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Date: Thu, 6 Feb 2014 11:58:26 -0800 (PST)
From: Tom Herbert <therbert@...gle.com>
To: davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com
Subject: [RFC PATCH] udp4: Don't take socket reference in receive path
The reference counting in the UDP receive path is quite expensive for
a socket that is share amoungst CPUs. This is probably true for normal
sockets, but really is painful when just using the socket for
receive encapsulation.
udp4_lib_lookup always takes a socket reference, and we also put back
the reference after calling udp_queue_rcv_skb in the normal receive
path, so the need for taking the reference seems to be to hold the
socket after doing rcu_read_unlock. This patch modifies udp_lib_lookup
to optionally take a reference and is always called with rcu_read_lock.
In udp4_lib_rcv we call lib_lookup and udp_queue_rcv under the
rcu_read_lock but without having taken the reference.
Requesting comments because I suspect there are nuances to this!
Signed-off-by: Tom Herbert <therbert@...gle.com>
---
net/ipv4/udp.c | 90 ++++++++++++++++++++++++++++++++++++++++------------------
1 file changed, 62 insertions(+), 28 deletions(-)
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 48d8cb2..6043a2f 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -424,7 +424,8 @@ static unsigned int udp_ehashfn(struct net *net, const __be32 laddr,
static struct sock *udp4_lib_lookup2(struct net *net,
__be32 saddr, __be16 sport,
__be32 daddr, unsigned int hnum, int dif,
- struct udp_hslot *hslot2, unsigned int slot2)
+ struct udp_hslot *hslot2, unsigned int slot2,
+ bool get_ref)
{
struct sock *sk, *result;
struct hlist_nulls_node *node;
@@ -461,12 +462,20 @@ begin:
if (get_nulls_value(node) != slot2)
goto begin;
if (result) {
- if (unlikely(!atomic_inc_not_zero_hint(&result->sk_refcnt, 2)))
- result = NULL;
- else if (unlikely(compute_score2(result, net, saddr, sport,
- daddr, hnum, dif) < badness)) {
- sock_put(result);
- goto begin;
+ if (get_ref) {
+ if (unlikely(!atomic_inc_not_zero_hint(&result->sk_refcnt, 2)))
+ result = NULL;
+ else if (unlikely(compute_score2(result, net, saddr, sport,
+- daddr, hnum, dif) < badness)) {
+ sock_put(result);
+ goto begin;
+ }
+ } else {
+ if (unlikely(atomic_read(&result->sk_refcnt) == 0))
+ result = NULL;
+ else if (unlikely(compute_score2(result, net, saddr, sport,
+- daddr, hnum, dif) < badness))
+ goto begin;
}
}
return result;
@@ -475,9 +484,10 @@ begin:
/* UDP is nearly always wildcards out the wazoo, it makes no sense to try
* harder than this. -DaveM
*/
-struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr,
+/* called with read_rcu_lock() */
+struct sock *___udp4_lib_lookup(struct net *net, __be32 saddr,
__be16 sport, __be32 daddr, __be16 dport,
- int dif, struct udp_table *udptable)
+ int dif, struct udp_table *udptable, bool get_ref)
{
struct sock *sk, *result;
struct hlist_nulls_node *node;
@@ -487,7 +497,6 @@ struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr,
int score, badness, matches = 0, reuseport = 0;
u32 hash = 0;
- rcu_read_lock();
if (hslot->count > 10) {
hash2 = udp4_portaddr_hash(net, daddr, hnum);
slot2 = hash2 & udptable->mask;
@@ -497,7 +506,7 @@ struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr,
result = udp4_lib_lookup2(net, saddr, sport,
daddr, hnum, dif,
- hslot2, slot2);
+ hslot2, slot2, get_ref);
if (!result) {
hash2 = udp4_portaddr_hash(net, htonl(INADDR_ANY), hnum);
slot2 = hash2 & udptable->mask;
@@ -507,9 +516,8 @@ struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr,
result = udp4_lib_lookup2(net, saddr, sport,
htonl(INADDR_ANY), hnum, dif,
- hslot2, slot2);
+ hslot2, slot2, get_ref);
}
- rcu_read_unlock();
return result;
}
begin:
@@ -543,28 +551,50 @@ begin:
goto begin;
if (result) {
- if (unlikely(!atomic_inc_not_zero_hint(&result->sk_refcnt, 2)))
- result = NULL;
- else if (unlikely(compute_score(result, net, saddr, hnum, sport,
- daddr, dport, dif) < badness)) {
- sock_put(result);
- goto begin;
+ if (get_ref) {
+ if (unlikely(!atomic_inc_not_zero_hint(&result->sk_refcnt, 2)))
+ result = NULL;
+ else if (unlikely(compute_score(result, net, saddr, hnum, sport,
+ daddr, dport, dif) < badness)) {
+ sock_put(result);
+ goto begin;
+ }
+ } else {
+ if (unlikely(atomic_read(&result->sk_refcnt) == 0))
+ result = NULL;
+ else if (unlikely(compute_score(result, net, saddr, hnum, sport,
+ daddr, dport, dif) < badness))
+ goto begin;
}
}
+ return result;
+}
+
+struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr,
+ __be16 sport, __be32 daddr, __be16 dport,
+ int dif, struct udp_table *udptable)
+{
+ struct sock *result;
+
+ rcu_read_lock();
+ result = ___udp4_lib_lookup(net, saddr, sport, daddr, dport, dif, udptable, true);
rcu_read_unlock();
+
return result;
}
+
EXPORT_SYMBOL_GPL(__udp4_lib_lookup);
+/* called with read_rcu_lock() */
static inline struct sock *__udp4_lib_lookup_skb(struct sk_buff *skb,
__be16 sport, __be16 dport,
struct udp_table *udptable)
{
const struct iphdr *iph = ip_hdr(skb);
- return __udp4_lib_lookup(dev_net(skb_dst(skb)->dev), iph->saddr, sport,
+ return ___udp4_lib_lookup(dev_net(skb_dst(skb)->dev), iph->saddr, sport,
iph->daddr, dport, inet_iif(skb),
- udptable);
+ udptable, false);
}
struct sock *udp4_lib_lookup(struct net *net, __be32 saddr, __be16 sport,
@@ -1755,19 +1785,21 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
if (ret > 0)
return -ret;
return 0;
- } else {
- if (rt->rt_flags & (RTCF_BROADCAST|RTCF_MULTICAST))
- return __udp4_lib_mcast_deliver(net, skb, uh,
- saddr, daddr, udptable);
-
- sk = __udp4_lib_lookup_skb(skb, uh->source, uh->dest, udptable);
}
+
+ if (rt->rt_flags & (RTCF_BROADCAST|RTCF_MULTICAST))
+ return __udp4_lib_mcast_deliver(net, skb, uh,
+ saddr, daddr, udptable);
+
+ rcu_read_lock();
+ sk = __udp4_lib_lookup_skb(skb, uh->source, uh->dest, udptable);
+
if (sk != NULL) {
int ret;
ret = udp_queue_rcv_skb(sk, skb);
- sock_put(sk);
+ rcu_read_unlock();
/* a return value > 0 means to resubmit the input, but
* it wants the return to be -protocol, or 0
@@ -1777,6 +1809,8 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
return 0;
}
+ rcu_read_unlock();
+
if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb))
goto drop;
nf_reset(skb);
--
1.9.0.rc1.175.g0b1dcb5
--
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