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

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

[Eric Dumazet]

Hi David

Please find this patch against net-2.6.22

Thank you

[PATCH] 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>

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index b7b7278..597646b 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);
 
@@ -684,7 +694,8 @@ int inet_sendmsg(struct kiocb *iocb, str
 }
 
 
-static ssize_t inet_sendpage(struct socket *sock, struct page *page, int offset, size_t size, int flags)
+static ssize_t inet_sendpage(struct socket *sock, struct page *page, int offset,
+	size_t size, int flags)
 {
 	struct sock *sk = sock->sk;
 

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

[David Miller]

From: Eric Dumazet <dada1@cosmosbay.com>
Date: Tue, 27 Mar 2007 12:13:43 +0200

> Hi David
> 
> Please find this patch against net-2.6.22
> 
> Thank you
> 
> [PATCH] 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>

Applied, but I left out this totally unrelated code formatting
change in your patch:

> @@ -684,7 +694,8 @@ int inet_sendmsg(struct kiocb *iocb, str
>  }
>  
>  
> -static ssize_t inet_sendpage(struct socket *sock, struct page *page, int offset, size_t size, int flags)
> +static ssize_t inet_sendpage(struct socket *sock, struct page *page, int offset,
> +	size_t size, int flags)
>  {
>  	struct sock *sk = sock->sk;
>  

Thanks!

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

[Eric Dumazet]

David Miller a écrit :
> From: Eric Dumazet <dada1@cosmosbay.com>
> Date: Tue, 27 Mar 2007 12:13:43 +0200
> 
>> Hi David
>>
>> Please find this patch against net-2.6.22
>>
>> Thank you
>>
>> [PATCH] 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>
> 
> Applied, but I left out this totally unrelated code formatting
> change in your patch:
> 
>> @@ -684,7 +694,8 @@ int inet_sendmsg(struct kiocb *iocb, str
>>  }
>>  
>>  
>> -static ssize_t inet_sendpage(struct socket *sock, struct page *page, int offset, size_t size, int flags)
>> +static ssize_t inet_sendpage(struct socket *sock, struct page *page, int offset,
>> +	size_t size, int flags)
>>  {
>>  	struct sock *sk = sock->sk;
>>  

Well... just a minor change to reduce length of this too long line...