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, you can access it online at 18 * http://www.gnu.org/licenses/gpl-2.0.html. 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 #ifdef CONFIG_RCU_BOOST 34 35 #include "../locking/rtmutex_common.h" 36 37 /* 38 * Control variables for per-CPU and per-rcu_node kthreads. These 39 * handle all flavors of RCU. 40 */ 41 static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task); 42 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status); 43 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops); 44 DEFINE_PER_CPU(char, rcu_cpu_has_work); 45 46 #else /* #ifdef CONFIG_RCU_BOOST */ 47 48 /* 49 * Some architectures do not define rt_mutexes, but if !CONFIG_RCU_BOOST, 50 * all uses are in dead code. Provide a definition to keep the compiler 51 * happy, but add WARN_ON_ONCE() to complain if used in the wrong place. 52 * This probably needs to be excluded from -rt builds. 53 */ 54 #define rt_mutex_owner(a) ({ WARN_ON_ONCE(1); NULL; }) 55 56 #endif /* #else #ifdef CONFIG_RCU_BOOST */ 57 58 #ifdef CONFIG_RCU_NOCB_CPU 59 static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */ 60 static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */ 61 static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */ 62 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ 63 64 /* 65 * Check the RCU kernel configuration parameters and print informative 66 * messages about anything out of the ordinary. 67 */ 68 static void __init rcu_bootup_announce_oddness(void) 69 { 70 if (IS_ENABLED(CONFIG_RCU_TRACE)) 71 pr_info("\tRCU debugfs-based tracing is enabled.\n"); 72 if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) || 73 (!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32)) 74 pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n", 75 RCU_FANOUT); 76 if (rcu_fanout_exact) 77 pr_info("\tHierarchical RCU autobalancing is disabled.\n"); 78 if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ)) 79 pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n"); 80 if (IS_ENABLED(CONFIG_PROVE_RCU)) 81 pr_info("\tRCU lockdep checking is enabled.\n"); 82 if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST_RUNNABLE)) 83 pr_info("\tRCU torture testing starts during boot.\n"); 84 if (RCU_NUM_LVLS >= 4) 85 pr_info("\tFour(or more)-level hierarchy is enabled.\n"); 86 if (RCU_FANOUT_LEAF != 16) 87 pr_info("\tBuild-time adjustment of leaf fanout to %d.\n", 88 RCU_FANOUT_LEAF); 89 if (rcu_fanout_leaf != RCU_FANOUT_LEAF) 90 pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf); 91 if (nr_cpu_ids != NR_CPUS) 92 pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids); 93 if (IS_ENABLED(CONFIG_RCU_BOOST)) 94 pr_info("\tRCU kthread priority: %d.\n", kthread_prio); 95 } 96 97 #ifdef CONFIG_PREEMPT_RCU 98 99 RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu); 100 static struct rcu_state *const rcu_state_p = &rcu_preempt_state; 101 static struct rcu_data __percpu *const rcu_data_p = &rcu_preempt_data; 102 103 static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, 104 bool wake); 105 106 /* 107 * Tell them what RCU they are running. 108 */ 109 static void __init rcu_bootup_announce(void) 110 { 111 pr_info("Preemptible hierarchical RCU implementation.\n"); 112 rcu_bootup_announce_oddness(); 113 } 114 115 /* Flags for rcu_preempt_ctxt_queue() decision table. */ 116 #define RCU_GP_TASKS 0x8 117 #define RCU_EXP_TASKS 0x4 118 #define RCU_GP_BLKD 0x2 119 #define RCU_EXP_BLKD 0x1 120 121 /* 122 * Queues a task preempted within an RCU-preempt read-side critical 123 * section into the appropriate location within the ->blkd_tasks list, 124 * depending on the states of any ongoing normal and expedited grace 125 * periods. The ->gp_tasks pointer indicates which element the normal 126 * grace period is waiting on (NULL if none), and the ->exp_tasks pointer 127 * indicates which element the expedited grace period is waiting on (again, 128 * NULL if none). If a grace period is waiting on a given element in the 129 * ->blkd_tasks list, it also waits on all subsequent elements. Thus, 130 * adding a task to the tail of the list blocks any grace period that is 131 * already waiting on one of the elements. In contrast, adding a task 132 * to the head of the list won't block any grace period that is already 133 * waiting on one of the elements. 134 * 135 * This queuing is imprecise, and can sometimes make an ongoing grace 136 * period wait for a task that is not strictly speaking blocking it. 137 * Given the choice, we needlessly block a normal grace period rather than 138 * blocking an expedited grace period. 139 * 140 * Note that an endless sequence of expedited grace periods still cannot 141 * indefinitely postpone a normal grace period. Eventually, all of the 142 * fixed number of preempted tasks blocking the normal grace period that are 143 * not also blocking the expedited grace period will resume and complete 144 * their RCU read-side critical sections. At that point, the ->gp_tasks 145 * pointer will equal the ->exp_tasks pointer, at which point the end of 146 * the corresponding expedited grace period will also be the end of the 147 * normal grace period. 148 */ 149 static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp) 150 __releases(rnp->lock) /* But leaves rrupts disabled. */ 151 { 152 int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) + 153 (rnp->exp_tasks ? RCU_EXP_TASKS : 0) + 154 (rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) + 155 (rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0); 156 struct task_struct *t = current; 157 158 /* 159 * Decide where to queue the newly blocked task. In theory, 160 * this could be an if-statement. In practice, when I tried 161 * that, it was quite messy. 