1 
2 #include <linux/user-return-notifier.h>
3 #include <linux/percpu.h>
4 #include <linux/sched.h>
5 #include <linux/module.h>
6 
7 static DEFINE_PER_CPU(struct hlist_head, return_notifier_list);
8 
9 #define URN_LIST_HEAD per_cpu(return_notifier_list, raw_smp_processor_id())
10 
11 /*
12  * Request a notification when the current cpu returns to userspace.  Must be
13  * called in atomic context.  The notifier will also be called in atomic
14  * context.
15  */
16 void user_return_notifier_register(struct user_return_notifier *urn)
17 {
18 	set_tsk_thread_flag(current, TIF_USER_RETURN_NOTIFY);
19 	hlist_add_head(&urn->link, &URN_LIST_HEAD);
20 }
21 EXPORT_SYMBOL_GPL(user_return_notifier_register);
22 
23 /*
24  * Removes a registered user return notifier.  Must be called from atomic
25  * context, and from the same cpu registration occured in.
26  */
27 void user_return_notifier_unregister(struct user_return_notifier *urn)
28 {
29 	hlist_del(&urn->link);
30 	if (hlist_empty(&URN_LIST_HEAD))
31 		clear_tsk_thread_flag(current, TIF_USER_RETURN_NOTIFY);
32 }
33 EXPORT_SYMBOL_GPL(user_return_notifier_unregister);
34 
35 /* Calls registered user return notifiers */
36 void fire_user_return_notifiers(void)
37 {
38 	struct user_return_notifier *urn;
39 	struct hlist_node *tmp1, *tmp2;
40 	struct hlist_head *head;
41 
42 	head = &get_cpu_var(return_notifier_list);
43 	hlist_for_each_entry_safe(urn, tmp1, tmp2, head, link)
44 		urn->on_user_return(urn);
45 	put_cpu_var();
46 }
47