From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wei Liu Subject: Re: [Xen-devel] [PATCH] xen-netfront: pull on receive skb may need to happen earlier Date: Tue, 9 Jul 2013 17:51:34 +0100 Message-ID: <20130709165134.GG19798@zion.uk.xensource.com> References: <8511913.uMAmUdIO30@eistomin.edss.local> <20130517085923.GC14401@zion.uk.xensource.com> <51D57C1F.8070909@hunenet.nl> <20130704150137.GW7483@zion.uk.xensource.com> <51D6AED902000078000E2EA9@nat28.tlf.novell.com> <20130705145319.GB9050@zion.uk.xensource.com> <51DAA9B202000078000E3357@nat28.tlf.novell.com> <51DAE6CA02000078000E3566@nat28.tlf.novell.com> <20130708154814.GI8027@zion.uk.xensource.com> <51DBCF4F02000078000E3793@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Cc: Wei Liu , Ian Campbell , , Dion Kant , , , To: Jan Beulich Return-path: Content-Disposition: inline In-Reply-To: <51DBCF4F02000078000E3793@nat28.tlf.novell.com> Sender: stable-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Tue, Jul 09, 2013 at 07:52:31AM +0100, Jan Beulich wrote: > >>> On 08.07.13 at 17:48, Wei Liu wrote: > > On Mon, Jul 08, 2013 at 03:20:26PM +0100, Jan Beulich wrote: > >> @@ -1014,7 +1025,7 @@ err: > >> > >> skb_shinfo(skb)->frags[0].page_offset = rx->offset; > >> skb_frag_size_set(&skb_shinfo(skb)->frags[0], rx->status); > >> - skb->data_len = rx->status; > >> + skb->len = skb->data_len = rx->status; > > > > This is not correct. You should not be needing this. Now you lose count > > of SKB head len. Try to go without the above line and see if it makes a > > difference? > > I don't follow - at this point, there's 0 bytes of head (this only > changes with the first call to __pskb_pull_tail()). Hence ->len == > ->data_len seems correct to me (and afaict pulling would do the > wrong thing if I dropped that change). > My bad, I suggested the wrong thing. :-( But I would prefer skb->len += skb->data_len. In the case that skb->len == 0 it's the same as your line while skb->len is not zero it would also do the right thing. As for the warning in skb_try_coalesce, I don't see any direct call to it in netfront, I will need to think about it. It looks like it's really something very deep in the stack. Wei. > Jan