Messages in this thread |  | | | Date | Thu, 31 Jan 2008 23:55:44 -0800 | | From | Andrew Morton <> | | Subject | Re: [patch] NULL pointer check for vma->vm_mm |
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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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