From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752462AbdIIW2r (ORCPT ); Sat, 9 Sep 2017 18:28:47 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:41822 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752001AbdIIWYy (ORCPT ); Sat, 9 Sep 2017 18:24:54 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "David S. Miller" , "=?UTF-8?q?Michal=20Kube=C4=8Dek?=" Date: Sat, 09 Sep 2017 22:47:15 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 222/233] net: handle NAPI_GRO_FREE_STOLEN_HEAD case also in napi_frags_finish() In-Reply-To: X-SA-Exim-Connect-IP: 2a02:8011:400e:2:6f00:88c8:c921:d332 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.48-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Michal Kubeček commit e44699d2c28067f69698ccb68dd3ddeacfebc434 upstream. Recently I started seeing warnings about pages with refcount -1. The problem was traced to packets being reused after their head was merged into a GRO packet by skb_gro_receive(). While bisecting the issue pointed to commit c21b48cc1bbf ("net: adjust skb->truesize in ___pskb_trim()") and I have never seen it on a kernel with it reverted, I believe the real problem appeared earlier when the option to merge head frag in GRO was implemented. Handling NAPI_GRO_FREE_STOLEN_HEAD state was only added to GRO_MERGED_FREE branch of napi_skb_finish() so that if the driver uses napi_gro_frags() and head is merged (which in my case happens after the skb_condense() call added by the commit mentioned above), the skb is reused including the head that has been merged. As a result, we release the page reference twice and eventually end up with negative page refcount. To fix the problem, handle NAPI_GRO_FREE_STOLEN_HEAD in napi_frags_finish() the same way it's done in napi_skb_finish(). Fixes: d7e8883cfcf4 ("net: make GRO aware of skb->head_frag") Signed-off-by: Michal Kubecek Signed-off-by: David S. Miller [bwh: Backported to 3.16: The necessary cleanup is just kmem_cache_free(), so don't bother adding a function for this.] Signed-off-by: Ben Hutchings --- --- a/net/core/dev.c +++ b/net/core/dev.c @@ -4166,10 +4166,16 @@ static gro_result_t napi_frags_finish(st break; case GRO_DROP: - case GRO_MERGED_FREE: napi_reuse_skb(napi, skb); break; + case GRO_MERGED_FREE: + if (NAPI_GRO_CB(skb)->free == NAPI_GRO_FREE_STOLEN_HEAD) + kmem_cache_free(skbuff_head_cache, skb); + else + napi_reuse_skb(napi, skb); + break; + case GRO_MERGED: break; }