Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422789AbaGRRr7 (ORCPT ); Fri, 18 Jul 2014 13:47:59 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:48695 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030518AbaGRRr6 (ORCPT ); Fri, 18 Jul 2014 13:47:58 -0400 X-IronPort-AV: E=Sophos;i="5.01,686,1400025600"; d="scan'208";a="154173356" Message-ID: <53C95DCB.90806@citrix.com> Date: Fri, 18 Jul 2014 18:47:55 +0100 From: Zoltan Kiss User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: Wei Liu CC: Ian Campbell , , , Subject: Re: [PATCH net 1/4] xen-netback: Fix handling frag_list on grant op error path References: <1405624192-21722-1-git-send-email-zoltan.kiss@citrix.com> <1405624192-21722-2-git-send-email-zoltan.kiss@citrix.com> <20140718152435.GN7142@zion.uk.xensource.com> In-Reply-To: <20140718152435.GN7142@zion.uk.xensource.com> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.80.2.133] X-DLP: MIA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 18/07/14 16:24, Wei Liu wrote: > 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. There are already 3 things which prevents this - in count_requests we drop the packet if it has more than XEN_NETBK_LEGACY_SLOTS_MAX slots - in get_requests there is a BUG_ON(frag_overflow > MAX_SKB_FRAGS), which shouldn't really due to the prev point - in the same funciont we create a frag_list skb exactly once -- 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/