netdev - Re: [PATCH net-next-2.6] net: fix a lockdep rcu warning in __sk_dst

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Date:	Tue, 27 Apr 2010 09:17:16 -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-next-2.6] net: fix a lockdep rcu warning in
 __sk_dst_set()

On Tue, Apr 27, 2010 at 08:40:43AM +0200, Eric Dumazet wrote:
> __sk_dst_set() might be called while no state can be integrated in a
> rcu_dereference_check() condition.
> 
> So use rcu_dereference_raw() to shutup lockdep warnings (if
> CONFIG_PROVE_RCU is set)

Acked-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> ---
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 86a8ca1..94dbdbc 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -1236,8 +1236,11 @@ __sk_dst_set(struct sock *sk, struct dst_entry *dst)
>  	struct dst_entry *old_dst;
> 
>  	sk_tx_queue_clear(sk);
> -	old_dst = rcu_dereference_check(sk->sk_dst_cache,
> -					lockdep_is_held(&sk->sk_dst_lock));
> +	/*
> +	 * This can be called while sk is owned by the caller only,
> +	 * with no state that can be checked in a rcu_dereference_check() cond
> +	 */
> +	old_dst = rcu_dereference_raw(sk->sk_dst_cache);
>  	rcu_assign_pointer(sk->sk_dst_cache, dst);
>  	dst_release(old_dst);
>  }
> 
> 
> --
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