From patchwork Wed Oct 10 12:29:09 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [Xen-devel] compound skb frag pages appearing in start_xmit Date: Wed, 10 Oct 2012 02:29:09 -0000 From: Ian Campbell X-Patchwork-Id: 190631 Message-Id: <1349872149.10070.31.camel@zakaz.uk.xensource.com> To: Sander Eikelenboom Cc: Eric Dumazet , "netdev@vger.kernel.org" , Eric Dumazet , "Konrad Rzeszutek Wilk" , xen-devel On Wed, 2012-10-10 at 13:24 +0100, Sander Eikelenboom wrote: > Wednesday, October 10, 2012, 12:13:04 PM, you wrote: > > > On Tue, 2012-10-09 at 15:40 +0100, Ian Campbell wrote: > >> On Tue, 2012-10-09 at 15:27 +0100, Eric Dumazet wrote: > >> > On Tue, 2012-10-09 at 15:17 +0100, Ian Campbell wrote: > >> > > >> > > Does the higher order pages effectively reduce the number of frags which > >> > > are in use? e.g if MAX_SKB_FRAGS is 16, then for order-0 pages you could > >> > > have 64K worth of frag data. > >> > > > >> > > If we switch to order-3 pages everywhere then can the skb contain 512K > >> > > of data, or does the effective maximum number of frags in an skb reduce > >> > > to 2? > >> > > >> > effective number of frags reduce to 2 or 3 > >> > > >> > (We still limit GSO packets to ~63536 bytes) > >> > >> Great! Then I think the fix is more/less trivial... > > > The following seems to work for me. > > But it doesn't seem to work for me ... dmesg attached. > [ 191.777994] ------------[ cut here ]------------ > [ 191.784245] kernel BUG at drivers/net/xen-netback/netback.c:481! Looks like that BUG_ON is a little aggressive. It'll trigger if the data happens to end on a frame boundary. Hopefully this will fix it for you: --- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c index d747e30..f2d6b78 100644 --- a/drivers/net/xen-netback/netback.c +++ b/drivers/net/xen-netback/netback.c @@ -477,7 +477,7 @@ static void netbk_gop_frag_copy(struct xenvif *vif, struct sk_buff *skb, size -= bytes; /* Next frame */ - if (offset == PAGE_SIZE) { + if (offset == PAGE_SIZE && size) { BUG_ON(!PageCompound(page)); page++; offset = 0;