162 */ 163 switch (blkd_state) { 164 case 0: 165 case RCU_EXP_TASKS: 166 case RCU_EXP_TASKS + RCU_GP_BLKD: 167 case RCU_GP_TASKS: 168 case RCU_GP_TASKS + RCU_EXP_TASKS: 169 170 /* 171 * Blocking neither GP, or first task blocking the normal 172 * GP but not blocking the already-waiting expedited GP. 173 * Queue at the head of the list to avoid unnecessarily 174 * blocking the already-waiting GPs. 175 */ 176 list_add(&t->rcu_node_entry, &rnp->blkd_tasks); 177 break; 178 179 case RCU_EXP_BLKD: 180 case RCU_GP_BLKD: 181 case RCU_GP_BLKD + RCU_EXP_BLKD: 182 case RCU_GP_TASKS + RCU_EXP_BLKD: 183 case RCU_GP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD: 184 case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD: 185 186 /* 187 * First task arriving that blocks either GP, or first task 188 * arriving that blocks the expedited GP (with the normal 189 * GP already waiting), or a task arriving that blocks 190 * both GPs with both GPs already waiting. Queue at the 191 * tail of the list to avoid any GP waiting on any of the 192 * already queued tasks that are not blocking it. 193 */ 194 list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks); 195 break; 196 197 case RCU_EXP_TASKS + RCU_EXP_BLKD: 198 case RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD: 199 case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_EXP_BLKD: 200 201 /* 202 * Second or subsequent task blocking the expedited GP. 203 * The task either does not block the normal GP, or is the 204 * first task blocking the normal GP. Queue just after 205 * the first task blocking the expedited GP. 206 */ 207 list_add(&t->rcu_node_entry, rnp->exp_tasks); 208 break; 209 210 case RCU_GP_TASKS + RCU_GP_BLKD: 211 case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD: 212 213 /* 214 * Second or subsequent task blocking the normal GP. 215 * The task does not block the expedited GP. Queue just 216 * after the first task blocking the normal GP. 217 */ 218 list_add(&t->rcu_node_entry, rnp->gp_tasks); 219 break; 220 221 default: 222 223 /* Yet another exercise in excessive paranoia. */ 224 WARN_ON_ONCE(1); 225 break; 226 } 227 228 /* 229 * We have now queued the task. If it was the first one to 230 * block either grace period, update the ->gp_tasks and/or 231 * ->exp_tasks pointers, respectively, to reference the newly 232 * blocked tasks. 233 */ 234 if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD)) 235 rnp->gp_tasks = &t->rcu_node_entry; 236 if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD)) 237 rnp->exp_tasks = &t->rcu_node_entry; 238 raw_spin_unlock(&rnp->lock); /* rrupts remain disabled. */ 239 240 /* 241 * Report the quiescent state for the expedited GP. This expedited 242 * GP should not be able to end until we report, so there should be 243 * no need to check for a subsequent expedited GP. (Though we are 244 * still in a quiescent state in any case.) 245 */ 246 if (blkd_state & RCU_EXP_BLKD && 247 t->rcu_read_unlock_special.b.exp_need_qs) { 248 t->rcu_read_unlock_special.b.exp_need_qs = false; 249 rcu_report_exp_rdp(rdp->rsp, rdp, true); 250 } else { 251 WARN_ON_ONCE(t->rcu_read_unlock_special.b.exp_need_qs); 252 } 253 } 254 255 /* 256 * Record a preemptible-RCU quiescent state for the specified CPU. Note 257 * that this just means that the task currently running on the CPU is 258 * not in a quiescent state. There might be any number of tasks blocked 259 * while in an RCU read-side critical section. 260 * 261 * As with the other rcu_*_qs() functions, callers to this function 262 * must disable preemption. 263 */ 264 static void rcu_preempt_qs(void) 265 { 266 if (__this_cpu_read(rcu_data_p->cpu_no_qs.s)) { 267 trace_rcu_grace_period(TPS("rcu_preempt"), 268 __this_cpu_read(rcu_data_p->gpnum), 269 TPS("cpuqs")); 270 __this_cpu_write(rcu_data_p->cpu_no_qs.b.norm, false); 271 barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */ 272 current->rcu_read_unlock_special.b.need_qs = false; 273 } 274 } 275 276 /* 277 * We have entered the scheduler, and the current task might soon be 278 * context-switched away from. If this task is in an RCU read-side 279 * critical section, we will no longer be able to rely on the CPU to 280 * record that fact, so we enqueue the task on the blkd_tasks list. 281 * The task will dequeue itself when it exits the outermost enclosing 282 * RCU read-side critical section. Therefore, the current grace period 283 * cannot be permitted to complete until the blkd_tasks list entries 284 * predating the current grace period drain, in other words, until 285 * rnp->gp_tasks becomes NULL. 286 * 287 * Caller must disable interrupts. 288 */ 289 static void rcu_preempt_note_context_switch(void) 290 { 291 struct task_struct *t = current; 292 struct rcu_data *rdp; 293 struct rcu_node *rnp; 294 295 if (t->rcu_read_lock_nesting > 0 && 296 !t->rcu_read_unlock_special.b.blocked) { 297 298 /* Possibly blocking in an RCU read-side critical section. */ 299 rdp = this_cpu_ptr(rcu_state_p->rda); 300 rnp = rdp->mynode; 301 raw_spin_lock_rcu_node(rnp); 302 t->rcu_read_unlock_special.b.blocked = true; 303 t->rcu_blocked_node = rnp; 304 305 /* 306 * Verify the CPU's sanity, trace the preemption, and 307 * then queue the task as required based on the states 308 * of any ongoing and expedited grace periods. 309 */ 310 WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0); 311 WARN_ON_ONCE(!list_empty(&t->rcu_node_entry)); 312 trace_rcu_preempt_task(rdp->rsp->name, 313 t->pid, 314 (rnp->qsmask & rdp->grpmask) 315 ? rnp->gpnum 316 : rnp->gpnum + 1); 317 rcu_preempt_ctxt_queue(rnp, rdp); 318 } else if (t->rcu_read_lock_nesting < 0 && 319 t->rcu_read_unlock_special.s) { 320 321 /* 322 * Complete exit from RCU read-side critical section on 323 * behalf of preempted instance of __rcu_read_unlock(). 324 */ 325 rcu_read_unlock_special(t); 326 } 327 328 /* 329 * Either we were not in an RCU read-side critical section to 330 * begin with, or we have now recorded that critical section 331 * globally. Either way, we can now note a quiescent state 332 * for this CPU. Again, if we were in an RCU read-side critical 333 * section, and if that critical section was blocking the current 334 * grace period, then the fact that the task has been enqueued 335 * means that we continue to block the current grace period. 336 */ 337 rcu_preempt_qs(); 338 } 339 340 /* 341 * Check for preempted RCU readers blocking the current grace period 342 * for the specified rcu_node structure. If the caller needs a reliable 343 * answer, it must hold the rcu_node's ->lock. 344 */ 345 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) 346 { 347 return rnp->gp_tasks != NULL; 348 } 349 350 /* 351 * Advance a ->blkd_tasks-list pointer to the next entry, instead 352 * returning NULL if at the end of the list. 353 */ 354 static struct list_head *rcu_next_node_entry(struct task_struct *t, 355 struct rcu_node *rnp) 356 { 357 struct list_head *np; 358 359 np = t->rcu_node_entry.next; 360 if (np == &rnp->blkd_tasks) 361 np = NULL; 362 return np; 363 } 364 365 /* 366 * Return true if the specified rcu_node structure has tasks that were 367 * preempted within an RCU read-side critical section. 368 */ 369 static bool rcu_preempt_has_tasks(struct rcu_node *rnp) 370 { 371 return !list_empty(&rnp->blkd_tasks); 372 } 373 374 /* 375 * Handle special cases during rcu_read_unlock(), such as needing to 376 * notify RCU core processing or task having blocked during the RCU 377 * read-side critical section. 378 */ 379 void rcu_read_unlock_special(struct task_struct *t) 380 { 381 bool empty_exp; 382 bool empty_norm; 383 bool empty_exp_now; 384 unsigned long flags; 385 struct list_head *np; 386 bool drop_boost_mutex = false; 387 struct rcu_data *rdp; 388 struct rcu_node *rnp; 389 union rcu_special special; 390 391 /* NMI handlers cannot block and cannot safely manipulate state. */ 392 if (in_nmi()) 393 return; 394 395 local_irq_save(flags); 396 397 /* 398 * If RCU core is waiting for this CPU to exit its critical section, 399 * report the fact that it has exited. Because irqs are disabled, 400 * t->rcu_read_unlock_special cannot change. 401 */ 402 special = t->rcu_read_unlock_special; 403 if (special.b.need_qs) { 404 rcu_preempt_qs(); 405 t->rcu_read_unlock_special.b.need_qs = false; 406 if (!t->rcu_read_unlock_special.s) { 407 local_irq_restore(flags); 408 return; 409 } 410 } 411 412 /* 413 * Respond to a request for an expedited grace period, but only if 414 * we were not preempted, meaning that we were running on the same 415 * CPU throughout. If we were preempted, the exp_need_qs flag 416 * would have been cleared at the time of the first preemption, 417 * and the quiescent state would be reported when we were dequeued. 418 */ 419 if (special.b.exp_need_qs) { 420 WARN_ON_ONCE(special.b.blocked); 421 t->rcu_read_unlock_special.b.exp_need_qs = false; 422 rdp = this_cpu_ptr(rcu_state_p->rda); 423 rcu_report_exp_rdp(rcu_state_p, rdp, true); 424 if (!t->rcu_read_unlock_special.s) { 425 local_irq_restore(flags); 426 return; 427 } 428 } 429 430 /* Hardware IRQ handlers cannot block, complain if they get here. */ 431 if (in_irq() || in_serving_softirq()) { 432 lockdep_rcu_suspicious(__FILE__, __LINE__, 433 "rcu_read_unlock() from irq or softirq with blocking in critical section!!!\n"); 434 pr_alert("->rcu_read_unlock_special: %#x (b: %d, enq: %d nq: %d)\n", 435 t->rcu_read_unlock_special.s, 436 t->rcu_read_unlock_special.b.blocked, 437 t->rcu_read_unlock_special.b.exp_need_qs, 438 t->rcu_read_unlock_special.b.need_qs); 439 local_irq_restore(flags); 440 return; 441 } 442 443 /* Clean up if blocked during RCU read-side critical section. */ 444 if (special.b.blocked) { 445 t->rcu_read_unlock_special.b.blocked = false; 446 447 /* 448 * Remove this task from the list it blocked on. The task 449 * now remains queued on the rcu_node corresponding to the 450 * CPU it first blocked on, so there is no longer any need 451 * to loop. Retain a WARN_ON_ONCE() out of sheer paranoia. 452 */ 453 rnp = t->rcu_blocked_node; 454 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ 455 WARN_ON_ONCE(rnp != t->rcu_blocked_node); 456 empty_norm = !rcu_preempt_blocked_readers_cgp(rnp); 457 empty_exp = sync_rcu_preempt_exp_done(rnp); 458 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */ 459 np = rcu_next_node_entry(t, rnp); 460 list_del_init(&t->rcu_node_entry); 461 t->rcu_blocked_node = NULL; 462 trace_rcu_unlock_preempted_task(TPS("rcu_preempt"), 463 rnp->gpnum, t->pid); 464 if (&t->rcu_node_entry == rnp->gp_tasks) 465 rnp->gp_tasks = np; 466 if (&t->rcu_node_entry == rnp->exp_tasks) 467 rnp->exp_tasks = np; 468 if (IS_ENABLED(CONFIG_RCU_BOOST)) { 469 if (&t->rcu_node_entry == rnp->boost_tasks) 470 rnp->boost_tasks = np; 471 /* Snapshot ->boost_mtx ownership w/rnp->lock held. */ 472 drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t; 473 } 474 475 /* 476 * If this was the last task on the current list, and if 477 * we aren't waiting on any CPUs, report the quiescent state. 478 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock, 479 * so we must take a snapshot of the expedited state. 480 */ 481 empty_exp_now = sync_rcu_preempt_exp_done(rnp); 482 if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) { 483 trace_rcu_quiescent_state_report(TPS("preempt_rcu"), 484 rnp->gpnum, 485 0, rnp->qsmask, 486 rnp->level, 487 rnp->grplo, 488 rnp->grphi, 489 !!rnp->gp_tasks); 490 rcu_report_unblock_qs_rnp(rcu_state_p, rnp, flags); 491 } else { 492 raw_spin_unlock_irqrestore(&rnp->lock, flags); 493 } 494 495 /* Unboost if we were boosted. */ 496 if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex) 497 rt_mutex_unlock(&rnp->boost_mtx); 498 499 /* 500 * If this was the last task on the expedited lists, 501 * then we need to report up the rcu_node hierarchy. 502 */ 503 if (!empty_exp && empty_exp_now) 504 rcu_report_exp_rnp(rcu_state_p, rnp, true); 505 } else { 506 local_irq_restore(flags); 507 } 508 } 509 510 /* 511 * Dump detailed information for all tasks blocking the current RCU 512 * grace period on the specified rcu_node structure. 513 */ 514 static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) 515 { 516 unsigned long flags; 517 struct task_struct *t; 518 519 raw_spin_lock_irqsave_rcu_node(rnp, flags); 520 if (!rcu_preempt_blocked_readers_cgp(rnp)) { 521 raw_spin_unlock_irqrestore(&rnp->lock, flags); 522 return; 523 } 524 t = list_entry(rnp->gp_tasks->prev, 525 struct task_struct, rcu_node_entry); 526 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) 527 sched_show_task(t); 528 raw_spin_unlock_irqrestore(&rnp->lock, flags); 529 } 530 531 /* 532 * Dump detailed information for all tasks blocking the current RCU 533 * grace period. 