netdev - Re: [PATCH] net: fib: fix incorrect call_rcu

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Message-ID: <20120807163454.GF2378@linux.vnet.ibm.com>
Date:	Tue, 7 Aug 2012 09:34:54 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: fib: fix incorrect call_rcu_bh()

On Tue, Aug 07, 2012 at 12:47:11PM +0200, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> After IP route cache removal, I believe rcu_bh() has very little use and
> we should remove this RCU variant, since it adds some cycles in fast
> path.

Do you mean remove all uses of RCU-bh globally and also removing the
implementation itself?  That would actually be a good thing, from my
perspective.

Or were you meaning something more localized?

							Thanx, Paul

> Anyway, the call_rcu_bh() use in fib_true is obviously wrong, since
> some users only assert rcu_read_lock().
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> ---
>  net/ipv4/fib_trie.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
> index f0cdb30..57bd978 100644
> --- a/net/ipv4/fib_trie.c
> +++ b/net/ipv4/fib_trie.c
> @@ -367,7 +367,7 @@ static void __leaf_free_rcu(struct rcu_head *head)
> 
>  static inline void free_leaf(struct leaf *l)
>  {
> -	call_rcu_bh(&l->rcu, __leaf_free_rcu);
> +	call_rcu(&l->rcu, __leaf_free_rcu);
>  }
> 
>  static inline void free_leaf_info(struct leaf_info *leaf)
> 
> 

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