From 40ac240c2e06e4b5477705da1b37fb1d160572de Mon Sep 17 00:00:00 2001
From: Pavel Begunkov <asml.silence@gmail.com>
Date: Thu, 27 Jan 2022 00:36:30 +0000
Subject: ipv6: optimise dst refcounting on cork init
udpv6_sendmsg() doesn't need dst after calling ip6_make_skb(), so
instead of taking an additional reference inside ip6_setup_cork()
and releasing the initial one afterwards, we can hand over a reference
into ip6_make_skb() saving two atomics. The only other user of
ip6_setup_cork() is ip6_append_data() and it requires an extra
dst_hold().
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
net/ipv6/ip6_output.c | 13 +++++++++----
net/ipv6/udp.c | 3 ++-
2 files changed, 11 insertions(+), 5 deletions(-)
(limited to 'net/ipv6')
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 0cc490f2cfbf..0c6c971ce0a5 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1356,6 +1356,11 @@ static int ip6_setup_cork(struct sock *sk, struct inet_cork_full *cork,
unsigned int mtu;
struct ipv6_txoptions *nopt, *opt = ipc6->opt;
+ /* callers pass dst together with a reference, set it first so
+ * ip6_cork_release() can put it down even in case of an error.
+ */
+ cork->base.dst = &rt->dst;
+
/*
* setup for corking
*/
@@ -1389,8 +1394,6 @@ static int ip6_setup_cork(struct sock *sk, struct inet_cork_full *cork,
/* need source address above miyazawa*/
}
- dst_hold(&rt->dst);
- cork->base.dst = &rt->dst;
v6_cork->hop_limit = ipc6->hlimit;
v6_cork->tclass = ipc6->tclass;
if (rt->dst.flags & DST_XFRM_TUNNEL)
@@ -1784,6 +1787,7 @@ int ip6_append_data(struct sock *sk,
/*
* setup for corking
*/
+ dst_hold(&rt->dst);
err = ip6_setup_cork(sk, &inet->cork, &np->cork,
ipc6, rt);
if (err)
@@ -1974,15 +1978,16 @@ struct sk_buff *ip6_make_skb(struct sock *sk,
int exthdrlen = (ipc6->opt ? ipc6->opt->opt_flen : 0);
int err;
- if (flags & MSG_PROBE)
+ if (flags & MSG_PROBE) {
+ dst_release(&rt->dst);
return NULL;
+ }
__skb_queue_head_init(&queue);
cork->base.flags = 0;
cork->base.addr = 0;
cork->base.opt = NULL;
- cork->base.dst = NULL;
v6_cork.opt = NULL;
err = ip6_setup_cork(sk, cork, &v6_cork, ipc6, rt);
if (err) {
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index cfcf08c3df4d..c6872596b408 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -1541,7 +1541,8 @@ back_from_confirm:
err = PTR_ERR(skb);
if (!IS_ERR_OR_NULL(skb))
err = udp_v6_send_skb(skb, fl6, &cork.base);
- goto out;
+ /* ip6_make_skb steals dst reference */
+ goto out_no_dst;
}
lock_sock(sk);
--
cgit