[PATCH] net: don't use INIT_RCU_HEAD

[PATCH] net: don't use INIT_RCU_HEAD

[Alexey Dobriyan]

call_rcu() will unconditionally rewrite RCU head anyway.
Applies to 
	struct neigh_parms
	struct neigh_table
	struct net
	struct cipso_v4_doi
	struct in_ifaddr
	struct in_device
	rt->u.dst

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

 net/core/neighbour.c     |    2 --
 net/core/net_namespace.c |    2 --
 net/ipv4/cipso_ipv4.c    |    1 -
 net/ipv4/devinet.c       |    9 +--------
 net/ipv4/route.c         |    1 -
 5 files changed, 1 insertion(+), 14 deletions(-)

--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1340,7 +1340,6 @@ struct neigh_parms *neigh_parms_alloc(struct net_device *dev,
 	if (p) {
 		p->tbl		  = tbl;
 		atomic_set(&p->refcnt, 1);
-		INIT_RCU_HEAD(&p->rcu_head);
 		p->reachable_time =
 				neigh_rand_reach_time(p->base_reachable_time);
 
@@ -1412,7 +1411,6 @@ void neigh_table_init_no_netlink(struct neigh_table *tbl)
 	tbl->parms.net = &init_net;
 #endif
 	atomic_set(&tbl->parms.refcnt, 1);
-	INIT_RCU_HEAD(&tbl->parms.rcu_head);
 	tbl->parms.reachable_time =
 			  neigh_rand_reach_time(tbl->parms.base_reachable_time);
 
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -47,7 +47,6 @@ static __net_init int setup_net(struct net *net)
 		goto out;
 
 	ng->len = INITIAL_NET_GEN_PTRS;
-	INIT_RCU_HEAD(&ng->rcu);
 	rcu_assign_pointer(net->gen, ng);
 
 	error = 0;
@@ -446,7 +445,6 @@ int net_assign_generic(struct net *net, int id, void *data)
 	 */
 
 	ng->len = id;
-	INIT_RCU_HEAD(&ng->rcu);
 	memcpy(&ng->ptr, &old_ng->ptr, old_ng->len);
 
 	rcu_assign_pointer(net->gen, ng);
--- a/net/ipv4/cipso_ipv4.c
+++ b/net/ipv4/cipso_ipv4.c
@@ -490,7 +490,6 @@ int cipso_v4_doi_add(struct cipso_v4_doi *doi_def)
 	}
 
 	atomic_set(&doi_def->refcount, 1);
-	INIT_RCU_HEAD(&doi_def->rcu);
 
 	spin_lock(&cipso_v4_doi_list_lock);
 	if (cipso_v4_doi_search(doi_def->doi) != NULL)
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -112,13 +112,7 @@ static inline void devinet_sysctl_unregister(struct in_device *idev)
 
 static struct in_ifaddr *inet_alloc_ifa(void)
 {
-	struct in_ifaddr *ifa = kzalloc(sizeof(*ifa), GFP_KERNEL);
-
-	if (ifa) {
-		INIT_RCU_HEAD(&ifa->rcu_head);
-	}
-
-	return ifa;
+	return kzalloc(sizeof(struct in_ifaddr), GFP_KERNEL);
 }
 
 static void inet_rcu_free_ifa(struct rcu_head *head)
@@ -161,7 +155,6 @@ static struct in_device *inetdev_init(struct net_device *dev)
 	in_dev = kzalloc(sizeof(*in_dev), GFP_KERNEL);
 	if (!in_dev)
 		goto out;
-	INIT_RCU_HEAD(&in_dev->rcu_head);
 	memcpy(&in_dev->cnf, dev_net(dev)->ipv4.devconf_dflt,
 			sizeof(in_dev->cnf));
 	in_dev->cnf.sysctl = NULL;
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1386,7 +1386,6 @@ void ip_rt_redirect(__be32 old_gw, __be32 daddr, __be32 new_gw,
 
 				/* Copy all the information. */
 				*rt = *rth;
-				INIT_RCU_HEAD(&rt->u.dst.rcu_head);
 				rt->u.dst.__use		= 1;
 				atomic_set(&rt->u.dst.__refcnt, 1);
 				rt->u.dst.child		= NULL;

Re: [PATCH] net: don't use INIT_RCU_HEAD

[Patrick McHardy]

Alexey Dobriyan wrote:
> call_rcu() will unconditionally rewrite RCU head anyway.
> Applies to 
> 	struct neigh_parms
> 	struct neigh_table
> 	struct net
> 	struct cipso_v4_doi
> 	struct in_ifaddr
> 	struct in_device
> 	rt->u.dst

It would probably make sense to get a statement from Paul
whether this might be required in the future, f.i. for some
debugging feature.

