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 int rcu_scheduler_active __read_mostly; 37 38 static int init_srcu_struct_fields(struct srcu_struct *sp) 39 { 40 sp->srcu_lock_nesting[0] = 0; 41 sp->srcu_lock_nesting[1] = 0; 42 init_swait_queue_head(&sp->srcu_wq); 43 sp->srcu_cb_head = NULL; 44 sp->srcu_cb_tail = &sp->srcu_cb_head; 45 sp->srcu_gp_running = false; 46 sp->srcu_gp_waiting = false; 47 sp->srcu_idx = 0; 48 INIT_WORK(&sp->srcu_work, srcu_drive_gp); 49 return 0; 50 } 51 52 #ifdef CONFIG_DEBUG_LOCK_ALLOC 53 54 int __init_srcu_struct(struct srcu_struct *sp, const char *name, 55 struct lock_class_key *key) 56 { 57 /* Don't re-initialize a lock while it is held. */ 58 debug_check_no_locks_freed((void *)sp, sizeof(*sp)); 59 lockdep_init_map(&sp->dep_map, name, key, 0); 60 return init_srcu_struct_fields(sp); 61 } 62 EXPORT_SYMBOL_GPL(__init_srcu_struct); 63 64 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 65 66 /* 67 * init_srcu_struct - initialize a sleep-RCU structure 68 * @sp: structure to initialize. 69 * 70 * Must invoke this on a given srcu_struct before passing that srcu_struct 71 * to any other function. Each srcu_struct represents a separate domain 72 * of SRCU protection. 73 */ 74 int init_srcu_struct(struct srcu_struct *sp) 75 { 76 return init_srcu_struct_fields(sp); 77 } 78 EXPORT_SYMBOL_GPL(init_srcu_struct); 79 80 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 81 82 /* 83 * cleanup_srcu_struct - deconstruct a sleep-RCU structure 84 * @sp: structure to clean up. 85 * 86 * Must invoke this after you are finished using a given srcu_struct that 87 * was initialized via init_srcu_struct(), else you leak memory. 88 */ 89 void cleanup_srcu_struct(struct srcu_struct *sp) 90 { 91 WARN_ON(sp->srcu_lock_nesting[0] || sp->srcu_lock_nesting[1]); 92 flush_work(&sp->srcu_work); 93 WARN_ON(sp->srcu_gp_running); 94 WARN_ON(sp->srcu_gp_waiting); 95 WARN_ON(sp->srcu_cb_head); 96 WARN_ON(&sp->srcu_cb_head != sp->srcu_cb_tail); 97 } 98 EXPORT_SYMBOL_GPL(cleanup_srcu_struct); 99 100 /* 101 * Removes the count for the old reader from the appropriate element of 102 * the srcu_struct. 103 */ 104 void __srcu_read_unlock(struct srcu_struct *sp, int idx) 105 { 106 int newval = sp->srcu_lock_nesting[idx] - 1; 107 108 WRITE_ONCE(sp->srcu_lock_nesting[idx], newval); 109 if (!newval && READ_ONCE(sp->srcu_gp_waiting)) 110 swake_up(&sp->srcu_wq); 111 } 112 EXPORT_SYMBOL_GPL(__srcu_read_unlock); 113 114 /* 115 * Workqueue handler to drive one grace period and invoke any callbacks 116 * that become ready as a result. Single-CPU and !PREEMPT operation 117 * means that we get away with murder on synchronization. ;-) 118 */ 119 void srcu_drive_gp(struct work_struct *wp) 120 { 121 int idx; 122 struct rcu_head *lh; 123 struct rcu_head *rhp; 124 struct srcu_struct *sp; 125 126 sp = container_of(wp, struct srcu_struct, srcu_work); 127 if (sp->srcu_gp_running || !READ_ONCE(sp->srcu_cb_head)) 128 return; /* Already running or nothing to do. */ 129 130 /* Remove recently arrived callbacks and wait for readers. */ 131 WRITE_ONCE(sp->srcu_gp_running, true); 132 local_irq_disable(); 133 lh = sp->srcu_cb_head; 134 sp->srcu_cb_head = NULL; 135 sp->srcu_cb_tail = &sp->srcu_cb_head; 136 local_irq_enable(); 137 idx = sp->srcu_idx; 138 WRITE_ONCE(sp->srcu_idx, !sp->srcu_idx); 139 WRITE_ONCE(sp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */ 140 swait_event(sp->srcu_wq, !READ_ONCE(sp->srcu_lock_nesting[idx])); 141 WRITE_ONCE(sp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */ 142 143 /* Invoke the callbacks we removed above. */ 144 while (lh) { 145 rhp = lh; 146 lh = lh->next; 147 local_bh_disable(); 148 rhp->func(rhp); 149 local_bh_enable(); 150 } 151 152 /* 153 * Enable rescheduling, and if there are more callbacks, 154 * reschedule ourselves. This can race with a call_srcu() 155 * at interrupt level, but the ->srcu_gp_running checks will 156 * straighten that out. 157 */ 158 WRITE_ONCE(sp->srcu_gp_running, false); 159 if (READ_ONCE(sp->srcu_cb_head)) 160 schedule_work(&sp->srcu_work); 161 } 162 EXPORT_SYMBOL_GPL(srcu_drive_gp); 163 164 /* 165 * Enqueue an SRCU callback on the specified srcu_struct structure, 166 * initiating grace-period processing if it is not already running. 167 */ 168 void call_srcu(struct srcu_struct *sp, struct rcu_head *rhp, 169 rcu_callback_t func) 170 { 171 unsigned long flags; 172 173 rhp->func = func; 174 rhp->next = NULL; 175 local_irq_save(flags); 176 *sp->srcu_cb_tail = rhp; 177 sp->srcu_cb_tail = &rhp->next; 178 local_irq_restore(flags); 179 if (!READ_ONCE(sp->srcu_gp_running)) 180 schedule_work(&sp->srcu_work); 181 } 182 EXPORT_SYMBOL_GPL(call_srcu); 183 184 /* 185 * synchronize_srcu - wait for prior SRCU read-side critical-section completion 186 */ 187 void synchronize_srcu(struct srcu_struct *sp) 188 { 189 struct rcu_synchronize rs; 190 191 init_rcu_head_on_stack(&rs.head); 192 init_completion(&rs.completion); 193 call_srcu(sp, &rs.head, wakeme_after_rcu); 194 wait_for_completion(&rs.completion); 195 destroy_rcu_head_on_stack(&rs.head); 196 } 197 EXPORT_SYMBOL_GPL(synchronize_srcu); 198 199 /* Lockdep diagnostics. */ 200 void __init rcu_scheduler_starting(void) 201 { 202 rcu_scheduler_active = RCU_SCHEDULER_RUNNING; 203 } 204