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);