[patch 38/86] lib/rbtree: set successor's parent unconditionally

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From: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
Subject: lib/rbtree: set successor's parent unconditionally

Both in Case 2 and 3, we exchange n and s.  This mean no matter whether
child2 is NULL or not, successor's parent should be assigned to node's.

This patch takes this step out to make it explicit and reduce the
ambiguity.

Besides, this step reduces some symbol size like rb_erase().

   KERN_CONFIG       upstream       patched
   OPT_FOR_PERF      877            870
   OPT_FOR_SIZE      635            621

Link: http://lkml.kernel.org/r/20191028021442.5450-1-richardw.yang@xxxxxxxxxxxxxxx
Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Michel Lespinasse <walken@xxxxxxxxxx>
Reviewed-by: Davidlohr Bueso <dbueso@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 include/linux/rbtree_augmented.h |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/include/linux/rbtree_augmented.h~lib-rbtree-set-successors-parent-unconditionally
+++ a/include/linux/rbtree_augmented.h
@@ -283,14 +283,13 @@ __rb_erase_augmented(struct rb_node *nod
 		__rb_change_child(node, successor, tmp, root);
 
 		if (child2) {
-			successor->__rb_parent_color = pc;
 			rb_set_parent_color(child2, parent, RB_BLACK);
 			rebalance = NULL;
 		} else {
 			unsigned long pc2 = successor->__rb_parent_color;
-			successor->__rb_parent_color = pc;
 			rebalance = __rb_is_black(pc2) ? parent : NULL;
 		}
+		successor->__rb_parent_color = pc;
 		tmp = successor;
 	}
 
_




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