tree_plugin.h revision 2f33b512a5460578f6cf11d7b7867bed53157c7c
1/* 2 * Read-Copy Update mechanism for mutual exclusion (tree-based version) 3 * Internal non-public definitions that provide either classic 4 * or preemptible semantics. 5 * 6 * This program is free software; you can redistribute it and/or modify 7 * it under the terms of the GNU General Public License as published by 8 * the Free Software Foundation; either version 2 of the License, or 9 * (at your option) any later version. 10 * 11 * This program is distributed in the hope that it will be useful, 12 * but WITHOUT ANY WARRANTY; without even the implied warranty of 13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14 * GNU General Public License for more details. 15 * 16 * You should have received a copy of the GNU General Public License 17 * along with this program; if not, write to the Free Software 18 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. 19 * 20 * Copyright Red Hat, 2009 21 * Copyright IBM Corporation, 2009 22 * 23 * Author: Ingo Molnar <mingo@elte.hu> 24 * Paul E. McKenney <paulmck@linux.vnet.ibm.com> 25 */ 26 27#include <linux/delay.h> 28#include <linux/gfp.h> 29#include <linux/oom.h> 30#include <linux/smpboot.h> 31#include "../time/tick-internal.h" 32 33#define RCU_KTHREAD_PRIO 1 34 35#ifdef CONFIG_RCU_BOOST 36#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO 37#else 38#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO 39#endif 40 41#ifdef CONFIG_RCU_NOCB_CPU 42static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */ 43static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */ 44static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */ 45static char __initdata nocb_buf[NR_CPUS * 5]; 46#endif /* #ifdef CONFIG_RCU_NOCB_CPU */ 47 48/* 49 * Check the RCU kernel configuration parameters and print informative 50 * messages about anything out of the ordinary. If you like #ifdef, you 51 * will love this function. 52 */ 53static void __init rcu_bootup_announce_oddness(void) 54{ 55#ifdef CONFIG_RCU_TRACE 56 pr_info("\tRCU debugfs-based tracing is enabled.\n"); 57#endif 58#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32) 59 pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n", 60 CONFIG_RCU_FANOUT); 61#endif 62#ifdef CONFIG_RCU_FANOUT_EXACT 63 pr_info("\tHierarchical RCU autobalancing is disabled.\n"); 64#endif 65#ifdef CONFIG_RCU_FAST_NO_HZ 66 pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n"); 67#endif 68#ifdef CONFIG_PROVE_RCU 69 pr_info("\tRCU lockdep checking is enabled.\n"); 70#endif 71#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE 72 pr_info("\tRCU torture testing starts during boot.\n"); 73#endif 74#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE) 75 pr_info("\tDump stacks of tasks blocking RCU-preempt GP.\n"); 76#endif 77#if defined(CONFIG_RCU_CPU_STALL_INFO) 78 pr_info("\tAdditional per-CPU info printed with stalls.\n"); 79#endif 80#if NUM_RCU_LVL_4 != 0 81 pr_info("\tFour-level hierarchy is enabled.\n"); 82#endif 83 if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF) 84 pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf); 85 if (nr_cpu_ids != NR_CPUS) 86 pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids); 87#ifdef CONFIG_RCU_NOCB_CPU 88#ifndef CONFIG_RCU_NOCB_CPU_NONE 89 if (!have_rcu_nocb_mask) { 90 zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL); 91 have_rcu_nocb_mask = true; 92 } 93#ifdef CONFIG_RCU_NOCB_CPU_ZERO 94 pr_info("\tOffload RCU callbacks from CPU 0\n"); 95 cpumask_set_cpu(0, rcu_nocb_mask); 96#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */ 97#ifdef CONFIG_RCU_NOCB_CPU_ALL 98 pr_info("\tOffload RCU callbacks from all CPUs\n"); 99 cpumask_copy(rcu_nocb_mask, cpu_possible_mask); 100#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */ 101#endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */ 102 if (have_rcu_nocb_mask) { 103 if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) { 104 pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n"); 105 cpumask_and(rcu_nocb_mask, cpu_possible_mask, 106 rcu_nocb_mask); 107 } 108 cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask); 109 pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf); 110 if (rcu_nocb_poll) 111 pr_info("\tPoll for callbacks from no-CBs CPUs.\n"); 112 } 113#endif /* #ifdef CONFIG_RCU_NOCB_CPU */ 114} 115 116#ifdef CONFIG_TREE_PREEMPT_RCU 117 118RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu); 119static struct rcu_state *rcu_state = &rcu_preempt_state; 120 121static int rcu_preempted_readers_exp(struct rcu_node *rnp); 122 123/* 124 * Tell them what RCU they are running. 125 */ 126static void __init rcu_bootup_announce(void) 127{ 128 pr_info("Preemptible hierarchical RCU implementation.\n"); 129 rcu_bootup_announce_oddness(); 130} 131 132/* 133 * Return the number of RCU-preempt batches processed thus far 134 * for debug and statistics. 135 */ 136long rcu_batches_completed_preempt(void) 137{ 138 return rcu_preempt_state.completed; 139} 140EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt); 141 142/* 143 * Return the number of RCU batches processed thus far for debug & stats. 144 */ 145long rcu_batches_completed(void) 146{ 147 return rcu_batches_completed_preempt(); 148} 149EXPORT_SYMBOL_GPL(rcu_batches_completed); 150 151/* 152 * Force a quiescent state for preemptible RCU. 153 */ 154void rcu_force_quiescent_state(void) 155{ 156 force_quiescent_state(&rcu_preempt_state); 157} 158EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); 159 160/* 161 * Record a preemptible-RCU quiescent state for the specified CPU. Note 162 * that this just means that the task currently running on the CPU is 163 * not in a quiescent state. There might be any number of tasks blocked 164 * while in an RCU read-side critical section. 165 * 166 * Unlike the other rcu_*_qs() functions, callers to this function 167 * must disable irqs in order to protect the assignment to 168 * ->rcu_read_unlock_special. 169 */ 170static void rcu_preempt_qs(int cpu) 171{ 172 struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu); 173 174 if (rdp->passed_quiesce == 0) 175 trace_rcu_grace_period(TPS("rcu_preempt"), rdp->gpnum, TPS("cpuqs")); 176 rdp->passed_quiesce = 1; 177 current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; 178} 179 180/* 181 * We have entered the scheduler, and the current task might soon be 182 * context-switched away from. If this task is in an RCU read-side 183 * critical section, we will no longer be able to rely on the CPU to 184 * record that fact, so we enqueue the task on the blkd_tasks list. 185 * The task will dequeue itself when it exits the outermost enclosing 186 * RCU read-side critical section. Therefore, the current grace period 187 * cannot be permitted to complete until the blkd_tasks list entries 188 * predating the current grace period drain, in other words, until 189 * rnp->gp_tasks becomes NULL. 190 * 191 * Caller must disable preemption. 192 */ 193static void rcu_preempt_note_context_switch(int cpu) 194{ 195 struct task_struct *t = current; 196 unsigned long flags; 197 struct rcu_data *rdp; 198 struct rcu_node *rnp; 199 200 if (t->rcu_read_lock_nesting > 0 && 201 (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { 202 203 /* Possibly blocking in an RCU read-side critical section. */ 204 rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu); 205 rnp = rdp->mynode; 206 raw_spin_lock_irqsave(&rnp->lock, flags); 207 smp_mb__after_unlock_lock(); 208 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; 209 t->rcu_blocked_node = rnp; 210 211 /* 212 * If this CPU has already checked in, then this task 213 * will hold up the next grace period rather than the 214 * current grace period. Queue the task accordingly. 215 * If the task is queued for the current grace period 216 * (i.e., this CPU has not yet passed through a quiescent 217 * state for the current grace period), then as long 218 * as that task remains queued, the current grace period 219 * cannot end. Note that there is some uncertainty as 220 * to exactly when the current grace period started. 221 * We take a conservative approach, which can result 222 * in unnecessarily waiting on tasks that started very 223 * slightly after the current grace period began. C'est 224 * la vie!!! 225 * 226 * But first, note that the current CPU must still be 227 * on line! 228 */ 229 WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0); 230 WARN_ON_ONCE(!list_empty(&t->rcu_node_entry)); 231 if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) { 232 list_add(&t->rcu_node_entry, rnp->gp_tasks->prev); 233 rnp->gp_tasks = &t->rcu_node_entry; 234#ifdef CONFIG_RCU_BOOST 235 if (rnp->boost_tasks != NULL) 236 rnp->boost_tasks = rnp->gp_tasks; 237#endif /* #ifdef CONFIG_RCU_BOOST */ 238 } else { 239 list_add(&t->rcu_node_entry, &rnp->blkd_tasks); 240 if (rnp->qsmask & rdp->grpmask) 241 rnp->gp_tasks = &t->rcu_node_entry; 242 } 243 trace_rcu_preempt_task(rdp->rsp->name, 244 t->pid, 245 (rnp->qsmask & rdp->grpmask) 246 ? rnp->gpnum 247 : rnp->gpnum + 1); 248 raw_spin_unlock_irqrestore(&rnp->lock, flags); 249 } else if (t->rcu_read_lock_nesting < 0 && 250 t->rcu_read_unlock_special) { 251 252 /* 253 * Complete exit from RCU read-side critical section on 254 * behalf of preempted instance of __rcu_read_unlock(). 255 */ 256 rcu_read_unlock_special(t); 257 } 258 259 /* 260 * Either we were not in an RCU read-side critical section to 261 * begin with, or we have now recorded that critical section 262 * globally. Either way, we can now note a quiescent state 263 * for this CPU. Again, if we were in an RCU read-side critical 264 * section, and if that critical section was blocking the current 265 * grace period, then the fact that the task has been enqueued 266 * means that we continue to block the current grace period. 267 */ 268 local_irq_save(flags); 269 rcu_preempt_qs(cpu); 270 local_irq_restore(flags); 271} 272 273/* 274 * Check for preempted RCU readers blocking the current grace period 275 * for the specified rcu_node structure. If the caller needs a reliable 276 * answer, it must hold the rcu_node's ->lock. 277 */ 278static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) 279{ 280 return rnp->gp_tasks != NULL; 281} 282 283/* 284 * Record a quiescent state for all tasks that were previously queued 285 * on the specified rcu_node structure and that were blocking the current 286 * RCU grace period. The caller must hold the specified rnp->lock with 287 * irqs disabled, and this lock is released upon return, but irqs remain 288 * disabled. 289 */ 290static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) 291 __releases(rnp->lock) 292{ 293 unsigned long mask; 294 struct rcu_node *rnp_p; 295 296 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) { 297 raw_spin_unlock_irqrestore(&rnp->lock, flags); 298 return; /* Still need more quiescent states! */ 299 } 300 301 rnp_p = rnp->parent; 302 if (rnp_p == NULL) { 303 /* 304 * Either there is only one rcu_node in the tree, 305 * or tasks were kicked up to root rcu_node due to 306 * CPUs going offline. 307 */ 308 rcu_report_qs_rsp(&rcu_preempt_state, flags); 309 return; 310 } 311 312 /* Report up the rest of the hierarchy. */ 313 mask = rnp->grpmask; 314 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ 315 raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */ 316 smp_mb__after_unlock_lock(); 317 rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags); 318} 319 320/* 321 * Advance a ->blkd_tasks-list pointer to the next entry, instead 322 * returning NULL if at the end of the list. 323 */ 324static struct list_head *rcu_next_node_entry(struct task_struct *t, 325 struct rcu_node *rnp) 326{ 327 struct list_head *np; 328 329 np = t->rcu_node_entry.next; 330 if (np == &rnp->blkd_tasks) 331 np = NULL; 332 return np; 333} 334 335/* 336 * Handle special cases during rcu_read_unlock(), such as needing to 337 * notify RCU core processing or task having blocked during the RCU 338 * read-side critical section. 