user-return-notifier.c

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#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);
}