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

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Message-Id: <1275581056.2833.2.camel@sbs-t61>
Date:	Thu, 03 Jun 2010 09:04:15 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Venkatesh Pallipadi <venki@...gle.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>,
	Fabio Checconi <fabio@...dalf.sssup.it>
Subject: Re: [PATCH] rbtree: undo augmented damage -v2

On Thu, 2010-06-03 at 00:48 -0700, Peter Zijlstra wrote:
> On Thu, 2010-06-03 at 09:13 +0200, Peter Zijlstra wrote:
> > On Wed, 2010-06-02 at 14:11 -0700, Suresh Siddha wrote:
> > >       P                       SL
> > >     /  \                     /  \
> > >    N    S       --->        N    S
> > >   /   /  \                 /      \
> > >  C   SL  SR               C        SR
> > > 
> > > If P needs to be removed, we need to re-augment S also in this case,
> > > right? It looks like we are not handling this case.
> > 
> > 
> > rb_augment_erase_begin(P) will return S if I read the code right, so
> > rb_augment_path(S) will the re-augment S, SL, N.
> 
> To be more explicit: P has two children, so we select the next entry,
> SL, as its substitute. Since SL doesn't have a right child we select its
> parent, S.
> 
> If SL were to represent a subtree with a right child, then we'd select
> that, lets call it SLR. SLR would then end up being a direct descendant
> of S, and hence rb_augment_path(SLR) would still pass S on its way up.

Yep. I missed the rb_parent() part in the rb_augment_erase_begin().

Thanks.

Acked-by: Suresh Siddha <suresh.b.siddha@...el.com>

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