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 static LIST_HEAD(srcu_boot_list); 38 static bool srcu_init_done; 39 40 static int init_srcu_struct_fields(struct srcu_struct *ssp) 41 { 42 ssp->srcu_lock_nesting[0] = 0; 43 ssp->srcu_lock_nesting[1] = 0; 44 init_swait_queue_head(&ssp->srcu_wq); 45 ssp->srcu_cb_head = NULL; 46 ssp->srcu_cb_tail = &ssp->srcu_cb_head; 47 ssp->srcu_gp_running = false; 48 ssp->srcu_gp_waiting = false; 49 ssp->srcu_idx = 0; 50 INIT_WORK(&ssp->srcu_work, srcu_drive_gp); 51 INIT_LIST_HEAD(&ssp->srcu_work.entry); 52 return 0; 53 } 54 55 #ifdef CONFIG_DEBUG_LOCK_ALLOC 56 57 int __init_srcu_struct(struct srcu_struct *ssp, const char *name, 58 struct lock_class_key *key) 59 { 60 /* Don't re-initialize a lock while it is held. */ 61 debug_check_no_locks_freed((void *)ssp, sizeof(*ssp)); 62 lockdep_init_map(&ssp->dep_map, name, key, 0); 63 return init_srcu_struct_fields(ssp); 64 } 65 EXPORT_SYMBOL_GPL(__init_srcu_struct); 66 67 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 68 69 /* 70 * init_srcu_struct - initialize a sleep-RCU structure 71 * @ssp: structure to initialize. 72 * 73 * Must invoke this on a given srcu_struct before passing that srcu_struct 74 * to any other function. Each srcu_struct represents a separate domain 75 * of SRCU protection. 76 */ 77 int init_srcu_struct(struct srcu_struct *ssp) 78 { 79 return init_srcu_struct_fields(ssp); 80 } 81 EXPORT_SYMBOL_GPL(init_srcu_struct); 82 83 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ 84 85 /* 86 * cleanup_srcu_struct - deconstruct a sleep-RCU structure 87 * @ssp: structure to clean up. 88 * 89 * Must invoke this after you are finished using a given srcu_struct that 90 * was initialized via init_srcu_struct(), else you leak memory. 91 */ 92 void _cleanup_srcu_struct(struct srcu_struct *ssp, bool quiesced) 93 { 94 WARN_ON(ssp->srcu_lock_nesting[0] || ssp->srcu_lock_nesting[1]); 95 if (quiesced) 96 WARN_ON(work_pending(&ssp->srcu_work)); 97 else 98 flush_work(&ssp->srcu_work); 99 WARN_ON(ssp->srcu_gp_running); 100 WARN_ON(ssp->srcu_gp_waiting); 101 WARN_ON(ssp->srcu_cb_head); 102 WARN_ON(&ssp->srcu_cb_head != ssp->srcu_cb_tail); 103 } 104 EXPORT_SYMBOL_GPL(_cleanup_srcu_struct); 105 106 /* 107 * Removes the count for the old reader from the appropriate element of 108 * the srcu_struct. 109 */ 110 void __srcu_read_unlock(struct srcu_struct *ssp, int idx) 111 { 112 int newval = ssp->srcu_lock_nesting[idx] - 1; 113 114 WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval); 115 if (!newval && READ_ONCE(ssp->srcu_gp_waiting)) 116 swake_up_one(&ssp->srcu_wq); 117 } 118 EXPORT_SYMBOL_GPL(__srcu_read_unlock); 119 120 /* 121 * Workqueue handler to drive one grace period and invoke any callbacks 122 * that become ready as a result. Single-CPU and !PREEMPT operation 123 * means that we get away with murder on synchronization. ;-) 124 */ 125 void srcu_drive_gp(struct work_struct *wp) 126 { 127 int idx; 128 struct rcu_head *lh; 129 struct rcu_head *rhp; 130 struct srcu_struct *ssp; 131 132 ssp = container_of(wp, struct srcu_struct, srcu_work); 