[PATCH] Check for wraps in copy_page_range

While browsing the 4 level page table changes (looking for a bug), I
noticed that copy_page_range, unlike others, do not check for
wraparound, which I suppose could be a problem with 4G/4G architectures
or that sort of thing.

This patch fixes it.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/memory.c

@@ -358,7 +358,7 @@ static int copy_pmd_range(struct mm_struct *dst_mm,  struct mm_struct *src_mm,
 
 	for (; addr < end; addr = next, src_pmd++, dst_pmd++) {
 		next = (addr + PMD_SIZE) & PMD_MASK;
-		if (next > end)
+		if (next > end || next <= addr)
 			next = end;
 		if (pmd_none(*src_pmd))
 			continue;
@@ -390,7 +390,7 @@ static int copy_pud_range(struct mm_struct *dst_mm,  struct mm_struct *src_mm,
 
 	for (; addr < end; addr = next, src_pud++, dst_pud++) {
 		next = (addr + PUD_SIZE) & PUD_MASK;
-		if (next > end)
+		if (next > end || next <= addr)
 			next = end;
 		if (pud_none(*src_pud))
 			continue;