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.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 #include <linux/trace_events.h> 39 40 #include "rcu.h" 41 42 /* Forward declarations for tiny_plugin.h. */ 43 struct rcu_ctrlblk; 44 static void __call_rcu(struct rcu_head *head, 45 rcu_callback_t func, 46 struct rcu_ctrlblk *rcp); 47 48 #include "tiny_plugin.h" 49 50 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) 51 52 /* 53 * Test whether RCU thinks that the current CPU is idle. 54 */ 55 bool notrace __rcu_is_watching(void) 56 { 57 return true; 58 } 59 EXPORT_SYMBOL(__rcu_is_watching); 60 61 #endif /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */ 62 63 /* 64 * Helper function for rcu_sched_qs() and rcu_bh_qs(). 65 * Also irqs are disabled to avoid confusion due to interrupt handlers 66 * invoking call_rcu(). 67 */ 68 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp) 69 { 70 RCU_TRACE(reset_cpu_stall_ticks(rcp)); 71 if (rcp->donetail != rcp->curtail) { 72 rcp->donetail = rcp->curtail; 73 return 1; 74 } 75 76 return 0; 77 } 78 79 /* 80 * Record an rcu quiescent state. And an rcu_bh quiescent state while we 81 * are at it, given that any rcu quiescent state is also an rcu_bh 82 * quiescent state. Use "+" instead of "||" to defeat short circuiting. 83 */ 84 void rcu_sched_qs(void) 85 { 86 unsigned long flags; 87 88 local_irq_save(flags); 89 if (rcu_qsctr_help(&rcu_sched_ctrlblk) + 90 rcu_qsctr_help(&rcu_bh_ctrlblk)) 91 raise_softirq(RCU_SOFTIRQ); 92 local_irq_restore(flags); 93 } 94 95 /* 96 * Record an rcu_bh quiescent state. 97 */ 98 void rcu_bh_qs(void) 99 { 100 unsigned long flags; 101 102 local_irq_save(flags); 103 if (rcu_qsctr_help(&rcu_bh_ctrlblk)) 104 raise_softirq(RCU_SOFTIRQ); 105 local_irq_restore(flags); 106 } 107 108 /* 109 * Check to see if the scheduling-clock interrupt came from an extended 110 * quiescent state, and, if so, tell RCU about it. This function must 111 * be called from hardirq context. It is normally called from the 112 * scheduling-clock interrupt. 113 */ 114 void rcu_check_callbacks(int user) 115 { 116 RCU_TRACE(check_cpu_stalls()); 117 if (user) 118 rcu_sched_qs(); 119 else if (!in_softirq()) 120 rcu_bh_qs(); 121 if (user) 122 rcu_note_voluntary_context_switch(current); 123 } 124 125 /* 126 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure 127 * whose grace period has elapsed. 128 */ 129 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp) 130 { 131 const char *rn = NULL; 132 struct rcu_head *next, *list; 133 unsigned long flags; 134 RCU_TRACE(int cb_count = 0); 135 136 /* Move the ready-to-invoke callbacks to a local list. */ 137 local_irq_save(flags); 138 if (rcp->donetail == &rcp->rcucblist) { 139 /* No callbacks ready, so just leave. */ 140 local_irq_restore(flags); 141 return; 142 } 143 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1)); 144 list = rcp->rcucblist; 145 rcp->rcucblist = *rcp->donetail; 146 *rcp->donetail = NULL; 147 if (rcp->curtail == rcp->donetail) 148 rcp->curtail = &rcp->rcucblist; 149 rcp->donetail = &rcp->rcucblist; 150 local_irq_restore(flags); 151 152 /* Invoke the callbacks on the local list. */ 153 RCU_TRACE(rn = rcp->name); 154 while (list) { 155 next = list->next; 156 prefetch(next); 157 debug_rcu_head_unqueue(list); 158 local_bh_disable(); 159 __rcu_reclaim(rn, list); 160 local_bh_enable(); 161 list = next; 162 RCU_TRACE(cb_count++); 163 } 164 RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count)); 165 RCU_TRACE(trace_rcu_batch_end(rcp->name, 166 cb_count, 0, need_resched(), 167 is_idle_task(current), 168 false)); 169 } 170 171 static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused) 172 { 173 __rcu_process_callbacks(&rcu_sched_ctrlblk); 174 __rcu_process_callbacks(&rcu_bh_ctrlblk); 175 } 176 177 /* 178 * Wait for a grace period to elapse. But it is illegal to invoke 179 * synchronize_sched() from within an RCU read-side critical section. 180 * Therefore, any legal call to synchronize_sched() is a quiescent 181 * state, and so on a UP system, synchronize_sched() need do nothing. 182 * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the 183 * benefits of doing might_sleep() to reduce latency.) 184 * 185 * Cool, huh? (Due to Josh Triplett.) 186 */ 187 void synchronize_sched(void) 188 { 189 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || 190 lock_is_held(&rcu_lock_map) || 191 lock_is_held(&rcu_sched_lock_map), 192 "Illegal synchronize_sched() in RCU read-side critical section"); 193 } 194 EXPORT_SYMBOL_GPL(synchronize_sched); 195 196 /* 197 * Helper function for call_rcu() and call_rcu_bh(). 198 */ 199 static void __call_rcu(struct rcu_head *head, 200 rcu_callback_t func, 201 struct rcu_ctrlblk *rcp) 202 { 203 unsigned long flags; 204 205 debug_rcu_head_queue(head); 206 head->func = func; 207 head->next = NULL; 208 209 local_irq_save(flags); 210 *rcp->curtail = head; 211 rcp->curtail = &head->next; 212 RCU_TRACE(rcp->qlen++); 213 local_irq_restore(flags); 214 215 if (unlikely(is_idle_task(current))) { 216 /* force scheduling for rcu_sched_qs() */ 217 resched_cpu(0); 218 } 219 } 220 221 /* 222 * Post an RCU callback to be invoked after the end of an RCU-sched grace 223 * period. But since we have but one CPU, that would be after any 224 * quiescent state. 225 */ 226 void call_rcu_sched(struct rcu_head *head, rcu_callback_t func) 227 { 228 __call_rcu(head, func, &rcu_sched_ctrlblk); 229 } 230 EXPORT_SYMBOL_GPL(call_rcu_sched); 231 232 /* 233 * Post an RCU bottom-half callback to be invoked after any subsequent 234 * quiescent state. 235 */ 236 void call_rcu_bh(struct rcu_head *head, rcu_callback_t func) 237 { 238 __call_rcu(head, func, &rcu_bh_ctrlblk); 239 } 240 EXPORT_SYMBOL_GPL(call_rcu_bh); 241 242 void __init rcu_init(void) 243 { 244 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); 245 RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk)); 246 RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk)); 247 248 rcu_early_boot_tests(); 249 } 250