linux-kernel - [PATCH] lib/rbtree: set successor's parent unconditionally

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Message-Id: <20190825011010.31072-1-richardw.yang@linux.intel.com>
Date:   Sun, 25 Aug 2019 09:10:10 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     akpm@...ux-foundation.org, gregkh@...uxfoundation.org,
        dbueso@...e.de, linux-kernel@...r.kernel.org
Cc:     Wei Yang <richardw.yang@...ux.intel.com>
Subject: [PATCH] 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

Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>
---
 include/linux/rbtree_augmented.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/include/linux/rbtree_augmented.h b/include/linux/rbtree_augmented.h
index 179faab29f52..8fcddfef7876 100644
--- a/include/linux/rbtree_augmented.h
+++ b/include/linux/rbtree_augmented.h
@@ -237,14 +237,13 @@ __rb_erase_augmented(struct rb_node *node, struct rb_root *root,
 		__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;
 	}
 
-- 
2.17.1