1 /* 2 * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition. 3 * 4 * This program is free software; you can redistribute it and/or modify 5 * it under the terms of the GNU General Public License as published by 6 * the Free Software Foundation; either version 2 of the License, or 7 * (at your option) any later version. 8 * 9 * This program is distributed in the hope that it will be useful, 10 * but WITHOUT ANY WARRANTY; without even the implied warranty of 11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 * GNU General Public License for more details. 13 * 14 * You should have received a copy of the GNU General Public License 15 * along with this program; if not, you can access it online at 16 * http://www.gnu.org/licenses/gpl-2.0.html. 17 * 18 * Copyright IBM Corporation, 2008 19 * 20 * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com> 21 * 22 * For detailed explanation of Read-Copy Update mechanism see - 23 * Documentation/RCU 24 */ 25 #include <linux/completion.h> 26 #include <linux/interrupt.h> 27 #include <linux/notifier.h> 28 #include <linux/rcupdate_wait.h> 29 #include <linux/kernel.h> 30 #include <linux/export.h> 31 #include <linux/mutex.h> 32 #include <linux/sched.h> 33 #include <linux/types.h> 34 #include <linux/init.h> 35 #include <linux/time.h> 36 #include <linux/cpu.h> 37 #include <linux/prefetch.h> 38 39 #include "rcu.h" 40 41 /* Global control variables for rcupdate callback mechanism. */ 42 struct rcu_ctrlblk { 43 struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */ 44 struct rcu_head **donetail; /* ->next pointer of last "done" CB. */ 45 struct rcu_head **curtail; /* ->next pointer of last CB. */ 46 }; 47 48 /* Definition for rcupdate control block. */ 49 static struct rcu_ctrlblk rcu_sched_ctrlblk = { 50 .donetail = &rcu_sched_ctrlblk.rcucblist, 51 .curtail = &rcu_sched_ctrlblk.rcucblist, 52 }; 53 54 static struct rcu_ctrlblk rcu_bh_ctrlblk = { 55 .donetail = &rcu_bh_ctrlblk.rcucblist, 56 .curtail = &rcu_bh_ctrlblk.rcucblist, 57 }; 58 59 #include "tiny_plugin.h" 60 61 void rcu_barrier_bh(void) 62 { 63 wait_rcu_gp(call_rcu_bh); 64 } 65 EXPORT_SYMBOL(rcu_barrier_bh); 66 67 void rcu_barrier_sched(void) 68 { 69 wait_rcu_gp(call_rcu_sched); 70 } 71 EXPORT_SYMBOL(rcu_barrier_sched); 72 73 /* 74 * Helper function for rcu_sched_qs() and rcu_bh_qs(). 75 * Also irqs are disabled to avoid confusion due to interrupt handlers 76 * invoking call_rcu(). 77 */ 78 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp) 79 { 80 if (rcp->donetail != rcp->curtail) { 81 rcp->donetail = rcp->curtail; 82 return 1; 83 } 84 85 return 0; 86 } 87 88 /* 89 * Record an rcu quiescent state. And an rcu_bh quiescent state while we 90 * are at it, given that any rcu quiescent state is also an rcu_bh 91 * quiescent state. Use "+" instead of "||" to defeat short circuiting. 92 */ 93 void rcu_sched_qs(void) 94 { 95 unsigned long flags; 96 97 local_irq_save(flags); 98 if (rcu_qsctr_help(&rcu_sched_ctrlblk) + 99 rcu_qsctr_help(&rcu_bh_ctrlblk)) 100 raise_softirq(RCU_SOFTIRQ); 101 local_irq_restore(flags); 102 } 103 104 /* 105 * Record an rcu_bh quiescent state. 106 */ 107 void rcu_bh_qs(void) 108 { 109 unsigned long flags; 110 111 local_irq_save(flags); 112 if (rcu_qsctr_help(&rcu_bh_ctrlblk)) 113 raise_softirq(RCU_SOFTIRQ); 114 local_irq_restore(flags); 115 } 116 117 /* 118 * Check to see if the scheduling-clock interrupt came from an extended 119 * quiescent state, and, if so, tell RCU about it. This function must 120 * be called from hardirq context. It is normally called from the 121 * scheduling-clock interrupt. 