net: ipv6: ioam6_iptunnel: mitigate 2-realloc issue

This patch mitigates the two-reallocations issue with ioam6_iptunnel by
providing the dst_entry (in the cache) to the first call to
skb_cow_head(). As a result, the very first iteration may still trigger
two reallocations (i.e., empty cache), while next iterations would only
trigger a single reallocation.

Performance tests before/after applying this patch, which clearly shows
the improvement:
- inline mode:
  - before: https://ibb.co/LhQ8V63
  - after: https://ibb.co/x5YT2bS
- encap mode:
  - before: https://ibb.co/3Cjm5m0
  - after: https://ibb.co/TwpsxTC
- encap mode with tunsrc:
  - before: https://ibb.co/Gpy9QPg
  - after: https://ibb.co/PW1bZFT

This patch also fixes an incorrect behavior: after the insertion, the
second call to skb_cow_head() makes sure that the dev has enough
headroom in the skb for layer 2 and stuff. In that case, the "old"
dst_entry was used, which is now fixed. After discussing with Paolo, it
appears that both patches can be merged into a single one -this one-
(for the sake of readability) and target net-next.

Signed-off-by: Justin Iurman <justin.iurman@uliege.be>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/ipv6/ioam6_iptunnel.c b/net/ipv6/ioam6_iptunnel.c
index 9d8422e350f8d5702c6abe3484fdc669c7f297b5..28e5a89dc2557493ff8b50f040bd5f1e73522a5f 100644 (file)
--- a/net/ipv6/ioam6_iptunnel.c
+++ b/net/ipv6/ioam6_iptunnel.c
@@ -253,14 +253,15 @@ static int ioam6_do_fill(struct net *net, struct sk_buff *skb)
 }
 
 static int ioam6_do_inline(struct net *net, struct sk_buff *skb,
-                          struct ioam6_lwt_encap *tuninfo)
+                          struct ioam6_lwt_encap *tuninfo,
+                          struct dst_entry *cache_dst)
 {
        struct ipv6hdr *oldhdr, *hdr;
        int hdrlen, err;
 
        hdrlen = (tuninfo->eh.hdrlen + 1) << 3;
 
-       err = skb_cow_head(skb, hdrlen + skb->mac_len);
+       err = skb_cow_head(skb, hdrlen + dst_dev_overhead(cache_dst, skb));
        if (unlikely(err))
                return err;
 
@@ -291,7 +292,8 @@ static int ioam6_do_encap(struct net *net, struct sk_buff *skb,
                          struct ioam6_lwt_encap *tuninfo,
                          bool has_tunsrc,
                          struct in6_addr *tunsrc,
-                         struct in6_addr *tundst)
+                         struct in6_addr *tundst,
+                         struct dst_entry *cache_dst)
 {
        struct dst_entry *dst = skb_dst(skb);
        struct ipv6hdr *hdr, *inner_hdr;
@@ -300,7 +302,7 @@ static int ioam6_do_encap(struct net *net, struct sk_buff *skb,
        hdrlen = (tuninfo->eh.hdrlen + 1) << 3;
        len = sizeof(*hdr) + hdrlen;
 
-       err = skb_cow_head(skb, len + skb->mac_len);
+       err = skb_cow_head(skb, len + dst_dev_overhead(cache_dst, skb));
        if (unlikely(err))
                return err;
 
@@ -334,7 +336,7 @@ static int ioam6_do_encap(struct net *net, struct sk_buff *skb,
 
 static int ioam6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 {
-       struct dst_entry *dst = skb_dst(skb);
+       struct dst_entry *dst = skb_dst(skb), *cache_dst;
        struct in6_addr orig_daddr;
        struct ioam6_lwt *ilwt;
        int err = -EINVAL;
@@ -352,6 +354,10 @@ static int ioam6_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 
        orig_daddr = ipv6_hdr(skb)->daddr;
 
+       local_bh_disable();
+       cache_dst = dst_cache_get(&ilwt->cache);
+       local_bh_enable();
+
        switch (ilwt->mode) {
        case IOAM6_IPTUNNEL_MODE_INLINE:
 do_inline:
@@ -359,7 +365,7 @@ do_inline:
                if (ipv6_hdr(skb)->nexthdr == NEXTHDR_HOP)
                        goto out;
 
-               err = ioam6_do_inline(net, skb, &ilwt->tuninfo);
+               err = ioam6_do_inline(net, skb, &ilwt->tuninfo, cache_dst);
                if (unlikely(err))
                        goto drop;
 
@@ -369,7 +375,7 @@ do_encap:
                /* Encapsulation (ip6ip6) */
                err = ioam6_do_encap(net, skb, &ilwt->tuninfo,
                                     ilwt->has_tunsrc, &ilwt->tunsrc,
-                                    &ilwt->tundst);
+                                    &ilwt->tundst, cache_dst);
                if (unlikely(err))
                        goto drop;
 
@@ -387,41 +393,36 @@ do_encap:
                goto drop;
        }
 
-       err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
-       if (unlikely(err))
-               goto drop;
+       if (unlikely(!cache_dst)) {
+               struct ipv6hdr *hdr = ipv6_hdr(skb);
+               struct flowi6 fl6;
+
+               memset(&fl6, 0, sizeof(fl6));
+               fl6.daddr = hdr->daddr;
+               fl6.saddr = hdr->saddr;
+               fl6.flowlabel = ip6_flowinfo(hdr);
+               fl6.flowi6_mark = skb->mark;
+               fl6.flowi6_proto = hdr->nexthdr;
+
+               cache_dst = ip6_route_output(net, NULL, &fl6);
+               if (cache_dst->error) {
+                       err = cache_dst->error;
+                       dst_release(cache_dst);
+                       goto drop;
+               }
 
-       if (!ipv6_addr_equal(&orig_daddr, &ipv6_hdr(skb)->daddr)) {
                local_bh_disable();
-               dst = dst_cache_get(&ilwt->cache);
+               dst_cache_set_ip6(&ilwt->cache, cache_dst, &fl6.saddr);
                local_bh_enable();
 
-               if (unlikely(!dst)) {
-                       struct ipv6hdr *hdr = ipv6_hdr(skb);
-                       struct flowi6 fl6;
-
-                       memset(&fl6, 0, sizeof(fl6));
-                       fl6.daddr = hdr->daddr;
-                       fl6.saddr = hdr->saddr;
-                       fl6.flowlabel = ip6_flowinfo(hdr);
-                       fl6.flowi6_mark = skb->mark;
-                       fl6.flowi6_proto = hdr->nexthdr;
-
-                       dst = ip6_route_output(net, NULL, &fl6);
-                       if (dst->error) {
-                               err = dst->error;
-                               dst_release(dst);
-                               goto drop;
-                       }
-
-                       local_bh_disable();
-                       dst_cache_set_ip6(&ilwt->cache, dst, &fl6.saddr);
-                       local_bh_enable();
-               }
+               err = skb_cow_head(skb, LL_RESERVED_SPACE(cache_dst->dev));
+               if (unlikely(err))
+                       goto drop;
+       }
 
+       if (!ipv6_addr_equal(&orig_daddr, &ipv6_hdr(skb)->daddr)) {
                skb_dst_drop(skb);
-               skb_dst_set(skb, dst);
-
+               skb_dst_set(skb, cache_dst);
                return dst_output(net, sk, skb);
        }
 out: