kernel/user-return-notifier.c

   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(return_notifier_list);
  46 }