339 */ 340void rcu_read_unlock_special(struct task_struct *t) 341{ 342 int empty; 343 int empty_exp; 344 int empty_exp_now; 345 unsigned long flags; 346 struct list_head *np; 347#ifdef CONFIG_RCU_BOOST 348 struct rt_mutex *rbmp = NULL; 349#endif /* #ifdef CONFIG_RCU_BOOST */ 350 struct rcu_node *rnp; 351 int special; 352 353 /* NMI handlers cannot block and cannot safely manipulate state. */ 354 if (in_nmi()) 355 return; 356 357 local_irq_save(flags); 358 359 /* 360 * If RCU core is waiting for this CPU to exit critical section, 361 * let it know that we have done so. 362 */ 363 special = t->rcu_read_unlock_special; 364 if (special & RCU_READ_UNLOCK_NEED_QS) { 365 rcu_preempt_qs(smp_processor_id()); 366 if (!t->rcu_read_unlock_special) { 367 local_irq_restore(flags); 368 return; 369 } 370 } 371 372 /* Hardware IRQ handlers cannot block, complain if they get here. */ 373 if (WARN_ON_ONCE(in_irq() || in_serving_softirq())) { 374 local_irq_restore(flags); 375 return; 376 } 377 378 /* Clean up if blocked during RCU read-side critical section. */ 379 if (special & RCU_READ_UNLOCK_BLOCKED) { 380 t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; 381 382 /* 383 * Remove this task from the list it blocked on. The 384 * task can migrate while we acquire the lock, but at 385 * most one time. So at most two passes through loop. 386 */ 387 for (;;) { 388 rnp = t->rcu_blocked_node; 389 raw_spin_lock(&rnp->lock); /* irqs already disabled. */ 390 smp_mb__after_unlock_lock(); 391 if (rnp == t->rcu_blocked_node) 392 break; 393 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ 394 } 395 empty = !rcu_preempt_blocked_readers_cgp(rnp); 396 empty_exp = !rcu_preempted_readers_exp(rnp); 397 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */ 398 np = rcu_next_node_entry(t, rnp); 399 list_del_init(&t->rcu_node_entry); 400 t->rcu_blocked_node = NULL; 401 trace_rcu_unlock_preempted_task(TPS("rcu_preempt"), 402 rnp->gpnum, t->pid); 403 if (&t->rcu_node_entry == rnp->gp_tasks) 404 rnp->gp_tasks = np; 405 if (&t->rcu_node_entry == rnp->exp_tasks) 406 rnp->exp_tasks = np; 407#ifdef CONFIG_RCU_BOOST 408 if (&t->rcu_node_entry == rnp->boost_tasks) 409 rnp->boost_tasks = np; 410 /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */ 411 if (t->rcu_boost_mutex) { 412 rbmp = t->rcu_boost_mutex; 413 t->rcu_boost_mutex = NULL; 414 } 415#endif /* #ifdef CONFIG_RCU_BOOST */ 416 417 /* 418 * If this was the last task on the current list, and if 419 * we aren't waiting on any CPUs, report the quiescent state. 420 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock, 421 * so we must take a snapshot of the expedited state. 422 */ 423 empty_exp_now = !rcu_preempted_readers_exp(rnp); 424 if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) { 425 trace_rcu_quiescent_state_report(TPS("preempt_rcu"), 426 rnp->gpnum, 427 0, rnp->qsmask, 428 rnp->level, 429 rnp->grplo, 430 rnp->grphi, 431 !!rnp->gp_tasks); 432 rcu_report_unblock_qs_rnp(rnp, flags); 433 } else { 434 raw_spin_unlock_irqrestore(&rnp->lock, flags); 435 } 436 437#ifdef CONFIG_RCU_BOOST 438 /* Unboost if we were boosted. */ 439 if (rbmp) 440 rt_mutex_unlock(rbmp); 441#endif /* #ifdef CONFIG_RCU_BOOST */ 442 443 /* 444 * If this was the last task on the expedited lists, 445 * then we need to report up the rcu_node hierarchy. 446 */ 447 if (!empty_exp && empty_exp_now) 448 rcu_report_exp_rnp(&rcu_preempt_state, rnp, true); 449 } else { 450 local_irq_restore(flags); 451 } 452} 453 454#ifdef CONFIG_RCU_CPU_STALL_VERBOSE 455 456/* 457 * Dump detailed information for all tasks blocking the current RCU 458 * grace period on the specified rcu_node structure. 459 */ 460static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) 461{ 462 unsigned long flags; 463 struct task_struct *t; 464 465 raw_spin_lock_irqsave(&rnp->lock, flags); 466 if (!rcu_preempt_blocked_readers_cgp(rnp)) { 467 raw_spin_unlock_irqrestore(&rnp->lock, flags); 468 return; 469 } 470 t = list_entry(rnp->gp_tasks, 471 struct task_struct, rcu_node_entry); 472 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) 473 sched_show_task(t); 474 raw_spin_unlock_irqrestore(&rnp->lock, flags); 475} 476 477/* 478 * Dump detailed information for all tasks blocking the current RCU 479 * grace period. 480 */ 481static void rcu_print_detail_task_stall(struct rcu_state *rsp) 482{ 483 struct rcu_node *rnp = rcu_get_root(rsp); 484 485 rcu_print_detail_task_stall_rnp(rnp); 486 rcu_for_each_leaf_node(rsp, rnp) 487 rcu_print_detail_task_stall_rnp(rnp); 488} 489 490#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ 491 492static void rcu_print_detail_task_stall(struct rcu_state *rsp) 493{ 494} 495 496#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ 497 498#ifdef CONFIG_RCU_CPU_STALL_INFO 499 500static void rcu_print_task_stall_begin(struct rcu_node *rnp) 501{ 502 pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):", 503 rnp->level, rnp->grplo, rnp->grphi); 504} 505 506static void rcu_print_task_stall_end(void) 507{ 508 pr_cont("\n"); 509} 510 511#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */ 512 513static void rcu_print_task_stall_begin(struct rcu_node *rnp) 514{ 515} 516 517static void rcu_print_task_stall_end(void) 518{ 519} 520 521#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */ 522 523/* 524 * Scan the current list of tasks blocked within RCU read-side critical 525 * sections, printing out the tid of each. 526 */ 527static int rcu_print_task_stall(struct rcu_node *rnp) 528{ 529 struct task_struct *t; 530 int ndetected = 0; 531 532 if (!rcu_preempt_blocked_readers_cgp(rnp)) 533 return 0; 534 rcu_print_task_stall_begin(rnp); 535 t = list_entry(rnp->gp_tasks, 536 struct task_struct, rcu_node_entry); 537 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { 538 pr_cont(" P%d", t->pid); 539 ndetected++; 540 } 541 rcu_print_task_stall_end(); 542 return ndetected; 543} 544 545/* 546 * Check that the list of blocked tasks for the newly completed grace 547 * period is in fact empty. It is a serious bug to complete a grace 548 * period that still has RCU readers blocked! This function must be 549 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock 550 * must be held by the caller. 551 * 552 * Also, if there are blocked tasks on the list, they automatically 553 * block the newly created grace period, so set up ->gp_tasks accordingly. 554 */ 555static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) 556{ 557 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)); 558 if (!list_empty(&rnp->blkd_tasks)) 559 rnp->gp_tasks = rnp->blkd_tasks.next; 560 WARN_ON_ONCE(rnp->qsmask); 561} 562 563#ifdef CONFIG_HOTPLUG_CPU 564 565/* 566 * Handle tasklist migration for case in which all CPUs covered by the 567 * specified rcu_node have gone offline. Move them up to the root 568 * rcu_node. The reason for not just moving them to the immediate 569 * parent is to remove the need for rcu_read_unlock_special() to 570 * make more than two attempts to acquire the target rcu_node's lock. 571 * Returns true if there were tasks blocking the current RCU grace 572 * period. 573 * 574 * Returns 1 if there was previously a task blocking the current grace 575 * period on the specified rcu_node structure. 576 * 577 * The caller must hold rnp->lock with irqs disabled. 578 */ 579static int rcu_preempt_offline_tasks(struct rcu_state *rsp, 580 struct rcu_node *rnp, 581 struct rcu_data *rdp) 582{ 583 struct list_head *lp; 584 struct list_head *lp_root; 585 int retval = 0; 586 struct rcu_node *rnp_root = rcu_get_root(rsp); 587 struct task_struct *t; 588 589 if (rnp == rnp_root) { 590 WARN_ONCE(1, "Last CPU thought to be offlined?"); 591 return 0; /* Shouldn't happen: at least one CPU online. */ 592 } 593 594 /* If we are on an internal node, complain bitterly. */ 595 WARN_ON_ONCE(rnp != rdp->mynode); 596 597 /* 598 * Move tasks up to root rcu_node. Don't try to get fancy for 599 * this corner-case operation -- just put this node's tasks 600 * at the head of the root node's list, and update the root node's 601 * ->gp_tasks and ->exp_tasks pointers to those of this node's, 602 * if non-NULL. This might result in waiting for more tasks than 603 * absolutely necessary, but this is a good performance/complexity 604 * tradeoff. 605 */ 606 if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0) 607 retval |= RCU_OFL_TASKS_NORM_GP; 608 if (rcu_preempted_readers_exp(rnp)) 609 retval |= RCU_OFL_TASKS_EXP_GP; 610 lp = &rnp->blkd_tasks; 611 lp_root = &rnp_root->blkd_tasks; 612 while (!list_empty(lp)) { 613 t = list_entry(lp->next, typeof(*t), rcu_node_entry); 614 raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ 615 smp_mb__after_unlock_lock(); 616 list_del(&t->rcu_node_entry); 617 t->rcu_blocked_node = rnp_root; 618 list_add(&t->rcu_node_entry, lp_root); 619 if (&t->rcu_node_entry == rnp->gp_tasks) 620 rnp_root->gp_tasks = rnp->gp_tasks; 621 if (&t->rcu_node_entry == rnp->exp_tasks) 622 rnp_root->exp_tasks = rnp->exp_tasks; 623#ifdef CONFIG_RCU_BOOST 624 if (&t->rcu_node_entry == rnp->boost_tasks) 625 rnp_root->boost_tasks = rnp->boost_tasks; 626#endif /* #ifdef CONFIG_RCU_BOOST */ 627 raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ 628 } 629 630 rnp->gp_tasks = NULL; 631 rnp->exp_tasks = NULL; 632#ifdef CONFIG_RCU_BOOST 633 rnp->boost_tasks = NULL; 634 /* 635 * In case root is being boosted and leaf was not. Make sure 636 * that we boost the tasks blocking the current grace period 637 * in this case. 638 */ 639 raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ 640 smp_mb__after_unlock_lock(); 641 if (rnp_root->boost_tasks != NULL && 642 rnp_root->boost_tasks != rnp_root->gp_tasks && 643 rnp_root->boost_tasks != rnp_root->exp_tasks) 644 rnp_root->boost_tasks = rnp_root->gp_tasks; 645 raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ 646#endif /* #ifdef CONFIG_RCU_BOOST */ 647 648 return retval; 649} 650 651#endif /* #ifdef CONFIG_HOTPLUG_CPU */ 652 653/* 654 * Check for a quiescent state from the current CPU. When a task blocks, 655 * the task is recorded in the corresponding CPU's rcu_node structure, 656 * which is checked elsewhere. 657 * 658 * Caller must disable hard irqs. 659 */ 660static void rcu_preempt_check_callbacks(int cpu) 661{ 662 struct task_struct *t = current; 663 664 if (t->rcu_read_lock_nesting == 0) { 665 rcu_preempt_qs(cpu); 666 return; 667 } 668 if (t->rcu_read_lock_nesting > 0 && 669 per_cpu(rcu_preempt_data, cpu).qs_pending) 670 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; 671} 672 673#ifdef CONFIG_RCU_BOOST 674 675static void rcu_preempt_do_callbacks(void) 676{ 677 rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data)); 678} 679 680#endif /* #ifdef CONFIG_RCU_BOOST */ 681 682/* 683 * Queue a preemptible-RCU callback for invocation after a grace period. 684 */ 685void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) 686{ 687 __call_rcu(head, func, &rcu_preempt_state, -1, 0); 688} 689EXPORT_SYMBOL_GPL(call_rcu); 690 691/* 692 * Queue an RCU callback for lazy invocation after a grace period. 693 * This will likely be later named something like "call_rcu_lazy()", 694 * but this change will require some way of tagging the lazy RCU 695 * callbacks in the list of pending callbacks. Until then, this 696 * function may only be called from __kfree_rcu(). 697 */ 698void kfree_call_rcu(struct rcu_head *head, 699 void (*func)(struct rcu_head *rcu)) 700{ 701 __call_rcu(head, func, &rcu_preempt_state, -1, 1); 702} 703EXPORT_SYMBOL_GPL(kfree_call_rcu); 704 705/** 706 * synchronize_rcu - wait until a grace period has elapsed. 