[PATCH v4 net-next 19/19] inet: frags: get rid of nf_ct_frag6_skb_cb/NFCT_FRAG6_CB

[Eric Dumazet]

nf_ct_frag6_queue() uses skb->cb[] to store the fragment offset,
meaning that we could use two cache lines per skb when finding
the insertion point, if for some reason inet6_skb_parm size
is increased in the future.

By using skb->ip_defrag_offset instead of skb->cb[] we pack all the fields
in a single cache line, matching what we did for IPv4.

Signed-off-by: Eric Dumazet <eduma...@google.com>
---
 net/ipv6/netfilter/nf_conntrack_reasm.c | 29 ++++++++++---------------
 1 file changed, 11 insertions(+), 18 deletions(-)

diff --git a/net/ipv6/netfilter/nf_conntrack_reasm.c 
b/net/ipv6/netfilter/nf_conntrack_reasm.c
index 
603a395928593a071aff28105578d3bfdbf1b31e..3622aac343aea3cd0d8165d8681f42595735cd90
 100644
--- a/net/ipv6/netfilter/nf_conntrack_reasm.c
+++ b/net/ipv6/netfilter/nf_conntrack_reasm.c
@@ -52,14 +52,6 @@
 
 static const char nf_frags_cache_name[] = "nf-frags";
 
-struct nf_ct_frag6_skb_cb
-{
-       struct inet6_skb_parm   h;
-       int                     offset;
-};
-
-#define NFCT_FRAG6_CB(skb)     ((struct nf_ct_frag6_skb_cb *)((skb)->cb))
-
 static struct inet_frags nf_frags;
 
 #ifdef CONFIG_SYSCTL
@@ -270,13 +262,13 @@ static int nf_ct_frag6_queue(struct frag_queue *fq, 
struct sk_buff *skb,
         * this fragment, right?
         */
        prev = fq->q.fragments_tail;
-       if (!prev || NFCT_FRAG6_CB(prev)->offset < offset) {
+       if (!prev || prev->ip_defrag_offset < offset) {
                next = NULL;
                goto found;
        }
        prev = NULL;
        for (next = fq->q.fragments; next != NULL; next = next->next) {
-               if (NFCT_FRAG6_CB(next)->offset >= offset)
+               if (next->ip_defrag_offset >= offset)
                        break;  /* bingo! */
                prev = next;
        }
@@ -292,14 +284,19 @@ static int nf_ct_frag6_queue(struct frag_queue *fq, 
struct sk_buff *skb,
 
        /* Check for overlap with preceding fragment. */
        if (prev &&
-           (NFCT_FRAG6_CB(prev)->offset + prev->len) > offset)
+           (prev->ip_defrag_offset + prev->len) > offset)
                goto discard_fq;
 
        /* Look for overlap with succeeding segment. */
-       if (next && NFCT_FRAG6_CB(next)->offset < end)
+       if (next && next->ip_defrag_offset < end)
                goto discard_fq;
 
-       NFCT_FRAG6_CB(skb)->offset = offset;
+       /* Note : skb->ip_defrag_offset and skb->dev share the same location */
+       if (skb->dev)
+               fq->iif = skb->dev->ifindex;
+       /* Makes sure compiler wont do silly aliasing games */
+       barrier();
+       skb->ip_defrag_offset = offset;
 
        /* Insert this fragment in the chain of fragments. */
        skb->next = next;
@@ -310,10 +307,6 @@ static int nf_ct_frag6_queue(struct frag_queue *fq, struct 
sk_buff *skb,
        else
                fq->q.fragments = skb;
 
-       if (skb->dev) {
-               fq->iif = skb->dev->ifindex;
-               skb->dev = NULL;
-       }
        fq->q.stamp = skb->tstamp;
        fq->q.meat += skb->len;
        fq->ecn |= ecn;
@@ -357,7 +350,7 @@ nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff 
*prev,  struct net_devic
        inet_frag_kill(&fq->q);
 
        WARN_ON(head == NULL);
-       WARN_ON(NFCT_FRAG6_CB(head)->offset != 0);
+       WARN_ON(head->ip_defrag_offset != 0);
 
        ecn = ip_frag_ecn_table[fq->ecn];
        if (unlikely(ecn == 0xff))
-- 
2.17.0.rc1.321.gba9d0f2565-goog