From: Eric Dumazet <dada1@cosmosbay.com>
Date: Tue, 27 Mar 2007 20:53:04 +0000 (-0700)
Subject: [NET]: inet_ehash_secret should be __read_mostly and set only once
X-Git-Tag: v2.6.22-rc1~1128^2~154
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=be776281aee54626a474ba06f91926b98bdd180d;p=linux-2.6

[NET]: inet_ehash_secret should be __read_mostly and set only once

There is a very tiny probability that build_ehash_secret() is called
at the same time by different CPUS.

Also, using __read_mostly is a must for inet_ehash_secret

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index b7b7278d80..45ced52c03 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -218,13 +218,23 @@ out:
 	return err;
 }
 
-u32 inet_ehash_secret;
+u32 inet_ehash_secret __read_mostly;
 EXPORT_SYMBOL(inet_ehash_secret);
 
+/*
+ * inet_ehash_secret must be set exactly once
+ * Instead of using a dedicated spinlock, we (ab)use inetsw_lock
+ */
 void build_ehash_secret(void)
 {
-	while (!inet_ehash_secret)
-		get_random_bytes(&inet_ehash_secret, 4);
+	u32 rnd;
+	do {
+		get_random_bytes(&rnd, sizeof(rnd));
+	} while (rnd == 0);
+	spin_lock_bh(&inetsw_lock);
+	if (!inet_ehash_secret)
+		inet_ehash_secret = rnd;
+	spin_unlock_bh(&inetsw_lock);
 }
 EXPORT_SYMBOL(build_ehash_secret);