Subject: Re: [PATCH] [IPV4]: Remove warning in node_set_parent.

From: Stephen Hemminger <[email-masked]>
Date: Mon, 11 Feb 2008 11:48:49 -0800

On Mon, 11 Feb 2008 11:47:17 +0300
"Denis V. Lunev" <[email-masked]> wrote:

> net/ipv4/fib_trie.c: In function 'node_set_parent':
> net/ipv4/fib_trie.c:184: warning: assignment makes integer from pointer
> without a cast
> 
> Signed-off-by: Denis V. Lunev <[email-masked]>
> ---
>  net/ipv4/fib_trie.c |    7 ++++---
>  1 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
> index f5fba3f..1753cd4 100644
> --- a/net/ipv4/fib_trie.c
> +++ b/net/ipv4/fib_trie.c
> @@ -177,10 +177,11 @@ static inline struct tnode *node_parent_rcu(struct node *node)
>  	return rcu_dereference(ret);
>  }
>  
> -static inline void node_set_parent(struct node *node, struct tnode *ptr)
> +static inline void node_set_parent(struct node *node, struct tnode *__ptr)
>  {
> -	rcu_assign_pointer(node->parent,
> -			   (unsigned long)ptr | NODE_TYPE(node));
> +	struct node *ptr;
> +	ptr = (struct node *)((unsigned long)__ptr | NODE_TYPE(node));
> +	rcu_assign_pointer(node->parent, ptr);
>  }
>  
>  static inline struct node *tnode_get_child(struct tnode *tn, unsigned int i)

No, this causes new warning from assigning pointer (ptr) to integer node->parent.

Why not just change rcupdate.h to do the right thing.

>>From a00f7cbf1c2f2282eced236e1e8b99b0fecd213a Mon Sep 17 00:00:00 2001
From: Stephen Hemminger <[email-masked]>
Date: Mon, 11 Feb 2008 11:28:13 -0800
Subject: [PATCH] eliminate warnings when rcu_assign_pointer is used with unsigned long

It is reasonable to use RCU with non-pointer values, and describe
the optimization.

Signed-off-by: Stephen Hemminger <[email-masked]>
---
 include/linux/rcupdate.h |   13 +++++++------
 1 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 37a642c..c44ac87 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -172,14 +172,15 @@ struct rcu_head {
  * structure after the pointer assignment.  More importantly, this
  * call documents which pointers will be dereferenced by RCU read-side
  * code.
+ *
+ * If value is the NULL (constant 0), then no barrier is needed.
  */
 
-#define rcu_assign_pointer(p, v) \
-	({ \
-		if (!__builtin_constant_p(v) || \
-		    ((v) != NULL)) \
-			smp_wmb(); \
-		(p) = (v); \
+#define rcu_assign_pointer(p, v)			\
+	({						\
+		if (!(__builtin_constant_p(v) && v))	\
+			smp_wmb();			\
+		(p) = (v);				\
 	})
 
 /**
-- 
1.5.3.8

-- 
Stephen Hemminger <[email-masked]>