From 344824c0f4b6aae3deca1e8b15d4e3f26a761682 Mon Sep 17 00:00:00 2001 From: Michel Lespinasse Date: Wed, 20 Dec 2017 18:02:12 +0100 Subject: [PATCH] rbtree: break out of rb_insert_color loop after tree rotation It is a well known property of rbtrees that insertion never requires more than two tree rotations. In our implementation, after one loop iteration identified one or two necessary tree rotations, we would iterate and look for more. However at that point the node's parent would always be black, which would cause us to exit the loop. We can make the code flow more obvious by just adding a break statement after the tree rotations, where we know we are done. Additionally, in the cases where two tree rotations are necessary, we don't have to update the 'node' pointer as it wouldn't be used until the next loop iteration, which we now avoid due to this break statement. Signed-off-by: Michel Lespinasse Acked-by: David Woodhouse Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds [Linux commit 1f0528653e41ec230c60f5738820e8a544731399] Ported to Xen. Signed-off-by: Praveen Kumar Acked-by: Jan Beulich --- xen/common/rbtree.c | 14 ++++---------- 1 file changed, 4 insertions(+), 10 deletions(-) diff --git a/xen/common/rbtree.c b/xen/common/rbtree.c index a75b336ba2..9dc296e0d8 100644 --- a/xen/common/rbtree.c +++ b/xen/common/rbtree.c @@ -109,18 +109,15 @@ void rb_insert_color(struct rb_node *node, struct rb_root *root) } } - if (parent->rb_right == node) - { - register struct rb_node *tmp; + if (parent->rb_right == node) { __rb_rotate_left(parent, root); - tmp = parent; parent = node; - node = tmp; } rb_set_black(parent); rb_set_red(gparent); __rb_rotate_right(gparent, root); + break; } else { { register struct rb_node *uncle = gparent->rb_left; @@ -134,18 +131,15 @@ void rb_insert_color(struct rb_node *node, struct rb_root *root) } } - if (parent->rb_left == node) - { - register struct rb_node *tmp; + if (parent->rb_left == node) { __rb_rotate_right(parent, root); - tmp = parent; parent = node; - node = tmp; } rb_set_black(parent); rb_set_red(gparent); __rb_rotate_left(gparent, root); + break; } } -- 2.39.5