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