Re: [patch] NULL pointer check for vma->vm_mm

[Andrew Morton]

On Fri, 1 Feb 2008 16:39:07 +0900 "Kenichi Okuyama" <kenichi.okuyama@xxxxxxxxx> 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.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/