707 * 708 * Control will return to the caller some time after a full grace 709 * period has elapsed, in other words after all currently executing RCU 710 * read-side critical sections have completed. Note, however, that 711 * upon return from synchronize_rcu(), the caller might well be executing 712 * concurrently with new RCU read-side critical sections that began while 713 * synchronize_rcu() was waiting. RCU read-side critical sections are 714 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. 715 * 716 * See the description of synchronize_sched() for more detailed information 717 * on memory ordering guarantees. 718 */ 719void synchronize_rcu(void) 720{ 721 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) && 722 !lock_is_held(&rcu_lock_map) && 723 !lock_is_held(&rcu_sched_lock_map), 724 "Illegal synchronize_rcu() in RCU read-side critical section"); 725 if (!rcu_scheduler_active) 726 return; 727 if (rcu_expedited) 728 synchronize_rcu_expedited(); 729 else 730 wait_rcu_gp(call_rcu); 731} 732EXPORT_SYMBOL_GPL(synchronize_rcu); 733 734static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); 735static unsigned long sync_rcu_preempt_exp_count; 736static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); 737 738/* 739 * Return non-zero if there are any tasks in RCU read-side critical 740 * sections blocking the current preemptible-RCU expedited grace period. 741 * If there is no preemptible-RCU expedited grace period currently in 742 * progress, returns zero unconditionally. 743 */ 744static int rcu_preempted_readers_exp(struct rcu_node *rnp) 745{ 746 return rnp->exp_tasks != NULL; 747} 748 749/* 750 * return non-zero if there is no RCU expedited grace period in progress 751 * for the specified rcu_node structure, in other words, if all CPUs and 752 * tasks covered by the specified rcu_node structure have done their bit 753 * for the current expedited grace period. Works only for preemptible 754 * RCU -- other RCU implementation use other means. 755 * 756 * Caller must hold sync_rcu_preempt_exp_mutex. 757 */ 758static int sync_rcu_preempt_exp_done(struct rcu_node *rnp) 759{ 760 return !rcu_preempted_readers_exp(rnp) && 761 ACCESS_ONCE(rnp->expmask) == 0; 762} 763 764/* 765 * Report the exit from RCU read-side critical section for the last task 766 * that queued itself during or before the current expedited preemptible-RCU 767 * grace period. This event is reported either to the rcu_node structure on 768 * which the task was queued or to one of that rcu_node structure's ancestors, 769 * recursively up the tree. (Calm down, calm down, we do the recursion 770 * iteratively!) 771 * 772 * Most callers will set the "wake" flag, but the task initiating the 773 * expedited grace period need not wake itself. 774 * 775 * Caller must hold sync_rcu_preempt_exp_mutex. 776 */ 777static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, 778 bool wake) 779{ 780 unsigned long flags; 781 unsigned long mask; 782 783 raw_spin_lock_irqsave(&rnp->lock, flags); 784 smp_mb__after_unlock_lock(); 785 for (;;) { 786 if (!sync_rcu_preempt_exp_done(rnp)) { 787 raw_spin_unlock_irqrestore(&rnp->lock, flags); 788 break; 789 } 790 if (rnp->parent == NULL) { 791 raw_spin_unlock_irqrestore(&rnp->lock, flags); 792 if (wake) { 793 smp_mb(); /* EGP done before wake_up(). */ 794 wake_up(&sync_rcu_preempt_exp_wq); 795 } 796 break; 797 } 798 mask = rnp->grpmask; 799 raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ 800 rnp = rnp->parent; 801 raw_spin_lock(&rnp->lock); /* irqs already disabled */ 802 smp_mb__after_unlock_lock(); 803 rnp->expmask &= ~mask; 804 } 805} 806 807/* 808 * Snapshot the tasks blocking the newly started preemptible-RCU expedited 809 * grace period for the specified rcu_node structure. If there are no such 810 * tasks, report it up the rcu_node hierarchy. 811 * 812 * Caller must hold sync_rcu_preempt_exp_mutex and must exclude 813 * CPU hotplug operations. 814 */ 815static void 816sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp) 817{ 818 unsigned long flags; 819 int must_wait = 0; 820 821 raw_spin_lock_irqsave(&rnp->lock, flags); 822 smp_mb__after_unlock_lock(); 823 if (list_empty(&rnp->blkd_tasks)) { 824 raw_spin_unlock_irqrestore(&rnp->lock, flags); 825 } else { 826 rnp->exp_tasks = rnp->blkd_tasks.next; 827 rcu_initiate_boost(rnp, flags); /* releases rnp->lock */ 828 must_wait = 1; 829 } 830 if (!must_wait) 831 rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */ 832} 833 834/** 835 * synchronize_rcu_expedited - Brute-force RCU grace period 836 * 837 * Wait for an RCU-preempt grace period, but expedite it. The basic 838 * idea is to invoke synchronize_sched_expedited() to push all the tasks to 839 * the ->blkd_tasks lists and wait for this list to drain. This consumes 840 * significant time on all CPUs and is unfriendly to real-time workloads, 841 * so is thus not recommended for any sort of common-case code. 842 * In fact, if you are using synchronize_rcu_expedited() in a loop, 843 * please restructure your code to batch your updates, and then Use a 844 * single synchronize_rcu() instead. 845 * 846 * Note that it is illegal to call this function while holding any lock 847 * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal 848 * to call this function from a CPU-hotplug notifier. Failing to observe 849 * these restriction will result in deadlock. 850 */ 851void synchronize_rcu_expedited(void) 852{ 853 unsigned long flags; 854 struct rcu_node *rnp; 855 struct rcu_state *rsp = &rcu_preempt_state; 856 unsigned long snap; 857 int trycount = 0; 858 859 smp_mb(); /* Caller's modifications seen first by other CPUs. */ 860 snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1; 861 smp_mb(); /* Above access cannot bleed into critical section. */ 862 863 /* 864 * Block CPU-hotplug operations. This means that any CPU-hotplug 865 * operation that finds an rcu_node structure with tasks in the 866 * process of being boosted will know that all tasks blocking 867 * this expedited grace period will already be in the process of 868 * being boosted. This simplifies the process of moving tasks 869 * from leaf to root rcu_node structures. 870 */ 871 get_online_cpus(); 872 873 /* 874 * Acquire lock, falling back to synchronize_rcu() if too many 875 * lock-acquisition failures. Of course, if someone does the 876 * expedited grace period for us, just leave. 877 */ 878 while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) { 879 if (ULONG_CMP_LT(snap, 880 ACCESS_ONCE(sync_rcu_preempt_exp_count))) { 881 put_online_cpus(); 882 goto mb_ret; /* Others did our work for us. */ 883 } 884 if (trycount++ < 10) { 885 udelay(trycount * num_online_cpus()); 886 } else { 887 put_online_cpus(); 888 wait_rcu_gp(call_rcu); 889 return; 890 } 891 } 892 if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) { 893 put_online_cpus(); 894 goto unlock_mb_ret; /* Others did our work for us. */ 895 } 896 897 /* force all RCU readers onto ->blkd_tasks lists. */ 898 synchronize_sched_expedited(); 899 900 /* Initialize ->expmask for all non-leaf rcu_node structures. */ 901 rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) { 902 raw_spin_lock_irqsave(&rnp->lock, flags); 903 smp_mb__after_unlock_lock(); 904 rnp->expmask = rnp->qsmaskinit; 905 raw_spin_unlock_irqrestore(&rnp->lock, flags); 906 } 907 908 /* Snapshot current state of ->blkd_tasks lists. */ 909 rcu_for_each_leaf_node(rsp, rnp) 910 sync_rcu_preempt_exp_init(rsp, rnp); 911 if (NUM_RCU_NODES > 1) 912 sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp)); 913 914 put_online_cpus(); 915 916 /* Wait for snapshotted ->blkd_tasks lists to drain. */ 917 rnp = rcu_get_root(rsp); 918 wait_event(sync_rcu_preempt_exp_wq, 919 sync_rcu_preempt_exp_done(rnp)); 920 921 /* Clean up and exit. */ 922 smp_mb(); /* ensure expedited GP seen before counter increment. */ 923 ACCESS_ONCE(sync_rcu_preempt_exp_count)++; 924unlock_mb_ret: 925 mutex_unlock(&sync_rcu_preempt_exp_mutex); 926mb_ret: 927 smp_mb(); /* ensure subsequent action seen after grace period. */ 928} 929EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); 930 931/** 932 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. 933 * 934 * Note that this primitive does not necessarily wait for an RCU grace period 935 * to complete. For example, if there are no RCU callbacks queued anywhere 936 * in the system, then rcu_barrier() is within its rights to return 937 * immediately, without waiting for anything, much less an RCU grace period. 938 */ 939void rcu_barrier(void) 940{ 941 _rcu_barrier(&rcu_preempt_state); 942} 943EXPORT_SYMBOL_GPL(rcu_barrier); 944 945/* 946 * Initialize preemptible RCU's state structures. 947 */ 948static void __init __rcu_init_preempt(void) 949{ 950 rcu_init_one(&rcu_preempt_state, &rcu_preempt_data); 951} 952 953/* 954 * Check for a task exiting while in a preemptible-RCU read-side 955 * critical section, clean up if so. No need to issue warnings, 956 * as debug_check_no_locks_held() already does this if lockdep 957 * is enabled. 958 */ 959void exit_rcu(void) 960{ 961 struct task_struct *t = current; 962 963 if (likely(list_empty(¤t->rcu_node_entry))) 964 return; 965 t->rcu_read_lock_nesting = 1; 966 barrier(); 967 t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED; 968 __rcu_read_unlock(); 969} 970 971#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ 972 973static struct rcu_state *rcu_state = &rcu_sched_state; 974 975/* 976 * Tell them what RCU they are running. 977 */ 978static void __init rcu_bootup_announce(void) 979{ 980 pr_info("Hierarchical RCU implementation.\n"); 981 rcu_bootup_announce_oddness(); 982} 983 984/* 985 * Return the number of RCU batches processed thus far for debug & stats. 986 */ 987long rcu_batches_completed(void) 988{ 989 return rcu_batches_completed_sched(); 990} 991EXPORT_SYMBOL_GPL(rcu_batches_completed); 992 993/* 994 * Force a quiescent state for RCU, which, because there is no preemptible 995 * RCU, becomes the same as rcu-sched. 996 */ 997void rcu_force_quiescent_state(void) 998{ 999 rcu_sched_force_quiescent_state(); 1000} 1001EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); 1002 1003/* 1004 * Because preemptible RCU does not exist, we never have to check for 1005 * CPUs being in quiescent states. 1006 */ 1007static void rcu_preempt_note_context_switch(int cpu) 1008{ 1009} 1010 1011/* 1012 * Because preemptible RCU does not exist, there are never any preempted 1013 * RCU readers. 1014 */ 1015static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) 1016{ 1017 return 0; 1018} 1019 1020#ifdef CONFIG_HOTPLUG_CPU 1021 1022/* Because preemptible RCU does not exist, no quieting of tasks. */ 1023static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) 1024{ 1025 raw_spin_unlock_irqrestore(&rnp->lock, flags); 1026} 1027 1028#endif /* #ifdef CONFIG_HOTPLUG_CPU */ 1029 1030/* 1031 * Because preemptible RCU does not exist, we never have to check for 1032 * tasks blocked within RCU read-side critical sections. 1033 */ 1034static void rcu_print_detail_task_stall(struct rcu_state *rsp) 1035{ 1036} 1037 1038/* 1039 * Because preemptible RCU does not exist, we never have to check for 1040 * tasks blocked within RCU read-side critical sections. 1041 */ 1042static int rcu_print_task_stall(struct rcu_node *rnp) 1043{ 1044 return 0; 1045} 1046 1047/* 1048 * Because there is no preemptible RCU, there can be no readers blocked, 1049 * so there is no need to check for blocked tasks. So check only for 1050 * bogus qsmask values. 1051 */ 1052static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) 1053{ 1054 WARN_ON_ONCE(rnp->qsmask); 1055} 1056 1057#ifdef CONFIG_HOTPLUG_CPU 1058 1059/* 1060 * Because preemptible RCU does not exist, it never needs to migrate 1061 * tasks that were blocked within RCU read-side critical sections, and 1062 * such non-existent tasks cannot possibly have been blocking the current 1063 * grace period. 