VM: can't go through the inner loop in unmap_vmas() more than once...

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

mm/memory.c

@@ -1354,7 +1354,7 @@ unsigned long unmap_vmas(struct mmu_gather *tlb,
 		if (unlikely(is_pfn_mapping(vma)))
 			untrack_pfn_vma(vma, 0, 0);
 
-		while (start != end) {
+		if (start != end) {
 			if (unlikely(is_vm_hugetlb_page(vma))) {
 				/*
 				 * It is undesirable to test vma->vm_file as it
@@ -1371,8 +1371,8 @@ unsigned long unmap_vmas(struct mmu_gather *tlb,
 					unmap_hugepage_range(vma, start, end, NULL);
 			} else
 				unmap_page_range(tlb, vma, start, end, details);
-			start = end;
 		}
+		start = end;
 	}
 
 	mmu_notifier_invalidate_range_end(mm, start_addr, end_addr);