[PATCH net-next] tcp: Add stats for socket migration.

From: Kuniyuki Iwashima
Date: Tue Jun 22 2021 - 19:36:24 EST

This commit adds two stats for the socket migration feature to evaluate the
effectiveness: LINUX_MIB_TCPMIGRATEREQ(SUCCESS|FAILURE).

If the migration fails because of the own_req race in receiving ACK and
sending SYN+ACK paths, we do not increment the failure stat. Then another
CPU is responsible for the req.

Link: https://lore.kernel.org/bpf/CAK6E8=cgFKuGecTzSCSQ8z3YJ_163C0uwO9yRvfDSE7vOe9mJA@xxxxxxxxxxxxxx/
Suggested-by: Yuchung Cheng <ycheng@xxxxxxxxxx>
Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxxxx>
---
include/uapi/linux/snmp.h | 2 ++
net/core/sock_reuseport.c | 15 +++++++++++----
net/ipv4/inet_connection_sock.c | 15 +++++++++++++--
net/ipv4/proc.c | 2 ++
net/ipv4/tcp_minisocks.c | 3 +++
5 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h
index 26fc60ce9298..904909d020e2 100644
--- a/include/uapi/linux/snmp.h
+++ b/include/uapi/linux/snmp.h
@@ -290,6 +290,8 @@ enum
LINUX_MIB_TCPDUPLICATEDATAREHASH, /* TCPDuplicateDataRehash */
LINUX_MIB_TCPDSACKRECVSEGS, /* TCPDSACKRecvSegs */
LINUX_MIB_TCPDSACKIGNOREDDUBIOUS, /* TCPDSACKIgnoredDubious */
+ LINUX_MIB_TCPMIGRATEREQSUCCESS, /* TCPMigrateReqSuccess */
+ LINUX_MIB_TCPMIGRATEREQFAILURE, /* TCPMigrateReqFailure */
__LINUX_MIB_MAX
};

diff --git a/net/core/sock_reuseport.c b/net/core/sock_reuseport.c
index de5ee3ae86d5..3f00a28fe762 100644
--- a/net/core/sock_reuseport.c
+++ b/net/core/sock_reuseport.c
@@ -6,6 +6,7 @@
* selecting the socket index from the array of available sockets.
*/

+#include <net/ip.h>
#include <net/sock_reuseport.h>
#include <linux/bpf.h>
#include <linux/idr.h>
@@ -536,7 +537,7 @@ struct sock *reuseport_migrate_sock(struct sock *sk,

socks = READ_ONCE(reuse->num_socks);
if (unlikely(!socks))
- goto out;
+ goto failure;

/* paired with smp_wmb() in __reuseport_add_sock() */
smp_rmb();
@@ -546,13 +547,13 @@ struct sock *reuseport_migrate_sock(struct sock *sk,
if (!prog || prog->expected_attach_type != BPF_SK_REUSEPORT_SELECT_OR_MIGRATE) {
if (sock_net(sk)->ipv4.sysctl_tcp_migrate_req)
goto select_by_hash;
- goto out;
+ goto failure;
}

if (!skb) {
skb = alloc_skb(0, GFP_ATOMIC);
if (!skb)
- goto out;
+ goto failure;
allocated = true;
}

@@ -565,12 +566,18 @@ struct sock *reuseport_migrate_sock(struct sock *sk,
if (!nsk)
nsk = reuseport_select_sock_by_hash(reuse, hash, socks);

- if (IS_ERR_OR_NULL(nsk) || unlikely(!refcount_inc_not_zero(&nsk->sk_refcnt)))
+ if (IS_ERR_OR_NULL(nsk) || unlikely(!refcount_inc_not_zero(&nsk->sk_refcnt))) {
nsk = NULL;
+ goto failure;
+ }

out:
rcu_read_unlock();
return nsk;
+
+failure:
+ __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE);
+ goto out;
}
EXPORT_SYMBOL(reuseport_migrate_sock);

