxxxxxxxx>

Well, now that I'm back at work, I'm glad to report
that I tested both variants of the patch, and as Eric
points out - it works both ways.

So, which ever fits you guys better.

Thanks a lot!
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