1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _LINUX_ONCE_H
3 #define _LINUX_ONCE_H
4
5 #include <linux/types.h>
6 #include <linux/jump_label.h>
7
8 /* Helpers used from arbitrary contexts.
9 * Hard irqs are blocked, be cautious.
10 */
11 bool __do_once_start(bool *done, unsigned long *flags);
12 void __do_once_done(bool *done, struct static_key_true *once_key,
13 unsigned long *flags, struct module *mod);
14
15 /* Variant for process contexts only. */
16 bool __do_once_sleepable_start(bool *done);
17 void __do_once_sleepable_done(bool *done, struct static_key_true *once_key,
18 struct module *mod);
19
20 /* Call a function exactly once. The idea of DO_ONCE() is to perform
21 * a function call such as initialization of random seeds, etc, only
22 * once, where DO_ONCE() can live in the fast-path. After @func has
23 * been called with the passed arguments, the static key will patch
24 * out the condition into a nop. DO_ONCE() guarantees type safety of
25 * arguments!
26 *
27 * Note that the following is not equivalent ...
28 *
29 * DO_ONCE(func, arg);
30 * DO_ONCE(func, arg);
31 *
32 * ... to this version:
33 *
34 * void foo(void)
35 * {
36 * DO_ONCE(func, arg);
37 * }
38 *
39 * foo();
40 * foo();
41 *
42 * In case the one-time invocation could be triggered from multiple
43 * places, then a common helper function must be defined, so that only
44 * a single static key will be placed there!
45 */
46 #define DO_ONCE(func, ...) \
47 ({ \
48 bool ___ret = false; \
49 static bool __section(".data.once") ___done = false; \
50 static DEFINE_STATIC_KEY_TRUE(___once_key); \
51 if (static_branch_unlikely(&___once_key)) { \
52 unsigned long ___flags; \
53 ___ret = __do_once_start(&___done, &___flags); \
54 if (unlikely(___ret)) { \
55 func(__VA_ARGS__); \
56 __do_once_done(&___done, &___once_key, \
57 &___flags, THIS_MODULE); \
58 } \
59 } \
60 ___ret; \
61 })
62
63 /* Variant of DO_ONCE() for process/sleepable contexts. */
64 #define DO_ONCE_SLEEPABLE(func, ...) \
65 ({ \
66 bool ___ret = false; \
67 static bool __section(".data.once") ___done = false; \
68 static DEFINE_STATIC_KEY_TRUE(___once_key); \
69 if (static_branch_unlikely(&___once_key)) { \
70 ___ret = __do_once_sleepable_start(&___done); \
71 if (unlikely(___ret)) { \
72 func(__VA_ARGS__); \
73 __do_once_sleepable_done(&___done, &___once_key,\
74 THIS_MODULE); \
75 } \
76 } \
77 ___ret; \
78 })
79
80 #define get_random_once(buf, nbytes) \
81 DO_ONCE(get_random_bytes, (buf), (nbytes))
82
83 #define get_random_sleepable_once(buf, nbytes) \
84 DO_ONCE_SLEEPABLE(get_random_bytes, (buf), (nbytes))
85
86 #endif /* _LINUX_ONCE_H */
87
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