linux-kernel - Re: [PATCH 3/3] rbtree_test: add more rbtree integrity checks

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Date:	Thu, 21 Mar 2013 20:36:52 -0700
From:	Michel Lespinasse <walken@...gle.com>
To:	Davidlohr Bueso <davidlohr.bueso@...com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] rbtree_test: add more rbtree integrity checks

On Mon, Mar 18, 2013 at 4:21 PM, Davidlohr Bueso <davidlohr.bueso@...com> wrote:
> When checking the rbtree, account for more properties:
>
>    - Both children of a red node are black.
>    - The tree has at least 2**bh(v)-1 internal nodes.

> -               WARN_ON_ONCE(is_red(rb) &&
> -                            (!rb_parent(rb) || is_red(rb_parent(rb))));
> +
> +               if (is_red(rb)) {
> +                       /*
> +                        * root must be black and no path contains two
> +                        * consecutive red nodes.
> +                        */
> +                       WARN_ON_ONCE(!rb_parent(rb) || is_red(rb_parent(rb)));
> +
> +                       /* both children of a red node are black */
> +                       WARN_ON_ONCE(is_red(rb->rb_left) || is_red(rb->rb_right));
> +               }

This seems quite redundant with the previous test - if we're going to
visit each children, then at that point we're going to check that they
can't be black if their parent (the current node) is black. So I don't
see that the tests adds any coverage.

>         WARN_ON_ONCE(count != nr_nodes);
> +       WARN_ON_ONCE(count < (1 << black_path_count(rb_last(&root))) - 1);

I like this last check - it can also be seen as a consequence of the
others, but it it's only one line and it nicely sums up what the other
properties are for :)

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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