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

Andrew Morton
2019-12-05T00:51:50Z

From: Wei Yang <richardw.yang@linux.intel.com>
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@linux.intel.com
Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Michel Lespinasse <walken@google.com>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

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;
}

_