Re: [PATCH] radix-tree: fix radix_tree_prev_hole underflow case

From: Wu Fengguang
Date: Thu May 13 2010 - 22:37:46 EST


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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