netdev - [PATCH net-next] tcp: fix RFS vs lockless listeners

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Date:	Thu, 08 Oct 2015 11:16:48 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>,
	Willem de Bruijn <willemb@...gle.com>,
	Tom Herbert <tom@...bertland.com>
Subject: [PATCH net-next] tcp: fix RFS vs lockless listeners

From: Eric Dumazet <edumazet@...gle.com>

Before recent TCP listener patches, we were updating listener
sk->sk_rxhash before the cloning of master socket.

children sk_rxhash was therefore correct after the normal 3WHS.

But with lockless listener, we no longer dirty/change listener sk_rxhash
as it would be racy.

We need to correctly update the child sk_rxhash, otherwise first data
packet wont hit correct cpu if RFS is used.

Fixes: 079096f103fa ("tcp/dccp: install syn_recv requests into ehash table")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reported-by: Willem de Bruijn <willemb@...gle.com>
Cc: Tom Herbert <tom@...bertland.com>
---
 net/ipv4/syncookies.c    |    1 +
 net/ipv4/tcp_minisocks.c |    1 +
 2 files changed, 2 insertions(+)

diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 8113c30ccf96..2dbb11331f6c 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -225,6 +225,7 @@ struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
 	child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst);
 	if (child) {
 		atomic_set(&req->rsk_refcnt, 1);
+		sock_rps_save_rxhash(child, skb);
 		inet_csk_reqsk_queue_add(sk, req, child);
 	} else {
 		reqsk_free(req);
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 9adf1e2c3170..1079e6ad77fe 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -768,6 +768,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 	if (!child)
 		goto listen_overflow;
 
+	sock_rps_save_rxhash(child, skb);
 	tcp_synack_rtt_meas(child, req);
 	inet_csk_reqsk_queue_drop(sk, req);
 	inet_csk_reqsk_queue_add(sk, req, child);


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