From: Tejun Heo <tj@kernel.org>
To: Christoph Lameter <cl@linux.com>
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
Date: Mon, 30 Jan 2012 09:54:34 -0800 [thread overview]
Message-ID: <20120130175434.GG3355@google.com> (raw)
In-Reply-To: <alpine.DEB.2.00.1201301145570.28693@router.home>
Hello, Christoph.
On Mon, Jan 30, 2012 at 11:52:23AM -0600, Christoph Lameter wrote:
> We have two possibilities now:
>
> 1. We say that the value returned from the per cpu allocator is an opaque
> value.
>
> This means that we have to remove the NULL check from the free
> function. And audit the kernel code for all occurrences where
> a per cpu pointer value of NULL is assumed to mean that no per
> cpu allocation has occurred.
No, NULL is never gonna be a valid return from any allocator including
percpu. Percpu allocator doesn't and will never do so.
> 2. We say that there are special values for the per cpu pointers (NULL,
> ZERO_SIZE_PTR)
>
> Then we would have to guarantee that the per cpu allocator never
> returns those values.
>
> Plus then the ZERO_SIZE_PTR patch will be fine.
>
> The danger exist of these values being passed as
> parameters to functions that do not support them (per_cpu_ptr
> etc). Those would need VM_BUG_ONs or some other checks to detect
> potential problems.
I'm saying we don't have this for ZERO_SIZE_PTR in any meaningful way
at this point. If somebody wants to implement it properly, please
feel free to, but simply applying ZERO_SIZE_PTR without other changes
doesn't make any sense.
Thanks.
--
tejun
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next prev parent reply other threads:[~2012-01-30 17:54 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-30 8:37 [PATCH 1/3] percpu: use ZERO_SIZE_PTR / ZERO_OR_NULL_PTR Dmitry Antipov
2012-01-30 16:15 ` Christoph Lameter
2012-01-30 17:15 ` Tejun Heo
2012-01-30 17:19 ` Tejun Heo
2012-01-30 17:22 ` Christoph Lameter
2012-01-30 17:33 ` Tejun Heo
2012-01-30 17:35 ` Christoph Lameter
2012-01-30 17:22 ` Christoph Lameter
2012-01-30 17:42 ` Tejun Heo
2012-01-30 17:52 ` Christoph Lameter
2012-01-30 17:54 ` Tejun Heo [this message]
2012-01-30 17:58 ` Christoph Lameter
2012-01-30 18:02 ` Tejun Heo
2012-01-30 18:12 ` Christoph Lameter
2012-01-30 18:16 ` Tejun Heo
2012-01-31 4:48 ` Rusty Russell
2012-01-30 18:13 ` Tejun Heo
2012-01-30 18:15 ` Christoph Lameter
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