From 96f30d3ea5241db59cc9ae9787df195e19f3d2bd Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Michal=20Kube=C4=8Dek?= Date: Thu, 29 Jun 2017 11:13:36 +0200 Subject: [PATCH] net: handle NAPI_GRO_FREE_STOLEN_HEAD case also in napi_frags_finish() 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 --- net/core/dev.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/net/core/dev.c b/net/core/dev.c index 278faa3933ad..869a04d5558d 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -4166,10 +4166,16 @@ static gro_result_t napi_frags_finish(struct napi_struct *napi, 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; }