534 */ 535 static void rcu_print_detail_task_stall(struct rcu_state *rsp) 536 { 537 struct rcu_node *rnp = rcu_get_root(rsp); 538 539 rcu_print_detail_task_stall_rnp(rnp); 540 rcu_for_each_leaf_node(rsp, rnp) 541 rcu_print_detail_task_stall_rnp(rnp); 542 } 543 544 static void rcu_print_task_stall_begin(struct rcu_node *rnp) 545 { 546 pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):", 547 rnp->level, rnp->grplo, rnp->grphi); 548 } 549 550 static void rcu_print_task_stall_end(void) 551 { 552 pr_cont("\n"); 553 } 554 555 /* 556 * Scan the current list of tasks blocked within RCU read-side critical 557 * sections, printing out the tid of each. 558 */ 559 static int rcu_print_task_stall(struct rcu_node *rnp) 560 { 561 struct task_struct *t; 562 int ndetected = 0; 563 564 if (!rcu_preempt_blocked_readers_cgp(rnp)) 565 return 0; 566 rcu_print_task_stall_begin(rnp); 567 t = list_entry(rnp->gp_tasks->prev, 568 struct task_struct, rcu_node_entry); 569 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { 570 pr_cont(" P%d", t->pid); 571 ndetected++; 572 } 573 rcu_print_task_stall_end(); 574 return ndetected; 575 } 576 577 /* 578 * Scan the current list of tasks blocked within RCU read-side critical 579 * sections, printing out the tid of each that is blocking the current 580 * expedited grace period. 581 */ 582 static int rcu_print_task_exp_stall(struct rcu_node *rnp) 583 { 584 struct task_struct *t; 585 int ndetected = 0; 586 587 if (!rnp->exp_tasks) 588 return 0; 589 t = list_entry(rnp->exp_tasks->prev, 590 struct task_struct, rcu_node_entry); 591 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { 592 pr_cont(" P%d", t->pid); 593 ndetected++; 594 } 595 return ndetected; 596 } 597 598 /* 599 * Check that the list of blocked tasks for the newly completed grace 600 * period is in fact empty. It is a serious bug to complete a grace 601 * period that still has RCU readers blocked! This function must be 602 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock 603 * must be held by the caller. 604 * 605 * Also, if there are blocked tasks on the list, they automatically 606 * block the newly created grace period, so set up ->gp_tasks accordingly. 607 */ 608 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) 609 { 610 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)); 611 if (rcu_preempt_has_tasks(rnp)) 612 rnp->gp_tasks = rnp->blkd_tasks.next; 613 WARN_ON_ONCE(rnp->qsmask); 614 } 615 616 /* 617 * Check for a quiescent state from the current CPU. When a task blocks, 618 * the task is recorded in the corresponding CPU's rcu_node structure, 619 * which is checked elsewhere. 620 * 621 * Caller must disable hard irqs. 622 */ 623 static void rcu_preempt_check_callbacks(void) 624 { 625 struct task_struct *t = current; 626 627 if (t->rcu_read_lock_nesting == 0) { 628 rcu_preempt_qs(); 629 return; 630 } 631 if (t->rcu_read_lock_nesting > 0 && 632 __this_cpu_read(rcu_data_p->core_needs_qs) && 633 __this_cpu_read(rcu_data_p->cpu_no_qs.b.norm)) 634 t->rcu_read_unlock_special.b.need_qs = true; 635 } 636 637 #ifdef CONFIG_RCU_BOOST 638 639 static void rcu_preempt_do_callbacks(void) 640 { 641 rcu_do_batch(rcu_state_p, this_cpu_ptr(rcu_data_p)); 642 } 643 644 #endif /* #ifdef CONFIG_RCU_BOOST */ 645 646 /* 647 * Queue a preemptible-RCU callback for invocation after a grace period. 648 */ 649 void call_rcu(struct rcu_head *head, rcu_callback_t func) 650 { 651 __call_rcu(head, func, rcu_state_p, -1, 0); 652 } 653 EXPORT_SYMBOL_GPL(call_rcu); 654 655 /** 656 * synchronize_rcu - wait until a grace period has elapsed. 657 * 658 * Control will return to the caller some time after a full grace 659 * period has elapsed, in other words after all currently executing RCU 660 * read-side critical sections have completed. Note, however, that 661 * upon return from synchronize_rcu(), the caller might well be executing 662 * concurrently with new RCU read-side critical sections that began while 663 * synchronize_rcu() was waiting. RCU read-side critical sections are 664 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. 665 * 666 * See the description of synchronize_sched() for more detailed information 667 * on memory ordering guarantees. 668 */ 669 void synchronize_rcu(void) 670 { 671 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || 672 lock_is_held(&rcu_lock_map) || 673 lock_is_held(&rcu_sched_lock_map), 674 "Illegal synchronize_rcu() in RCU read-side critical section"); 675 if (!rcu_scheduler_active) 676 return; 677 if (rcu_gp_is_expedited()) 678 synchronize_rcu_expedited(); 679 else 680 wait_rcu_gp(call_rcu); 681 } 682 EXPORT_SYMBOL_GPL(synchronize_rcu); 683 684 /* 685 * Remote handler for smp_call_function_single(). If there is an 686 * RCU read-side critical section in effect, request that the 687 * next rcu_read_unlock() record the quiescent state up the 688 * ->expmask fields in the rcu_node tree. Otherwise, immediately 689 * report the quiescent state. 690 */ 691 static void sync_rcu_exp_handler(void *info) 692 { 693 struct rcu_data *rdp; 694 struct rcu_state *rsp = info; 695 struct task_struct *t = current; 696 697 /* 698 * Within an RCU read-side critical section, request that the next 699 * rcu_read_unlock() report. Unless this RCU read-side critical 700 * section has already blocked, in which case it is already set 701 * up for the expedited grace period to wait on it. 702 */ 703 if (t->rcu_read_lock_nesting > 0 && 704 !t->rcu_read_unlock_special.b.blocked) { 705 t->rcu_read_unlock_special.b.exp_need_qs = true; 706 return; 707 } 708 709 /* 710 * We are either exiting an RCU read-side critical section (negative 711 * values of t->rcu_read_lock_nesting) or are not in one at all 712 * (zero value of t->rcu_read_lock_nesting). Or we are in an RCU 713 * read-side critical section that blocked before this expedited 714 * grace period started. Either way, we can immediately report 715 * the quiescent state. 716 */ 717 rdp = this_cpu_ptr(rsp->rda); 718 rcu_report_exp_rdp(rsp, rdp, true); 719 } 720 721 /** 722 * synchronize_rcu_expedited - Brute-force RCU grace period 723 * 724 * Wait for an RCU-preempt grace period, but expedite it. The basic 725 * idea is to invoke synchronize_sched_expedited() to push all the tasks to 726 * the ->blkd_tasks lists and wait for this list to drain. This consumes 727 * significant time on all CPUs and is unfriendly to real-time workloads, 728 * so is thus not recommended for any sort of common-case code. 729 * In fact, if you are using synchronize_rcu_expedited() in a loop, 730 * please restructure your code to batch your updates, and then Use a 731 * single synchronize_rcu() instead. 