[PATCH 6.1 139/176] net: ipv6: seg6_iptunnel: mitigate 2-realloc issue

5 Mar 2025

6.1-stable review patch.  If anyone has any objections, please let me know.
------------------
From: Justin Iurman justin.iurman@uliege.be
[ Upstream commit 40475b63761abb6f8fdef960d03228a08662c9c4 ]
This patch mitigates the two-reallocations issue with seg6_iptunnel by
providing the dst_entry (in the cache) to the first call to
skb_cow_head(). As a result, the very first iteration would 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:
- before: https://ibb.co/3Cg4sNH
- after: https://ibb.co/8rQ350r
Signed-off-by: Justin Iurman justin.iurman@uliege.be
Cc: David Lebrun dlebrun@google.com
Signed-off-by: Paolo Abeni pabeni@redhat.com
Stable-dep-of: c64a0727f9b1 ("net: ipv6: fix dst ref loop on input in seg6 lwt")
Signed-off-by: Sasha Levin sashal@kernel.org
---
 net/ipv6/seg6_iptunnel.c | 85 ++++++++++++++++++++++++----------------
 1 file changed, 52 insertions(+), 33 deletions(-)

diff --git a/net/ipv6/seg6_iptunnel.c b/net/ipv6/seg6_iptunnel.c
index ae5299c277bcf..c161298c8b335 100644
--- a/net/ipv6/seg6_iptunnel.c
+++ b/net/ipv6/seg6_iptunnel.c
@@ -124,8 +124,8 @@ static __be32 seg6_make_flowlabel(struct net *net, struct sk_buff *skb,
    return flowlabel;
 }
-/* encapsulate an IPv6 packet within an outer IPv6 header with a given SRH */
-int seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh, int proto)
+static int __seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh,
+			       int proto, struct dst_entry *cache_dst)
 {
    struct dst_entry *dst = skb_dst(skb);
    struct net *net = dev_net(dst->dev);
@@ -137,7 +137,7 @@ int seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh, int proto)
    hdrlen = (osrh->hdrlen + 1) << 3;
    tot_len = hdrlen + sizeof(*hdr);
-	err = skb_cow_head(skb, tot_len + skb->mac_len);
+	err = skb_cow_head(skb, tot_len + dst_dev_overhead(cache_dst, skb));
    if (unlikely(err))
    	return err;
@@ -197,11 +197,18 @@ int seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh, int proto)
return 0;
 }
+
+/* encapsulate an IPv6 packet within an outer IPv6 header with a given SRH */
+int seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh, int proto)
+{
+	return __seg6_do_srh_encap(skb, osrh, proto, NULL);
+}
 EXPORT_SYMBOL_GPL(seg6_do_srh_encap);
/* encapsulate an IPv6 packet within an outer IPv6 header with reduced SRH */
 static int seg6_do_srh_encap_red(struct sk_buff *skb,
-				 struct ipv6_sr_hdr *osrh, int proto)
+				 struct ipv6_sr_hdr *osrh, int proto,
+				 struct dst_entry *cache_dst)
 {
    __u8 first_seg = osrh->first_segment;
    struct dst_entry *dst = skb_dst(skb);
@@ -230,7 +237,7 @@ static int seg6_do_srh_encap_red(struct sk_buff *skb,
tot_len = red_hdrlen + sizeof(struct ipv6hdr);
-	err = skb_cow_head(skb, tot_len + skb->mac_len);
+	err = skb_cow_head(skb, tot_len + dst_dev_overhead(cache_dst, skb));
    if (unlikely(err))
    	return err;
@@ -317,8 +324,8 @@ static int seg6_do_srh_encap_red(struct sk_buff *skb,
    return 0;
 }
-/* insert an SRH within an IPv6 packet, just after the IPv6 header */
-int seg6_do_srh_inline(struct sk_buff *skb, struct ipv6_sr_hdr *osrh)
+static int __seg6_do_srh_inline(struct sk_buff *skb, struct ipv6_sr_hdr *osrh,
+				struct dst_entry *cache_dst)
 {
    struct ipv6hdr *hdr, *oldhdr;
    struct ipv6_sr_hdr *isrh;
@@ -326,7 +333,7 @@ int seg6_do_srh_inline(struct sk_buff *skb, struct ipv6_sr_hdr *osrh)
hdrlen = (osrh->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;
@@ -369,9 +376,8 @@ int seg6_do_srh_inline(struct sk_buff *skb, struct ipv6_sr_hdr *osrh)
return 0;
 }
-EXPORT_SYMBOL_GPL(seg6_do_srh_inline);
-static int seg6_do_srh(struct sk_buff *skb)
+static int seg6_do_srh(struct sk_buff *skb, struct dst_entry *cache_dst)
 {
    struct dst_entry *dst = skb_dst(skb);
    struct seg6_iptunnel_encap *tinfo;
