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 static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; 51 52 #include "tiny_plugin.h" 53 54 /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */ 55 static void rcu_idle_enter_common(long long newval) 56 { 57 if (newval) { 58 RCU_TRACE(trace_rcu_dyntick(TPS("--="), 59 rcu_dynticks_nesting, newval)); 60 rcu_dynticks_nesting = newval; 61 return; 62 } 63 RCU_TRACE(trace_rcu_dyntick(TPS("Start"), 64 rcu_dynticks_nesting, newval)); 65 if (!is_idle_task(current)) { 66 struct task_struct *idle __maybe_unused = idle_task(smp_processor_id()); 67 68 RCU_TRACE(trace_rcu_dyntick(TPS("Entry error: not idle task"), 69 rcu_dynticks_nesting, newval)); 70 ftrace_dump(DUMP_ALL); 71 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s", 72 current->pid, current->comm, 73 idle->pid, idle->comm); /* must be idle task! */ 74 } 75 rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */ 76 barrier(); 77 rcu_dynticks_nesting = newval; 78 } 79 80 /* 81 * Enter idle, which is an extended quiescent state if we have fully 82 * entered that mode (i.e., if the new value of dynticks_nesting is zero). 83 */ 84 void rcu_idle_enter(void) 85 { 86 unsigned long flags; 87 long long newval; 88 89 local_irq_save(flags); 90 WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0); 91 if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 92 DYNTICK_TASK_NEST_VALUE) 93 newval = 0; 94 else 95 newval = rcu_dynticks_nesting - DYNTICK_TASK_NEST_VALUE; 96 rcu_idle_enter_common(newval); 97 local_irq_restore(flags); 98 } 99 EXPORT_SYMBOL_GPL(rcu_idle_enter); 100 101 /* 102 * Exit an interrupt handler towards idle. 103 */ 104 void rcu_irq_exit(void) 105 { 106 unsigned long flags; 107 long long newval; 108 109 local_irq_save(flags); 110 newval = rcu_dynticks_nesting - 1; 111 WARN_ON_ONCE(newval < 0); 112 rcu_idle_enter_common(newval); 113 local_irq_restore(flags); 114 } 115 EXPORT_SYMBOL_GPL(rcu_irq_exit); 116 117 /* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */ 118 static void rcu_idle_exit_common(long long oldval) 119 { 120 if (oldval) { 121 RCU_TRACE(trace_rcu_dyntick(TPS("++="), 122 oldval, rcu_dynticks_nesting)); 123 return; 124 } 125 RCU_TRACE(trace_rcu_dyntick(TPS("End"), oldval, rcu_dynticks_nesting)); 126 if (!is_idle_task(current)) { 127 struct task_struct *idle __maybe_unused = idle_task(smp_processor_id()); 128 129 RCU_TRACE(trace_rcu_dyntick(TPS("Exit error: not idle task"), 130 oldval, rcu_dynticks_nesting)); 131 ftrace_dump(DUMP_ALL); 132 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s", 133 current->pid, current->comm, 134 idle->pid, idle->comm); /* must be idle task! */ 135 } 136 } 137 138 /* 139 * Exit idle, so that we are no longer in an extended quiescent state. 140 */ 141 void rcu_idle_exit(void) 142 { 143 unsigned long flags; 144 long long oldval; 145 146 local_irq_save(flags); 147 oldval = rcu_dynticks_nesting; 148 WARN_ON_ONCE(rcu_dynticks_nesting < 0); 149 if (rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) 150 rcu_dynticks_nesting += DYNTICK_TASK_NEST_VALUE; 151 else 152 rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; 153 rcu_idle_exit_common(oldval); 154 local_irq_restore(flags); 155 } 156 EXPORT_SYMBOL_GPL(rcu_idle_exit); 157 158 /* 159 * Enter an interrupt handler, moving away from idle. 160 */ 161 void rcu_irq_enter(void) 162 { 163 unsigned long flags; 164 long long oldval; 165 166 local_irq_save(flags); 167 oldval = rcu_dynticks_nesting; 168 rcu_dynticks_nesting++; 169 WARN_ON_ONCE(rcu_dynticks_nesting == 0); 170 rcu_idle_exit_common(oldval); 171 local_irq_restore(flags); 172 } 173 EXPORT_SYMBOL_GPL(rcu_irq_enter); 174 175 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) 176 177 /* 178 * Test whether RCU thinks that the current CPU is idle. 179 */ 180 bool notrace __rcu_is_watching(void) 181 { 182 return rcu_dynticks_nesting; 183 } 184 EXPORT_SYMBOL(__rcu_is_watching); 185 186 #endif /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */ 187 188 /* 189 * Test whether the current CPU was interrupted from idle. Nested 190 * interrupts don't count, we must be running at the first interrupt 191 * level. 192 */ 193 static int rcu_is_cpu_rrupt_from_idle(void) 194 { 195 return rcu_dynticks_nesting <= 1; 196 } 197 198 /* 199 * Helper function for rcu_sched_qs() and rcu_bh_qs(). 200 * Also irqs are disabled to avoid confusion due to interrupt handlers 201 * invoking call_rcu(). 202 */ 203 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp) 204 { 205 RCU_TRACE(reset_cpu_stall_ticks(rcp)); 206 if (rcp->rcucblist != NULL && 207 rcp->donetail != rcp->curtail) { 208 rcp->donetail = rcp->curtail; 209 return 1; 210 } 211 212 return 0; 213 } 214 215 /* 216 * Record an rcu quiescent state. And an rcu_bh quiescent state while we 217 * are at it, given that any rcu quiescent state is also an rcu_bh 218 * quiescent state. Use "+" instead of "||" to defeat short circuiting. 