From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH 1/2] remove rcu_assign_pointer(NULL) penalty with type/macro safety Date: Wed, 13 Feb 2008 17:34:27 -0800 Message-ID: <20080214013427.GT12393@linux.vnet.ibm.com> References: <20080213220024.GA30729@linux.vnet.ibm.com> <20080213143537.1b806790@extreme> <20080213224134.GK12393@linux.vnet.ibm.com> <20080213144233.05e860cb@extreme> <20080213233744.GO12393@linux.vnet.ibm.com> <20080213155158.1b621359@extreme> <20080214001404.GQ12393@linux.vnet.ibm.com> <20080213162700.0a32000d@extreme> <20080214004253.GR12393@linux.vnet.ibm.com> <20080213165356.11d02092@extreme> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Stephen Hemminger <"stephen.hemminger@vyatta.com"@mail.vyatta.com>, linux-kernel@vger.kernel.org, davem@davemloft.net, netdev@vger.kernel.org, dipankar@in.ibm.com, ego@in.ibm.com, herbert@gondor.apana.org.au, akpm@linux-foundation.org To: Stephen Hemminger Return-path: Received: from e32.co.us.ibm.com ([32.97.110.150]:32956 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757483AbYBNBen (ORCPT ); Wed, 13 Feb 2008 20:34:43 -0500 Content-Disposition: inline In-Reply-To: <20080213165356.11d02092@extreme> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, Feb 13, 2008 at 04:53:56PM -0800, Stephen Hemminger wrote: > On Wed, 13 Feb 2008 16:42:53 -0800 > "Paul E. McKenney" wrote: > > On Wed, Feb 13, 2008 at 04:27:00PM -0800, Stephen Hemminger wrote: [ . . . ] > > > That is heading towards ugly... Maybe not using the macro at all (for this case) would be best: > > > > > > static inline void node_set_parent(struct node *node, struct tnode *ptr) > > > { > > > smp_wmb(); > > > node->parent = (unsigned long)ptr | NODE_TYPE(node); > > > } > > > > Or, alternatively, the rcu_assign_index() patch sent earlier to avoid > > the bare memory barrier? > > > > Thanx, Paul > > I am fine with rcu_assign_index(), and add a comment in node_set_parent. OK, how about the following? Signed-off-by: Paul E. McKenney --- fib_trie.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff -urpNa -X dontdiff linux-2.6.25-rc1/net/ipv4/fib_trie.c linux-2.6.25-rc1-fib_trie-warn.compile/net/ipv4/fib_trie.c --- linux-2.6.25-rc1/net/ipv4/fib_trie.c 2008-02-13 14:38:12.000000000 -0800 +++ linux-2.6.25-rc1-fib_trie-warn.compile/net/ipv4/fib_trie.c 2008-02-13 17:31:16.000000000 -0800 @@ -96,6 +96,14 @@ typedef unsigned int t_key; #define IS_TNODE(n) (!(n->parent & T_LEAF)) #define IS_LEAF(n) (n->parent & T_LEAF) +/* + * The "parent" fields in struct node and struct leaf are really pointers, + * but with the possibility that the T_LEAF bit is set. Therefore, both + * the C compiler and RCU see them as integers rather than pointers. + * This in turn means that rcu_assign_index() must be used to assign + * values to these fields, rather than the usual rcu_assign_pointer(). + */ + struct node { unsigned long parent; t_key key; @@ -179,8 +187,7 @@ static inline struct tnode *node_parent_ static inline void node_set_parent(struct node *node, struct tnode *ptr) { - rcu_assign_pointer(node->parent, - (unsigned long)ptr | NODE_TYPE(node)); + rcu_assign_index(node->parent, (unsigned long)ptr | NODE_TYPE(node)); } static inline struct node *tnode_get_child(struct tnode *tn, unsigned int i)