1 /* 2 * Sleepable Read-Copy Update mechanism for mutual exclusion, 3 * tiny version for non-preemptible single-CPU use. 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 <paulmck@us.ibm.com> 22 */ 23 24 #include <linux/export.h> 25 #include <linux/mutex.h> 26 #include <linux/preempt.h> 27 #include <linux/rcupdate_wait.h> 28 #include <linux/sched.h> 29 #include <linux/delay.h> 30 #include <linux/srcu.h> 31 32 #include <linux/rcu_node_tree.h> 33 #include "rcu_segcblist.h" 34 #include "rcu.h" 35 36 static int init_srcu_struct_fields(struct srcu_struct *sp) 37 { 38 sp->srcu_lock_nesting[0] = 0; 39 sp->srcu_lock_nesting[1] = 0; 40 init_swait_queue_head(&sp->srcu_wq); 41 sp->srcu_gp_seq = 0; 42 rcu_segcblist_init(&sp->srcu_cblist); 43 sp->srcu_gp_running = false; 44 sp->srcu_gp_waiting = false; 45 sp->srcu_idx = 0; 46 INIT_WORK(&sp->srcu_work, srcu_drive_gp); 47 return 0; 48 } 49 50 #ifdef CONFIG_DEBUG_LOCK_ALLOC 51 52 int __init_srcu_struct(struct srcu_struct *sp, const char *name, 53 struct lock_class_key *key) 54 { 55 /* Don't re-initialize a lock while it is held. */ 56 debug_check_no_locks_freed((void *)sp, sizeof(*sp)); 57 lockdep_init_map(&sp->dep_map, name, key, 0); 58 return init_srcu_struct_fields(sp); 59 } 60 EXPORT_SYMBOL_GPL(__init_srcu_struct); 61 62 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 63 64 /* 65 * init_srcu_struct - initialize a sleep-RCU structure 66 * @sp: structure to initialize. 67 * 68 * Must invoke this on a given srcu_struct before passing that srcu_struct 69 * to any other function. Each srcu_struct represents a separate domain 70 * of SRCU protection. 71 */ 72 int init_srcu_struct(struct srcu_struct *sp) 73 { 74 return init_srcu_struct_fields(sp); 75 } 76 EXPORT_SYMBOL_GPL(init_srcu_struct); 77 78 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 79 80 /* 81 * cleanup_srcu_struct - deconstruct a sleep-RCU structure 82 * @sp: structure to clean up. 83 * 84 * Must invoke this after you are finished using a given srcu_struct that 85 * was initialized via init_srcu_struct(), else you leak memory. 86 */ 87 void cleanup_srcu_struct(struct srcu_struct *sp) 88 { 89 WARN_ON(sp->srcu_lock_nesting[0] || sp->srcu_lock_nesting[1]); 90 flush_work(&sp->srcu_work); 91 WARN_ON(rcu_seq_state(sp->srcu_gp_seq)); 92 WARN_ON(sp->srcu_gp_running); 93 WARN_ON(sp->srcu_gp_waiting); 94 WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist)); 95 } 96 EXPORT_SYMBOL_GPL(cleanup_srcu_struct); 97 98 /* 99 * Counts the new reader in the appropriate per-CPU element of the 100 * srcu_struct. Can be invoked from irq/bh handlers, but the matching 101 * __srcu_read_unlock() must be in the same handler instance. Returns an 102 * index that must be passed to the matching srcu_read_unlock(). 103 */ 104 int __srcu_read_lock(struct srcu_struct *sp) 105 { 106 int idx; 107 108 idx = READ_ONCE(sp->srcu_idx); 109 WRITE_ONCE(sp->srcu_lock_nesting[idx], sp->srcu_lock_nesting[idx] + 1); 110 return idx; 111 } 112 EXPORT_SYMBOL_GPL(__srcu_read_lock); 113 114 /* 115 * Removes the count for the old reader from the appropriate element of 116 * the srcu_struct. 