Re: [PATCH v3 4/4] mm/vmap: move BUG_ON() check to the unlink_va()

From: Roman Gushchin
Date: Tue May 28 2019 - 18:54:51 EST

On Mon, May 27, 2019 at 11:38:42AM +0200, Uladzislau Rezki (Sony) wrote:
> Move the BUG_ON()/RB_EMPTY_NODE() check under unlink_va()
> function, it means if an empty node gets freed it is a BUG
> thus is considered as faulty behaviour.

It's not exactly clear from the description, why it's better.

Also, do we really need a BUG_ON() in either place?

Isn't something like this better?

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index c42872ed82ac..2df0e86d6aff 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1118,7 +1118,8 @@ EXPORT_SYMBOL_GPL(unregister_vmap_purge_notifier);

static void __free_vmap_area(struct vmap_area *va)
- BUG_ON(RB_EMPTY_NODE(&va->rb_node));
+ if (WARN_ON_ONCE(RB_EMPTY_NODE(&va->rb_node)))
+ return;

* Remove from the busy tree/list.