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/ftrace_event.h> 39 40 #include "rcu.h" 41 42 /* Forward declarations for tiny_plugin.h. */ 43 struct rcu_ctrlblk; 44 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp); 45 static void rcu_process_callbacks(struct softirq_action *unused); 46 static void __call_rcu(struct rcu_head *head, 47 void (*func)(struct rcu_head *rcu), 48 struct rcu_ctrlblk *rcp); 49 50 #include "tiny_plugin.h" 51 52 /* 53 * Enter idle, which is an extended quiescent state if we have fully 54 * entered that mode. 55 */ 56 void rcu_idle_enter(void) 57 { 58 } 59 EXPORT_SYMBOL_GPL(rcu_idle_enter); 60 61 /* 62 * Exit an interrupt handler towards idle. 63 */ 64 void rcu_irq_exit(void) 65 { 66 } 67 EXPORT_SYMBOL_GPL(rcu_irq_exit); 68 69 /* 70 * Exit idle, so that we are no longer in an extended quiescent state. 71 */ 72 void rcu_idle_exit(void) 73 { 74 } 75 EXPORT_SYMBOL_GPL(rcu_idle_exit); 76 77 /* 78 * Enter an interrupt handler, moving away from idle. 79 */ 80 void rcu_irq_enter(void) 81 { 82 } 83 EXPORT_SYMBOL_GPL(rcu_irq_enter); 84 85 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) 86 87 /* 88 * Test whether RCU thinks that the current CPU is idle. 89 */ 90 bool notrace __rcu_is_watching(void) 91 { 92 return true; 93 } 94 EXPORT_SYMBOL(__rcu_is_watching); 95 96 #endif /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */ 97 98 /* 99 * Helper function for rcu_sched_qs() and rcu_bh_qs(). 100 * Also irqs are disabled to avoid confusion due to interrupt handlers 101 * invoking call_rcu(). 102 */ 103 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp) 104 { 105 RCU_TRACE(reset_cpu_stall_ticks(rcp)); 106 if (rcp->rcucblist != NULL && 107 rcp->donetail != rcp->curtail) { 108 rcp->donetail = rcp->curtail; 109 return 1; 110 } 111 112 return 0; 113 } 114 115 /* 116 * Record an rcu quiescent state. And an rcu_bh quiescent state while we 117 * are at it, given that any rcu quiescent state is also an rcu_bh 118 * quiescent state. Use "+" instead of "||" to defeat short circuiting. 119 */ 120 void rcu_sched_qs(void) 121 { 122 unsigned long flags; 123 124 local_irq_save(flags); 125 if (rcu_qsctr_help(&rcu_sched_ctrlblk) + 126 rcu_qsctr_help(&rcu_bh_ctrlblk)) 127 raise_softirq(RCU_SOFTIRQ); 128 local_irq_restore(flags); 129 } 130 131 /* 132 * Record an rcu_bh quiescent state. 133 */ 134 void rcu_bh_qs(void) 135 { 136 unsigned long flags; 137 138 local_irq_save(flags); 139 if (rcu_qsctr_help(&rcu_bh_ctrlblk)) 140 raise_softirq(RCU_SOFTIRQ); 141 local_irq_restore(flags); 142 } 143 144 /* 145 * Check to see if the scheduling-clock interrupt came from an extended 146 * quiescent state, and, if so, tell RCU about it. This function must 147 * be called from hardirq context. It is normally called from the 148 * scheduling-clock interrupt. 149 */ 150 void rcu_check_callbacks(int user) 151 { 152 RCU_TRACE(check_cpu_stalls()); 153 if (user) 154 rcu_sched_qs(); 155 else if (!in_softirq()) 156 rcu_bh_qs(); 157 if (user) 158 rcu_note_voluntary_context_switch(current); 159 } 160 161 /* 162 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure 163 * whose grace period has elapsed. 