linux-kernel - Re: [patch 3/4 -mm] flex_array: poison free elements

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Message-Id: <1251148618.22398.8188.camel@nimitz>
Date:	Mon, 24 Aug 2009 14:16:58 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Ben Blum <bblum@...gle.com>
Subject: Re: [patch 3/4 -mm] flex_array: poison free elements

On Mon, 2009-08-24 at 13:41 -0700, David Rientjes wrote:
> LEX_ARRAY_FREE (or an additional poison value to 
> distinguish between use-uninitialized vs. use-after-free) must be used in 
> flex_array_clear() otherwise the cgroup patchset, the only proposed user 
> of this library code, could never shrink this array when pid's are free 
> like the kmalloc vs. vmalloc patchset could do.

Are you saying that you expected it to never reallocate the array, but
have a permanent flex_array and that it just calls flex_array_clear() on
the elements that it doesn't want any more, and the array ends up
sparsely populated?  I can see why we'd need a poison value in that
case.

Or, are we just talking about a situation where we need to truncate the
pidlist?

-- Dave

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