linux-kernel - Re: [PATCH] radix-tree: fix radix_tree_prev

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Message-ID: <20100514023737.GB8695@localhost>
Date:	Fri, 14 May 2010 10:37:37 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Cesar Eduardo Barros <cesarb@...arb.net>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] radix-tree: fix radix_tree_prev_hole underflow case

On Fri, May 14, 2010 at 10:28:50AM +0800, Cesar Eduardo Barros wrote:
> Em 13-05-2010 23:15, Wu Fengguang escreveu:
> > On Fri, May 14, 2010 at 10:05:24AM +0800, Cesar Eduardo Barros wrote:
> >> radix_tree_prev_hole() used LONG_MAX to detect underflow; however,
> >> ULONG_MAX is clearly what was intended, both here and by its only user
> >> (count_history_pages at mm/readahead.c).
> >
> > Good catch, thanks! I actually have a more smart
> > radix_tree_prev_hole() that uses ULONG_MAX.
> 
> I saw it already ([PATCH 14/16] radixtree: speed up the search for 
> hole), but it misses the LONG_MAX in the documentation comment.

Yes, thanks!

> > Andrew, fortunately this bug has little impact on readahead.
> 
> I agree, if I read it correctly it should only have any impact either 
> when very near LONG_MAX or in the unlikely case that there is no hole at 
> ULONG_MAX. And even then, the impact should be limited.

Right.
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