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