1064 */ 1065static int rcu_preempt_offline_tasks(struct rcu_state *rsp, 1066 struct rcu_node *rnp, 1067 struct rcu_data *rdp) 1068{ 1069 return 0; 1070} 1071 1072#endif /* #ifdef CONFIG_HOTPLUG_CPU */ 1073 1074/* 1075 * Because preemptible RCU does not exist, it never has any callbacks 1076 * to check. 1077 */ 1078static void rcu_preempt_check_callbacks(int cpu) 1079{ 1080} 1081 1082/* 1083 * Queue an RCU callback for lazy invocation after a grace period. 1084 * This will likely be later named something like "call_rcu_lazy()", 1085 * but this change will require some way of tagging the lazy RCU 1086 * callbacks in the list of pending callbacks. Until then, this 1087 * function may only be called from __kfree_rcu(). 1088 * 1089 * Because there is no preemptible RCU, we use RCU-sched instead. 1090 */ 1091void kfree_call_rcu(struct rcu_head *head, 1092 void (*func)(struct rcu_head *rcu)) 1093{ 1094 __call_rcu(head, func, &rcu_sched_state, -1, 1); 1095} 1096EXPORT_SYMBOL_GPL(kfree_call_rcu); 1097 1098/* 1099 * Wait for an rcu-preempt grace period, but make it happen quickly. 1100 * But because preemptible RCU does not exist, map to rcu-sched. 1101 */ 1102void synchronize_rcu_expedited(void) 1103{ 1104 synchronize_sched_expedited(); 1105} 1106EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); 1107 1108#ifdef CONFIG_HOTPLUG_CPU 1109 1110/* 1111 * Because preemptible RCU does not exist, there is never any need to 1112 * report on tasks preempted in RCU read-side critical sections during 1113 * expedited RCU grace periods. 1114 */ 1115static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, 1116 bool wake) 1117{ 1118} 1119 1120#endif /* #ifdef CONFIG_HOTPLUG_CPU */ 1121 1122/* 1123 * Because preemptible RCU does not exist, rcu_barrier() is just 1124 * another name for rcu_barrier_sched(). 1125 */ 1126void rcu_barrier(void) 1127{ 1128 rcu_barrier_sched(); 1129} 1130EXPORT_SYMBOL_GPL(rcu_barrier); 1131 1132/* 1133 * Because preemptible RCU does not exist, it need not be initialized. 1134 */ 1135static void __init __rcu_init_preempt(void) 1136{ 1137} 1138 1139/* 1140 * Because preemptible RCU does not exist, tasks cannot possibly exit 1141 * while in preemptible RCU read-side critical sections. 1142 */ 1143void exit_rcu(void) 1144{ 1145} 1146 1147#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ 1148 1149#ifdef CONFIG_RCU_BOOST 1150 1151#include "../locking/rtmutex_common.h" 1152 1153#ifdef CONFIG_RCU_TRACE 1154 1155static void rcu_initiate_boost_trace(struct rcu_node *rnp) 1156{ 1157 if (list_empty(&rnp->blkd_tasks)) 1158 rnp->n_balk_blkd_tasks++; 1159 else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL) 1160 rnp->n_balk_exp_gp_tasks++; 1161 else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL) 1162 rnp->n_balk_boost_tasks++; 1163 else if (rnp->gp_tasks != NULL && rnp->qsmask != 0) 1164 rnp->n_balk_notblocked++; 1165 else if (rnp->gp_tasks != NULL && 1166 ULONG_CMP_LT(jiffies, rnp->boost_time)) 1167 rnp->n_balk_notyet++; 1168 else 1169 rnp->n_balk_nos++; 1170} 1171 1172#else /* #ifdef CONFIG_RCU_TRACE */ 1173 1174static void rcu_initiate_boost_trace(struct rcu_node *rnp) 1175{ 1176} 1177 1178#endif /* #else #ifdef CONFIG_RCU_TRACE */ 1179 1180static void rcu_wake_cond(struct task_struct *t, int status) 1181{ 1182 /* 1183 * If the thread is yielding, only wake it when this 1184 * is invoked from idle 1185 */ 1186 if (status != RCU_KTHREAD_YIELDING || is_idle_task(current)) 1187 wake_up_process(t); 1188} 1189 1190/* 1191 * Carry out RCU priority boosting on the task indicated by ->exp_tasks 1192 * or ->boost_tasks, advancing the pointer to the next task in the 1193 * ->blkd_tasks list. 1194 * 1195 * Note that irqs must be enabled: boosting the task can block. 1196 * Returns 1 if there are more tasks needing to be boosted. 1197 */ 1198static int rcu_boost(struct rcu_node *rnp) 1199{ 1200 unsigned long flags; 1201 struct rt_mutex mtx; 1202 struct task_struct *t; 1203 struct list_head *tb; 1204 1205 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) 1206 return 0; /* Nothing left to boost. */ 1207 1208 raw_spin_lock_irqsave(&rnp->lock, flags); 1209 smp_mb__after_unlock_lock(); 1210 1211 /* 1212 * Recheck under the lock: all tasks in need of boosting 1213 * might exit their RCU read-side critical sections on their own. 1214 */ 1215 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) { 1216 raw_spin_unlock_irqrestore(&rnp->lock, flags); 1217 return 0; 1218 } 1219 1220 /* 1221 * Preferentially boost tasks blocking expedited grace periods. 1222 * This cannot starve the normal grace periods because a second 1223 * expedited grace period must boost all blocked tasks, including 1224 * those blocking the pre-existing normal grace period. 1225 */ 1226 if (rnp->exp_tasks != NULL) { 1227 tb = rnp->exp_tasks; 1228 rnp->n_exp_boosts++; 1229 } else { 1230 tb = rnp->boost_tasks; 1231 rnp->n_normal_boosts++; 1232 } 1233 rnp->n_tasks_boosted++; 1234 1235 /* 1236 * We boost task t by manufacturing an rt_mutex that appears to 1237 * be held by task t. We leave a pointer to that rt_mutex where 1238 * task t can find it, and task t will release the mutex when it 1239 * exits its outermost RCU read-side critical section. Then 1240 * simply acquiring this artificial rt_mutex will boost task 1241 * t's priority. (Thanks to tglx for suggesting this approach!) 1242 * 1243 * Note that task t must acquire rnp->lock to remove itself from 1244 * the ->blkd_tasks list, which it will do from exit() if from 1245 * nowhere else. We therefore are guaranteed that task t will 1246 * stay around at least until we drop rnp->lock. Note that 1247 * rnp->lock also resolves races between our priority boosting 1248 * and task t's exiting its outermost RCU read-side critical 1249 * section. 1250 */ 1251 t = container_of(tb, struct task_struct, rcu_node_entry); 1252 rt_mutex_init_proxy_locked(&mtx, t); 1253 t->rcu_boost_mutex = &mtx; 1254 raw_spin_unlock_irqrestore(&rnp->lock, flags); 1255 rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */ 1256 rt_mutex_unlock(&mtx); /* Keep lockdep happy. */ 1257 1258 return ACCESS_ONCE(rnp->exp_tasks) != NULL || 1259 ACCESS_ONCE(rnp->boost_tasks) != NULL; 1260} 1261 1262/* 1263 * Priority-boosting kthread. One per leaf rcu_node and one for the 1264 * root rcu_node. 1265 */ 1266static int rcu_boost_kthread(void *arg) 1267{ 1268 struct rcu_node *rnp = (struct rcu_node *)arg; 1269 int spincnt = 0; 1270 int more2boost; 1271 1272 trace_rcu_utilization(TPS("Start boost kthread@init")); 1273 for (;;) { 1274 rnp->boost_kthread_status = RCU_KTHREAD_WAITING; 1275 trace_rcu_utilization(TPS("End boost kthread@rcu_wait")); 1276 rcu_wait(rnp->boost_tasks || rnp->exp_tasks); 1277 trace_rcu_utilization(TPS("Start boost kthread@rcu_wait")); 1278 rnp->boost_kthread_status = RCU_KTHREAD_RUNNING; 1279 more2boost = rcu_boost(rnp); 1280 if (more2boost) 1281 spincnt++; 1282 else 1283 spincnt = 0; 1284 if (spincnt > 10) { 1285 rnp->boost_kthread_status = RCU_KTHREAD_YIELDING; 1286 trace_rcu_utilization(TPS("End boost kthread@rcu_yield")); 1287 schedule_timeout_interruptible(2); 1288 trace_rcu_utilization(TPS("Start boost kthread@rcu_yield")); 1289 spincnt = 0; 1290 } 1291 } 1292 /* NOTREACHED */ 1293 trace_rcu_utilization(TPS("End boost kthread@notreached")); 1294 return 0; 1295} 1296 1297/* 1298 * Check to see if it is time to start boosting RCU readers that are 1299 * blocking the current grace period, and, if so, tell the per-rcu_node 1300 * kthread to start boosting them. If there is an expedited grace 1301 * period in progress, it is always time to boost. 1302 * 1303 * The caller must hold rnp->lock, which this function releases. 1304 * The ->boost_kthread_task is immortal, so we don't need to worry 1305 * about it going away. 1306 */ 1307static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) 1308{ 1309 struct task_struct *t; 1310 1311 if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) { 1312 rnp->n_balk_exp_gp_tasks++; 1313 raw_spin_unlock_irqrestore(&rnp->lock, flags); 1314 return; 1315 } 1316 if (rnp->exp_tasks != NULL || 1317 (rnp->gp_tasks != NULL && 1318 rnp->boost_tasks == NULL && 1319 rnp->qsmask == 0 && 1320 ULONG_CMP_GE(jiffies, rnp->boost_time))) { 1321 if (rnp->exp_tasks == NULL) 1322 rnp->boost_tasks = rnp->gp_tasks; 1323 raw_spin_unlock_irqrestore(&rnp->lock, flags); 1324 t = rnp->boost_kthread_task; 1325 if (t) 1326 rcu_wake_cond(t, rnp->boost_kthread_status); 1327 } else { 1328 rcu_initiate_boost_trace(rnp); 1329 raw_spin_unlock_irqrestore(&rnp->lock, flags); 1330 } 1331} 1332 1333/* 1334 * Wake up the per-CPU kthread to invoke RCU callbacks. 1335 */ 1336static void invoke_rcu_callbacks_kthread(void) 1337{ 1338 unsigned long flags; 1339 1340 local_irq_save(flags); 1341 __this_cpu_write(rcu_cpu_has_work, 1); 1342 if (__this_cpu_read(rcu_cpu_kthread_task) != NULL && 1343 current != __this_cpu_read(rcu_cpu_kthread_task)) { 1344 rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task), 1345 __this_cpu_read(rcu_cpu_kthread_status)); 1346 } 1347 local_irq_restore(flags); 1348} 1349 1350/* 1351 * Is the current CPU running the RCU-callbacks kthread? 1352 * Caller must have preemption disabled. 1353 */ 1354static bool rcu_is_callbacks_kthread(void) 1355{ 1356 return __this_cpu_read(rcu_cpu_kthread_task) == current; 1357} 1358 1359#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) 1360 1361/* 1362 * Do priority-boost accounting for the start of a new grace period. 1363 */ 1364static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) 1365{ 1366 rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; 1367} 1368 1369/* 1370 * Create an RCU-boost kthread for the specified node if one does not 1371 * already exist. We only create this kthread for preemptible RCU. 1372 * Returns zero if all is well, a negated errno otherwise. 1373 */ 1374static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp, 1375 struct rcu_node *rnp) 1376{ 1377 int rnp_index = rnp - &rsp->node[0]; 1378 unsigned long flags; 1379 struct sched_param sp; 1380 struct task_struct *t; 1381 1382 if (&rcu_preempt_state != rsp) 1383 return 0; 1384 1385 if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0) 1386 return 0; 1387 1388 rsp->boost = 1; 1389 if (rnp->boost_kthread_task != NULL) 1390 return 0; 1391 t = kthread_create(rcu_boost_kthread, (void *)rnp, 1392 "rcub/%d", rnp_index); 1393 if (IS_ERR(t)) 1394 return PTR_ERR(t); 1395 raw_spin_lock_irqsave(&rnp->lock, flags); 1396 smp_mb__after_unlock_lock(); 1397 rnp->boost_kthread_task = t; 1398 raw_spin_unlock_irqrestore(&rnp->lock, flags); 1399 sp.sched_priority = RCU_BOOST_PRIO; 1400 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); 1401 wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ 1402 return 0; 1403} 1404 1405static void rcu_kthread_do_work(void) 1406{ 1407 rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data)); 1408 rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data)); 1409 rcu_preempt_do_callbacks(); 1410} 1411 1412static void rcu_cpu_kthread_setup(unsigned int cpu) 1413{ 1414 struct sched_param sp; 1415 1416 sp.sched_priority = RCU_KTHREAD_PRIO; 1417 sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); 1418} 1419 1420static void rcu_cpu_kthread_park(unsigned int cpu) 1421{ 1422 per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; 1423} 1424 1425static int rcu_cpu_kthread_should_run(unsigned int cpu) 1426{ 1427 return __this_cpu_read(rcu_cpu_has_work); 1428} 1429 1430/* 1431 * Per-CPU kernel thread that invokes RCU callbacks. This replaces the 1432 * RCU softirq used in flavors and configurations of RCU that do not 1433 * support RCU priority boosting. 