linux-kernel - Re: [RFC][PATCH] mm: Remove ZERO_SIZE

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Message-Id: <201002270959.EEI05786.OOFFQVMFJLOtSH@I-love.SAKURA.ne.jp>
Date:	Sat, 27 Feb 2010 09:59:49 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	cl@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] mm: Remove ZERO_SIZE_PTR.

Christoph Lameter wrote:
> On Fri, 26 Feb 2010, Tetsuo Handa wrote:
> 
> > Everybody should check for ptr != NULL, and most callers are actually checking
> > for ptr != NULL. But nobody is checking for ptr != ZERO_SIZE_PTR.
> 
> That is so intentionally because some kernel subsystem can do a zero size
> allocation.
> 
So, not only users *can* do zero size allocation,
but also there *are* users who are intentionally doing zero size allocation.
Then, we can't remove ZERO_SIZE_PTR.

> > Yes, this is the fault of caller. But ZERO_SIZE_PTR is too small value to
> > distinguish "NULL pointer dereference" and "ZERO_SIZE_PTR dereference" because
> > address printed by oops message can easily exceed ZERO_SIZE_PTR when
> > "struct foo" is large.
> 
> Correct.

Maybe PAGE_SIZE / 2 is better than 16?

Thanks.
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