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 __random_once_work {
   7         struct work_struct work;
   8         struct static_key *key;
   9 };
  10
  11 static void __random_once_deferred(struct work_struct *w)
  12 {
  13         struct __random_once_work *work;
  14
  15         work = container_of(w, struct __random_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 __random_once_disable_jump(struct static_key *key)
  22 {
  23         struct __random_once_work *w;
  24
  25         w = kmalloc(sizeof(*w), GFP_ATOMIC);
  26         if (!w)
  27                 return;
  28
  29         INIT_WORK(&w->work, __random_once_deferred);
  30         w->key = key;
  31         schedule_work(&w->work);
  32 }
  33
  34 bool __get_random_once(void *buf, int nbytes, bool *done,
  35                        struct static_key *once_key)
  36 {
  37         static DEFINE_SPINLOCK(lock);
  38         unsigned long flags;
  39
  40         spin_lock_irqsave(&lock, flags);
  41         if (*done) {
  42                 spin_unlock_irqrestore(&lock, flags);
  43                 return false;
  44         }
  45
  46         get_random_bytes(buf, nbytes);
  47         *done = true;
  48         spin_unlock_irqrestore(&lock, flags);
  49
  50         __random_once_disable_jump(once_key);
  51
  52         return true;
  53 }
  54 EXPORT_SYMBOL(__get_random_once);