117 */ 118 void __srcu_read_unlock(struct srcu_struct *sp, int idx) 119 { 120 int newval = sp->srcu_lock_nesting[idx] - 1; 121 122 WRITE_ONCE(sp->srcu_lock_nesting[idx], newval); 123 if (!newval && READ_ONCE(sp->srcu_gp_waiting)) 124 swake_up(&sp->srcu_wq); 125 } 126 EXPORT_SYMBOL_GPL(__srcu_read_unlock); 127 128 /* 129 * Workqueue handler to drive one grace period and invoke any callbacks 130 * that become ready as a result. Single-CPU and !PREEMPT operation 131 * means that we get away with murder on synchronization. ;-) 132 */ 133 void srcu_drive_gp(struct work_struct *wp) 134 { 135 int idx; 136 struct rcu_cblist ready_cbs; 137 struct srcu_struct *sp; 138 struct rcu_head *rhp; 139 140 sp = container_of(wp, struct srcu_struct, srcu_work); 141 if (sp->srcu_gp_running || rcu_segcblist_empty(&sp->srcu_cblist)) 142 return; /* Already running or nothing to do. */ 143 144 /* Tag recently arrived callbacks and wait for readers. */ 145 WRITE_ONCE(sp->srcu_gp_running, true); 146 rcu_segcblist_accelerate(&sp->srcu_cblist, 147 rcu_seq_snap(&sp->srcu_gp_seq)); 148 rcu_seq_start(&sp->srcu_gp_seq); 149 idx = sp->srcu_idx; 150 WRITE_ONCE(sp->srcu_idx, !sp->srcu_idx); 151 WRITE_ONCE(sp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */ 152 swait_event(sp->srcu_wq, !READ_ONCE(sp->srcu_lock_nesting[idx])); 153 WRITE_ONCE(sp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */ 154 rcu_seq_end(&sp->srcu_gp_seq); 155 156 /* Update callback list based on GP, and invoke ready callbacks. */ 157 rcu_segcblist_advance(&sp->srcu_cblist, 158 rcu_seq_current(&sp->srcu_gp_seq)); 159 if (rcu_segcblist_ready_cbs(&sp->srcu_cblist)) { 160 rcu_cblist_init(&ready_cbs); 161 local_irq_disable(); 162 rcu_segcblist_extract_done_cbs(&sp->srcu_cblist, &ready_cbs); 163 local_irq_enable(); 164 rhp = rcu_cblist_dequeue(&ready_cbs); 165 for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) { 166 local_bh_disable(); 167 rhp->func(rhp); 168 local_bh_enable(); 169 } 170 local_irq_disable(); 171 rcu_segcblist_insert_count(&sp->srcu_cblist, &ready_cbs); 172 local_irq_enable(); 173 } 174 WRITE_ONCE(sp->srcu_gp_running, false); 175 176 /* 177 * If more callbacks, reschedule ourselves. This can race with 178 * a call_srcu() at interrupt level, but the ->srcu_gp_running 179 * checks will straighten that out. 180 */ 181 if (!rcu_segcblist_empty(&sp->srcu_cblist)) 182 schedule_work(&sp->srcu_work); 183 } 184 EXPORT_SYMBOL_GPL(srcu_drive_gp); 185 186 /* 187 * Enqueue an SRCU callback on the specified srcu_struct structure, 188 * initiating grace-period processing if it is not already running. 189 */ 190 void call_srcu(struct srcu_struct *sp, struct rcu_head *head, 191 rcu_callback_t func) 192 { 193 unsigned long flags; 194 195 head->func = func; 196 local_irq_save(flags); 197 rcu_segcblist_enqueue(&sp->srcu_cblist, head, false); 198 local_irq_restore(flags); 199 if (!READ_ONCE(sp->srcu_gp_running)) 200 schedule_work(&sp->srcu_work); 201 } 202 EXPORT_SYMBOL_GPL(call_srcu); 203 204 /* 205 * synchronize_srcu - wait for prior SRCU read-side critical-section completion 206 */ 207 void synchronize_srcu(struct srcu_struct *sp) 208 { 209 struct rcu_synchronize rs; 210 211 init_rcu_head_on_stack(&rs.head); 212 init_completion(&rs.completion); 213 call_srcu(sp, &rs.head, wakeme_after_rcu); 214 wait_for_completion(&rs.completion); 215 destroy_rcu_head_on_stack(&rs.head); 216 } 217 EXPORT_SYMBOL_GPL(synchronize_srcu); 218