732 */ 733 void synchronize_rcu_expedited(void) 734 { 735 struct rcu_node *rnp; 736 struct rcu_node *rnp_unlock; 737 struct rcu_state *rsp = rcu_state_p; 738 unsigned long s; 739 740 /* If expedited grace periods are prohibited, fall back to normal. */ 741 if (rcu_gp_is_normal()) { 742 wait_rcu_gp(call_rcu); 743 return; 744 } 745 746 s = rcu_exp_gp_seq_snap(rsp); 747 748 rnp_unlock = exp_funnel_lock(rsp, s); 749 if (rnp_unlock == NULL) 750 return; /* Someone else did our work for us. */ 751 752 rcu_exp_gp_seq_start(rsp); 753 754 /* Initialize the rcu_node tree in preparation for the wait. */ 755 sync_rcu_exp_select_cpus(rsp, sync_rcu_exp_handler); 756 757 /* Wait for snapshotted ->blkd_tasks lists to drain. */ 758 rnp = rcu_get_root(rsp); 759 synchronize_sched_expedited_wait(rsp); 760 761 /* Clean up and exit. */ 762 rcu_exp_gp_seq_end(rsp); 763 mutex_unlock(&rnp_unlock->exp_funnel_mutex); 764 } 765 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); 766 767 /** 768 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. 769 * 770 * Note that this primitive does not necessarily wait for an RCU grace period 771 * to complete. For example, if there are no RCU callbacks queued anywhere 772 * in the system, then rcu_barrier() is within its rights to return 773 * immediately, without waiting for anything, much less an RCU grace period. 774 */ 775 void rcu_barrier(void) 776 { 777 _rcu_barrier(rcu_state_p); 778 } 779 EXPORT_SYMBOL_GPL(rcu_barrier); 780 781 /* 782 * Initialize preemptible RCU's state structures. 783 */ 784 static void __init __rcu_init_preempt(void) 785 { 786 rcu_init_one(rcu_state_p); 787 } 788 789 /* 790 * Check for a task exiting while in a preemptible-RCU read-side 791 * critical section, clean up if so. No need to issue warnings, 792 * as debug_check_no_locks_held() already does this if lockdep 793 * is enabled. 794 */ 795 void exit_rcu(void) 796 { 797 struct task_struct *t = current; 798 799 if (likely(list_empty(¤t->rcu_node_entry))) 800 return; 801 t->rcu_read_lock_nesting = 1; 802 barrier(); 803 t->rcu_read_unlock_special.b.blocked = true; 804 __rcu_read_unlock(); 805 } 806 807 #else /* #ifdef CONFIG_PREEMPT_RCU */ 808 809 static struct rcu_state *const rcu_state_p = &rcu_sched_state; 810 static struct rcu_data __percpu *const rcu_data_p = &rcu_sched_data; 811 812 /* 813 * Tell them what RCU they are running. 814 */ 815 static void __init rcu_bootup_announce(void) 816 { 817 pr_info("Hierarchical RCU implementation.\n"); 818 rcu_bootup_announce_oddness(); 819 } 820 821 /* 822 * Because preemptible RCU does not exist, we never have to check for 823 * CPUs being in quiescent states. 824 */ 825 static void rcu_preempt_note_context_switch(void) 826 { 827 } 828 829 /* 830 * Because preemptible RCU does not exist, there are never any preempted 831 * RCU readers. 832 */ 833 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) 834 { 835 return 0; 836 } 837 838 /* 839 * Because there is no preemptible RCU, there can be no readers blocked. 840 */ 841 static bool rcu_preempt_has_tasks(struct rcu_node *rnp) 842 { 843 return false; 844 } 845 846 /* 847 * Because preemptible RCU does not exist, we never have to check for 848 * tasks blocked within RCU read-side critical sections. 849 */ 850 static void rcu_print_detail_task_stall(struct rcu_state *rsp) 851 { 852 } 853 854 /* 855 * Because preemptible RCU does not exist, we never have to check for 856 * tasks blocked within RCU read-side critical sections. 857 */ 858 static int rcu_print_task_stall(struct rcu_node *rnp) 859 { 860 return 0; 861 } 862 863 /* 864 * Because preemptible RCU does not exist, we never have to check for 865 * tasks blocked within RCU read-side critical sections that are 866 * blocking the current expedited grace period. 867 */ 868 static int rcu_print_task_exp_stall(struct rcu_node *rnp) 869 { 870 return 0; 871 } 872 873 /* 874 * Because there is no preemptible RCU, there can be no readers blocked, 875 * so there is no need to check for blocked tasks. So check only for 876 * bogus qsmask values. 877 */ 878 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) 879 { 880 WARN_ON_ONCE(rnp->qsmask); 881 } 882 883 /* 884 * Because preemptible RCU does not exist, it never has any callbacks 885 * to check. 886 */ 887 static void rcu_preempt_check_callbacks(void) 888 { 889 } 890 891 /* 892 * Wait for an rcu-preempt grace period, but make it happen quickly. 893 * But because preemptible RCU does not exist, map to rcu-sched. 894 */ 895 void synchronize_rcu_expedited(void) 896 { 897 synchronize_sched_expedited(); 898 } 899 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); 900 901 /* 902 * Because preemptible RCU does not exist, rcu_barrier() is just 903 * another name for rcu_barrier_sched(). 904 */ 905 void rcu_barrier(void) 906 { 907 rcu_barrier_sched(); 908 } 909 EXPORT_SYMBOL_GPL(rcu_barrier); 910 911 /* 912 * Because preemptible RCU does not exist, it need not be initialized. 913 */ 914 static void __init __rcu_init_preempt(void) 915 { 916 } 917 918 /* 919 * Because preemptible RCU does not exist, tasks cannot possibly exit 920 * while in preemptible RCU read-side critical sections. 921 */ 922 void exit_rcu(void) 923 { 924 } 925 926 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ 927 928 #ifdef CONFIG_RCU_BOOST 929 930 #include "../locking/rtmutex_common.h" 931 932 #ifdef CONFIG_RCU_TRACE 933 934 static void rcu_initiate_boost_trace(struct rcu_node *rnp) 935 { 936 if (!rcu_preempt_has_tasks(rnp)) 937 rnp->n_balk_blkd_tasks++; 938 else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL) 939 rnp->n_balk_exp_gp_tasks++; 940 else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL) 941 rnp->n_balk_boost_tasks++; 942 else if (rnp->gp_tasks != NULL && rnp->qsmask != 0) 943 rnp->n_balk_notblocked++; 944 else if (rnp->gp_tasks != NULL && 945 ULONG_CMP_LT(jiffies, rnp->boost_time)) 946 rnp->n_balk_notyet++; 947 else 948 rnp->n_balk_nos++; 949 } 950 951 #else /* #ifdef CONFIG_RCU_TRACE */ 952 953 static void rcu_initiate_boost_trace(struct rcu_node *rnp) 954 { 955 } 956 957 #endif /* #else #ifdef CONFIG_RCU_TRACE */ 958 959 static void rcu_wake_cond(struct task_struct *t, int status) 960 { 961 /* 962 * If the thread is yielding, only wake it when this 963 * is invoked from idle 964 */ 965 if (status != RCU_KTHREAD_YIELDING || is_idle_task(current)) 966 wake_up_process(t); 967 } 968 969 /* 970 * Carry out RCU priority boosting on the task indicated by ->exp_tasks 971 * or ->boost_tasks, advancing the pointer to the next task in the 972 * ->blkd_tasks list. 973 * 974 * Note that irqs must be enabled: boosting the task can block. 