linux-kernel - Re: [PATCH] include/linux/slab.h: new KFREE() macro.

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Message-Id: <E1H3zFK-0001Bw-NI@be1.lrz>
Date:	Mon, 08 Jan 2007 19:29:22 +0100
From:	Bodo Eggert <7eggert@....de>
To:	Amit Choudhary <amit2030@...oo.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH] include/linux/slab.h: new KFREE() macro.

Amit Choudhary <amit2030@...oo.com> wrote:
> --- Christoph Hellwig <hch@...radead.org> wrote:
>> On Sun, Jan 07, 2007 at 12:46:50AM -0800, Amit Choudhary wrote:

>> > Well, I am not proposing this as a debugging aid. The idea is about correct
>> > programming,
>> atleast
>> > from my view. Ideally, if you kfree(x), then you should set x to NULL. So,
>> > either programmers
>> do
>> > it themselves or a ready made macro do it for them.
>> 
>> No, you should not.  I suspect that's the basic point you're missing.

> Any strong reason why not? x has some value that does not make sense and can
> create only problems. And as I explained, it can result in longer code too.
> So, why keep this value around. Why not re-initialize it to NULL.

1) Because some magic value like 0x23 would be better.
2) Because it hides bugs like double frees or dangeling references while
   creating a race condition. In the end, you'll get more hard-to-find bugs
   in exchange for papering over some easy-to-spot bugs.

> If x should not be re-initialized to NULL, then by the same logic, we should
> not even initialize local variables. And all of us know that local variables
> should be initialized.

That may hide bugs, too. Therefore this isn't done in the kernel unless you
intend to depend on an initial value.
-- 
Ich danke GMX dafür, die Verwendung meiner Adressen mittels per SPF
verbreiteten Lügen zu sabotieren.

http://david.woodhou.se/why-not-spf.html
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