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Date: Mon, 30 Jan 2012 11:22:14 -0600 (CST)
From: Christoph Lameter <cl@linux.com>
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To: Tejun Heo <tj@kernel.org>
cc: Dmitry Antipov <dmitry.antipov@linaro.org>,
        Rusty Russell <rusty@rustcorp.com.au>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, patches@linaro.org,
        linaro-dev@lists.linaro.org
Subject: Re: [PATCH 1/3] percpu: use ZERO_SIZE_PTR / ZERO_OR_NULL_PTR
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On Mon, 30 Jan 2012, Tejun Heo wrote:

> Percpu pointers are in a different address space and using
> ZERO_SIZE_PTR directly will trigger sparse address space warning.
> Also, I'm not entirely sure whether 16 is guaranteed to be unused in
> percpu address space (maybe it is but I don't think we have anything
> enforcing that).

We are already checking for NULL on free. So there is a presumption that
these numbers are unused.