linux-kernel - Re: [PATCH 1/2] btree: Fix tree corruption in btree_get

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Message-Id: <20120606182938.f8f6178d.akpm@linux-foundation.org>
Date:	Wed, 6 Jun 2012 18:29:38 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Roland Dreier <roland@...nel.org>
Cc:	Joern Engel <joern@...fs.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] btree: Fix tree corruption in btree_get_prev()

On Wed, 6 Jun 2012 17:44:20 -0700 Roland Dreier <roland@...nel.org> wrote:

> On Wed, Jun 6, 2012 at 4:36 PM, Roland Dreier <roland@...nel.org> wrote:
> > On the other hand, your change makes me think we don't
> > even need a separate iterator (and we can avoid the variable
> > length array declaration)
> 
> FWIW with that change on top of my patch, I see
> 
> add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-123 (-123)
> function                                     old     new   delta
> btree_get_prev                               646     523    -123
> 
> on x86-64, so avoiding the variable length array is definitely
> worth something.
> 
> So the issue for me is whether messing with the caller's
> __key storage is OK, or if it's worth having a temporary
> local variable.
> 

Sometimes altering the caller's *__key when lookup fails is pretty rude
behavior :(

Perhaps we could add an arg to btree_get_prev(), provide it with
separate input and output key pointers?
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