1 // SPDX-License-Identifier: GPL-2.0-only
2 
3 #include <linux/user-return-notifier.h>
4 #include <linux/percpu.h>
5 #include <linux/sched.h>
6 #include <linux/export.h>
7 
8 static DEFINE_PER_CPU(struct hlist_head, return_notifier_list);
9 
10 /*
11  * Request a notification when the current cpu returns to userspace.  Must be
12  * called in atomic context.  The notifier will also be called in atomic
13  * context.
14  */
15 void user_return_notifier_register(struct user_return_notifier *urn)
16 {
17 	set_tsk_thread_flag(current, TIF_USER_RETURN_NOTIFY);
18 	hlist_add_head(&urn->link, this_cpu_ptr(&return_notifier_list));
19 }
20 EXPORT_SYMBOL_GPL(user_return_notifier_register);
21 
22 /*
23  * Removes a registered user return notifier.  Must be called from atomic
24  * context, and from the same cpu registration occurred in.
25  */
26 void user_return_notifier_unregister(struct user_return_notifier *urn)
27 {
28 	hlist_del(&urn->link);
29 	if (hlist_empty(this_cpu_ptr(&return_notifier_list)))
30 		clear_tsk_thread_flag(current, TIF_USER_RETURN_NOTIFY);
31 }
32 EXPORT_SYMBOL_GPL(user_return_notifier_unregister);
33 
34 /* Calls registered user return notifiers */
35 void fire_user_return_notifiers(void)
36 {
37 	struct user_return_notifier *urn;
38 	struct hlist_node *tmp2;
39 	struct hlist_head *head;
40 
41 	head = &get_cpu_var(return_notifier_list);
42 	hlist_for_each_entry_safe(urn, tmp2, head, link)
43 		urn->on_user_return(urn);
44 	put_cpu_var(return_notifier_list);
45 }
46