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 0eea878edc30..754013fa393b 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -703,6 +703,8 @@ static struct request_sock *inet_reqsk_clone(struct request_sock *req,

nreq = kmem_cache_alloc(req->rsk_ops->slab, GFP_ATOMIC | __GFP_NOWARN);
if (!nreq) {
+ __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE);
+
/* paired with refcount_inc_not_zero() in reuseport_migrate_sock() */
sock_put(sk);
return NULL;
@@ -876,9 +878,10 @@ static void reqsk_timer_handler(struct timer_list *t)
if (!inet_ehash_insert(req_to_sk(nreq), req_to_sk(oreq), NULL)) {
/* delete timer */
inet_csk_reqsk_queue_drop(sk_listener, nreq);
- goto drop;
+ goto no_ownership;
}

+ __NET_INC_STATS(net, LINUX_MIB_TCPMIGRATEREQSUCCESS);
reqsk_migrate_reset(oreq);
reqsk_queue_removed(&inet_csk(oreq->rsk_listener)->icsk_accept_queue, oreq);
reqsk_put(oreq);
@@ -887,17 +890,19 @@ static void reqsk_timer_handler(struct timer_list *t)
return;
}

-drop:
/* Even if we can clone the req, we may need not retransmit any more
* SYN+ACKs (nreq->num_timeout > max_syn_ack_retries, etc), or another
* CPU may win the "own_req" race so that inet_ehash_insert() fails.
*/
if (nreq) {
+ __NET_INC_STATS(net, LINUX_MIB_TCPMIGRATEREQFAILURE);
+no_ownership:
reqsk_migrate_reset(nreq);
reqsk_queue_removed(queue, nreq);
__reqsk_free(nreq);
}

+drop:
inet_csk_reqsk_queue_drop_and_put(oreq->rsk_listener, oreq);
}

@@ -1135,11 +1140,13 @@ struct sock *inet_csk_complete_hashdance(struct sock *sk, struct sock *child,

refcount_set(&nreq->rsk_refcnt, 1);
if (inet_csk_reqsk_queue_add(sk, nreq, child)) {
+ __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQSUCCESS);
reqsk_migrate_reset(req);
reqsk_put(req);
return child;
}

+ __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE);
reqsk_migrate_reset(nreq);
__reqsk_free(nreq);
} else if (inet_csk_reqsk_queue_add(sk, req, child)) {
@@ -1188,8 +1195,12 @@ void inet_csk_listen_stop(struct sock *sk)
refcount_set(&nreq->rsk_refcnt, 1);

if (inet_csk_reqsk_queue_add(nsk, nreq, child)) {
+ __NET_INC_STATS(sock_net(nsk),
+ LINUX_MIB_TCPMIGRATEREQSUCCESS);
reqsk_migrate_reset(req);
} else {
+ __NET_INC_STATS(sock_net(nsk),
+ LINUX_MIB_TCPMIGRATEREQFAILURE);
reqsk_migrate_reset(nreq);
__reqsk_free(nreq);
}
diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index 6d46297a99f8..b0d3a09dc84e 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -295,6 +295,8 @@ static const struct snmp_mib snmp4_net_list[] = {
SNMP_MIB_ITEM("TcpDuplicateDataRehash", LINUX_MIB_TCPDUPLICATEDATAREHASH),
SNMP_MIB_ITEM("TCPDSACKRecvSegs", LINUX_MIB_TCPDSACKRECVSEGS),
SNMP_MIB_ITEM("TCPDSACKIgnoredDubious", LINUX_MIB_TCPDSACKIGNOREDDUBIOUS),
+ SNMP_MIB_ITEM("TCPMigrateReqSuccess", LINUX_MIB_TCPMIGRATEREQSUCCESS),
+ SNMP_MIB_ITEM("TCPMigrateReqFailure", LINUX_MIB_TCPMIGRATEREQFAILURE),
SNMP_MIB_SENTINEL
};

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index f258a4c0da71..0a4f3f16140a 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -786,6 +786,9 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
return inet_csk_complete_hashdance(sk, child, req, own_req);

listen_overflow:
+ if (sk != req->rsk_listener)
+ __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE);
+
if (!sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow) {
inet_rsk(req)->acked = 1;
return NULL;
--
2.30.2