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 <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>
[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 <ben@decadent.org.uk>

diff --git a/net/core/dev.c b/net/core/dev.c
index 278faa3933adc9e3427f26beb67ba423a51eab97..869a04d5558d14785a4d75d59c194bd4614bd80d 100644 (file)
--- 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;
        }