Hi Andrew,

On Tue, Aug 23, 2011 at 02:14:45PM -0700, Andrew Morton wrote:

quoted

+	if ((old_addr & ~HPAGE_PMD_MASK) ||
+	    (new_addr & ~HPAGE_PMD_MASK) ||
+	    (old_addr + HPAGE_PMD_SIZE) > old_end ||

Can (old_addr + HPAGE_PMD_SIZE) wrap past zero?

Good question. old_addr is hpage aligned so to overflow it'd need to
be exactly at address 0-HPAGE_PMD_SIZE. Can any userland map an
address there? I doubt and surely not x86* or sparc (currently THP is
only enabled on x86 anyway so answer is it can't wrap past zero). But
probably we should add a wrap check for other archs in the future
unless we have a real guarantee from all archs to avoid the check. I
only can guarantee about x86*.

-	if (!pmd_none(*new_pmd)) {
-		WARN_ON(1);
+	if (!WARN_ON(pmd_none(*new_pmd))) {

WARN_ON(!pmd_none

Thanks for the cleanups!

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