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