Re: [PATCH] net: don't use INIT_RCU_HEAD

[Alexey Dobriyan]

On Tue, Oct 28, 2008 at 04:29:06PM +0100, Patrick McHardy wrote:
> Alexey Dobriyan wrote:
>> call_rcu() will unconditionally rewrite RCU head anyway.
>> Applies to 	struct neigh_parms
>> 	struct neigh_table
>> 	struct net
>> 	struct cipso_v4_doi
>> 	struct in_ifaddr
>> 	struct in_device
>> 	rt->u.dst
>
> It would probably make sense to get a statement from Paul
> whether this might be required in the future, f.i. for some
> debugging feature.

Let's cc him :-)

Re: [PATCH] net: don't use INIT_RCU_HEAD

[Paul E. McKenney]

On Tue, Oct 28, 2008 at 06:43:41PM +0300, Alexey Dobriyan wrote:
> On Tue, Oct 28, 2008 at 04:29:06PM +0100, Patrick McHardy wrote:
> > Alexey Dobriyan wrote:
> >> call_rcu() will unconditionally rewrite RCU head anyway.
> >> Applies to 	struct neigh_parms
> >> 	struct neigh_table
> >> 	struct net
> >> 	struct cipso_v4_doi
> >> 	struct in_ifaddr
> >> 	struct in_device
> >> 	rt->u.dst
> >
> > It would probably make sense to get a statement from Paul
> > whether this might be required in the future, f.i. for some
> > debugging feature.
> 
> Let's cc him :-)

Can't say that I would be all that upset if INIT_RCU_HEAD() were to
simply vanish.  So I have no problem with it being removed from the
above functions.

Suppose I might as well find the original and Ack it.  ;-)

							Thanx, Paul

Re: [PATCH] net: don't use INIT_RCU_HEAD

[Paul E. McKenney]

On Tue, Oct 28, 2008 at 04:31:24PM +0300, Alexey Dobriyan wrote:
> call_rcu() will unconditionally rewrite RCU head anyway.
> Applies to 
> 	struct neigh_parms
> 	struct neigh_table
> 	struct net
> 	struct cipso_v4_doi
> 	struct in_ifaddr
> 	struct in_device
> 	rt->u.dst

Assuming that no code outside of RCU is testing the rcu_head fields...
That would usually be a bad idea in any case, as call_rcu() makes no
guarantee about the values of these fields after the callback is invoked.
Furthermore, there have been serious proposals that would change the
call_rcu() field names and layout.

Therefore:

Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
> ---
> 
>  net/core/neighbour.c     |    2 --
>  net/core/net_namespace.c |    2 --
>  net/ipv4/cipso_ipv4.c    |    1 -
>  net/ipv4/devinet.c       |    9 +--------
>  net/ipv4/route.c         |    1 -
>  5 files changed, 1 insertion(+), 14 deletions(-)
> 
> --- a/net/core/neighbour.c
> +++ b/net/core/neighbour.c
> @@ -1340,7 +1340,6 @@ struct neigh_parms *neigh_parms_alloc(struct net_device *dev,
>  	if (p) {
>  		p->tbl		  = tbl;
>  		atomic_set(&p->refcnt, 1);
> -		INIT_RCU_HEAD(&p->rcu_head);
>  		p->reachable_time =
>  				neigh_rand_reach_time(p->base_reachable_time);
> 
> @@ -1412,7 +1411,6 @@ void neigh_table_init_no_netlink(struct neigh_table *tbl)
>  	tbl->parms.net = &init_net;
>  #endif
>  	atomic_set(&tbl->parms.refcnt, 1);
> -	INIT_RCU_HEAD(&tbl->parms.rcu_head);
>  	tbl->parms.reachable_time =
>  			  neigh_rand_reach_time(tbl->parms.base_reachable_time);
> 
> --- a/net/core/net_namespace.c
> +++ b/net/core/net_namespace.c
> @@ -47,7 +47,6 @@ static __net_init int setup_net(struct net *net)
>  		goto out;
> 
>  	ng->len = INITIAL_NET_GEN_PTRS;
> -	INIT_RCU_HEAD(&ng->rcu);
>  	rcu_assign_pointer(net->gen, ng);
> 
>  	error = 0;
> @@ -446,7 +445,6 @@ int net_assign_generic(struct net *net, int id, void *data)
>  	 */
> 
>  	ng->len = id;
> -	INIT_RCU_HEAD(&ng->rcu);
>  	memcpy(&ng->ptr, &old_ng->ptr, old_ng->len);
> 
>  	rcu_assign_pointer(net->gen, ng);
> --- a/net/ipv4/cipso_ipv4.c
> +++ b/net/ipv4/cipso_ipv4.c
> @@ -490,7 +490,6 @@ int cipso_v4_doi_add(struct cipso_v4_doi *doi_def)
>  	}
> 
>  	atomic_set(&doi_def->refcount, 1);
> -	INIT_RCU_HEAD(&doi_def->rcu);
> 
>  	spin_lock(&cipso_v4_doi_list_lock);
>  	if (cipso_v4_doi_search(doi_def->doi) != NULL)
> --- a/net/ipv4/devinet.c
> +++ b/net/ipv4/devinet.c
> @@ -112,13 +112,7 @@ static inline void devinet_sysctl_unregister(struct in_device *idev)
> 
>  static struct in_ifaddr *inet_alloc_ifa(void)
>  {
> -	struct in_ifaddr *ifa = kzalloc(sizeof(*ifa), GFP_KERNEL);
> -
> -	if (ifa) {
> -		INIT_RCU_HEAD(&ifa->rcu_head);
> -	}
> -
> -	return ifa;
> +	return kzalloc(sizeof(struct in_ifaddr), GFP_KERNEL);
>  }
> 
>  static void inet_rcu_free_ifa(struct rcu_head *head)
> @@ -161,7 +155,6 @@ static struct in_device *inetdev_init(struct net_device *dev)
>  	in_dev = kzalloc(sizeof(*in_dev), GFP_KERNEL);
>  	if (!in_dev)
>  		goto out;
> -	INIT_RCU_HEAD(&in_dev->rcu_head);
>  	memcpy(&in_dev->cnf, dev_net(dev)->ipv4.devconf_dflt,
>  			sizeof(in_dev->cnf));
>  	in_dev->cnf.sysctl = NULL;
> --- a/net/ipv4/route.c
> +++ b/net/ipv4/route.c
> @@ -1386,7 +1386,6 @@ void ip_rt_redirect(__be32 old_gw, __be32 daddr, __be32 new_gw,
> 
>  				/* Copy all the information. */
>  				*rt = *rth;
> -				INIT_RCU_HEAD(&rt->u.dst.rcu_head);
>  				rt->u.dst.__use		= 1;
>  				atomic_set(&rt->u.dst.__refcnt, 1);
>  				rt->u.dst.child		= NULL;
> --
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Re: [PATCH] net: don't use INIT_RCU_HEAD

[David Miller]

From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Date: Tue, 28 Oct 2008 09:10:17 -0700

> On Tue, Oct 28, 2008 at 04:31:24PM +0300, Alexey Dobriyan wrote:
> > call_rcu() will unconditionally rewrite RCU head anyway.
> > Applies to 
> > 	struct neigh_parms
> > 	struct neigh_table
> > 	struct net
> > 	struct cipso_v4_doi
> > 	struct in_ifaddr
> > 	struct in_device
> > 	rt->u.dst
> 
> Assuming that no code outside of RCU is testing the rcu_head fields...
> That would usually be a bad idea in any case, as call_rcu() makes no
> guarantee about the values of these fields after the callback is invoked.
> Furthermore, there have been serious proposals that would change the
> call_rcu() field names and layout.
> 
> Therefore:
> 
> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

I've applied this patch, thanks everyone.