mm/mmap.c: logic of find_vma_intersection repeated in __do_munmap

Logic of find_vma_intersection() is repeated in __do_munmap().

Also, prev is assigned a value before checking vma->vm_start >= end which
might end up on a return statement making that assignment useless.

Calling find_vma_intersection() checks that condition and returns NULL if
no vma is found, hence only the !vma check is needed in __do_munmap().

Link: https://lkml.kernel.org/r/20210409162129.18313-1-gmjuareztello@gmail.comSigned-off-by: Gonzalo Matias Juarez Tello <gmjuareztello@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mmap.c

@@ -2828,16 +2828,11 @@ int __do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
 	 */
 	arch_unmap(mm, start, end);
 
-	/* Find the first overlapping VMA */
-	vma = find_vma(mm, start);
+	/* Find the first overlapping VMA where start < vma->vm_end */
+	vma = find_vma_intersection(mm, start, end);
 	if (!vma)
 		return 0;
 	prev = vma->vm_prev;
-	/* we have  start < vma->vm_end  */
-
-	/* if it doesn't overlap, we have nothing.. */
-	if (vma->vm_start >= end)
-		return 0;
 
 	/*
 	 * If we need to split any vma, do it now to save pain later.