linux-kernel - [PATCH 3.14 01/46] tcp: make challenge acks faster

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Date:	Thu, 18 Aug 2016 15:54:23 +0200
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Yue Cao <ycao009@....edu>,
	Eric Dumazet <edumazet@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Yuchung Cheng <ycheng@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Chas Williams <ciwillia@...cade.com>, Willy Tarreau <w@....eu>
Subject: [PATCH 3.14 01/46] tcp: make challenge acks faster

3.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

When backporting upstream commit 75ff39ccc1bd ("tcp: make challenge acks
less predictable") I negelected to use the correct ACCESS* type macros.
This fixes that up to hopefully speed things up a bit more.

Thanks to Chas Wiliams for the 3.10 backport which reminded me of this.

Cc: Yue Cao <ycao009@....edu>
Cc: Eric Dumazet <edumazet@...gle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Yuchung Cheng <ycheng@...gle.com>
Cc: Neal Cardwell <ncardwell@...gle.com>
Cc: Neal Cardwell <ncardwell@...gle.com>
Cc: Yuchung Cheng <ycheng@...gle.com>
Cc: David S. Miller <davem@...emloft.net>
Cc: Chas Williams <ciwillia@...cade.com>
Cc: Willy Tarreau <w@....eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/ipv4/tcp_input.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3299,12 +3299,12 @@ static void tcp_send_challenge_ack(struc
 		u32 half = (sysctl_tcp_challenge_ack_limit + 1) >> 1;

 		challenge_timestamp = now;
-		challenge_count = half +
+		ACCESS_ONCE(challenge_count) = half +
 				  prandom_u32_max(sysctl_tcp_challenge_ack_limit);
 	}
-	count = challenge_count;
+	count = ACCESS_ONCE(challenge_count);
 	if (count > 0) {
-		challenge_count = count - 1;
+		ACCESS_ONCE(challenge_count) = count - 1;
 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPCHALLENGEACK);
 		tcp_send_ack(sk);
 	}