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Linux/lib/once.c

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  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);
 63 

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