mm/mmap: move anon_vma setting in __vma_adjust()

Move the anon_vma setting & warn_no up the function.  This is done to
clear up the locking later.

Link: https://lkml.kernel.org/r/20230120162650.984577-40-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mmap.c

@@ -682,6 +682,14 @@ int __vma_adjust(struct vma_iterator *vmi, struct vm_area_struct *vma,
 	if (vma_iter_prealloc(vmi))
 		return -ENOMEM;
 
+	anon_vma = vma->anon_vma;
+	if (!anon_vma && adjust_next)
+		anon_vma = next->anon_vma;
+
+	if (anon_vma)
+		VM_WARN_ON(adjust_next && next->anon_vma &&
+			   anon_vma != next->anon_vma);
+
 	vma_adjust_trans_huge(orig_vma, start, end, adjust_next);
 	if (file) {
 		mapping = file->f_mapping;
@@ -703,12 +711,7 @@ int __vma_adjust(struct vma_iterator *vmi, struct vm_area_struct *vma,
 		}
 	}
 
-	anon_vma = vma->anon_vma;
-	if (!anon_vma && adjust_next)
-		anon_vma = next->anon_vma;
 	if (anon_vma) {
-		VM_WARN_ON(adjust_next && next->anon_vma &&
-			   anon_vma != next->anon_vma);
 		anon_vma_lock_write(anon_vma);
 		anon_vma_interval_tree_pre_update_vma(vma);
 		if (adjust_next)