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

Benjamin Poirier
2012-04-27T18:30:06Z

This mutex protects a single pointer.
---
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