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

From: "Paul E. McKenney" <[email-masked]>
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 <[email-masked]>

> Signed-off-by: Alexey Dobriyan <[email-masked]>
> ---
> 
>  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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