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On Fri, Aug 20, 2010 at 10:33:21PM +0900, Simon Horman wrote:
> Signed-off-by: Simon Horman <horms@xxxxxxxxxxxx>
>
> ---
>
> 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);
On further reading, I believe that I need a synchronize_rcu(); here,
>
> /* decrease the module use count */
> ip_vs_use_count_dec();
> --
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