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, bool quiesced) 90 { 91 WARN_ON(sp->srcu_lock_nesting[0] || sp->srcu_lock_nesting[1]); 92 if (quiesced) 93 WARN_ON(work_pending(&sp->srcu_work)); 94 else 95 flush_work(&sp->srcu_work); 96 WARN_ON(sp->srcu_gp_running); 97 WARN_ON(sp->srcu_gp_waiting); 98 WARN_ON(sp->srcu_cb_head); 99 WARN_ON(&sp->srcu_cb_head != sp->srcu_cb_tail); 100 } 101 EXPORT_SYMBOL_GPL(_cleanup_srcu_struct); 102 103 /* 104 * Removes the count for the old reader from the appropriate element of 105 * the srcu_struct. 106 */ 107 void __srcu_read_unlock(struct srcu_struct *sp, int idx) 108 { 109 int newval = sp->srcu_lock_nesting[idx] - 1; 110 111 WRITE_ONCE(sp->srcu_lock_nesting[idx], newval); 112 if (!newval && READ_ONCE(sp->srcu_gp_waiting)) 113 swake_up(&sp->srcu_wq); 114 } 115 EXPORT_SYMBOL_GPL(__srcu_read_unlock); 116 117 /* 118 * Workqueue handler to drive one grace period and invoke any callbacks 119 * that become ready as a result. Single-CPU and !PREEMPT operation 120 * means that we get away with murder on synchronization. ;-) 121 */ 122 void srcu_drive_gp(struct work_struct *wp) 123 { 124 int idx; 125 struct rcu_head *lh; 126 struct rcu_head *rhp; 127 struct srcu_struct *sp; 128 129 sp = container_of(wp, struct srcu_struct, srcu_work); 130 if (sp->srcu_gp_running || !READ_ONCE(sp->srcu_cb_head)) 131 return; /* Already running or nothing to do. */ 132 133 /* Remove recently arrived callbacks and wait for readers. */ 134 WRITE_ONCE(sp->srcu_gp_running, true); 135 local_irq_disable(); 136 lh = sp->srcu_cb_head; 137 sp->srcu_cb_head = NULL; 138 sp->srcu_cb_tail = &sp->srcu_cb_head; 139 local_irq_enable(); 140 idx = sp->srcu_idx; 141 WRITE_ONCE(sp->srcu_idx, !sp->srcu_idx); 142 WRITE_ONCE(sp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */ 143 swait_event(sp->srcu_wq, !READ_ONCE(sp->srcu_lock_nesting[idx])); 144 WRITE_ONCE(sp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */ 145 146 /* Invoke the callbacks we removed above. */ 147 while (lh) { 148 rhp = lh; 149 lh = lh->next; 150 local_bh_disable(); 151 rhp->func(rhp); 152 local_bh_enable(); 153 } 154 155 /* 156 * Enable rescheduling, and if there are more callbacks, 157 * reschedule ourselves. This can race with a call_srcu() 158 * at interrupt level, but the ->srcu_gp_running checks will 159 * straighten that out. 160 */ 161 WRITE_ONCE(sp->srcu_gp_running, false); 162 if (READ_ONCE(sp->srcu_cb_head)) 163 schedule_work(&sp->srcu_work); 164 } 165 EXPORT_SYMBOL_GPL(srcu_drive_gp); 166 167 /* 168 * Enqueue an SRCU callback on the specified srcu_struct structure, 169 * initiating grace-period processing if it is not already running. 170 */ 171 void call_srcu(struct srcu_struct *sp, struct rcu_head *rhp, 172 rcu_callback_t func) 173 { 174 unsigned long flags; 175 176 rhp->func = func; 177 rhp->next = NULL; 178 local_irq_save(flags); 179 *sp->srcu_cb_tail = rhp; 180 sp->srcu_cb_tail = &rhp->next; 181 local_irq_restore(flags); 182 if (!READ_ONCE(sp->srcu_gp_running)) 183 schedule_work(&sp->srcu_work); 184 } 185 EXPORT_SYMBOL_GPL(call_srcu); 186 187 /* 188 * synchronize_srcu - wait for prior SRCU read-side critical-section completion 189 */ 190 void synchronize_srcu(struct srcu_struct *sp) 191 { 192 struct rcu_synchronize rs; 193 194 init_rcu_head_on_stack(&rs.head); 195 init_completion(&rs.completion); 196 call_srcu(sp, &rs.head, wakeme_after_rcu); 197 wait_for_completion(&rs.completion); 198 destroy_rcu_head_on_stack(&rs.head); 199 } 200 EXPORT_SYMBOL_GPL(synchronize_srcu); 201 202 /* Lockdep diagnostics. */ 203 void __init rcu_scheduler_starting(void) 204 { 205 rcu_scheduler_active = RCU_SCHEDULER_RUNNING; 206 } 207