1 /* 2 * Sleepable Read-Copy Update mechanism for mutual exclusion, 3 * tiny variant. 4 * 5 * This program is free software; you can redistribute it and/or modify 6 * it under the terms of the GNU General Public License as published by 7 * the Free Software Foundation; either version 2 of the License, or 8 * (at your option) any later version. 9 * 10 * This program is distributed in the hope that it will be useful, 11 * but WITHOUT ANY WARRANTY; without even the implied warranty of 12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 13 * GNU General Public License for more details. 14 * 15 * You should have received a copy of the GNU General Public License 16 * along with this program; if not, you can access it online at 17 * http://www.gnu.org/licenses/gpl-2.0.html. 18 * 19 * Copyright (C) IBM Corporation, 2017 20 * 21 * Author: Paul McKenney <[email protected]> 22 */ 23 24 #ifndef _LINUX_SRCU_TINY_H 25 #define _LINUX_SRCU_TINY_H 26 27 #include <linux/swait.h> 28 29 struct srcu_struct { 30 short srcu_lock_nesting[2]; /* srcu_read_lock() nesting depth. */ 31 short srcu_idx; /* Current reader array element. */ 32 u8 srcu_gp_running; /* GP workqueue running? */ 33 u8 srcu_gp_waiting; /* GP waiting for readers? */ 34 struct swait_queue_head srcu_wq; 35 /* Last srcu_read_unlock() wakes GP. */ 36 struct rcu_head *srcu_cb_head; /* Pending callbacks: Head. */ 37 struct rcu_head **srcu_cb_tail; /* Pending callbacks: Tail. */ 38 struct work_struct srcu_work; /* For driving grace periods. */ 39 struct list_head srcu_boot_entry; /* Early-boot callbacks. */ 40 #ifdef CONFIG_DEBUG_LOCK_ALLOC 41 struct lockdep_map dep_map; 42 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 43 }; 44 45 void srcu_drive_gp(struct work_struct *wp); 46 47 #define __SRCU_STRUCT_INIT(name, __ignored) \ 48 { \ 49 .srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq), \ 50 .srcu_cb_tail = &name.srcu_cb_head, \ 51 .srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp), \ 52 .srcu_boot_entry = LIST_HEAD_INIT(name.srcu_boot_entry), \ 53 __SRCU_DEP_MAP_INIT(name) \ 54 } 55 56 /* 57 * This odd _STATIC_ arrangement is needed for API compatibility with 58 * Tree SRCU, which needs some per-CPU data. 59 */ 60 #define DEFINE_SRCU(name) \ 61 struct srcu_struct name = __SRCU_STRUCT_INIT(name, name) 62 #define DEFINE_STATIC_SRCU(name) \ 63 static struct srcu_struct name = __SRCU_STRUCT_INIT(name, name) 64 65 void synchronize_srcu(struct srcu_struct *sp); 66 67 /* 68 * Counts the new reader in the appropriate per-CPU element of the 69 * srcu_struct. Can be invoked from irq/bh handlers, but the matching 70 * __srcu_read_unlock() must be in the same handler instance. Returns an 71 * index that must be passed to the matching srcu_read_unlock(). 72 */ 73 static inline int __srcu_read_lock(struct srcu_struct *sp) 74 { 75 int idx; 76 77 idx = READ_ONCE(sp->srcu_idx); 78 WRITE_ONCE(sp->srcu_lock_nesting[idx], sp->srcu_lock_nesting[idx] + 1); 79 return idx; 80 } 81 82 static inline void synchronize_srcu_expedited(struct srcu_struct *sp) 83 { 84 synchronize_srcu(sp); 85 } 86 87 static inline void srcu_barrier(struct srcu_struct *sp) 88 { 89 synchronize_srcu(sp); 90 } 91 92 /* Defined here to avoid size increase for non-torture kernels. */ 93 static inline void srcu_torture_stats_print(struct srcu_struct *sp, 94 char *tt, char *tf) 95 { 96 int idx; 97 98 idx = READ_ONCE(sp->srcu_idx) & 0x1; 99 pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd)\n", 100 tt, tf, idx, 101 READ_ONCE(sp->srcu_lock_nesting[!idx]), 102 READ_ONCE(sp->srcu_lock_nesting[idx])); 103 } 104 105 #endif 106