133 if (ssp->srcu_gp_running || !READ_ONCE(ssp->srcu_cb_head)) 134 return; /* Already running or nothing to do. */ 135 136 /* Remove recently arrived callbacks and wait for readers. */ 137 WRITE_ONCE(ssp->srcu_gp_running, true); 138 local_irq_disable(); 139 lh = ssp->srcu_cb_head; 140 ssp->srcu_cb_head = NULL; 141 ssp->srcu_cb_tail = &ssp->srcu_cb_head; 142 local_irq_enable(); 143 idx = ssp->srcu_idx; 144 WRITE_ONCE(ssp->srcu_idx, !ssp->srcu_idx); 145 WRITE_ONCE(ssp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */ 146 swait_event_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx])); 147 WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */ 148 149 /* Invoke the callbacks we removed above. */ 150 while (lh) { 151 rhp = lh; 152 lh = lh->next; 153 local_bh_disable(); 154 rhp->func(rhp); 155 local_bh_enable(); 156 } 157 158 /* 159 * Enable rescheduling, and if there are more callbacks, 160 * reschedule ourselves. This can race with a call_srcu() 161 * at interrupt level, but the ->srcu_gp_running checks will 162 * straighten that out. 163 */ 164 WRITE_ONCE(ssp->srcu_gp_running, false); 165 if (READ_ONCE(ssp->srcu_cb_head)) 166 schedule_work(&ssp->srcu_work); 167 } 168 EXPORT_SYMBOL_GPL(srcu_drive_gp); 169 170 /* 171 * Enqueue an SRCU callback on the specified srcu_struct structure, 172 * initiating grace-period processing if it is not already running. 173 */ 174 void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, 175 rcu_callback_t func) 176 { 177 unsigned long flags; 178 179 rhp->func = func; 180 rhp->next = NULL; 181 local_irq_save(flags); 182 *ssp->srcu_cb_tail = rhp; 183 ssp->srcu_cb_tail = &rhp->next; 184 local_irq_restore(flags); 185 if (!READ_ONCE(ssp->srcu_gp_running)) { 186 if (likely(srcu_init_done)) 187 schedule_work(&ssp->srcu_work); 188 else if (list_empty(&ssp->srcu_work.entry)) 189 list_add(&ssp->srcu_work.entry, &srcu_boot_list); 190 } 191 } 192 EXPORT_SYMBOL_GPL(call_srcu); 193 194 /* 195 * synchronize_srcu - wait for prior SRCU read-side critical-section completion 196 */ 197 void synchronize_srcu(struct srcu_struct *ssp) 198 { 199 struct rcu_synchronize rs; 200 201 init_rcu_head_on_stack(&rs.head); 202 init_completion(&rs.completion); 203 call_srcu(ssp, &rs.head, wakeme_after_rcu); 204 wait_for_completion(&rs.completion); 205 destroy_rcu_head_on_stack(&rs.head); 206 } 207 EXPORT_SYMBOL_GPL(synchronize_srcu); 208 209 /* Lockdep diagnostics. */ 210 void __init rcu_scheduler_starting(void) 211 { 212 rcu_scheduler_active = RCU_SCHEDULER_RUNNING; 213 } 214 215 /* 216 * Queue work for srcu_struct structures with early boot callbacks. 217 * The work won't actually execute until the workqueue initialization 218 * phase that takes place after the scheduler starts. 219 */ 220 void __init srcu_init(void) 221 { 222 struct srcu_struct *ssp; 223 224 srcu_init_done = true; 225 while (!list_empty(&srcu_boot_list)) { 226 ssp = list_first_entry(&srcu_boot_list, 227 struct srcu_struct, srcu_work.entry); 228 list_del_init(&ssp->srcu_work.entry); 229 schedule_work(&ssp->srcu_work); 230 } 231 } 232