LXR linux/lib/once.c

   1// SPDX-License-Identifier: GPL-2.0
   2#include <linux/slab.h>
   3#include <linux/spinlock.h>
   4#include <linux/once.h>
   5#include <linux/random.h>
   6
   7struct once_work {
   8        struct work_struct work;
   9        struct static_key_true *key;
  10};
  11
  12static void once_deferred(struct work_struct *w)
  13{
  14        struct once_work *work;
  15
  16        work = container_of(w, struct once_work, work);
  17        BUG_ON(!static_key_enabled(work->key));
  18        static_branch_disable(work->key);
  19        kfree(work);
  20}
  21
  22static void once_disable_jump(struct static_key_true *key)
  23{
  24        struct once_work *w;
  25
  26        w = kmalloc(sizeof(*w), GFP_ATOMIC);
  27        if (!w)
  28                return;
  29
  30        INIT_WORK(&w->work, once_deferred);
  31        w->key = key;
  32        schedule_work(&w->work);
  33}
  34
  35static DEFINE_SPINLOCK(once_lock);
  36
  37bool __do_once_start(bool *done, unsigned long *flags)
  38        __acquires(once_lock)
  39{
  40        spin_lock_irqsave(&once_lock, *flags);
  41        if (*done) {
  42                spin_unlock_irqrestore(&once_lock, *flags);
  43                /* Keep sparse happy by restoring an even lock count on
  44                 * this lock. In case we return here, we don't call into
  45                 * __do_once_done but return early in the DO_ONCE() macro.
  46                 */
  47                __acquire(once_lock);
  48                return false;
  49        }
  50
  51        return true;
  52}
  53EXPORT_SYMBOL(__do_once_start);
  54
  55void __do_once_done(bool *done, struct static_key_true *once_key,
  56                    unsigned long *flags)
  57        __releases(once_lock)
  58{
  59        *done = true;
  60        spin_unlock_irqrestore(&once_lock, *flags);
  61        once_disable_jump(once_key);
  62}
  63EXPORT_SYMBOL(__do_once_done);
  64