975 * Returns 1 if there are more tasks needing to be boosted. 976 */ 977 static int rcu_boost(struct rcu_node *rnp) 978 { 979 unsigned long flags; 980 struct task_struct *t; 981 struct list_head *tb; 982 983 if (READ_ONCE(rnp->exp_tasks) == NULL && 984 READ_ONCE(rnp->boost_tasks) == NULL) 985 return 0; /* Nothing left to boost. */ 986 987 raw_spin_lock_irqsave_rcu_node(rnp, flags); 988 989 /* 990 * Recheck under the lock: all tasks in need of boosting 991 * might exit their RCU read-side critical sections on their own. 992 */ 993 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) { 994 raw_spin_unlock_irqrestore(&rnp->lock, flags); 995 return 0; 996 } 997 998 /* 999 * Preferentially boost tasks blocking expedited grace periods. 1000 * This cannot starve the normal grace periods because a second 1001 * expedited grace period must boost all blocked tasks, including 1002 * those blocking the pre-existing normal grace period. 1003 */ 1004 if (rnp->exp_tasks != NULL) { 1005 tb = rnp->exp_tasks; 1006 rnp->n_exp_boosts++; 1007 } else { 1008 tb = rnp->boost_tasks; 1009 rnp->n_normal_boosts++; 1010 } 1011 rnp->n_tasks_boosted++; 1012 1013 /* 1014 * We boost task t by manufacturing an rt_mutex that appears to 1015 * be held by task t. We leave a pointer to that rt_mutex where 1016 * task t can find it, and task t will release the mutex when it 1017 * exits its outermost RCU read-side critical section. Then 1018 * simply acquiring this artificial rt_mutex will boost task 1019 * t's priority. (Thanks to tglx for suggesting this approach!) 1020 * 1021 * Note that task t must acquire rnp->lock to remove itself from 1022 * the ->blkd_tasks list, which it will do from exit() if from 1023 * nowhere else. We therefore are guaranteed that task t will 1024 * stay around at least until we drop rnp->lock. Note that 1025 * rnp->lock also resolves races between our priority boosting 1026 * and task t's exiting its outermost RCU read-side critical 1027 * section. 1028 */ 1029 t = container_of(tb, struct task_struct, rcu_node_entry); 1030 rt_mutex_init_proxy_locked(&rnp->boost_mtx, t); 1031 raw_spin_unlock_irqrestore(&rnp->lock, flags); 1032 /* Lock only for side effect: boosts task t's priority. */ 1033 rt_mutex_lock(&rnp->boost_mtx); 1034 rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */ 1035 1036 return READ_ONCE(rnp->exp_tasks) != NULL || 1037 READ_ONCE(rnp->boost_tasks) != NULL; 1038 } 1039 1040 /* 1041 * Priority-boosting kthread, one per leaf rcu_node. 1042 */ 1043 static int rcu_boost_kthread(void *arg) 1044 { 1045 struct rcu_node *rnp = (struct rcu_node *)arg; 1046 int spincnt = 0; 1047 int more2boost; 1048 1049 trace_rcu_utilization(TPS("Start boost kthread@init")); 1050 for (;;) { 1051 rnp->boost_kthread_status = RCU_KTHREAD_WAITING; 1052 trace_rcu_utilization(TPS("End boost kthread@rcu_wait")); 1053 rcu_wait(rnp->boost_tasks || rnp->exp_tasks); 1054 trace_rcu_utilization(TPS("Start boost kthread@rcu_wait")); 1055 rnp->boost_kthread_status = RCU_KTHREAD_RUNNING; 1056 more2boost = rcu_boost(rnp); 1057 if (more2boost) 1058 spincnt++; 1059 else 1060 spincnt = 0; 1061 if (spincnt > 10) { 1062 rnp->boost_kthread_status = RCU_KTHREAD_YIELDING; 1063 trace_rcu_utilization(TPS("End boost kthread@rcu_yield")); 1064 schedule_timeout_interruptible(2); 1065 trace_rcu_utilization(TPS("Start boost kthread@rcu_yield")); 1066 spincnt = 0; 1067 } 1068 } 1069 /* NOTREACHED */ 1070 trace_rcu_utilization(TPS("End boost kthread@notreached")); 1071 return 0; 1072 } 1073 1074 /* 1075 * Check to see if it is time to start boosting RCU readers that are 1076 * blocking the current grace period, and, if so, tell the per-rcu_node 1077 * kthread to start boosting them. If there is an expedited grace 1078 * period in progress, it is always time to boost. 1079 * 1080 * The caller must hold rnp->lock, which this function releases. 1081 * The ->boost_kthread_task is immortal, so we don't need to worry 1082 * about it going away. 1083 */ 1084 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) 1085 __releases(rnp->lock) 1086 { 1087 struct task_struct *t; 1088 1089 if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) { 1090 rnp->n_balk_exp_gp_tasks++; 1091 raw_spin_unlock_irqrestore(&rnp->lock, flags); 1092 return; 1093 } 1094 if (rnp->exp_tasks != NULL || 1095 (rnp->gp_tasks != NULL && 1096 rnp->boost_tasks == NULL && 1097 rnp->qsmask == 0 && 1098 ULONG_CMP_GE(jiffies, rnp->boost_time))) { 1099 if (rnp->exp_tasks == NULL) 1100 rnp->boost_tasks = rnp->gp_tasks; 1101 raw_spin_unlock_irqrestore(&rnp->lock, flags); 1102 t = rnp->boost_kthread_task; 1103 if (t) 1104 rcu_wake_cond(t, rnp->boost_kthread_status); 1105 } else { 1106 rcu_initiate_boost_trace(rnp); 1107 raw_spin_unlock_irqrestore(&rnp->lock, flags); 1108 } 1109 } 1110 1111 /* 1112 * Wake up the per-CPU kthread to invoke RCU callbacks. 1113 */ 1114 static void invoke_rcu_callbacks_kthread(void) 1115 { 1116 unsigned long flags; 1117 1118 local_irq_save(flags); 1119 __this_cpu_write(rcu_cpu_has_work, 1); 1120 if (__this_cpu_read(rcu_cpu_kthread_task) != NULL && 1121 current != __this_cpu_read(rcu_cpu_kthread_task)) { 1122 rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task), 1123 __this_cpu_read(rcu_cpu_kthread_status)); 1124 } 1125 local_irq_restore(flags); 1126 } 1127 1128 /* 1129 * Is the current CPU running the RCU-callbacks kthread? 1130 * Caller must have preemption disabled. 