#include <linux/user-return-notifier.h>#include <linux/percpu.h>#include <linux/sched.h>#include <linux/export.h> static DEFINE_PER_CPU(struct hlist_head, return_notifier_list); /* * Request a notification when the current cpu returns to userspace.  Must be * called in atomic context.  The notifier will also be called in atomic * context. */void user_return_notifier_register(struct user_return_notifier *urn){	set_tsk_thread_flag(current, TIF_USER_RETURN_NOTIFY);	hlist_add_head(&urn->link, &__get_cpu_var(return_notifier_list));}EXPORT_SYMBOL_GPL(user_return_notifier_register); /* * Removes a registered user return notifier.  Must be called from atomic * context, and from the same cpu registration occurred in. */void user_return_notifier_unregister(struct user_return_notifier *urn){	hlist_del(&urn->link);	if (hlist_empty(&__get_cpu_var(return_notifier_list)))		clear_tsk_thread_flag(current, TIF_USER_RETURN_NOTIFY);}EXPORT_SYMBOL_GPL(user_return_notifier_unregister); /* Calls registered user return notifiers */void fire_user_return_notifiers(void){	struct user_return_notifier *urn;	struct hlist_node *tmp1, *tmp2;	struct hlist_head *head; 	head = &get_cpu_var(return_notifier_list);	hlist_for_each_entry_safe(urn, tmp1, tmp2, head, link)		urn->on_user_return(urn);	put_cpu_var(return_notifier_list);}