1434 */ 1435static void rcu_cpu_kthread(unsigned int cpu) 1436{ 1437 unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status); 1438 char work, *workp = this_cpu_ptr(&rcu_cpu_has_work); 1439 int spincnt; 1440 1441 for (spincnt = 0; spincnt < 10; spincnt++) { 1442 trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait")); 1443 local_bh_disable(); 1444 *statusp = RCU_KTHREAD_RUNNING; 1445 this_cpu_inc(rcu_cpu_kthread_loops); 1446 local_irq_disable(); 1447 work = *workp; 1448 *workp = 0; 1449 local_irq_enable(); 1450 if (work) 1451 rcu_kthread_do_work(); 1452 local_bh_enable(); 1453 if (*workp == 0) { 1454 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait")); 1455 *statusp = RCU_KTHREAD_WAITING; 1456 return; 1457 } 1458 } 1459 *statusp = RCU_KTHREAD_YIELDING; 1460 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield")); 1461 schedule_timeout_interruptible(2); 1462 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield")); 1463 *statusp = RCU_KTHREAD_WAITING; 1464} 1465 1466/* 1467 * Set the per-rcu_node kthread's affinity to cover all CPUs that are 1468 * served by the rcu_node in question. The CPU hotplug lock is still 1469 * held, so the value of rnp->qsmaskinit will be stable. 1470 * 1471 * We don't include outgoingcpu in the affinity set, use -1 if there is 1472 * no outgoing CPU. If there are no CPUs left in the affinity set, 1473 * this function allows the kthread to execute on any CPU. 1474 */ 1475static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) 1476{ 1477 struct task_struct *t = rnp->boost_kthread_task; 1478 unsigned long mask = rnp->qsmaskinit; 1479 cpumask_var_t cm; 1480 int cpu; 1481 1482 if (!t) 1483 return; 1484 if (!zalloc_cpumask_var(&cm, GFP_KERNEL)) 1485 return; 1486 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) 1487 if ((mask & 0x1) && cpu != outgoingcpu) 1488 cpumask_set_cpu(cpu, cm); 1489 if (cpumask_weight(cm) == 0) { 1490 cpumask_setall(cm); 1491 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) 1492 cpumask_clear_cpu(cpu, cm); 1493 WARN_ON_ONCE(cpumask_weight(cm) == 0); 1494 } 1495 set_cpus_allowed_ptr(t, cm); 1496 free_cpumask_var(cm); 1497} 1498 1499static struct smp_hotplug_thread rcu_cpu_thread_spec = { 1500 .store = &rcu_cpu_kthread_task, 1501 .thread_should_run = rcu_cpu_kthread_should_run, 1502 .thread_fn = rcu_cpu_kthread, 1503 .thread_comm = "rcuc/%u", 1504 .setup = rcu_cpu_kthread_setup, 1505 .park = rcu_cpu_kthread_park, 1506}; 1507 1508/* 1509 * Spawn all kthreads -- called as soon as the scheduler is running. 1510 */ 1511static int __init rcu_spawn_kthreads(void) 1512{ 1513 struct rcu_node *rnp; 1514 int cpu; 1515 1516 rcu_scheduler_fully_active = 1; 1517 for_each_possible_cpu(cpu) 1518 per_cpu(rcu_cpu_has_work, cpu) = 0; 1519 BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec)); 1520 rnp = rcu_get_root(rcu_state); 1521 (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); 1522 if (NUM_RCU_NODES > 1) { 1523 rcu_for_each_leaf_node(rcu_state, rnp) 1524 (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); 1525 } 1526 return 0; 1527} 1528early_initcall(rcu_spawn_kthreads); 1529 1530static void rcu_prepare_kthreads(int cpu) 1531{ 1532 struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu); 1533 struct rcu_node *rnp = rdp->mynode; 1534 1535 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */ 1536 if (rcu_scheduler_fully_active) 1537 (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); 1538} 1539 1540#else /* #ifdef CONFIG_RCU_BOOST */ 1541 1542static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) 1543{ 1544 raw_spin_unlock_irqrestore(&rnp->lock, flags); 1545} 1546 1547static void invoke_rcu_callbacks_kthread(void) 1548{ 1549 WARN_ON_ONCE(1); 1550} 1551 1552static bool rcu_is_callbacks_kthread(void) 1553{ 1554 return false; 1555} 1556 1557static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) 1558{ 1559} 1560 1561static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) 1562{ 1563} 1564 1565static int __init rcu_scheduler_really_started(void) 1566{ 1567 rcu_scheduler_fully_active = 1; 1568 return 0; 1569} 1570early_initcall(rcu_scheduler_really_started); 1571 1572static void rcu_prepare_kthreads(int cpu) 1573{ 1574} 1575 1576#endif /* #else #ifdef CONFIG_RCU_BOOST */ 1577 1578#if !defined(CONFIG_RCU_FAST_NO_HZ) 1579 1580/* 1581 * Check to see if any future RCU-related work will need to be done 1582 * by the current CPU, even if none need be done immediately, returning 1583 * 1 if so. This function is part of the RCU implementation; it is -not- 1584 * an exported member of the RCU API. 1585 * 1586 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs 1587 * any flavor of RCU. 1588 */ 1589int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies) 1590{ 1591 *delta_jiffies = ULONG_MAX; 1592 return rcu_cpu_has_callbacks(cpu, NULL); 1593} 1594 1595/* 1596 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up 1597 * after it. 1598 */ 1599static void rcu_cleanup_after_idle(int cpu) 1600{ 1601} 1602 1603/* 1604 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n, 1605 * is nothing. 1606 */ 1607static void rcu_prepare_for_idle(int cpu) 1608{ 1609} 1610 1611/* 1612 * Don't bother keeping a running count of the number of RCU callbacks 1613 * posted because CONFIG_RCU_FAST_NO_HZ=n. 1614 */ 1615static void rcu_idle_count_callbacks_posted(void) 1616{ 1617} 1618 1619#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ 1620 1621/* 1622 * This code is invoked when a CPU goes idle, at which point we want 1623 * to have the CPU do everything required for RCU so that it can enter 1624 * the energy-efficient dyntick-idle mode. This is handled by a 1625 * state machine implemented by rcu_prepare_for_idle() below. 1626 * 1627 * The following three proprocessor symbols control this state machine: 1628 * 1629 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted 1630 * to sleep in dyntick-idle mode with RCU callbacks pending. This 1631 * is sized to be roughly one RCU grace period. Those energy-efficiency 1632 * benchmarkers who might otherwise be tempted to set this to a large 1633 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your 1634 * system. And if you are -that- concerned about energy efficiency, 1635 * just power the system down and be done with it! 1636 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is 1637 * permitted to sleep in dyntick-idle mode with only lazy RCU 1638 * callbacks pending. Setting this too high can OOM your system. 1639 * 1640 * The values below work well in practice. If future workloads require 1641 * adjustment, they can be converted into kernel config parameters, though 1642 * making the state machine smarter might be a better option. 1643 */ 1644#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */ 1645#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */ 1646 1647static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY; 1648module_param(rcu_idle_gp_delay, int, 0644); 1649static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY; 1650module_param(rcu_idle_lazy_gp_delay, int, 0644); 1651 1652extern int tick_nohz_active; 1653 1654/* 1655 * Try to advance callbacks for all flavors of RCU on the current CPU, but 1656 * only if it has been awhile since the last time we did so. Afterwards, 1657 * if there are any callbacks ready for immediate invocation, return true. 1658 */ 1659static bool rcu_try_advance_all_cbs(void) 1660{ 1661 bool cbs_ready = false; 1662 struct rcu_data *rdp; 1663 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); 1664 struct rcu_node *rnp; 1665 struct rcu_state *rsp; 1666 1667 /* Exit early if we advanced recently. */ 1668 if (jiffies == rdtp->last_advance_all) 1669 return 0; 1670 rdtp->last_advance_all = jiffies; 1671 1672 for_each_rcu_flavor(rsp) { 1673 rdp = this_cpu_ptr(rsp->rda); 1674 rnp = rdp->mynode; 1675 1676 /* 1677 * Don't bother checking unless a grace period has 1678 * completed since we last checked and there are 1679 * callbacks not yet ready to invoke. 1680 */ 1681 if (rdp->completed != rnp->completed && 1682 rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL]) 1683 note_gp_changes(rsp, rdp); 1684 1685 if (cpu_has_callbacks_ready_to_invoke(rdp)) 1686 cbs_ready = true; 1687 } 1688 return cbs_ready; 1689} 1690 1691/* 1692 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready 1693 * to invoke. If the CPU has callbacks, try to advance them. Tell the 1694 * caller to set the timeout based on whether or not there are non-lazy 1695 * callbacks. 1696 * 1697 * The caller must have disabled interrupts. 1698 */ 1699int rcu_needs_cpu(int cpu, unsigned long *dj) 1700{ 1701 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); 1702 1703 /* Snapshot to detect later posting of non-lazy callback. */ 1704 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; 1705 1706 /* If no callbacks, RCU doesn't need the CPU. */ 1707 if (!rcu_cpu_has_callbacks(cpu, &rdtp->all_lazy)) { 1708 *dj = ULONG_MAX; 1709 return 0; 1710 } 1711 1712 /* Attempt to advance callbacks. */ 1713 if (rcu_try_advance_all_cbs()) { 1714 /* Some ready to invoke, so initiate later invocation. */ 1715 invoke_rcu_core(); 1716 return 1; 1717 } 1718 rdtp->last_accelerate = jiffies; 1719 1720 /* Request timer delay depending on laziness, and round. */ 1721 if (!rdtp->all_lazy) { 1722 *dj = round_up(rcu_idle_gp_delay + jiffies, 1723 rcu_idle_gp_delay) - jiffies; 1724 } else { 1725 *dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies; 1726 } 1727 return 0; 1728} 1729 1730/* 1731 * Prepare a CPU for idle from an RCU perspective. The first major task 1732 * is to sense whether nohz mode has been enabled or disabled via sysfs. 1733 * The second major task is to check to see if a non-lazy callback has 1734 * arrived at a CPU that previously had only lazy callbacks. The third 1735 * major task is to accelerate (that is, assign grace-period numbers to) 1736 * any recently arrived callbacks. 1737 * 1738 * The caller must have disabled interrupts. 1739 */ 1740static void rcu_prepare_for_idle(int cpu) 1741{ 1742 struct rcu_data *rdp; 1743 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); 1744 struct rcu_node *rnp; 1745 struct rcu_state *rsp; 1746 int tne; 1747 1748 /* Handle nohz enablement switches conservatively. */ 1749 tne = ACCESS_ONCE(tick_nohz_active); 1750 if (tne != rdtp->tick_nohz_enabled_snap) { 1751 if (rcu_cpu_has_callbacks(cpu, NULL)) 1752 invoke_rcu_core(); /* force nohz to see update. */ 1753 rdtp->tick_nohz_enabled_snap = tne; 1754 return; 1755 } 1756 if (!tne) 1757 return; 1758 1759 /* If this is a no-CBs CPU, no callbacks, just return. */ 1760 if (rcu_is_nocb_cpu(cpu)) 1761 return; 1762 1763 /* 1764 * If a non-lazy callback arrived at a CPU having only lazy 1765 * callbacks, invoke RCU core for the side-effect of recalculating 1766 * idle duration on re-entry to idle. 1767 */ 1768 if (rdtp->all_lazy && 1769 rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) { 1770 rdtp->all_lazy = false; 1771 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; 1772 invoke_rcu_core(); 1773 return; 1774 } 1775 1776 /* 1777 * If we have not yet accelerated this jiffy, accelerate all 1778 * callbacks on this CPU. 1779 */ 1780 if (rdtp->last_accelerate == jiffies) 1781 return; 1782 rdtp->last_accelerate = jiffies; 1783 for_each_rcu_flavor(rsp) { 1784 rdp = per_cpu_ptr(rsp->rda, cpu); 1785 if (!*rdp->nxttail[RCU_DONE_TAIL]) 1786 continue; 1787 rnp = rdp->mynode; 1788 raw_spin_lock(&rnp->lock); /* irqs already disabled. */ 1789 smp_mb__after_unlock_lock(); 1790 rcu_accelerate_cbs(rsp, rnp, rdp); 1791 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ 1792 } 1793} 1794 1795/* 1796 * Clean up for exit from idle. Attempt to advance callbacks based on 1797 * any grace periods that elapsed while the CPU was idle, and if any 1798 * callbacks are now ready to invoke, initiate invocation. 1799 */ 1800static void rcu_cleanup_after_idle(int cpu) 1801{ 1802 1803 if (rcu_is_nocb_cpu(cpu)) 1804 return; 1805 if (rcu_try_advance_all_cbs()) 1806 invoke_rcu_core(); 1807} 1808 1809/* 1810 * Keep a running count of the number of non-lazy callbacks posted 1811 * on this CPU. This running counter (which is never decremented) allows 1812 * rcu_prepare_for_idle() to detect when something out of the idle loop 1813 * posts a callback, even if an equal number of callbacks are invoked. 