uml-mmapper: BKL pushdown

Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/um/drivers/mmapper_kern.c

@@ -16,6 +16,7 @@
 #include <linux/miscdevice.h>
 #include <linux/module.h>
 #include <linux/mm.h>
+#include <linux/smp_lock.h>
 #include <asm/uaccess.h>
 #include "mem_user.h"
 
@@ -77,6 +78,7 @@ out:
 
 static int mmapper_open(struct inode *inode, struct file *file)
 {
+	cycle_kernel_lock();
 	return 0;
 }