linux-kernel - Re: [PATCH RFC 2/2] netfilter: conntrack: replace mutex with cmpxchg

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Date:	Wed, 2 May 2012 02:51:02 +0200
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	Benjamin Poirier <bpoirier@...e.de>
Cc:	netdev@...r.kernel.org, Patrick McHardy <kaber@...sh.net>,
	"David S. Miller" <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Mike Frysinger <vapier@...too.org>,
	Arun Sharma <asharma@...com>, netfilter-devel@...r.kernel.org,
	netfilter@...r.kernel.org, coreteam@...filter.org,
	linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH RFC 2/2] netfilter: conntrack: replace mutex with
 cmpxchg

On Fri, Apr 27, 2012 at 02:28:53PM -0400, Benjamin Poirier wrote:
> This mutex protects a single pointer.

You seem to be using an old Linux kernel tree. This doesn't apply.

> ---
>  net/netfilter/nf_conntrack_ecache.c |   38 +++++++++-------------------------
>  1 files changed, 10 insertions(+), 28 deletions(-)
> 
> diff --git a/net/netfilter/nf_conntrack_ecache.c b/net/netfilter/nf_conntrack_ecache.c
> index 0134009..603eb69 100644
> --- a/net/netfilter/nf_conntrack_ecache.c
> +++ b/net/netfilter/nf_conntrack_ecache.c
> @@ -25,8 +25,6 @@
>  #include <net/netfilter/nf_conntrack_core.h>
>  #include <net/netfilter/nf_conntrack_extend.h>
>  
> -static DEFINE_MUTEX(nf_ct_ecache_mutex);
> -
>  /* deliver cached events and clear cache entry - must be called with locally
>   * disabled softirqs */
>  void nf_ct_deliver_cached_events(struct nf_conn *ct)
> @@ -80,52 +78,36 @@ EXPORT_SYMBOL_GPL(nf_ct_deliver_cached_events);
>  int nf_conntrack_register_notifier(struct net *net,
>  				   struct nf_ct_event_notifier *new)
>  {
> -	int ret = 0;
> -
> -	mutex_lock(&nf_ct_ecache_mutex);
> -	if (net->ct.nf_conntrack_event_cb != NULL)
> -		ret = -EBUSY;
> +	if (cmpxchg(&net->ct.nf_conntrack_event_cb, NULL, new) != NULL)
> +		return -EBUSY;
>  	else
> -		net->ct.nf_conntrack_event_cb = new;
> -	mutex_unlock(&nf_ct_ecache_mutex);
> -
> -	return ret;
> +		return 0;
>  }
>  EXPORT_SYMBOL_GPL(nf_conntrack_register_notifier);
>  
>  void nf_conntrack_unregister_notifier(struct net *net,
>  				      struct nf_ct_event_notifier *new)
>  {
> -	mutex_lock(&nf_ct_ecache_mutex);
> -	BUG_ON(net->ct.nf_conntrack_event_cb != new);
> -	net->ct.nf_conntrack_event_cb = NULL;
> -	mutex_unlock(&nf_ct_ecache_mutex);
> +	if (xchg(&net->ct.nf_conntrack_event_cb, NULL) != new)
> +		BUG();
>  }
>  EXPORT_SYMBOL_GPL(nf_conntrack_unregister_notifier);
>  
>  int nf_ct_expect_register_notifier(struct net *net,
>  				   struct nf_exp_event_notifier *new)
>  {
> -	int ret = 0;
> -
> -	mutex_lock(&nf_ct_ecache_mutex);
> -	if (net->ct.nf_expect_event_cb != NULL)
> -		ret = -EBUSY;
> +	if (cmpxchg(&net->ct.nf_expect_event_cb, NULL, new) != NULL)
> +		return -EBUSY;
>  	else
> -		net->ct.nf_expect_event_cb = new;
> -	mutex_unlock(&nf_ct_ecache_mutex);
> -
> -	return ret;
> +		return 0;
>  }
>  EXPORT_SYMBOL_GPL(nf_ct_expect_register_notifier);
>  
>  void nf_ct_expect_unregister_notifier(struct net *net,
>  				      struct nf_exp_event_notifier *new)
>  {
> -	mutex_lock(&nf_ct_ecache_mutex);
> -	BUG_ON(net->ct.nf_expect_event_cb != new);
> -	net->ct.nf_expect_event_cb = NULL;
> -	mutex_unlock(&nf_ct_ecache_mutex);
> +	if (xchg(&net->ct.nf_expect_event_cb, NULL) != new)
> +		BUG();
>  }
>  EXPORT_SYMBOL_GPL(nf_ct_expect_unregister_notifier);
>  
> -- 
> 1.7.7
> 
> --
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