mm/mmap: add inline munmap_vma_range() for code readability

There are two locations that have a block of code for munmapping a vma
range.  Change those two locations to use a function and add meaningful
comments about what happens to the arguments, which was unclear in the
previous code.
Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20200818154707.2515169-2-Liam.Howlett@Oracle.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mmap.c

@@ -575,6 +575,33 @@ static inline struct vm_area_struct *vma_next(struct mm_struct *mm,
 
 	return vma->vm_next;
 }
+
+/*
+ * munmap_vma_range() - munmap VMAs that overlap a range.
+ * @mm: The mm struct
+ * @start: The start of the range.
+ * @len: The length of the range.
+ * @pprev: pointer to the pointer that will be set to previous vm_area_struct
+ * @rb_link: the rb_node
+ * @rb_parent: the parent rb_node
+ *
+ * Find all the vm_area_struct that overlap from @start to
+ * @end and munmap them.  Set @pprev to the previous vm_area_struct.
+ *
+ * Returns: -ENOMEM on munmap failure or 0 on success.
+ */
+static inline int
+munmap_vma_range(struct mm_struct *mm, unsigned long start, unsigned long len,
+		 struct vm_area_struct **pprev, struct rb_node ***link,
+		 struct rb_node **parent, struct list_head *uf)
+{
+
+	while (find_vma_links(mm, start, start + len, pprev, link, parent))
+		if (do_munmap(mm, start, len, uf))
+			return -ENOMEM;
+
+	return 0;
+}
 static unsigned long count_vma_pages_range(struct mm_struct *mm,
 		unsigned long addr, unsigned long end)
 {
@@ -1721,13 +1748,9 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 			return -ENOMEM;
 	}
 
-	/* Clear old maps */
-	while (find_vma_links(mm, addr, addr + len, &prev, &rb_link,
-			      &rb_parent)) {
-		if (do_munmap(mm, addr, len, uf))
+	/* Clear old maps, set up prev, rb_link, rb_parent, and uf */
+	if (munmap_vma_range(mm, addr, len, &prev, &rb_link, &rb_parent, uf))
 		return -ENOMEM;
-	}
-
 	/*
 	 * Private writable mapping: check memory availability
 	 */
@@ -3063,14 +3086,9 @@ static int do_brk_flags(unsigned long addr, unsigned long len, unsigned long fla
 	if (error)
 		return error;
 
-	/*
-	 * Clear old maps.  this also does some error checking for us
-	 */
-	while (find_vma_links(mm, addr, addr + len, &prev, &rb_link,
-			      &rb_parent)) {
-		if (do_munmap(mm, addr, len, uf))
+	/* Clear old maps, set up prev, rb_link, rb_parent, and uf */
+	if (munmap_vma_range(mm, addr, len, &prev, &rb_link, &rb_parent, uf))
 		return -ENOMEM;
-	}
 
 	/* Check against address space limits *after* clearing old maps... */
 	if (!may_expand_vm(mm, flags, len >> PAGE_SHIFT))