This is a note to let you know that I've just added the patch titled net: handle NAPI_GRO_FREE_STOLEN_HEAD case also in napi_frags_finish() to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: net-handle-napi_gro_free_stolen_head-case-also-in-napi_frags_finish.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From e44699d2c28067f69698ccb68dd3ddeacfebc434 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Michal=20Kube=C4=8Dek?= <mkubecek@xxxxxxx> Date: Thu, 29 Jun 2017 11:13:36 +0200 Subject: net: handle NAPI_GRO_FREE_STOLEN_HEAD case also in napi_frags_finish() From: Michal Kubeček <mkubecek@xxxxxxx> 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 <mkubecek@xxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/core/dev.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-) --- a/net/core/dev.c +++ b/net/core/dev.c @@ -4375,6 +4375,12 @@ struct packet_offload *gro_find_complete } EXPORT_SYMBOL(gro_find_complete_by_type); +static void napi_skb_free_stolen_head(struct sk_buff *skb) +{ + skb_dst_drop(skb); + kmem_cache_free(skbuff_head_cache, skb); +} + static gro_result_t napi_skb_finish(gro_result_t ret, struct sk_buff *skb) { switch (ret) { @@ -4388,12 +4394,10 @@ static gro_result_t napi_skb_finish(gro_ break; case GRO_MERGED_FREE: - if (NAPI_GRO_CB(skb)->free == NAPI_GRO_FREE_STOLEN_HEAD) { - skb_dst_drop(skb); - kmem_cache_free(skbuff_head_cache, skb); - } else { + if (NAPI_GRO_CB(skb)->free == NAPI_GRO_FREE_STOLEN_HEAD) + napi_skb_free_stolen_head(skb); + else __kfree_skb(skb); - } break; case GRO_HELD: @@ -4459,10 +4463,16 @@ 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) + napi_skb_free_stolen_head(skb); + else + napi_reuse_skb(napi, skb); + break; + case GRO_MERGED: break; } Patches currently in stable-queue which might be from mkubecek@xxxxxxx are queue-4.4/net-handle-napi_gro_free_stolen_head-case-also-in-napi_frags_finish.patch