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SubjectRe: [patch] NULL pointer check for vma->vm_mm
On Fri, 1 Feb 2008 16:39:07 +0900 "Kenichi Okuyama" <kenichi.okuyama@gmail.com> wrote:

> Dear all,
>
> I was looking at the ./mm/rmap.c .. I found that, in function
> "page_referenced_one()",
> struct mm_struct *mm = vma->vm_mm;
> was being refererred without NULL check.
>
> Though I do agree that this works for most of the cases, I thought it
> is better to add
> BUG_ON() for case of mm being NULL.
>
> attached is the patch for this

If we dereference NULL then the kernel will display basically the same
information as would a BUG, and it takes the same action. So adding a
BUG_ON here really doesn't gain us anything.

Also, I think vma->vm_mm == 0 is not a valid state, so this just shouldn't
happen - the code is OK to assume that a particular invariant is being
honoured.



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