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

Pablo Neira Ayuso
2012-05-02T00:51:12Z

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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