1131 */ 1132 static bool rcu_is_callbacks_kthread(void) 1133 { 1134 return __this_cpu_read(rcu_cpu_kthread_task) == current; 1135 } 1136 1137 #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) 1138 1139 /* 1140 * Do priority-boost accounting for the start of a new grace period. 1141 */ 1142 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) 1143 { 1144 rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; 1145 } 1146 1147 /* 1148 * Create an RCU-boost kthread for the specified node if one does not 1149 * already exist. We only create this kthread for preemptible RCU. 1150 * Returns zero if all is well, a negated errno otherwise. 1151 */ 1152 static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp, 1153 struct rcu_node *rnp) 1154 { 1155 int rnp_index = rnp - &rsp->node[0]; 1156 unsigned long flags; 1157 struct sched_param sp; 1158 struct task_struct *t; 1159 1160 if (rcu_state_p != rsp) 1161 return 0; 1162 1163 if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0) 1164 return 0; 1165 1166 rsp->boost = 1; 1167 if (rnp->boost_kthread_task != NULL) 1168 return 0; 1169 t = kthread_create(rcu_boost_kthread, (void *)rnp, 1170 "rcub/%d", rnp_index); 1171 if (IS_ERR(t)) 1172 return PTR_ERR(t); 1173 raw_spin_lock_irqsave_rcu_node(rnp, flags); 1174 rnp->boost_kthread_task = t; 1175 raw_spin_unlock_irqrestore(&rnp->lock, flags); 1176 sp.sched_priority = kthread_prio; 1177 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); 1178 wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ 1179 return 0; 1180 } 1181 1182 static void rcu_kthread_do_work(void) 1183 { 1184 rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data)); 1185 rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data)); 1186 rcu_preempt_do_callbacks(); 1187 } 1188 1189 static void rcu_cpu_kthread_setup(unsigned int cpu) 1190 { 1191 struct sched_param sp; 1192 1193 sp.sched_priority = kthread_prio; 1194 sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); 1195 } 1196 1197 static void rcu_cpu_kthread_park(unsigned int cpu) 1198 { 1199 per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; 1200 } 1201 1202 static int rcu_cpu_kthread_should_run(unsigned int cpu) 1203 { 1204 return __this_cpu_read(rcu_cpu_has_work); 1205 } 1206 1207 /* 1208 * Per-CPU kernel thread that invokes RCU callbacks. This replaces the 1209 * RCU softirq used in flavors and configurations of RCU that do not 1210 * support RCU priority boosting. 1211 */ 1212 static void rcu_cpu_kthread(unsigned int cpu) 1213 { 1214 unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status); 1215 char work, *workp = this_cpu_ptr(&rcu_cpu_has_work); 1216 int spincnt; 1217 1218 for (spincnt = 0; spincnt < 10; spincnt++) { 1219 trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait")); 1220 local_bh_disable(); 1221 *statusp = RCU_KTHREAD_RUNNING; 1222 this_cpu_inc(rcu_cpu_kthread_loops); 1223 local_irq_disable(); 1224 work = *workp; 1225 *workp = 0; 1226 local_irq_enable(); 1227 if (work) 1228 rcu_kthread_do_work(); 1229 local_bh_enable(); 1230 if (*workp == 0) { 1231 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait")); 1232 *statusp = RCU_KTHREAD_WAITING; 1233 return; 1234 } 1235 } 1236 *statusp = RCU_KTHREAD_YIELDING; 1237 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield")); 1238 schedule_timeout_interruptible(2); 1239 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield")); 1240 *statusp = RCU_KTHREAD_WAITING; 1241 } 1242 1243 /* 1244 * Set the per-rcu_node kthread's affinity to cover all CPUs that are 1245 * served by the rcu_node in question. The CPU hotplug lock is still 1246 * held, so the value of rnp->qsmaskinit will be stable. 1247 * 1248 * We don't include outgoingcpu in the affinity set, use -1 if there is 1249 * no outgoing CPU. If there are no CPUs left in the affinity set, 1250 * this function allows the kthread to execute on any CPU. 1251 */ 1252 static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) 1253 { 1254 struct task_struct *t = rnp->boost_kthread_task; 1255 unsigned long mask = rcu_rnp_online_cpus(rnp); 1256 cpumask_var_t cm; 1257 int cpu; 1258 1259 if (!t) 1260 return; 1261 if (!zalloc_cpumask_var(&cm, GFP_KERNEL)) 1262 return; 1263 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) 1264 if ((mask & 0x1) && cpu != outgoingcpu) 1265 cpumask_set_cpu(cpu, cm); 1266 if (cpumask_weight(cm) == 0) 1267 cpumask_setall(cm); 1268 set_cpus_allowed_ptr(t, cm); 1269 free_cpumask_var(cm); 1270 } 1271 1272 static struct smp_hotplug_thread rcu_cpu_thread_spec = { 1273 .store = &rcu_cpu_kthread_task, 1274 .thread_should_run = rcu_cpu_kthread_should_run, 1275 .thread_fn = rcu_cpu_kthread, 1276 .thread_comm = "rcuc/%u", 1277 .setup = rcu_cpu_kthread_setup, 1278 .park = rcu_cpu_kthread_park, 1279 }; 1280 1281 /* 1282 * Spawn boost kthreads -- called as soon as the scheduler is running. 1283 */ 1284 static void __init rcu_spawn_boost_kthreads(void) 1285 { 1286 struct rcu_node *rnp; 1287 int cpu; 1288 1289 for_each_possible_cpu(cpu) 1290 per_cpu(rcu_cpu_has_work, cpu) = 0; 1291 BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec)); 1292 rcu_for_each_leaf_node(rcu_state_p, rnp) 1293 (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp); 1294 } 1295 1296 static void rcu_prepare_kthreads(int cpu) 1297 { 1298 struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu); 1299 struct rcu_node *rnp = rdp->mynode; 1300 1301 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */ 1302 if (rcu_scheduler_fully_active) 1303 (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp); 1304 } 1305 1306 #else /* #ifdef CONFIG_RCU_BOOST */ 1307 1308 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) 1309 __releases(rnp->lock) 1310 { 1311 raw_spin_unlock_irqrestore(&rnp->lock, flags); 1312 } 1313 1314 static void invoke_rcu_callbacks_kthread(void) 1315 { 1316 WARN_ON_ONCE(1); 1317 } 1318 1319 static bool rcu_is_callbacks_kthread(void) 1320 { 1321 return false; 1322 } 1323 1324 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) 1325 { 1326 } 1327 1328 static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) 1329 { 1330 } 1331 1332 static void __init rcu_spawn_boost_kthreads(void) 1333 { 1334 } 1335 1336 static void rcu_prepare_kthreads(int cpu) 1337 { 1338 } 1339 1340 #endif /* #else #ifdef CONFIG_RCU_BOOST */ 1341 1342 #if !defined(CONFIG_RCU_FAST_NO_HZ) 1343 1344 /* 1345 * Check to see if any future RCU-related work will need to be done 1346 * by the current CPU, even if none need be done immediately, returning 1347 * 1 if so. This function is part of the RCU implementation; it is -not- 1348 * an exported member of the RCU API. 1349 * 1350 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs 1351 * any flavor of RCU. 1352 */ 1353 int rcu_needs_cpu(u64 basemono, u64 *nextevt) 1354 { 1355 *nextevt = KTIME_MAX; 1356 return IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL) 1357 ? 