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
   7 struct once_work {
   8         struct work_struct work;
   9         struct static_key *key;
  10 };
  11
  12 static 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_key_slow_dec(work->key);
  19         kfree(work);
  20 }
  21
  22 static void once_disable_jump(struct static_key *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
  35 static DEFINE_SPINLOCK(once_lock);
  36
  37 bool __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 }
  53 EXPORT_SYMBOL(__do_once_start);
  54
  55 void __do_once_done(bool *done, struct static_key *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 }
  63 EXPORT_SYMBOL(__do_once_done);