mm/madvise: use vma_lookup() instead of find_vma()

Using vma_lookup() verifies the address is contained in the found vma. 
This results in easier to read the code.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: ZhangPeng <[email protected]>
Reviewed-by: Liam R. Howlett <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: ZhangPeng

mm/madvise.c

@@ -852,21 +852,9 @@ static long madvise_dontneed_free(struct vm_area_struct *vma,
 		*prev = NULL; /* mmap_lock has been dropped, prev is stale */
 
 		mmap_read_lock(mm);
-		vma = find_vma(mm, start);
+		vma = vma_lookup(mm, start);
 		if (!vma)
 			return -ENOMEM;
-		if (start < vma->vm_start) {
-			/*
-			 * This "vma" under revalidation is the one
-			 * with the lowest vma->vm_start where start
-			 * is also < vma->vm_end. If start <
-			 * vma->vm_start it means an hole materialized
-			 * in the user address space within the
-			 * virtual range passed to MADV_DONTNEED
-			 * or MADV_FREE.
-			 */
-			return -ENOMEM;
-		}
 		/*
 		 * Potential end adjustment for hugetlb vma is OK as
 		 * the check below keeps end within vma.