219 */ 220 void rcu_sched_qs(int cpu) 221 { 222 unsigned long flags; 223 224 local_irq_save(flags); 225 if (rcu_qsctr_help(&rcu_sched_ctrlblk) + 226 rcu_qsctr_help(&rcu_bh_ctrlblk)) 227 raise_softirq(RCU_SOFTIRQ); 228 local_irq_restore(flags); 229 } 230 231 /* 232 * Record an rcu_bh quiescent state. 233 */ 234 void rcu_bh_qs(int cpu) 235 { 236 unsigned long flags; 237 238 local_irq_save(flags); 239 if (rcu_qsctr_help(&rcu_bh_ctrlblk)) 240 raise_softirq(RCU_SOFTIRQ); 241 local_irq_restore(flags); 242 } 243 244 /* 245 * Check to see if the scheduling-clock interrupt came from an extended 246 * quiescent state, and, if so, tell RCU about it. This function must 247 * be called from hardirq context. It is normally called from the 248 * scheduling-clock interrupt. 249 */ 250 void rcu_check_callbacks(int cpu, int user) 251 { 252 RCU_TRACE(check_cpu_stalls()); 253 if (user || rcu_is_cpu_rrupt_from_idle()) 254 rcu_sched_qs(cpu); 255 else if (!in_softirq()) 256 rcu_bh_qs(cpu); 257 } 258 259 /* 260 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure 261 * whose grace period has elapsed. 262 */ 263 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp) 264 { 265 const char *rn = NULL; 266 struct rcu_head *next, *list; 267 unsigned long flags; 268 RCU_TRACE(int cb_count = 0); 269 270 /* If no RCU callbacks ready to invoke, just return. */ 271 if (&rcp->rcucblist == rcp->donetail) { 272 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1)); 273 RCU_TRACE(trace_rcu_batch_end(rcp->name, 0, 274 !!ACCESS_ONCE(rcp->rcucblist), 275 need_resched(), 276 is_idle_task(current), 277 false)); 278 return; 279 } 280 281 /* Move the ready-to-invoke callbacks to a local list. */ 282 local_irq_save(flags); 283 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1)); 284 list = rcp->rcucblist; 285 rcp->rcucblist = *rcp->donetail; 286 *rcp->donetail = NULL; 287 if (rcp->curtail == rcp->donetail) 288 rcp->curtail = &rcp->rcucblist; 289 rcp->donetail = &rcp->rcucblist; 290 local_irq_restore(flags); 291 292 /* Invoke the callbacks on the local list. */ 293 RCU_TRACE(rn = rcp->name); 294 while (list) { 295 next = list->next; 296 prefetch(next); 297 debug_rcu_head_unqueue(list); 298 local_bh_disable(); 299 __rcu_reclaim(rn, list); 300 local_bh_enable(); 301 list = next; 302 RCU_TRACE(cb_count++); 303 } 304 RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count)); 305 RCU_TRACE(trace_rcu_batch_end(rcp->name, 306 cb_count, 0, need_resched(), 307 is_idle_task(current), 308 false)); 309 } 310 311 static void rcu_process_callbacks(struct softirq_action *unused) 312 { 313 __rcu_process_callbacks(&rcu_sched_ctrlblk); 314 __rcu_process_callbacks(&rcu_bh_ctrlblk); 315 } 316 317 /* 318 * Wait for a grace period to elapse. But it is illegal to invoke 319 * synchronize_sched() from within an RCU read-side critical section. 320 * Therefore, any legal call to synchronize_sched() is a quiescent 321 * state, and so on a UP system, synchronize_sched() need do nothing. 322 * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the 323 * benefits of doing might_sleep() to reduce latency.) 324 * 325 * Cool, huh? (Due to Josh Triplett.) 326 * 327 * But we want to make this a static inline later. The cond_resched() 328 * currently makes this problematic. 329 */ 330 void synchronize_sched(void) 331 { 332 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) && 333 !lock_is_held(&rcu_lock_map) && 334 !lock_is_held(&rcu_sched_lock_map), 335 "Illegal synchronize_sched() in RCU read-side critical section"); 336 cond_resched(); 337 } 338 EXPORT_SYMBOL_GPL(synchronize_sched); 339 340 /* 341 * Helper function for call_rcu() and call_rcu_bh(). 342 */ 343 static void __call_rcu(struct rcu_head *head, 344 void (*func)(struct rcu_head *rcu), 345 struct rcu_ctrlblk *rcp) 346 { 347 unsigned long flags; 348 349 debug_rcu_head_queue(head); 350 head->func = func; 351 head->next = NULL; 352 353 local_irq_save(flags); 354 *rcp->curtail = head; 355 rcp->curtail = &head->next; 356 RCU_TRACE(rcp->qlen++); 357 local_irq_restore(flags); 358 } 359 360 /* 361 * Post an RCU callback to be invoked after the end of an RCU-sched grace 362 * period. But since we have but one CPU, that would be after any 363 * quiescent state. 364 */ 365 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) 366 { 367 __call_rcu(head, func, &rcu_sched_ctrlblk); 368 } 369 EXPORT_SYMBOL_GPL(call_rcu_sched); 370 371 /* 372 * Post an RCU bottom-half callback to be invoked after any subsequent 373 * quiescent state. 374 */ 375 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) 376 { 377 __call_rcu(head, func, &rcu_bh_ctrlblk); 378 } 379 EXPORT_SYMBOL_GPL(call_rcu_bh); 380 381 void rcu_init(void) 382 { 383 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); 384 } 385