1*4882a593Smuzhiyun /* SPDX-License-Identifier: GPL-2.0 */ 2*4882a593Smuzhiyun #ifndef _LINUX_ONCE_H 3*4882a593Smuzhiyun #define _LINUX_ONCE_H 4*4882a593Smuzhiyun 5*4882a593Smuzhiyun #include <linux/types.h> 6*4882a593Smuzhiyun #include <linux/jump_label.h> 7*4882a593Smuzhiyun 8*4882a593Smuzhiyun /* Helpers used from arbitrary contexts. 9*4882a593Smuzhiyun * Hard irqs are blocked, be cautious. 10*4882a593Smuzhiyun */ 11*4882a593Smuzhiyun bool __do_once_start(bool *done, unsigned long *flags); 12*4882a593Smuzhiyun void __do_once_done(bool *done, struct static_key_true *once_key, 13*4882a593Smuzhiyun unsigned long *flags); 14*4882a593Smuzhiyun 15*4882a593Smuzhiyun /* Variant for process contexts only. */ 16*4882a593Smuzhiyun bool __do_once_slow_start(bool *done); 17*4882a593Smuzhiyun void __do_once_slow_done(bool *done, struct static_key_true *once_key, 18*4882a593Smuzhiyun struct module *mod); 19*4882a593Smuzhiyun 20*4882a593Smuzhiyun /* Call a function exactly once. The idea of DO_ONCE() is to perform 21*4882a593Smuzhiyun * a function call such as initialization of random seeds, etc, only 22*4882a593Smuzhiyun * once, where DO_ONCE() can live in the fast-path. After @func has 23*4882a593Smuzhiyun * been called with the passed arguments, the static key will patch 24*4882a593Smuzhiyun * out the condition into a nop. DO_ONCE() guarantees type safety of 25*4882a593Smuzhiyun * arguments! 26*4882a593Smuzhiyun * 27*4882a593Smuzhiyun * Not that the following is not equivalent ... 28*4882a593Smuzhiyun * 29*4882a593Smuzhiyun * DO_ONCE(func, arg); 30*4882a593Smuzhiyun * DO_ONCE(func, arg); 31*4882a593Smuzhiyun * 32*4882a593Smuzhiyun * ... to this version: 33*4882a593Smuzhiyun * 34*4882a593Smuzhiyun * void foo(void) 35*4882a593Smuzhiyun * { 36*4882a593Smuzhiyun * DO_ONCE(func, arg); 37*4882a593Smuzhiyun * } 38*4882a593Smuzhiyun * 39*4882a593Smuzhiyun * foo(); 40*4882a593Smuzhiyun * foo(); 41*4882a593Smuzhiyun * 42*4882a593Smuzhiyun * In case the one-time invocation could be triggered from multiple 43*4882a593Smuzhiyun * places, then a common helper function must be defined, so that only 44*4882a593Smuzhiyun * a single static key will be placed there! 45*4882a593Smuzhiyun */ 46*4882a593Smuzhiyun #define DO_ONCE(func, ...) \ 47*4882a593Smuzhiyun ({ \ 48*4882a593Smuzhiyun bool ___ret = false; \ 49*4882a593Smuzhiyun static bool ___done = false; \ 50*4882a593Smuzhiyun static DEFINE_STATIC_KEY_TRUE(___once_key); \ 51*4882a593Smuzhiyun if (static_branch_unlikely(&___once_key)) { \ 52*4882a593Smuzhiyun unsigned long ___flags; \ 53*4882a593Smuzhiyun ___ret = __do_once_start(&___done, &___flags); \ 54*4882a593Smuzhiyun if (unlikely(___ret)) { \ 55*4882a593Smuzhiyun func(__VA_ARGS__); \ 56*4882a593Smuzhiyun __do_once_done(&___done, &___once_key, \ 57*4882a593Smuzhiyun &___flags); \ 58*4882a593Smuzhiyun } \ 59*4882a593Smuzhiyun } \ 60*4882a593Smuzhiyun ___ret; \ 61*4882a593Smuzhiyun }) 62*4882a593Smuzhiyun 63*4882a593Smuzhiyun /* Variant of DO_ONCE() for process/sleepable contexts. */ 64*4882a593Smuzhiyun #define DO_ONCE_SLOW(func, ...) \ 65*4882a593Smuzhiyun ({ \ 66*4882a593Smuzhiyun bool ___ret = false; \ 67*4882a593Smuzhiyun static bool __section(".data.once") ___done = false; \ 68*4882a593Smuzhiyun static DEFINE_STATIC_KEY_TRUE(___once_key); \ 69*4882a593Smuzhiyun if (static_branch_unlikely(&___once_key)) { \ 70*4882a593Smuzhiyun ___ret = __do_once_slow_start(&___done); \ 71*4882a593Smuzhiyun if (unlikely(___ret)) { \ 72*4882a593Smuzhiyun func(__VA_ARGS__); \ 73*4882a593Smuzhiyun __do_once_slow_done(&___done, &___once_key, \ 74*4882a593Smuzhiyun THIS_MODULE); \ 75*4882a593Smuzhiyun } \ 76*4882a593Smuzhiyun } \ 77*4882a593Smuzhiyun ___ret; \ 78*4882a593Smuzhiyun }) 79*4882a593Smuzhiyun 80*4882a593Smuzhiyun #define get_random_once(buf, nbytes) \ 81*4882a593Smuzhiyun DO_ONCE(get_random_bytes, (buf), (nbytes)) 82*4882a593Smuzhiyun #define get_random_once_wait(buf, nbytes) \ 83*4882a593Smuzhiyun DO_ONCE(get_random_bytes_wait, (buf), (nbytes)) \ 84*4882a593Smuzhiyun 85*4882a593Smuzhiyun #define get_random_slow_once(buf, nbytes) \ 86*4882a593Smuzhiyun DO_ONCE_SLOW(get_random_bytes, (buf), (nbytes)) 87*4882a593Smuzhiyun 88*4882a593Smuzhiyun #endif /* _LINUX_ONCE_H */ 89