mm/mmap: leverage vma_rb_erase_ignore() to implement vma_rb_erase()

These two functions share the same logic except ignore a different vma.

Let's reuse the code.
Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Link: https://lkml.kernel.org/r/20200809232057.23477-2-richard.weiyang@linux.alibaba.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mmap.c

@@ -474,8 +474,12 @@ static __always_inline void vma_rb_erase_ignore(struct vm_area_struct *vma,
 {
 	/*
 	 * All rb_subtree_gap values must be consistent prior to erase,
-	 * with the possible exception of the "next" vma being erased if
-	 * next->vm_start was reduced.
+	 * with the possible exception of
+	 *
+	 * a. the "next" vma being erased if next->vm_start was reduced in
+	 *    __vma_adjust() -> __vma_unlink()
+	 * b. the vma being erased in detach_vmas_to_be_unmapped() ->
+	 *    vma_rb_erase()
 	 */
 	validate_mm_rb(root, ignore);
 
@@ -485,13 +489,7 @@ static __always_inline void vma_rb_erase_ignore(struct vm_area_struct *vma,
 static __always_inline void vma_rb_erase(struct vm_area_struct *vma,
 					 struct rb_root *root)
 {
-	/*
-	 * All rb_subtree_gap values must be consistent prior to erase,
-	 * with the possible exception of the vma being erased.
-	 */
-	validate_mm_rb(root, vma);
-
-	__vma_rb_erase(vma, root);
+	vma_rb_erase_ignore(vma, root, vma);
 }
 
 /*