1814 * Of course, callbacks should only be posted from within a trace event 1815 * designed to be called from idle or from within RCU_NONIDLE(). 1816 */ 1817static void rcu_idle_count_callbacks_posted(void) 1818{ 1819 __this_cpu_add(rcu_dynticks.nonlazy_posted, 1); 1820} 1821 1822/* 1823 * Data for flushing lazy RCU callbacks at OOM time. 1824 */ 1825static atomic_t oom_callback_count; 1826static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq); 1827 1828/* 1829 * RCU OOM callback -- decrement the outstanding count and deliver the 1830 * wake-up if we are the last one. 1831 */ 1832static void rcu_oom_callback(struct rcu_head *rhp) 1833{ 1834 if (atomic_dec_and_test(&oom_callback_count)) 1835 wake_up(&oom_callback_wq); 1836} 1837 1838/* 1839 * Post an rcu_oom_notify callback on the current CPU if it has at 1840 * least one lazy callback. This will unnecessarily post callbacks 1841 * to CPUs that already have a non-lazy callback at the end of their 1842 * callback list, but this is an infrequent operation, so accept some 1843 * extra overhead to keep things simple. 1844 */ 1845static void rcu_oom_notify_cpu(void *unused) 1846{ 1847 struct rcu_state *rsp; 1848 struct rcu_data *rdp; 1849 1850 for_each_rcu_flavor(rsp) { 1851 rdp = __this_cpu_ptr(rsp->rda); 1852 if (rdp->qlen_lazy != 0) { 1853 atomic_inc(&oom_callback_count); 1854 rsp->call(&rdp->oom_head, rcu_oom_callback); 1855 } 1856 } 1857} 1858 1859/* 1860 * If low on memory, ensure that each CPU has a non-lazy callback. 1861 * This will wake up CPUs that have only lazy callbacks, in turn 1862 * ensuring that they free up the corresponding memory in a timely manner. 1863 * Because an uncertain amount of memory will be freed in some uncertain 1864 * timeframe, we do not claim to have freed anything. 1865 */ 1866static int rcu_oom_notify(struct notifier_block *self, 1867 unsigned long notused, void *nfreed) 1868{ 1869 int cpu; 1870 1871 /* Wait for callbacks from earlier instance to complete. */ 1872 wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0); 1873 smp_mb(); /* Ensure callback reuse happens after callback invocation. */ 1874 1875 /* 1876 * Prevent premature wakeup: ensure that all increments happen 1877 * before there is a chance of the counter reaching zero. 1878 */ 1879 atomic_set(&oom_callback_count, 1); 1880 1881 get_online_cpus(); 1882 for_each_online_cpu(cpu) { 1883 smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1); 1884 cond_resched(); 1885 } 1886 put_online_cpus(); 1887 1888 /* Unconditionally decrement: no need to wake ourselves up. */ 1889 atomic_dec(&oom_callback_count); 1890 1891 return NOTIFY_OK; 1892} 1893 1894static struct notifier_block rcu_oom_nb = { 1895 .notifier_call = rcu_oom_notify 1896}; 1897 1898static int __init rcu_register_oom_notifier(void) 1899{ 1900 register_oom_notifier(&rcu_oom_nb); 1901 return 0; 1902} 1903early_initcall(rcu_register_oom_notifier); 1904 1905#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ 1906 1907#ifdef CONFIG_RCU_CPU_STALL_INFO 1908 1909#ifdef CONFIG_RCU_FAST_NO_HZ 1910 1911static void print_cpu_stall_fast_no_hz(char *cp, int cpu) 1912{ 1913 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); 1914 unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap; 1915 1916 sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c", 1917 rdtp->last_accelerate & 0xffff, jiffies & 0xffff, 1918 ulong2long(nlpd), 1919 rdtp->all_lazy ? 'L' : '.', 1920 rdtp->tick_nohz_enabled_snap ? '.' : 'D'); 1921} 1922 1923#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ 1924 1925static void print_cpu_stall_fast_no_hz(char *cp, int cpu) 1926{ 1927 *cp = '\0'; 1928} 1929 1930#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */ 1931 1932/* Initiate the stall-info list. */ 1933static void print_cpu_stall_info_begin(void) 1934{ 1935 pr_cont("\n"); 1936} 1937 1938/* 1939 * Print out diagnostic information for the specified stalled CPU. 1940 * 1941 * If the specified CPU is aware of the current RCU grace period 1942 * (flavor specified by rsp), then print the number of scheduling 1943 * clock interrupts the CPU has taken during the time that it has 1944 * been aware. Otherwise, print the number of RCU grace periods 1945 * that this CPU is ignorant of, for example, "1" if the CPU was 1946 * aware of the previous grace period. 1947 * 1948 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info. 1949 */ 1950static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) 1951{ 1952 char fast_no_hz[72]; 1953 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); 1954 struct rcu_dynticks *rdtp = rdp->dynticks; 1955 char *ticks_title; 1956 unsigned long ticks_value; 1957 1958 if (rsp->gpnum == rdp->gpnum) { 1959 ticks_title = "ticks this GP"; 1960 ticks_value = rdp->ticks_this_gp; 1961 } else { 1962 ticks_title = "GPs behind"; 1963 ticks_value = rsp->gpnum - rdp->gpnum; 1964 } 1965 print_cpu_stall_fast_no_hz(fast_no_hz, cpu); 1966 pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n", 1967 cpu, ticks_value, ticks_title, 1968 atomic_read(&rdtp->dynticks) & 0xfff, 1969 rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting, 1970 rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu), 1971 fast_no_hz); 1972} 1973 1974/* Terminate the stall-info list. */ 1975static void print_cpu_stall_info_end(void) 1976{ 1977 pr_err("\t"); 1978} 1979 1980/* Zero ->ticks_this_gp for all flavors of RCU. */ 1981static void zero_cpu_stall_ticks(struct rcu_data *rdp) 1982{ 1983 rdp->ticks_this_gp = 0; 1984 rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id()); 1985} 1986 1987/* Increment ->ticks_this_gp for all flavors of RCU. */ 1988static void increment_cpu_stall_ticks(void) 1989{ 1990 struct rcu_state *rsp; 1991 1992 for_each_rcu_flavor(rsp) 1993 __this_cpu_ptr(rsp->rda)->ticks_this_gp++; 1994} 1995 1996#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */ 1997 1998static void print_cpu_stall_info_begin(void) 1999{ 2000 pr_cont(" {"); 2001} 2002 2003static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) 2004{ 2005 pr_cont(" %d", cpu); 2006} 2007 2008static void print_cpu_stall_info_end(void) 2009{ 2010 pr_cont("} "); 2011} 2012 2013static void zero_cpu_stall_ticks(struct rcu_data *rdp) 2014{ 2015} 2016 2017static void increment_cpu_stall_ticks(void) 2018{ 2019} 2020 2021#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */ 2022 2023#ifdef CONFIG_RCU_NOCB_CPU 2024 2025/* 2026 * Offload callback processing from the boot-time-specified set of CPUs 2027 * specified by rcu_nocb_mask. For each CPU in the set, there is a 2028 * kthread created that pulls the callbacks from the corresponding CPU, 2029 * waits for a grace period to elapse, and invokes the callbacks. 2030 * The no-CBs CPUs do a wake_up() on their kthread when they insert 2031 * a callback into any empty list, unless the rcu_nocb_poll boot parameter 2032 * has been specified, in which case each kthread actively polls its 2033 * CPU. (Which isn't so great for energy efficiency, but which does 2034 * reduce RCU's overhead on that CPU.) 2035 * 2036 * This is intended to be used in conjunction with Frederic Weisbecker's 2037 * adaptive-idle work, which would seriously reduce OS jitter on CPUs 2038 * running CPU-bound user-mode computations. 2039 * 2040 * Offloading of callback processing could also in theory be used as 2041 * an energy-efficiency measure because CPUs with no RCU callbacks 2042 * queued are more aggressive about entering dyntick-idle mode. 2043 */ 2044 2045 2046/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */ 2047static int __init rcu_nocb_setup(char *str) 2048{ 2049 alloc_bootmem_cpumask_var(&rcu_nocb_mask); 2050 have_rcu_nocb_mask = true; 2051 cpulist_parse(str, rcu_nocb_mask); 2052 return 1; 2053} 2054__setup("rcu_nocbs=", rcu_nocb_setup); 2055 2056static int __init parse_rcu_nocb_poll(char *arg) 2057{ 2058 rcu_nocb_poll = 1; 2059 return 0; 2060} 2061early_param("rcu_nocb_poll", parse_rcu_nocb_poll); 2062 2063/* 2064 * Do any no-CBs CPUs need another grace period? 2065 * 2066 * Interrupts must be disabled. If the caller does not hold the root 2067 * rnp_node structure's ->lock, the results are advisory only. 2068 */ 2069static int rcu_nocb_needs_gp(struct rcu_state *rsp) 2070{ 2071 struct rcu_node *rnp = rcu_get_root(rsp); 2072 2073 return rnp->need_future_gp[(ACCESS_ONCE(rnp->completed) + 1) & 0x1]; 2074} 2075 2076/* 2077 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended 2078 * grace period. 2079 */ 2080static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) 2081{ 2082 wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]); 2083} 2084 2085/* 2086 * Set the root rcu_node structure's ->need_future_gp field 2087 * based on the sum of those of all rcu_node structures. This does 2088 * double-count the root rcu_node structure's requests, but this 2089 * is necessary to handle the possibility of a rcu_nocb_kthread() 2090 * having awakened during the time that the rcu_node structures 2091 * were being updated for the end of the previous grace period. 2092 */ 2093static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) 2094{ 2095 rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq; 2096} 2097 2098static void rcu_init_one_nocb(struct rcu_node *rnp) 2099{ 2100 init_waitqueue_head(&rnp->nocb_gp_wq[0]); 2101 init_waitqueue_head(&rnp->nocb_gp_wq[1]); 2102} 2103 2104#ifndef CONFIG_RCU_NOCB_CPU_ALL 2105/* Is the specified CPU a no-CPUs CPU? */ 2106bool rcu_is_nocb_cpu(int cpu) 2107{ 2108 if (have_rcu_nocb_mask) 2109 return cpumask_test_cpu(cpu, rcu_nocb_mask); 2110 return false; 2111} 2112#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */ 2113 2114/* 2115 * Enqueue the specified string of rcu_head structures onto the specified 2116 * CPU's no-CBs lists. The CPU is specified by rdp, the head of the 2117 * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy 2118 * counts are supplied by rhcount and rhcount_lazy. 2119 * 2120 * If warranted, also wake up the kthread servicing this CPUs queues. 2121 */ 2122static void __call_rcu_nocb_enqueue(struct rcu_data *rdp, 2123 struct rcu_head *rhp, 2124 struct rcu_head **rhtp, 2125 int rhcount, int rhcount_lazy, 2126 unsigned long flags) 2127{ 2128 int len; 2129 struct rcu_head **old_rhpp; 2130 struct task_struct *t; 2131 2132 /* Enqueue the callback on the nocb list and update counts. */ 2133 old_rhpp = xchg(&rdp->nocb_tail, rhtp); 2134 ACCESS_ONCE(*old_rhpp) = rhp; 2135 atomic_long_add(rhcount, &rdp->nocb_q_count); 2136 atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy); 2137 2138 /* If we are not being polled and there is a kthread, awaken it ... */ 2139 t = ACCESS_ONCE(rdp->nocb_kthread); 2140 if (rcu_nocb_poll || !t) { 2141 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 2142 TPS("WakeNotPoll")); 2143 return; 2144 } 2145 len = atomic_long_read(&rdp->nocb_q_count); 2146 if (old_rhpp == &rdp->nocb_head) { 2147 if (!irqs_disabled_flags(flags)) { 2148 wake_up(&rdp->nocb_wq); /* ... if queue was empty ... */ 2149 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 2150 TPS("WakeEmpty")); 2151 } else { 2152 rdp->nocb_defer_wakeup = true; 2153 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 2154 TPS("WakeEmptyIsDeferred")); 2155 } 2156 rdp->qlen_last_fqs_check = 0; 2157 } else if (len > rdp->qlen_last_fqs_check + qhimark) { 2158 wake_up_process(t); /* ... or if many callbacks queued. */ 2159 rdp->qlen_last_fqs_check = LONG_MAX / 2; 2160 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeOvf")); 2161 } else { 2162 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot")); 2163 } 2164 return; 2165} 2166 2167/* 2168 * This is a helper for __call_rcu(), which invokes this when the normal 2169 * callback queue is inoperable. If this is not a no-CBs CPU, this 2170 * function returns failure back to __call_rcu(), which can complain 2171 * appropriately. 