Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761967AbaGRPYp (ORCPT ); Fri, 18 Jul 2014 11:24:45 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:64799 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761928AbaGRPYn (ORCPT ); Fri, 18 Jul 2014 11:24:43 -0400 X-IronPort-AV: E=Sophos;i="5.01,685,1400025600"; d="scan'208";a="154127268" Date: Fri, 18 Jul 2014 16:24:35 +0100 From: Wei Liu To: Zoltan Kiss CC: Wei Liu , Ian Campbell , , , Subject: Re: [PATCH net 1/4] xen-netback: Fix handling frag_list on grant op error path Message-ID: <20140718152435.GN7142@zion.uk.xensource.com> References: <1405624192-21722-1-git-send-email-zoltan.kiss@citrix.com> <1405624192-21722-2-git-send-email-zoltan.kiss@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <1405624192-21722-2-git-send-email-zoltan.kiss@citrix.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-DLP: MIA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 17, 2014 at 08:09:49PM +0100, Zoltan Kiss wrote: > The error handling for skb's with frag_list was completely wrong, it caused > double unmap attempts to happen if the error was on the first skb. Move it to > the right place in the loop. > > Signed-off-by: Zoltan Kiss > Reported-by: Armin Zentai > Cc: netdev@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Cc: xen-devel@lists.xenproject.org > --- > diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c > index 1844a47..604ff71 100644 > --- a/drivers/net/xen-netback/netback.c > +++ b/drivers/net/xen-netback/netback.c > @@ -1030,10 +1030,16 @@ static int xenvif_tx_check_gop(struct xenvif_queue *queue, > { > struct gnttab_map_grant_ref *gop_map = *gopp_map; > u16 pending_idx = XENVIF_TX_CB(skb)->pending_idx; > + /* This points to the shinfo of the actually checked skb, which could be > + * either the first or the one on the frag_list > + */ I think "checked skb" should be "skb being checked". Feel free to disagree as I'm not native English speaker. :-/ > struct skb_shared_info *shinfo = skb_shinfo(skb); > + /* If this is non-NULL, we are currently checking the frag_list skb, and > + * this points to the shinfo of the first one > + */ > + struct skb_shared_info *first_shinfo = NULL; > int nr_frags = shinfo->nr_frags; > int i, err; > - struct sk_buff *first_skb = NULL; > > /* Check status of header. */ > err = (*gopp_copy)->status; > @@ -1086,31 +1092,28 @@ check_frags: > xenvif_idx_unmap(queue, pending_idx); > } > > + /* And if we found the error while checking the frag_list, unmap > + * the first skb's frags > + */ > + if (first_shinfo) { > + for (j = 0; j < first_shinfo->nr_frags; j++) { > + pending_idx = frag_get_pending_idx(&first_shinfo->frags[j]); > + xenvif_idx_unmap(queue, pending_idx); > + } > + } > + > /* Remember the error: invalidate all subsequent fragments. */ > err = newerr; > } > > - if (skb_has_frag_list(skb)) { > - first_skb = skb; > - skb = shinfo->frag_list; > - shinfo = skb_shinfo(skb); > + if (skb_has_frag_list(skb) && !first_shinfo) { Will it ever come to the point that we have another skb in this skb's frag list? Is there any reason prevents you from looping over the (possible) subsequent skbs? I guess if the error is deep in the list it's a bit hard to bookkeep... > + first_shinfo = skb_shinfo(skb); > + shinfo = skb_shinfo(skb_shinfo(skb)->frag_list); In that case I would suggest you add BUG_ON(skb_has_frag_list(skb_shinfo(skb)->frag_list)). I think having more nested frag_list should be a bug in current design. Wei. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/