[rfc] IPVS: convert scheduler management to RCU

[Simon Horman <horms@verge.net.au>]

Signed-off-by: Simon Horman <horms@verge.net.au>

--- 

I'm still getting my head around RCU, so review would be greatly appreciated.

It occurs to me that this code is not performance critical, so
perhaps simply replacing the rwlock with a spinlock would be better?

Index: nf-next-2.6/net/netfilter/ipvs/ip_vs_sched.c
===================================================================
--- nf-next-2.6.orig/net/netfilter/ipvs/ip_vs_sched.c	2010-08-20 22:21:01.000000000 +0900
+++ nf-next-2.6/net/netfilter/ipvs/ip_vs_sched.c	2010-08-20 22:21:51.000000000 +0900
@@ -35,7 +35,7 @@
 static LIST_HEAD(ip_vs_schedulers);
 
 /* lock for service table */
-static DEFINE_RWLOCK(__ip_vs_sched_lock);
+static DEFINE_SPINLOCK(ip_vs_sched_mutex);
 
 
 /*
@@ -91,9 +91,9 @@ static struct ip_vs_scheduler *ip_vs_sch
 
 	IP_VS_DBG(2, "%s(): sched_name \"%s\"\n", __func__, sched_name);
 
-	read_lock_bh(&__ip_vs_sched_lock);
+	rcu_read_lock_bh();
 
-	list_for_each_entry(sched, &ip_vs_schedulers, n_list) {
+	list_for_each_entry_rcu(sched, &ip_vs_schedulers, n_list) {
 		/*
 		 * Test and get the modules atomically
 		 */
@@ -105,14 +105,14 @@ static struct ip_vs_scheduler *ip_vs_sch
 		}
 		if (strcmp(sched_name, sched->name)==0) {
 			/* HIT */
-			read_unlock_bh(&__ip_vs_sched_lock);
+			rcu_read_unlock_bh();
 			return sched;
 		}
 		if (sched->module)
 			module_put(sched->module);
 	}
 
-	read_unlock_bh(&__ip_vs_sched_lock);
+	rcu_read_unlock_bh();
 	return NULL;
 }
 
@@ -167,10 +167,10 @@ int register_ip_vs_scheduler(struct ip_v
 	/* increase the module use count */
 	ip_vs_use_count_inc();
 
-	write_lock_bh(&__ip_vs_sched_lock);
+	spin_lock_bh(&ip_vs_sched_mutex);
 
 	if (!list_empty(&scheduler->n_list)) {
-		write_unlock_bh(&__ip_vs_sched_lock);
+		spin_unlock_bh(&ip_vs_sched_mutex);
 		ip_vs_use_count_dec();
 		pr_err("%s(): [%s] scheduler already linked\n",
 		       __func__, scheduler->name);
@@ -181,9 +181,9 @@ int register_ip_vs_scheduler(struct ip_v
 	 *  Make sure that the scheduler with this name doesn't exist
 	 *  in the scheduler list.
 	 */
-	list_for_each_entry(sched, &ip_vs_schedulers, n_list) {
+	list_for_each_entry_rcu(sched, &ip_vs_schedulers, n_list) {
 		if (strcmp(scheduler->name, sched->name) == 0) {
-			write_unlock_bh(&__ip_vs_sched_lock);
+			spin_unlock_bh(&ip_vs_sched_mutex);
 			ip_vs_use_count_dec();
 			pr_err("%s(): [%s] scheduler already existed "
 			       "in the system\n", __func__, scheduler->name);
@@ -193,8 +193,8 @@ int register_ip_vs_scheduler(struct ip_v
 	/*
 	 *	Add it into the d-linked scheduler list
 	 */
-	list_add(&scheduler->n_list, &ip_vs_schedulers);
-	write_unlock_bh(&__ip_vs_sched_lock);
+	list_add_rcu(&scheduler->n_list, &ip_vs_schedulers);
+	spin_unlock_bh(&ip_vs_sched_mutex);
 
 	pr_info("[%s] scheduler registered.\n", scheduler->name);
 
@@ -212,9 +212,9 @@ int unregister_ip_vs_scheduler(struct ip
 		return -EINVAL;
 	}
 
-	write_lock_bh(&__ip_vs_sched_lock);
+	spin_lock_bh(&ip_vs_sched_mutex);
 	if (list_empty(&scheduler->n_list)) {
-		write_unlock_bh(&__ip_vs_sched_lock);
+		spin_unlock_bh(&ip_vs_sched_mutex);
 		pr_err("%s(): [%s] scheduler is not in the list. failed\n",
 		       __func__, scheduler->name);
 		return -EINVAL;
@@ -223,8 +223,8 @@ int unregister_ip_vs_scheduler(struct ip
 	/*
 	 *	Remove it from the d-linked scheduler list
 	 */
-	list_del(&scheduler->n_list);
-	write_unlock_bh(&__ip_vs_sched_lock);
+	list_del_rcu(&scheduler->n_list);
+	spin_unlock_bh(&ip_vs_sched_mutex);
 
 	/* decrease the module use count */
 	ip_vs_use_count_dec();