mm/vmalloc: initialize VA's list node after unlink

A vmap_area can travel between different places.  For example
attached/detached to/from different rb-trees.  In order to prevent fancy
bugs, initialize a VA's list node after it is removed from the list, so it
pairs with VA's rb_node which is also initialized.

There is no functional change as a result of this patch.

Link: https://lkml.kernel.org/r/20220607093449.3100-4-urezki@gmail.comSigned-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sony.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/vmalloc.c

@@ -977,7 +977,7 @@ __unlink_va(struct vmap_area *va, struct rb_root *root, bool augment)
 	else
 		rb_erase(&va->rb_node, root);
 
-	list_del(&va->list);
+	list_del_init(&va->list);
 	RB_CLEAR_NODE(&va->rb_node);
 }