From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: compound skb frag pages appearing in start_xmit Date: Tue, 09 Oct 2012 16:01:45 +0200 Message-ID: <1349791305.21172.4425.camel@edumazet-glaptop> References: <1349790467.21847.185.camel@zakaz.uk.xensource.com> <1349790863.21172.4406.camel@edumazet-glaptop> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Eric Dumazet , xen-devel , netdev@vger.kernel.org, Konrad Rzeszutek Wilk , Sander Eikelenboom To: Ian Campbell Return-path: Received: from mail-bk0-f46.google.com ([209.85.214.46]:34880 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752262Ab2JIOCw (ORCPT ); Tue, 9 Oct 2012 10:02:52 -0400 Received: by mail-bk0-f46.google.com with SMTP id jk13so2668683bkc.19 for ; Tue, 09 Oct 2012 07:02:51 -0700 (PDT) In-Reply-To: <1349790863.21172.4406.camel@edumazet-glaptop> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, 2012-10-09 at 15:54 +0200, Eric Dumazet wrote: > On Tue, 2012-10-09 at 14:47 +0100, Ian Campbell wrote: > > Hi Eric, > > > > Hi Ian > > > Sander has discovered an issue where xen-netback is given a compound > > page as one of the skb frag pages to transmit. Currently netback can > > only handle PAGE_SIZE'd frags and bugs out. > > > > I suspect this is something to do with 69b08f62e174 "net: use bigger > > pages in __netdev_alloc_frag", although perhaps not because it looks > > like only tg3 uses it and Sander has an r8169. Also tg3 seems to only > > call netdev_alloc_frag for sizes < PAGE_SIZE. I'm probably missing > > something. > > > Its not the commit you want ;) Hmm, I take it back. It also can give you the same problem : We use this allocator for rx path of drivers : __netdev_alloc_skb() So its now absolutely possible that one skb->head is backed by a order-3 page. Is the problem coming from xen_netbk_count_skb_slots() ? Give me more information if you want me to help.