@@ -384,7 +390,7 @@ static int seg6_do_srh(struct sk_buff *skb)
    	if (skb->protocol != htons(ETH_P_IPV6))
    		return -EINVAL;
-		err = seg6_do_srh_inline(skb, tinfo->srh);
+		err = __seg6_do_srh_inline(skb, tinfo->srh, cache_dst);
    	if (err)
    		return err;
    	break;
@@ -402,9 +408,11 @@ static int seg6_do_srh(struct sk_buff *skb)
    		return -EINVAL;
if (tinfo->mode == SEG6_IPTUN_MODE_ENCAP)
-			err = seg6_do_srh_encap(skb, tinfo->srh, proto);
+			err = __seg6_do_srh_encap(skb, tinfo->srh,
+						  proto, cache_dst);
    	else
-			err = seg6_do_srh_encap_red(skb, tinfo->srh, proto);
+			err = seg6_do_srh_encap_red(skb, tinfo->srh,
+						    proto, cache_dst);
if (err)
    		return err;
@@ -425,11 +433,13 @@ static int seg6_do_srh(struct sk_buff *skb)
    	skb_push(skb, skb->mac_len);
if (tinfo->mode == SEG6_IPTUN_MODE_L2ENCAP)
-			err = seg6_do_srh_encap(skb, tinfo->srh,
-						IPPROTO_ETHERNET);
+			err = __seg6_do_srh_encap(skb, tinfo->srh,
+						  IPPROTO_ETHERNET,
+						  cache_dst);
    	else
    		err = seg6_do_srh_encap_red(skb, tinfo->srh,
-						    IPPROTO_ETHERNET);
+						    IPPROTO_ETHERNET,
+						    cache_dst);
if (err)
    		return err;
@@ -444,6 +454,13 @@ static int seg6_do_srh(struct sk_buff *skb)
    return 0;
 }
+/* insert an SRH within an IPv6 packet, just after the IPv6 header */
+int seg6_do_srh_inline(struct sk_buff *skb, struct ipv6_sr_hdr *osrh)
+{
+	return __seg6_do_srh_inline(skb, osrh, NULL);
+}
+EXPORT_SYMBOL_GPL(seg6_do_srh_inline);
+
 static int seg6_input_finish(struct net *net, struct sock *sk,
    		     struct sk_buff *skb)
 {
@@ -458,14 +475,15 @@ static int seg6_input_core(struct net *net, struct sock *sk,
    struct seg6_lwt *slwt;
    int err;
-	err = seg6_do_srh(skb);
-	if (unlikely(err))
-		goto drop;
-
    slwt = seg6_lwt_lwtunnel(orig_dst->lwtstate);
local_bh_disable();
    dst = dst_cache_get(&slwt->cache);
+	local_bh_enable();
+
+	err = seg6_do_srh(skb, dst);
+	if (unlikely(err))
+		goto drop;
skb_dst_drop(skb);
@@ -473,17 +491,18 @@ static int seg6_input_core(struct net *net, struct sock *sk,
    	ip6_route_input(skb);
    	dst = skb_dst(skb);
    	if (!dst->error) {
+			local_bh_disable();
    		dst_cache_set_ip6(&slwt->cache, dst,
    				  &ipv6_hdr(skb)->saddr);
+			local_bh_enable();
    	}
+
+		err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
+		if (unlikely(err))
+			goto drop;
    } else {
    	skb_dst_set(skb, dst);
    }
-	local_bh_enable();
-
-	err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
-	if (unlikely(err))
-		goto drop;
if (static_branch_unlikely(&nf_hooks_lwtunnel_enabled))
    	return NF_HOOK(NFPROTO_IPV6, NF_INET_LOCAL_OUT,
@@ -529,16 +548,16 @@ static int seg6_output_core(struct net *net, struct sock *sk,
    struct seg6_lwt *slwt;
    int err;
-	err = seg6_do_srh(skb);
-	if (unlikely(err))
-		goto drop;
-
    slwt = seg6_lwt_lwtunnel(orig_dst->lwtstate);
local_bh_disable();
    dst = dst_cache_get(&slwt->cache);
    local_bh_enable();
+	err = seg6_do_srh(skb, dst);
+	if (unlikely(err))
+		goto drop;
+
    if (unlikely(!dst)) {
    	struct ipv6hdr *hdr = ipv6_hdr(skb);
    	struct flowi6 fl6;
@@ -560,15 +579,15 @@ static int seg6_output_core(struct net *net, struct sock *sk,
    	local_bh_disable();
    	dst_cache_set_ip6(&slwt->cache, dst, &fl6.saddr);
    	local_bh_enable();
+
+		err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
+		if (unlikely(err))
+			goto drop;
    }
skb_dst_drop(skb);
    skb_dst_set(skb, dst);
-	err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
-	if (unlikely(err))
-		goto drop;
-
    if (static_branch_unlikely(&nf_hooks_lwtunnel_enabled))
    	return NF_HOOK(NFPROTO_IPV6, NF_INET_LOCAL_OUT, net, sk, skb,
    		       NULL, skb_dst(skb)->dev, dst_output);
-- 
2.39.5





    

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[PATCH 6.1 139/176] net: ipv6: seg6_iptunnel: mitigate 2-realloc issue