1 
2 #include <linux/user-return-notifier.h>
3 #include <linux/percpu.h>
4 #include <linux/sched.h>
5 #include <linux/export.h>
6 
7 static DEFINE_PER_CPU(struct hlist_head, return_notifier_list);
8 
9 /*
10  * Request a notification when the current cpu returns to userspace.  Must be
11  * called in atomic context.  The notifier will also be called in atomic
12  * context.
13  */
14 void user_return_notifier_register(struct user_return_notifier *urn)
15 {
16 	set_tsk_thread_flag(current, TIF_USER_RETURN_NOTIFY);
17 	hlist_add_head(&urn->link, this_cpu_ptr(&return_notifier_list));
18 }
19 EXPORT_SYMBOL_GPL(user_return_notifier_register);
20 
21 /*
22  * Removes a registered user return notifier.  Must be called from atomic
23  * context, and from the same cpu registration occurred in.
24  */
25 void user_return_notifier_unregister(struct user_return_notifier *urn)
26 {
27 	hlist_del(&urn->link);
28 	if (hlist_empty(this_cpu_ptr(&return_notifier_list)))
29 		clear_tsk_thread_flag(current, TIF_USER_RETURN_NOTIFY);
30 }
31 EXPORT_SYMBOL_GPL(user_return_notifier_unregister);
32 
33 /* Calls registered user return notifiers */
34 void fire_user_return_notifiers(void)
35 {
36 	struct user_return_notifier *urn;
37 	struct hlist_node *tmp2;
38 	struct hlist_head *head;
39 
40 	head = &get_cpu_var(return_notifier_list);
41 	hlist_for_each_entry_safe(urn, tmp2, head, link)
42 		urn->on_user_return(urn);
43 	put_cpu_var(return_notifier_list);
44 }
45