2172 * 2173 * Otherwise, this function queues the callback where the corresponding 2174 * "rcuo" kthread can find it. 2175 */ 2176static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, 2177 bool lazy, unsigned long flags) 2178{ 2179 2180 if (!rcu_is_nocb_cpu(rdp->cpu)) 2181 return 0; 2182 __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags); 2183 if (__is_kfree_rcu_offset((unsigned long)rhp->func)) 2184 trace_rcu_kfree_callback(rdp->rsp->name, rhp, 2185 (unsigned long)rhp->func, 2186 -atomic_long_read(&rdp->nocb_q_count_lazy), 2187 -atomic_long_read(&rdp->nocb_q_count)); 2188 else 2189 trace_rcu_callback(rdp->rsp->name, rhp, 2190 -atomic_long_read(&rdp->nocb_q_count_lazy), 2191 -atomic_long_read(&rdp->nocb_q_count)); 2192 return 1; 2193} 2194 2195/* 2196 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is 2197 * not a no-CBs CPU. 2198 */ 2199static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, 2200 struct rcu_data *rdp, 2201 unsigned long flags) 2202{ 2203 long ql = rsp->qlen; 2204 long qll = rsp->qlen_lazy; 2205 2206 /* If this is not a no-CBs CPU, tell the caller to do it the old way. */ 2207 if (!rcu_is_nocb_cpu(smp_processor_id())) 2208 return 0; 2209 rsp->qlen = 0; 2210 rsp->qlen_lazy = 0; 2211 2212 /* First, enqueue the donelist, if any. This preserves CB ordering. */ 2213 if (rsp->orphan_donelist != NULL) { 2214 __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist, 2215 rsp->orphan_donetail, ql, qll, flags); 2216 ql = qll = 0; 2217 rsp->orphan_donelist = NULL; 2218 rsp->orphan_donetail = &rsp->orphan_donelist; 2219 } 2220 if (rsp->orphan_nxtlist != NULL) { 2221 __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist, 2222 rsp->orphan_nxttail, ql, qll, flags); 2223 ql = qll = 0; 2224 rsp->orphan_nxtlist = NULL; 2225 rsp->orphan_nxttail = &rsp->orphan_nxtlist; 2226 } 2227 return 1; 2228} 2229 2230/* 2231 * If necessary, kick off a new grace period, and either way wait 2232 * for a subsequent grace period to complete. 2233 */ 2234static void rcu_nocb_wait_gp(struct rcu_data *rdp) 2235{ 2236 unsigned long c; 2237 bool d; 2238 unsigned long flags; 2239 struct rcu_node *rnp = rdp->mynode; 2240 2241 raw_spin_lock_irqsave(&rnp->lock, flags); 2242 smp_mb__after_unlock_lock(); 2243 c = rcu_start_future_gp(rnp, rdp); 2244 raw_spin_unlock_irqrestore(&rnp->lock, flags); 2245 2246 /* 2247 * Wait for the grace period. Do so interruptibly to avoid messing 2248 * up the load average. 2249 */ 2250 trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait")); 2251 for (;;) { 2252 wait_event_interruptible( 2253 rnp->nocb_gp_wq[c & 0x1], 2254 (d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c))); 2255 if (likely(d)) 2256 break; 2257 flush_signals(current); 2258 trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait")); 2259 } 2260 trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait")); 2261 smp_mb(); /* Ensure that CB invocation happens after GP end. */ 2262} 2263 2264/* 2265 * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes 2266 * callbacks queued by the corresponding no-CBs CPU. 2267 */ 2268static int rcu_nocb_kthread(void *arg) 2269{ 2270 int c, cl; 2271 bool firsttime = 1; 2272 struct rcu_head *list; 2273 struct rcu_head *next; 2274 struct rcu_head **tail; 2275 struct rcu_data *rdp = arg; 2276 2277 /* Each pass through this loop invokes one batch of callbacks */ 2278 for (;;) { 2279 /* If not polling, wait for next batch of callbacks. */ 2280 if (!rcu_nocb_poll) { 2281 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 2282 TPS("Sleep")); 2283 wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head); 2284 /* Memory barrier provide by xchg() below. */ 2285 } else if (firsttime) { 2286 firsttime = 0; 2287 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 2288 TPS("Poll")); 2289 } 2290 list = ACCESS_ONCE(rdp->nocb_head); 2291 if (!list) { 2292 if (!rcu_nocb_poll) 2293 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 2294 TPS("WokeEmpty")); 2295 schedule_timeout_interruptible(1); 2296 flush_signals(current); 2297 continue; 2298 } 2299 firsttime = 1; 2300 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 2301 TPS("WokeNonEmpty")); 2302 2303 /* 2304 * Extract queued callbacks, update counts, and wait 2305 * for a grace period to elapse. 2306 */ 2307 ACCESS_ONCE(rdp->nocb_head) = NULL; 2308 tail = xchg(&rdp->nocb_tail, &rdp->nocb_head); 2309 c = atomic_long_xchg(&rdp->nocb_q_count, 0); 2310 cl = atomic_long_xchg(&rdp->nocb_q_count_lazy, 0); 2311 ACCESS_ONCE(rdp->nocb_p_count) += c; 2312 ACCESS_ONCE(rdp->nocb_p_count_lazy) += cl; 2313 rcu_nocb_wait_gp(rdp); 2314 2315 /* Each pass through the following loop invokes a callback. */ 2316 trace_rcu_batch_start(rdp->rsp->name, cl, c, -1); 2317 c = cl = 0; 2318 while (list) { 2319 next = list->next; 2320 /* Wait for enqueuing to complete, if needed. */ 2321 while (next == NULL && &list->next != tail) { 2322 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 2323 TPS("WaitQueue")); 2324 schedule_timeout_interruptible(1); 2325 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 2326 TPS("WokeQueue")); 2327 next = list->next; 2328 } 2329 debug_rcu_head_unqueue(list); 2330 local_bh_disable(); 2331 if (__rcu_reclaim(rdp->rsp->name, list)) 2332 cl++; 2333 c++; 2334 local_bh_enable(); 2335 list = next; 2336 } 2337 trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1); 2338 ACCESS_ONCE(rdp->nocb_p_count) -= c; 2339 ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl; 2340 rdp->n_nocbs_invoked += c; 2341 } 2342 return 0; 2343} 2344 2345/* Is a deferred wakeup of rcu_nocb_kthread() required? */ 2346static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) 2347{ 2348 return ACCESS_ONCE(rdp->nocb_defer_wakeup); 2349} 2350 2351/* Do a deferred wakeup of rcu_nocb_kthread(). */ 2352static void do_nocb_deferred_wakeup(struct rcu_data *rdp) 2353{ 2354 if (!rcu_nocb_need_deferred_wakeup(rdp)) 2355 return; 2356 ACCESS_ONCE(rdp->nocb_defer_wakeup) = false; 2357 wake_up(&rdp->nocb_wq); 2358 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWakeEmpty")); 2359} 2360 2361/* Initialize per-rcu_data variables for no-CBs CPUs. */ 2362static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) 2363{ 2364 rdp->nocb_tail = &rdp->nocb_head; 2365 init_waitqueue_head(&rdp->nocb_wq); 2366} 2367 2368/* Create a kthread for each RCU flavor for each no-CBs CPU. */ 2369static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp) 2370{ 2371 int cpu; 2372 struct rcu_data *rdp; 2373 struct task_struct *t; 2374 2375 if (rcu_nocb_mask == NULL) 2376 return; 2377 for_each_cpu(cpu, rcu_nocb_mask) { 2378 rdp = per_cpu_ptr(rsp->rda, cpu); 2379 t = kthread_run(rcu_nocb_kthread, rdp, 2380 "rcuo%c/%d", rsp->abbr, cpu); 2381 BUG_ON(IS_ERR(t)); 2382 ACCESS_ONCE(rdp->nocb_kthread) = t; 2383 } 2384} 2385 2386/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */ 2387static bool init_nocb_callback_list(struct rcu_data *rdp) 2388{ 2389 if (rcu_nocb_mask == NULL || 2390 !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask)) 2391 return false; 2392 rdp->nxttail[RCU_NEXT_TAIL] = NULL; 2393 return true; 2394} 2395 2396#else /* #ifdef CONFIG_RCU_NOCB_CPU */ 2397 2398static int rcu_nocb_needs_gp(struct rcu_state *rsp) 2399{ 2400 return 0; 2401} 2402 2403static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) 2404{ 2405} 2406 2407static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) 2408{ 2409} 2410 2411static void rcu_init_one_nocb(struct rcu_node *rnp) 2412{ 2413} 2414 2415static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, 2416 bool lazy, unsigned long flags) 2417{ 2418 return 0; 2419} 2420 2421static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, 2422 struct rcu_data *rdp, 2423 unsigned long flags) 2424{ 2425 return 0; 2426} 2427 2428static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) 2429{ 2430} 2431 2432static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) 2433{ 2434 return false; 2435} 2436 2437static void do_nocb_deferred_wakeup(struct rcu_data *rdp) 2438{ 2439} 2440 2441static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp) 2442{ 2443} 2444 2445static bool init_nocb_callback_list(struct rcu_data *rdp) 2446{ 2447 return false; 2448} 2449 2450#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ 2451 2452/* 2453 * An adaptive-ticks CPU can potentially execute in kernel mode for an 2454 * arbitrarily long period of time with the scheduling-clock tick turned 2455 * off. RCU will be paying attention to this CPU because it is in the 2456 * kernel, but the CPU cannot be guaranteed to be executing the RCU state 2457 * machine because the scheduling-clock tick has been disabled. Therefore, 2458 * if an adaptive-ticks CPU is failing to respond to the current grace 2459 * period and has not be idle from an RCU perspective, kick it. 2460 */ 2461static void rcu_kick_nohz_cpu(int cpu) 2462{ 2463#ifdef CONFIG_NO_HZ_FULL 2464 if (tick_nohz_full_cpu(cpu)) 2465 smp_send_reschedule(cpu); 2466#endif /* #ifdef CONFIG_NO_HZ_FULL */ 2467} 2468 2469 2470#ifdef CONFIG_NO_HZ_FULL_SYSIDLE 2471 2472/* 2473 * Define RCU flavor that holds sysidle state. This needs to be the 2474 * most active flavor of RCU. 2475 */ 2476#ifdef CONFIG_PREEMPT_RCU 2477static struct rcu_state *rcu_sysidle_state = &rcu_preempt_state; 2478#else /* #ifdef CONFIG_PREEMPT_RCU */ 2479static struct rcu_state *rcu_sysidle_state = &rcu_sched_state; 2480#endif /* #else #ifdef CONFIG_PREEMPT_RCU */ 2481 2482static int full_sysidle_state; /* Current system-idle state. */ 2483#define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */ 2484#define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */ 2485#define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */ 2486#define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */ 2487#define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */ 2488 2489/* 2490 * Invoked to note exit from irq or task transition to idle. Note that 2491 * usermode execution does -not- count as idle here! After all, we want 2492 * to detect full-system idle states, not RCU quiescent states and grace 2493 * periods. The caller must have disabled interrupts. 2494 */ 2495static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq) 2496{ 2497 unsigned long j; 2498 2499 /* Adjust nesting, check for fully idle. */ 2500 if (irq) { 2501 rdtp->dynticks_idle_nesting--; 2502 WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0); 2503 if (rdtp->dynticks_idle_nesting != 0) 2504 return; /* Still not fully idle. */ 2505 } else { 2506 if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) == 2507 DYNTICK_TASK_NEST_VALUE) { 2508 rdtp->dynticks_idle_nesting = 0; 2509 } else { 2510 rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE; 2511 WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0); 2512 return; /* Still not fully idle. */ 2513 } 2514 } 2515 2516 /* Record start of fully idle period. */ 2517 j = jiffies; 2518 ACCESS_ONCE(rdtp->dynticks_idle_jiffies) = j; 2519 smp_mb__before_atomic_inc(); 2520 atomic_inc(&rdtp->dynticks_idle); 2521 smp_mb__after_atomic_inc(); 2522 WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1); 2523} 2524 2525/* 2526 * Unconditionally force exit from full system-idle state. This is 2527 * invoked when a normal CPU exits idle, but must be called separately 2528 * for the timekeeping CPU (tick_do_timer_cpu). The reason for this 2529 * is that the timekeeping CPU is permitted to take scheduling-clock 2530 * interrupts while the system is in system-idle state, and of course 2531 * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock 2532 * interrupt from any other type of interrupt. 