netdev - [PATCH net-next] tcp: fix the calculation of sysctl_max_tw_buckets in tcp_sk

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Message-Id: <1533556020-20778-1-git-send-email-laoar.shao@gmail.com>
Date:   Mon,  6 Aug 2018 19:47:00 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     edumazet@...gle.com, davem@...emloft.net,
        yanhaishuang@...s.chinamobile.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Yafang Shao <laoar.shao@...il.com>
Subject: [PATCH net-next] tcp: fix the calculation of sysctl_max_tw_buckets in tcp_sk_init()

tcp_hashinfo.ehash_mask is always an odd number, which is set in function
alloc_large_system_hash(). See bellow,
	if (_hash_mask)
		*_hash_mask = (1 << log2qty) - 1; <<< always odd number

Hence the local variable 'cnt' is a even number, as a result of that it is
no difference to do the incrementation here.

Maybe the compiler could also optimize it, but this code is a little ugly.

Fix: fee83d09 ("ipv4: Namespaceify tcp_max_syn_backlog knob")
Signed-off-by: Yafang Shao <laoar.shao@...il.com>
---
 net/ipv4/tcp_ipv4.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 9e041fa..a9b7c4b 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -2543,7 +2543,7 @@ static int __net_init tcp_sk_init(struct net *net)
 	net->ipv4.sysctl_tcp_tw_reuse = 2;
 
 	cnt = tcp_hashinfo.ehash_mask + 1;
-	net->ipv4.tcp_death_row.sysctl_max_tw_buckets = (cnt + 1) / 2;
+	net->ipv4.tcp_death_row.sysctl_max_tw_buckets = cnt / 2;
 	net->ipv4.tcp_death_row.hashinfo = &tcp_hashinfo;
 
 	net->ipv4.sysctl_max_syn_backlog = max(128, cnt / 256);
-- 
1.8.3.1