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

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

On Fri, Aug 20, 2010 at 09:44:08PM +0800, Changli Gao wrote:
> On Fri, Aug 20, 2010 at 9:33 PM, Simon Horman <horms@verge.net.au> wrote:
> > 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);
> 
> Need a rcu_barrier_bh().

Thanks.

> 
> >
> >        /* decrease the module use count */
> >        ip_vs_use_count_dec();
> 
> 
> 
> -- 
> Regards,
> Changli Gao(xiaosuo@gmail.com)
> --
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