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->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 */ 119 void 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 */ 133 void 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 */ 149 void 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 */ 164 static 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 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1)); 174 list = rcp->rcucblist; 175 rcp->rcucblist = *rcp->donetail; 176 *rcp->donetail = NULL; 177 if (rcp->curtail == rcp->donetail) 178 rcp->curtail = &rcp->rcucblist; 179 rcp->donetail = &rcp->rcucblist; 180 local_irq_restore(flags); 181 182 /* Invoke the callbacks on the local list. */ 183 RCU_TRACE(rn = rcp->name); 184 while (list) { 185 next = list->next; 186 prefetch(next); 187 debug_rcu_head_unqueue(list); 188 local_bh_disable(); 189 __rcu_reclaim(rn, list); 190 local_bh_enable(); 191 list = next; 192 RCU_TRACE(cb_count++); 193 } 194 RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count)); 195 RCU_TRACE(trace_rcu_batch_end(rcp->name, 196 cb_count, 0, need_resched(), 197 is_idle_task(current), 198 false)); 199 } 200 201 static void rcu_process_callbacks(struct softirq_action *unused) 202 { 203 __rcu_process_callbacks(&rcu_sched_ctrlblk); 204 __rcu_process_callbacks(&rcu_bh_ctrlblk); 205 } 206 207 /* 208 * Wait for a grace period to elapse. But it is illegal to invoke 209 * synchronize_sched() from within an RCU read-side critical section. 210 * Therefore, any legal call to synchronize_sched() is a quiescent 211 * state, and so on a UP system, synchronize_sched() need do nothing. 212 * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the 213 * benefits of doing might_sleep() to reduce latency.) 214 * 215 * Cool, huh? (Due to Josh Triplett.) 216 * 217 * But we want to make this a static inline later. The cond_resched() 218 * currently makes this problematic. 219 */ 220 void synchronize_sched(void) 221 { 222 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) && 223 !lock_is_held(&rcu_lock_map) && 224 !lock_is_held(&rcu_sched_lock_map), 225 "Illegal synchronize_sched() in RCU read-side critical section"); 226 cond_resched(); 227 } 228 EXPORT_SYMBOL_GPL(synchronize_sched); 229 230 /* 231 * Helper function for call_rcu() and call_rcu_bh(). 232 */ 233 static void __call_rcu(struct rcu_head *head, 234 void (*func)(struct rcu_head *rcu), 235 struct rcu_ctrlblk *rcp) 236 { 237 unsigned long flags; 238 239 debug_rcu_head_queue(head); 240 head->func = func; 241 head->next = NULL; 242 243 local_irq_save(flags); 244 *rcp->curtail = head; 245 rcp->curtail = &head->next; 246 RCU_TRACE(rcp->qlen++); 247 local_irq_restore(flags); 248 249 if (unlikely(is_idle_task(current))) { 250 /* force scheduling for rcu_sched_qs() */ 251 resched_cpu(0); 252 } 253 } 254 255 /* 256 * Post an RCU callback to be invoked after the end of an RCU-sched grace 257 * period. But since we have but one CPU, that would be after any 258 * quiescent state. 259 */ 260 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) 261 { 262 __call_rcu(head, func, &rcu_sched_ctrlblk); 263 } 264 EXPORT_SYMBOL_GPL(call_rcu_sched); 265 266 /* 267 * Post an RCU bottom-half callback to be invoked after any subsequent 268 * quiescent state. 269 */ 270 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) 271 { 272 __call_rcu(head, func, &rcu_bh_ctrlblk); 273 } 274 EXPORT_SYMBOL_GPL(call_rcu_bh); 275 276 void __init rcu_init(void) 277 { 278 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); 279 RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk)); 280 RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk)); 281 282 rcu_early_boot_tests(); 283 } 284