lib/once.c

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