rbtree: empty nodes have no color

Empty nodes have no color.  We can make use of this property to simplify
the code emitted by the RB_EMPTY_NODE and RB_CLEAR_NODE macros.  Also,
we can get rid of the rb_init_node function which had been introduced by
commit 88d19cf3 ("timers: Add rb_init_node() to allow for stack
allocated rb nodes") to avoid some issue with the empty node's color not
being initialized.

I'm not sure what the RB_EMPTY_NODE checks in rb_prev() / rb_next() are
doing there, though.  axboe introduced them in commit 10fd48f2
("rbtree: fixed reversed RB_EMPTY_NODE and rb_next/prev").  The way I
see it, the 'empty node' abstraction is only used by rbtree users to
flag nodes that they haven't inserted in any rbtree, so asking the
predecessor or successor of such nodes doesn't make any sense.

One final rb_init_node() caller was recently added in sysctl code to
implement faster sysctl name lookups.  This code doesn't make use of
RB_EMPTY_NODE at all, and from what I could see it only called
rb_init_node() under the mistaken assumption that such initialization was
required before node insertion.

[sfr@canb.auug.org.au: fix net/ceph/osd_client.c build]
Signed-off-by: Michel Lespinasse <walken@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: David Woodhouse <David.Woodhouse@intel.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Daniel Santos <daniel.santos@pobox.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: John Stultz <john.stultz@linaro.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/proc_sysctl.c

@@ -168,11 +168,9 @@ static void init_header(struct ctl_table_header *head,
 	head->node = node;
 	if (node) {
 		struct ctl_table *entry;
-		for (entry = table; entry->procname; entry++, node++) {
-			rb_init_node(&node->node);
+		for (entry = table; entry->procname; entry++, node++)
 			node->header = head;
 	}
-	}
 }
 
 static void erase_header(struct ctl_table_header *head)

include/linux/rbtree.h

@@ -68,16 +68,11 @@ static inline void rb_set_color(struct rb_node *rb, int color)
 #define	rb_entry(ptr, type, member) container_of(ptr, type, member)
 
 #define RB_EMPTY_ROOT(root)  ((root)->rb_node == NULL)
-#define RB_EMPTY_NODE(node)	(rb_parent(node) == node)
-#define RB_CLEAR_NODE(node)	(rb_set_parent(node, node))
 
-static inline void rb_init_node(struct rb_node *rb)
-{
-	rb->rb_parent_color = 0;
-	rb->rb_right = NULL;
-	rb->rb_left = NULL;
-	RB_CLEAR_NODE(rb);
-}
+/* 'empty' nodes are nodes that are known not to be inserted in an rbree */
+#define RB_EMPTY_NODE(node)  ((node)->rb_parent_color == (unsigned long)(node))
+#define RB_CLEAR_NODE(node)  ((node)->rb_parent_color = (unsigned long)(node))
+
 
 extern void rb_insert_color(struct rb_node *, struct rb_root *);
 extern void rb_erase(struct rb_node *, struct rb_root *);

include/linux/timerqueue.h

@@ -39,7 +39,7 @@ struct timerqueue_node *timerqueue_getnext(struct timerqueue_head *head)
 
 static inline void timerqueue_init(struct timerqueue_node *node)
 {
-	rb_init_node(&node->node);
+	RB_CLEAR_NODE(&node->node);
 }
 
 static inline void timerqueue_init_head(struct timerqueue_head *head)

lib/rbtree.c

@@ -387,7 +387,7 @@ struct rb_node *rb_next(const struct rb_node *node)
 {
 	struct rb_node *parent;
 
-	if (rb_parent(node) == node)
+	if (RB_EMPTY_NODE(node))
 		return NULL;
 
 	/* If we have a right-hand child, go down and then left as far
@@ -416,7 +416,7 @@ struct rb_node *rb_prev(const struct rb_node *node)
 {
 	struct rb_node *parent;
 
-	if (rb_parent(node) == node)
+	if (RB_EMPTY_NODE(node))
 		return NULL;
 
 	/* If we have a left-hand child, go down and then right as far

net/ceph/osd_client.c

@@ -221,7 +221,6 @@ struct ceph_osd_request *ceph_osdc_alloc_request(struct ceph_osd_client *osdc,
 	kref_init(&req->r_kref);
 	init_completion(&req->r_completion);
 	init_completion(&req->r_safe_completion);
-	rb_init_node(&req->r_node);
 	INIT_LIST_HEAD(&req->r_unsafe_item);
 	INIT_LIST_HEAD(&req->r_linger_item);
 	INIT_LIST_HEAD(&req->r_linger_osd);