Commit 6d58452d authored Oct 08, 2012 by Michel Lespinasse Committed by Linus Torvalds Oct 09, 2012

rbtree: adjust root color in rb_insert_color() only when necessary



The root node of an rbtree must always be black.  However,
rb_insert_color() only needs to maintain this invariant when it has been
broken - that is, when it exits the loop due to the current (red) node
being the root.  In all other cases (exiting after tree rotations, or
exiting due to an existing black parent) the invariant is already
satisfied, so there is no need to adjust the root node color.

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 1f052865

lib/rbtree.c

+15 −4

Original line number	Diff line number	Diff line
		@@ -91,8 +91,21 @@ void rb_insert_color(struct rb_node node, struct rb_root root)
		{
		struct rb_node parent, gparent;

		while ((parent = rb_parent(node)) && rb_is_red(parent))
		{
		while (true) {
		/*
		* Loop invariant: node is red
		*
		* If there is a black parent, we are done.
		* Otherwise, take some corrective action as we don't
		* want a red root or two consecutive red nodes.
		*/
		parent = rb_parent(node);
		if (!parent) {
		rb_set_black(node);
		break;
		} else if (rb_is_black(parent))
		break;

		gparent = rb_parent(parent);

		if (parent == gparent->rb_left)
		@@ -142,8 +155,6 @@ void rb_insert_color(struct rb_node node, struct rb_root root)
		break;
		}
		}

		rb_set_black(root->rb_node);
		}
		EXPORT_SYMBOL(rb_insert_color);

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