2533 */ 2534void rcu_sysidle_force_exit(void) 2535{ 2536 int oldstate = ACCESS_ONCE(full_sysidle_state); 2537 int newoldstate; 2538 2539 /* 2540 * Each pass through the following loop attempts to exit full 2541 * system-idle state. If contention proves to be a problem, 2542 * a trylock-based contention tree could be used here. 2543 */ 2544 while (oldstate > RCU_SYSIDLE_SHORT) { 2545 newoldstate = cmpxchg(&full_sysidle_state, 2546 oldstate, RCU_SYSIDLE_NOT); 2547 if (oldstate == newoldstate && 2548 oldstate == RCU_SYSIDLE_FULL_NOTED) { 2549 rcu_kick_nohz_cpu(tick_do_timer_cpu); 2550 return; /* We cleared it, done! */ 2551 } 2552 oldstate = newoldstate; 2553 } 2554 smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */ 2555} 2556 2557/* 2558 * Invoked to note entry to irq or task transition from idle. Note that 2559 * usermode execution does -not- count as idle here! The caller must 2560 * have disabled interrupts. 2561 */ 2562static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq) 2563{ 2564 /* Adjust nesting, check for already non-idle. */ 2565 if (irq) { 2566 rdtp->dynticks_idle_nesting++; 2567 WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0); 2568 if (rdtp->dynticks_idle_nesting != 1) 2569 return; /* Already non-idle. */ 2570 } else { 2571 /* 2572 * Allow for irq misnesting. Yes, it really is possible 2573 * to enter an irq handler then never leave it, and maybe 2574 * also vice versa. Handle both possibilities. 2575 */ 2576 if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) { 2577 rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE; 2578 WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0); 2579 return; /* Already non-idle. */ 2580 } else { 2581 rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE; 2582 } 2583 } 2584 2585 /* Record end of idle period. */ 2586 smp_mb__before_atomic_inc(); 2587 atomic_inc(&rdtp->dynticks_idle); 2588 smp_mb__after_atomic_inc(); 2589 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1)); 2590 2591 /* 2592 * If we are the timekeeping CPU, we are permitted to be non-idle 2593 * during a system-idle state. This must be the case, because 2594 * the timekeeping CPU has to take scheduling-clock interrupts 2595 * during the time that the system is transitioning to full 2596 * system-idle state. This means that the timekeeping CPU must 2597 * invoke rcu_sysidle_force_exit() directly if it does anything 2598 * more than take a scheduling-clock interrupt. 2599 */ 2600 if (smp_processor_id() == tick_do_timer_cpu) 2601 return; 2602 2603 /* Update system-idle state: We are clearly no longer fully idle! */ 2604 rcu_sysidle_force_exit(); 2605} 2606 2607/* 2608 * Check to see if the current CPU is idle. Note that usermode execution 2609 * does not count as idle. The caller must have disabled interrupts. 2610 */ 2611static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, 2612 unsigned long *maxj) 2613{ 2614 int cur; 2615 unsigned long j; 2616 struct rcu_dynticks *rdtp = rdp->dynticks; 2617 2618 /* 2619 * If some other CPU has already reported non-idle, if this is 2620 * not the flavor of RCU that tracks sysidle state, or if this 2621 * is an offline or the timekeeping CPU, nothing to do. 2622 */ 2623 if (!*isidle || rdp->rsp != rcu_sysidle_state || 2624 cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu) 2625 return; 2626 if (rcu_gp_in_progress(rdp->rsp)) 2627 WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu); 2628 2629 /* Pick up current idle and NMI-nesting counter and check. */ 2630 cur = atomic_read(&rdtp->dynticks_idle); 2631 if (cur & 0x1) { 2632 *isidle = false; /* We are not idle! */ 2633 return; 2634 } 2635 smp_mb(); /* Read counters before timestamps. */ 2636 2637 /* Pick up timestamps. */ 2638 j = ACCESS_ONCE(rdtp->dynticks_idle_jiffies); 2639 /* If this CPU entered idle more recently, update maxj timestamp. */ 2640 if (ULONG_CMP_LT(*maxj, j)) 2641 *maxj = j; 2642} 2643 2644/* 2645 * Is this the flavor of RCU that is handling full-system idle? 2646 */ 2647static bool is_sysidle_rcu_state(struct rcu_state *rsp) 2648{ 2649 return rsp == rcu_sysidle_state; 2650} 2651 2652/* 2653 * Bind the grace-period kthread for the sysidle flavor of RCU to the 2654 * timekeeping CPU. 2655 */ 2656static void rcu_bind_gp_kthread(void) 2657{ 2658 int cpu = ACCESS_ONCE(tick_do_timer_cpu); 2659 2660 if (cpu < 0 || cpu >= nr_cpu_ids) 2661 return; 2662 if (raw_smp_processor_id() != cpu) 2663 set_cpus_allowed_ptr(current, cpumask_of(cpu)); 2664} 2665 2666/* 2667 * Return a delay in jiffies based on the number of CPUs, rcu_node 2668 * leaf fanout, and jiffies tick rate. The idea is to allow larger 2669 * systems more time to transition to full-idle state in order to 2670 * avoid the cache thrashing that otherwise occur on the state variable. 2671 * Really small systems (less than a couple of tens of CPUs) should 2672 * instead use a single global atomically incremented counter, and later 2673 * versions of this will automatically reconfigure themselves accordingly. 2674 */ 2675static unsigned long rcu_sysidle_delay(void) 2676{ 2677 if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) 2678 return 0; 2679 return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000); 2680} 2681 2682/* 2683 * Advance the full-system-idle state. This is invoked when all of 2684 * the non-timekeeping CPUs are idle. 2685 */ 2686static void rcu_sysidle(unsigned long j) 2687{ 2688 /* Check the current state. */ 2689 switch (ACCESS_ONCE(full_sysidle_state)) { 2690 case RCU_SYSIDLE_NOT: 2691 2692 /* First time all are idle, so note a short idle period. */ 2693 ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_SHORT; 2694 break; 2695 2696 case RCU_SYSIDLE_SHORT: 2697 2698 /* 2699 * Idle for a bit, time to advance to next state? 2700 * cmpxchg failure means race with non-idle, let them win. 2701 */ 2702 if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay())) 2703 (void)cmpxchg(&full_sysidle_state, 2704 RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG); 2705 break; 2706 2707 case RCU_SYSIDLE_LONG: 2708 2709 /* 2710 * Do an additional check pass before advancing to full. 2711 * cmpxchg failure means race with non-idle, let them win. 2712 */ 2713 if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay())) 2714 (void)cmpxchg(&full_sysidle_state, 2715 RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL); 2716 break; 2717 2718 default: 2719 break; 2720 } 2721} 2722 2723/* 2724 * Found a non-idle non-timekeeping CPU, so kick the system-idle state 2725 * back to the beginning. 2726 */ 2727static void rcu_sysidle_cancel(void) 2728{ 2729 smp_mb(); 2730 ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT; 2731} 2732 2733/* 2734 * Update the sysidle state based on the results of a force-quiescent-state 2735 * scan of the CPUs' dyntick-idle state. 2736 */ 2737static void rcu_sysidle_report(struct rcu_state *rsp, int isidle, 2738 unsigned long maxj, bool gpkt) 2739{ 2740 if (rsp != rcu_sysidle_state) 2741 return; /* Wrong flavor, ignore. */ 2742 if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) 2743 return; /* Running state machine from timekeeping CPU. */ 2744 if (isidle) 2745 rcu_sysidle(maxj); /* More idle! */ 2746 else 2747 rcu_sysidle_cancel(); /* Idle is over. */ 2748} 2749 2750/* 2751 * Wrapper for rcu_sysidle_report() when called from the grace-period 2752 * kthread's context. 2753 */ 2754static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle, 2755 unsigned long maxj) 2756{ 2757 rcu_sysidle_report(rsp, isidle, maxj, true); 2758} 2759 2760/* Callback and function for forcing an RCU grace period. */ 2761struct rcu_sysidle_head { 2762 struct rcu_head rh; 2763 int inuse; 2764}; 2765 2766static void rcu_sysidle_cb(struct rcu_head *rhp) 2767{ 2768 struct rcu_sysidle_head *rshp; 2769 2770 /* 2771 * The following memory barrier is needed to replace the 2772 * memory barriers that would normally be in the memory 2773 * allocator. 2774 */ 2775 smp_mb(); /* grace period precedes setting inuse. */ 2776 2777 rshp = container_of(rhp, struct rcu_sysidle_head, rh); 2778 ACCESS_ONCE(rshp->inuse) = 0; 2779} 2780 2781/* 2782 * Check to see if the system is fully idle, other than the timekeeping CPU. 2783 * The caller must have disabled interrupts. 2784 */ 2785bool rcu_sys_is_idle(void) 2786{ 2787 static struct rcu_sysidle_head rsh; 2788 int rss = ACCESS_ONCE(full_sysidle_state); 2789 2790 if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu)) 2791 return false; 2792 2793 /* Handle small-system case by doing a full scan of CPUs. */ 2794 if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) { 2795 int oldrss = rss - 1; 2796 2797 /* 2798 * One pass to advance to each state up to _FULL. 2799 * Give up if any pass fails to advance the state. 2800 */ 2801 while (rss < RCU_SYSIDLE_FULL && oldrss < rss) { 2802 int cpu; 2803 bool isidle = true; 2804 unsigned long maxj = jiffies - ULONG_MAX / 4; 2805 struct rcu_data *rdp; 2806 2807 /* Scan all the CPUs looking for nonidle CPUs. */ 2808 for_each_possible_cpu(cpu) { 2809 rdp = per_cpu_ptr(rcu_sysidle_state->rda, cpu); 2810 rcu_sysidle_check_cpu(rdp, &isidle, &maxj); 2811 if (!isidle) 2812 break; 2813 } 2814 rcu_sysidle_report(rcu_sysidle_state, 2815 isidle, maxj, false); 2816 oldrss = rss; 2817 rss = ACCESS_ONCE(full_sysidle_state); 2818 } 2819 } 2820 2821 /* If this is the first observation of an idle period, record it. */ 2822 if (rss == RCU_SYSIDLE_FULL) { 2823 rss = cmpxchg(&full_sysidle_state, 2824 RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED); 2825 return rss == RCU_SYSIDLE_FULL; 2826 } 2827 2828 smp_mb(); /* ensure rss load happens before later caller actions. */ 2829 2830 /* If already fully idle, tell the caller (in case of races). */ 2831 if (rss == RCU_SYSIDLE_FULL_NOTED) 2832 return true; 2833 2834 /* 2835 * If we aren't there yet, and a grace period is not in flight, 2836 * initiate a grace period. Either way, tell the caller that 2837 * we are not there yet. We use an xchg() rather than an assignment 2838 * to make up for the memory barriers that would otherwise be 2839 * provided by the memory allocator. 2840 */ 2841 if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL && 2842 !rcu_gp_in_progress(rcu_sysidle_state) && 2843 !rsh.inuse && xchg(&rsh.inuse, 1) == 0) 2844 call_rcu(&rsh.rh, rcu_sysidle_cb); 2845 return false; 2846} 2847 2848/* 2849 * Initialize dynticks sysidle state for CPUs coming online. 2850 */ 2851static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp) 2852{ 2853 rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE; 2854} 2855 2856#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ 2857 2858static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq) 2859{ 2860} 2861 2862static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq) 2863{ 2864} 2865 2866static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, 2867 unsigned long *maxj) 2868{ 2869} 2870 2871static bool is_sysidle_rcu_state(struct rcu_state *rsp) 2872{ 2873 return false; 2874} 2875 2876static void rcu_bind_gp_kthread(void) 2877{ 2878} 2879 2880static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle, 2881 unsigned long maxj) 2882{ 2883} 2884 2885static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp) 2886{ 2887} 2888 2889#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ 2890 2891/* 2892 * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the 2893 * grace-period kthread will do force_quiescent_state() processing? 2894 * The idea is to avoid waking up RCU core processing on such a 2895 * CPU unless the grace period has extended for too long. 2896 * 2897 * This code relies on the fact that all NO_HZ_FULL CPUs are also 2898 * CONFIG_RCU_NOCB_CPUs. 2899 */ 2900static bool rcu_nohz_full_cpu(struct rcu_state *rsp) 2901{ 2902#ifdef CONFIG_NO_HZ_FULL 2903 if (tick_nohz_full_cpu(smp_processor_id()) && 2904 (!rcu_gp_in_progress(rsp) || 2905 ULONG_CMP_LT(jiffies, ACCESS_ONCE(rsp->gp_start) + HZ))) 2906 return 1; 2907#endif /* #ifdef CONFIG_NO_HZ_FULL */ 2908 return 0; 2909} 2910