Fixes building in userspace.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
---
 lib/closure.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/closure.c b/lib/closure.c
index b38ded00b9..0855e698ce 100644
--- a/lib/closure.c
+++ b/lib/closure.c
@@ -9,6 +9,7 @@
 #include <linux/closure.h>
 #include <linux/debugfs.h>
 #include <linux/export.h>
+#include <linux/rcupdate.h>
 #include <linux/seq_file.h>
 #include <linux/sched/debug.h>
 
-- 
2.40.1