linux-kernel - Re: [patch] NULL pointer check for vma->vm

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Date:	Fri, 1 Feb 2008 02:19:17 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Kenichi Okuyama" <kenichi.okuyama@...il.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [patch] NULL pointer check for vma->vm_mm

On Fri, 1 Feb 2008 17:24:17 +0900 "Kenichi Okuyama" <kenichi.okuyama@...il.com> wrote:

> First of all, thank you for looking at the patch.
> 
> I do agree that if mm is NULL, system will call Oops anyway.
> However, since it's oops, it does not stop the system, nor call kdump.

That would be a huge bug in kdump?  Surely it dumps when the kernel oopses?

> By calling BUG_ON(), it'll gives us chance of calling kdump at the first chance.
> 
> Since this is very rare to happen, I thought we should capture the incident
> whenever possible. On other hand, because BUG_ON macro is very light,
> I thought this will not harm any performance...
> 
> Forgive me in advance if I was wrong.
> I still think checking mm with BUG_ON here is better than counting on Oops.

But there are probably a million potential NULL-pointer dereferences in the 
kernel.  Why single out this one?
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