netdev - Re: [PATCH net-next 1/2] Phonet: put protocols array under RCU

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Date:	Mon, 16 Nov 2009 09:26:17 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Rémi Denis-Courmont <remi@...lab.net>
Cc:	netdev@...r.kernel.org,
	Rémi Denis-Courmont 
	<remi.denis-courmont@...ia.com>
Subject: Re: [PATCH net-next 1/2] Phonet: put protocols array under RCU

On Fri, Nov 13, 2009 at 05:01:18PM +0200, Rémi Denis-Courmont wrote:
> From: Rémi Denis-Courmont <remi.denis-courmont@...ia.com>
> 
> Signed-off-by: Rémi Denis-Courmont <remi.denis-courmont@...ia.com>
> ---
>  net/phonet/af_phonet.c |   20 +++++++++++---------
>  1 files changed, 11 insertions(+), 9 deletions(-)
> 
> diff --git a/net/phonet/af_phonet.c b/net/phonet/af_phonet.c
> index 8d3a55b..ed65da2 100644
> --- a/net/phonet/af_phonet.c
> +++ b/net/phonet/af_phonet.c
> @@ -35,7 +35,6 @@
> 
>  /* Transport protocol registration */
>  static struct phonet_protocol *proto_tab[PHONET_NPROTO] __read_mostly;
> -static DEFINE_SPINLOCK(proto_tab_lock);
> 
>  static struct phonet_protocol *phonet_proto_get(int protocol)
>  {
> @@ -44,11 +43,11 @@ static struct phonet_protocol *phonet_proto_get(int protocol)
>  	if (protocol >= PHONET_NPROTO)
>  		return NULL;
> 
> -	spin_lock(&proto_tab_lock);
> +	rcu_read_lock();
>  	pp = proto_tab[protocol];

Don't we need an rcu_dereference() in here somewhere?

Perhaps something like the following?

	pp = rcu_dereference(proto_tab[protocol]);

							Thanx, Paul

>  	if (pp && !try_module_get(pp->prot->owner))
>  		pp = NULL;
> -	spin_unlock(&proto_tab_lock);
> +	rcu_read_unlock();
> 
>  	return pp;
>  }
> @@ -439,6 +438,8 @@ static struct packet_type phonet_packet_type __read_mostly = {
>  	.func = phonet_rcv,
>  };
> 
> +static DEFINE_MUTEX(proto_tab_lock);
> +
>  int __init_or_module phonet_proto_register(int protocol,
>  						struct phonet_protocol *pp)
>  {
> @@ -451,12 +452,12 @@ int __init_or_module phonet_proto_register(int protocol,
>  	if (err)
>  		return err;
> 
> -	spin_lock(&proto_tab_lock);
> +	mutex_lock(&proto_tab_lock);
>  	if (proto_tab[protocol])
>  		err = -EBUSY;
>  	else
> -		proto_tab[protocol] = pp;
> -	spin_unlock(&proto_tab_lock);
> +		rcu_assign_pointer(proto_tab[protocol], pp);
> +	mutex_unlock(&proto_tab_lock);
> 
>  	return err;
>  }
> @@ -464,10 +465,11 @@ EXPORT_SYMBOL(phonet_proto_register);
> 
>  void phonet_proto_unregister(int protocol, struct phonet_protocol *pp)
>  {
> -	spin_lock(&proto_tab_lock);
> +	mutex_lock(&proto_tab_lock);
>  	BUG_ON(proto_tab[protocol] != pp);
> -	proto_tab[protocol] = NULL;
> -	spin_unlock(&proto_tab_lock);
> +	rcu_assign_pointer(proto_tab[protocol], NULL);
> +	mutex_unlock(&proto_tab_lock);
> +	synchronize_rcu();
>  	proto_unregister(pp->prot);
>  }
>  EXPORT_SYMBOL(phonet_proto_unregister);
> -- 
> 1.6.3.3
> 
> --
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