linux-kernel - Re: [PATCH] rbtree: undo augmented damage -v2

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Message-ID: <AANLkTil8ly_3P2DgEI9oI_ZbYP6FkwP2lCY2v47iAn9-@mail.gmail.com>
Date:	Tue, 1 Jun 2010 11:09:23 -0700
From:	Venkatesh Pallipadi <venki@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	suresh.b.siddha@...el.com, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org,
	Fabio Checconi <fabio@...dalf.sssup.it>
Subject: Re: [PATCH] rbtree: undo augmented damage -v2

On Tue, Jun 1, 2010 at 10:42 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Tue, 2010-06-01 at 10:34 -0700, Venkatesh Pallipadi wrote:
>>
>> Yes. This will cover all the cases on insert. But on erase, there is
>> still a case where a rotate of sibling node is done during the
>> re-coloration process. There we have a child change on sibling's
>> child. I am not able to think of any easy way to handle that case.
>
> Let me go draw some figures with pen and paper to match up the erase
> path with the rb_augment_erase_begin() code, because I can't quite spot
> the case we're missing.
>
> If you have it handy, ascii art might help..

It is this case

    P
   / \
  N   S
     / \
    SL SR

changing to

    P
   / \
  N  SL
      \
       S
        \
        SR

This can happen in __rb_erase_color, where 'other' points to sibling node.

Thanks,
Venki
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