1 /* SPDX-License-Identifier: GPL-2.0+ */ 2 /* 3 * Sleepable Read-Copy Update mechanism for mutual exclusion, 4 * tiny variant. 5 * 6 * Copyright (C) IBM Corporation, 2017 7 * 8 * Author: Paul McKenney <paulmck@linux.ibm.com> 9 */ 10 11 #ifndef _LINUX_SRCU_TINY_H 12 #define _LINUX_SRCU_TINY_H 13 14 #include <linux/swait.h> 15 16 struct srcu_struct { 17 short srcu_lock_nesting[2]; /* srcu_read_lock() nesting depth. */ 18 u8 srcu_gp_running; /* GP workqueue running? */ 19 u8 srcu_gp_waiting; /* GP waiting for readers? */ 20 unsigned long srcu_idx; /* Current reader array element in bit 0x2. */ 21 unsigned long srcu_idx_max; /* Furthest future srcu_idx request. */ 22 struct swait_queue_head srcu_wq; 23 /* Last srcu_read_unlock() wakes GP. */ 24 struct rcu_head *srcu_cb_head; /* Pending callbacks: Head. */ 25 struct rcu_head **srcu_cb_tail; /* Pending callbacks: Tail. */ 26 struct work_struct srcu_work; /* For driving grace periods. */ 27 #ifdef CONFIG_DEBUG_LOCK_ALLOC 28 struct lockdep_map dep_map; 29 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 30 }; 31 32 void srcu_drive_gp(struct work_struct *wp); 33 34 #define __SRCU_STRUCT_INIT(name, __ignored, ___ignored, ____ignored) \ 35 { \ 36 .srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq), \ 37 .srcu_cb_tail = &name.srcu_cb_head, \ 38 .srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp), \ 39 __SRCU_DEP_MAP_INIT(name) \ 40 } 41 42 /* 43 * This odd _STATIC_ arrangement is needed for API compatibility with 44 * Tree SRCU, which needs some per-CPU data. 45 */ 46 #define DEFINE_SRCU(name) \ 47 struct srcu_struct name = __SRCU_STRUCT_INIT(name, name, name, name) 48 #define DEFINE_STATIC_SRCU(name) \ 49 static struct srcu_struct name = __SRCU_STRUCT_INIT(name, name, name, name) 50 #define DEFINE_SRCU_FAST(name) DEFINE_SRCU(name) 51 #define DEFINE_STATIC_SRCU_FAST(name) \ 52 static struct srcu_struct name = __SRCU_STRUCT_INIT(name, name, name, name) 53 #define DEFINE_SRCU_FAST_UPDOWN(name) DEFINE_SRCU(name) 54 #define DEFINE_STATIC_SRCU_FAST_UPDOWN(name) \ 55 static struct srcu_struct name = __SRCU_STRUCT_INIT(name, name, name, name) 56 57 // Dummy structure for srcu_notifier_head. 58 struct srcu_usage { }; 59 #define __SRCU_USAGE_INIT(name) { } 60 #define __init_srcu_struct_fast __init_srcu_struct 61 #define __init_srcu_struct_fast_updown __init_srcu_struct 62 #ifndef CONFIG_DEBUG_LOCK_ALLOC 63 #define init_srcu_struct_fast init_srcu_struct 64 #define init_srcu_struct_fast_updown init_srcu_struct 65 #endif // #ifndef CONFIG_DEBUG_LOCK_ALLOC 66 67 void synchronize_srcu(struct srcu_struct *ssp); 68 69 /* 70 * Counts the new reader in the appropriate per-CPU element of the 71 * srcu_struct. Can be invoked from irq/bh handlers, but the matching 72 * __srcu_read_unlock() must be in the same handler instance. Returns an 73 * index that must be passed to the matching srcu_read_unlock(). 74 */ 75 static inline int __srcu_read_lock(struct srcu_struct *ssp) 76 __acquires_shared(ssp) 77 { 78 int idx; 79 80 preempt_disable(); // Needed for PREEMPT_LAZY 81 idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1; 82 WRITE_ONCE(ssp->srcu_lock_nesting[idx], READ_ONCE(ssp->srcu_lock_nesting[idx]) + 1); 83 preempt_enable(); 84 __acquire_shared(ssp); 85 return idx; 86 } 87 88 struct srcu_ctr; 89 90 static inline bool __srcu_ptr_to_ctr(struct srcu_struct *ssp, struct srcu_ctr __percpu *scpp) 91 { 92 return (int)(intptr_t)(struct srcu_ctr __force __kernel *)scpp; 93 } 94 95 static inline struct srcu_ctr __percpu *__srcu_ctr_to_ptr(struct srcu_struct *ssp, int idx) 96 { 97 return (struct srcu_ctr __percpu *)(intptr_t)idx; 98 } 99 100 static inline struct srcu_ctr __percpu *__srcu_read_lock_fast(struct srcu_struct *ssp) 101 __acquires_shared(ssp) 102 { 103 return __srcu_ctr_to_ptr(ssp, __srcu_read_lock(ssp)); 104 } 105 106 static inline void __srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp) 107 __releases_shared(ssp) 108 { 109 __srcu_read_unlock(ssp, __srcu_ptr_to_ctr(ssp, scp)); 110 } 111 112 static inline struct srcu_ctr __percpu *__srcu_read_lock_fast_updown(struct srcu_struct *ssp) 113 __acquires_shared(ssp) 114 { 115 return __srcu_ctr_to_ptr(ssp, __srcu_read_lock(ssp)); 116 } 117 118 static inline 119 void __srcu_read_unlock_fast_updown(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp) 120 __releases_shared(ssp) 121 { 122 __srcu_read_unlock(ssp, __srcu_ptr_to_ctr(ssp, scp)); 123 } 124 125 static inline void synchronize_srcu_expedited(struct srcu_struct *ssp) 126 { 127 synchronize_srcu(ssp); 128 } 129 130 static inline void srcu_barrier(struct srcu_struct *ssp) 131 { 132 synchronize_srcu(ssp); 133 } 134 135 static inline void srcu_expedite_current(struct srcu_struct *ssp) { } 136 #define srcu_check_read_flavor(ssp, read_flavor) do { } while (0) 137 138 /* Defined here to avoid size increase for non-torture kernels. */ 139 static inline void srcu_torture_stats_print(struct srcu_struct *ssp, 140 char *tt, char *tf) 141 { 142 int idx; 143 144 idx = ((data_race(READ_ONCE(ssp->srcu_idx)) + 1) & 0x2) >> 1; 145 pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd) gp: %lu->%lu\n", 146 tt, tf, idx, 147 data_race(READ_ONCE(ssp->srcu_lock_nesting[!idx])), 148 data_race(READ_ONCE(ssp->srcu_lock_nesting[idx])), 149 data_race(READ_ONCE(ssp->srcu_idx)), 150 data_race(READ_ONCE(ssp->srcu_idx_max))); 151 } 152 153 #endif 154