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Date: Wed, 13 Feb 2008 16:42:53 -0800 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Stephen Hemminger <shemminger@...tta.com> Cc: Stephen Hemminger <"stephen.hemminger@...tta.com"@mail.vyatta.com>, linux-kernel@...r.kernel.org, davem@...emloft.net, netdev@...r.kernel.org, dipankar@...ibm.com, ego@...ibm.com, herbert@...dor.apana.org.au, akpm@...ux-foundation.org Subject: Re: [PATCH 1/2] remove rcu_assign_pointer(NULL) penalty with type/macro safety On Wed, Feb 13, 2008 at 04:27:00PM -0800, Stephen Hemminger wrote: > On Wed, 13 Feb 2008 16:14:04 -0800 > "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote: > > On Wed, Feb 13, 2008 at 03:51:58PM -0800, Stephen Hemminger wrote: [ . . . ] > > > Maybe cast both sides to void * in this case: > > > > > > static inline void node_set_parent(struct node *node, struct tnode *ptr) > > > { > > > rcu_assign_pointer((void *) node->parent, (void *)((unsigned long)ptr | NODE_TYPE(node))); > > > } > > > > That gets me the following: > > > > net/ipv4/fib_trie.c: In function ‘node_set_parent’: > > net/ipv4/fib_trie.c:182: error: invalid lvalue in assignment > > > > However, as with much in computing, an extra level of indirection fixes > > things. Your call as to whether or not the cure is preferable to the > > disease. ;-) > > > > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> > > --- > > > > fib_trie.c | 4 ++-- > > 1 file changed, 2 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 16:10:07.000000000 -0800 > > @@ -179,8 +179,8 @@ 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_pointer((*(void **)&node->parent), > > + (void *)((unsigned long)ptr | NODE_TYPE(node))); > > } > > 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 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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