164 */ 165 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp) 166 { 167 const char *rn = NULL; 168 struct rcu_head *next, *list; 169 unsigned long flags; 170 RCU_TRACE(int cb_count = 0); 171 172 /* If no RCU callbacks ready to invoke, just return. */ 173 if (&rcp->rcucblist == rcp->donetail) { 174 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1)); 175 RCU_TRACE(trace_rcu_batch_end(rcp->name, 0, 176 !!ACCESS_ONCE(rcp->rcucblist), 177 need_resched(), 178 is_idle_task(current), 179 false)); 180 return; 181 } 182 183 /* Move the ready-to-invoke callbacks to a local list. */ 184 local_irq_save(flags); 185 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1)); 186 list = rcp->rcucblist; 187 rcp->rcucblist = *rcp->donetail; 188 *rcp->donetail = NULL; 189 if (rcp->curtail == rcp->donetail) 190 rcp->curtail = &rcp->rcucblist; 191 rcp->donetail = &rcp->rcucblist; 192 local_irq_restore(flags); 193 194 /* Invoke the callbacks on the local list. */ 195 RCU_TRACE(rn = rcp->name); 196 while (list) { 197 next = list->next; 198 prefetch(next); 199 debug_rcu_head_unqueue(list); 200 local_bh_disable(); 201 __rcu_reclaim(rn, list); 202 local_bh_enable(); 203 list = next; 204 RCU_TRACE(cb_count++); 205 } 206 RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count)); 207 RCU_TRACE(trace_rcu_batch_end(rcp->name, 208 cb_count, 0, need_resched(), 209 is_idle_task(current), 210 false)); 211 } 212 213 static void rcu_process_callbacks(struct softirq_action *unused) 214 { 215 __rcu_process_callbacks(&rcu_sched_ctrlblk); 216 __rcu_process_callbacks(&rcu_bh_ctrlblk); 217 } 218 219 /* 220 * Wait for a grace period to elapse. But it is illegal to invoke 221 * synchronize_sched() from within an RCU read-side critical section. 222 * Therefore, any legal call to synchronize_sched() is a quiescent 223 * state, and so on a UP system, synchronize_sched() need do nothing. 224 * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the 225 * benefits of doing might_sleep() to reduce latency.) 226 * 227 * Cool, huh? (Due to Josh Triplett.) 228 * 229 * But we want to make this a static inline later. The cond_resched() 230 * currently makes this problematic. 231 */ 232 void synchronize_sched(void) 233 { 234 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) && 235 !lock_is_held(&rcu_lock_map) && 236 !lock_is_held(&rcu_sched_lock_map), 237 "Illegal synchronize_sched() in RCU read-side critical section"); 238 cond_resched(); 239 } 240 EXPORT_SYMBOL_GPL(synchronize_sched); 241 242 /* 243 * Helper function for call_rcu() and call_rcu_bh(). 244 */ 245 static void __call_rcu(struct rcu_head *head, 246 void (*func)(struct rcu_head *rcu), 247 struct rcu_ctrlblk *rcp) 248 { 249 unsigned long flags; 250 251 debug_rcu_head_queue(head); 252 head->func = func; 253 head->next = NULL; 254 255 local_irq_save(flags); 256 *rcp->curtail = head; 257 rcp->curtail = &head->next; 258 RCU_TRACE(rcp->qlen++); 259 local_irq_restore(flags); 260 261 if (unlikely(is_idle_task(current))) { 262 /* force scheduling for rcu_sched_qs() */ 263 resched_cpu(0); 264 } 265 } 266 267 /* 268 * Post an RCU callback to be invoked after the end of an RCU-sched grace 269 * period. But since we have but one CPU, that would be after any 270 * quiescent state. 271 */ 272 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) 273 { 274 __call_rcu(head, func, &rcu_sched_ctrlblk); 275 } 276 EXPORT_SYMBOL_GPL(call_rcu_sched); 277 278 /* 279 * Post an RCU bottom-half callback to be invoked after any subsequent 280 * quiescent state. 281 */ 282 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) 283 { 284 __call_rcu(head, func, &rcu_bh_ctrlblk); 285 } 286 EXPORT_SYMBOL_GPL(call_rcu_bh); 287 288 void __init rcu_init(void) 289 { 290 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); 291 RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk)); 292 RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk)); 293 294 rcu_early_boot_tests(); 295 } 296