kernel/user-return-notifier.c

   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 }