netdev - Re: [rfc] IPVS: convert scheduler management to RCU

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Date:	Fri, 20 Aug 2010 22:59:19 +0900
From:	Simon Horman <horms@...ge.net.au>
To:	lvs-devel@...r.kernel.org, netdev@...r.kernel.org,
	netfilter-devel@...r.kernel.org
Cc:	Stephen Hemminger <shemminger@...tta.com>,
	Wensong Zhang <wensong@...ux-vs.org>,
	Julian Anastasov <ja@....bg>
Subject: Re: [rfc] IPVS: convert scheduler management to RCU

On Fri, Aug 20, 2010 at 10:33:21PM +0900, Simon Horman wrote:
> Signed-off-by: Simon Horman <horms@...ge.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);

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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