[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 b7b7278d801cf23eaf06b740d87f4e99bd4044d3..45ced52c03d46db84900228d10bfb391053d0248 100644 (file)
--- 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);