122 */ 123 void rcu_check_callbacks(int user) 124 { 125 if (user) 126 rcu_sched_qs(); 127 else if (!in_softirq()) 128 rcu_bh_qs(); 129 if (user) 130 rcu_note_voluntary_context_switch(current); 131 } 132 133 /* 134 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure 135 * whose grace period has elapsed. 136 */ 137 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp) 138 { 139 struct rcu_head *next, *list; 140 unsigned long flags; 141 142 /* Move the ready-to-invoke callbacks to a local list. */ 143 local_irq_save(flags); 144 if (rcp->donetail == &rcp->rcucblist) { 145 /* No callbacks ready, so just leave. */ 146 local_irq_restore(flags); 147 return; 148 } 149 list = rcp->rcucblist; 150 rcp->rcucblist = *rcp->donetail; 151 *rcp->donetail = NULL; 152 if (rcp->curtail == rcp->donetail) 153 rcp->curtail = &rcp->rcucblist; 154 rcp->donetail = &rcp->rcucblist; 155 local_irq_restore(flags); 156 157 /* Invoke the callbacks on the local list. */ 158 while (list) { 159 next = list->next; 160 prefetch(next); 161 debug_rcu_head_unqueue(list); 162 local_bh_disable(); 163 __rcu_reclaim("", list); 164 local_bh_enable(); 165 list = next; 166 } 167 } 168 169 static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused) 170 { 171 __rcu_process_callbacks(&rcu_sched_ctrlblk); 172 __rcu_process_callbacks(&rcu_bh_ctrlblk); 173 } 174 175 /* 176 * Wait for a grace period to elapse. But it is illegal to invoke 177 * synchronize_sched() from within an RCU read-side critical section. 178 * Therefore, any legal call to synchronize_sched() is a quiescent 179 * state, and so on a UP system, synchronize_sched() need do nothing. 180 * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the 181 * benefits of doing might_sleep() to reduce latency.) 182 * 183 * Cool, huh? (Due to Josh Triplett.) 184 */ 185 void synchronize_sched(void) 186 { 187 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || 188 lock_is_held(&rcu_lock_map) || 189 lock_is_held(&rcu_sched_lock_map), 190 "Illegal synchronize_sched() in RCU read-side critical section"); 191 } 192 EXPORT_SYMBOL_GPL(synchronize_sched); 193 194 /* 195 * Helper function for call_rcu() and call_rcu_bh(). 196 */ 197 static void __call_rcu(struct rcu_head *head, 198 rcu_callback_t func, 199 struct rcu_ctrlblk *rcp) 200 { 201 unsigned long flags; 202 203 debug_rcu_head_queue(head); 204 head->func = func; 205 head->next = NULL; 206 207 local_irq_save(flags); 208 *rcp->curtail = head; 209 rcp->curtail = &head->next; 210 local_irq_restore(flags); 211 212 if (unlikely(is_idle_task(current))) { 213 /* force scheduling for rcu_sched_qs() */ 214 resched_cpu(0); 215 } 216 } 217 218 /* 219 * Post an RCU callback to be invoked after the end of an RCU-sched grace 220 * period. But since we have but one CPU, that would be after any 221 * quiescent state. 222 */ 223 void call_rcu_sched(struct rcu_head *head, rcu_callback_t func) 224 { 225 __call_rcu(head, func, &rcu_sched_ctrlblk); 226 } 227 EXPORT_SYMBOL_GPL(call_rcu_sched); 228 229 /* 230 * Post an RCU bottom-half callback to be invoked after any subsequent 231 * quiescent state. 232 */ 233 void call_rcu_bh(struct rcu_head *head, rcu_callback_t func) 234 { 235 __call_rcu(head, func, &rcu_bh_ctrlblk); 236 } 237 EXPORT_SYMBOL_GPL(call_rcu_bh); 238 239 void __init rcu_init(void) 240 { 241 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); 242 rcu_early_boot_tests(); 243 } 244