LXR linux/lib/once.c

   1#include <linux/slab.h>
   2#include <linux/spinlock.h>
   3#include <linux/once.h>
   4#include <linux/random.h>
   5
   6struct once_work {
   7        struct work_struct work;
   8        struct static_key *key;
   9};
  10
  11static 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
  21static 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
  34static DEFINE_SPINLOCK(once_lock);
  35
  36bool __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}
  52EXPORT_SYMBOL(__do_once_start);
  53
  54void __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}
  62EXPORT_SYMBOL(__do_once_done);
  63