0 : rcu_cpu_has_callbacks(NULL); 1358 } 1359 1360 /* 1361 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up 1362 * after it. 1363 */ 1364 static void rcu_cleanup_after_idle(void) 1365 { 1366 } 1367 1368 /* 1369 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n, 1370 * is nothing. 1371 */ 1372 static void rcu_prepare_for_idle(void) 1373 { 1374 } 1375 1376 /* 1377 * Don't bother keeping a running count of the number of RCU callbacks 1378 * posted because CONFIG_RCU_FAST_NO_HZ=n. 1379 */ 1380 static void rcu_idle_count_callbacks_posted(void) 1381 { 1382 } 1383 1384 #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ 1385 1386 /* 1387 * This code is invoked when a CPU goes idle, at which point we want 1388 * to have the CPU do everything required for RCU so that it can enter 1389 * the energy-efficient dyntick-idle mode. This is handled by a 1390 * state machine implemented by rcu_prepare_for_idle() below. 1391 * 1392 * The following three proprocessor symbols control this state machine: 1393 * 1394 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted 1395 * to sleep in dyntick-idle mode with RCU callbacks pending. This 1396 * is sized to be roughly one RCU grace period. Those energy-efficiency 1397 * benchmarkers who might otherwise be tempted to set this to a large 1398 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your 1399 * system. And if you are -that- concerned about energy efficiency, 1400 * just power the system down and be done with it! 1401 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is 1402 * permitted to sleep in dyntick-idle mode with only lazy RCU 1403 * callbacks pending. Setting this too high can OOM your system. 1404 * 1405 * The values below work well in practice. If future workloads require 1406 * adjustment, they can be converted into kernel config parameters, though 1407 * making the state machine smarter might be a better option. 1408 */ 1409 #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */ 1410 #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */ 1411 1412 static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY; 1413 module_param(rcu_idle_gp_delay, int, 0644); 1414 static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY; 1415 module_param(rcu_idle_lazy_gp_delay, int, 0644); 1416 1417 /* 1418 * Try to advance callbacks for all flavors of RCU on the current CPU, but 1419 * only if it has been awhile since the last time we did so. Afterwards, 1420 * if there are any callbacks ready for immediate invocation, return true. 1421 */ 1422 static bool __maybe_unused rcu_try_advance_all_cbs(void) 1423 { 1424 bool cbs_ready = false; 1425 struct rcu_data *rdp; 1426 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); 1427 struct rcu_node *rnp; 1428 struct rcu_state *rsp; 1429 1430 /* Exit early if we advanced recently. */ 1431 if (jiffies == rdtp->last_advance_all) 1432 return false; 1433 rdtp->last_advance_all = jiffies; 1434 1435 for_each_rcu_flavor(rsp) { 1436 rdp = this_cpu_ptr(rsp->rda); 1437 rnp = rdp->mynode; 1438 1439 /* 1440 * Don't bother checking unless a grace period has 1441 * completed since we last checked and there are 1442 * callbacks not yet ready to invoke. 1443 */ 1444 if ((rdp->completed != rnp->completed || 1445 unlikely(READ_ONCE(rdp->gpwrap))) && 1446 rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL]) 1447 note_gp_changes(rsp, rdp); 1448 1449 if (cpu_has_callbacks_ready_to_invoke(rdp)) 1450 cbs_ready = true; 1451 } 1452 return cbs_ready; 1453 } 1454 1455 /* 1456 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready 1457 * to invoke. If the CPU has callbacks, try to advance them. Tell the 1458 * caller to set the timeout based on whether or not there are non-lazy 1459 * callbacks. 1460 * 1461 * The caller must have disabled interrupts. 1462 */ 1463 int rcu_needs_cpu(u64 basemono, u64 *nextevt) 1464 { 1465 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); 1466 unsigned long dj; 1467 1468 if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL)) { 1469 *nextevt = KTIME_MAX; 1470 return 0; 1471 } 1472 1473 /* Snapshot to detect later posting of non-lazy callback. */ 1474 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; 1475 1476 /* If no callbacks, RCU doesn't need the CPU. */ 1477 if (!rcu_cpu_has_callbacks(&rdtp->all_lazy)) { 1478 *nextevt = KTIME_MAX; 1479 return 0; 1480 } 1481 1482 /* Attempt to advance callbacks. */ 1483 if (rcu_try_advance_all_cbs()) { 1484 /* Some ready to invoke, so initiate later invocation. */ 1485 invoke_rcu_core(); 1486 return 1; 1487 } 1488 rdtp->last_accelerate = jiffies; 1489 1490 /* Request timer delay depending on laziness, and round. */ 1491 if (!rdtp->all_lazy) { 1492 dj = round_up(rcu_idle_gp_delay + jiffies, 1493 rcu_idle_gp_delay) - jiffies; 1494 } else { 1495 dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies; 1496 } 1497 *nextevt = basemono + dj * TICK_NSEC; 1498 return 0; 1499 } 1500 1501 /* 1502 * Prepare a CPU for idle from an RCU perspective. The first major task 1503 * is to sense whether nohz mode has been enabled or disabled via sysfs. 1504 * The second major task is to check to see if a non-lazy callback has 1505 * arrived at a CPU that previously had only lazy callbacks. The third 1506 * major task is to accelerate (that is, assign grace-period numbers to) 1507 * any recently arrived callbacks. 1508 * 1509 * The caller must have disabled interrupts. 1510 */ 1511 static void rcu_prepare_for_idle(void) 1512 { 1513 bool needwake; 1514 struct rcu_data *rdp; 1515 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); 1516 struct rcu_node *rnp; 1517 struct rcu_state *rsp; 1518 int tne; 1519 1520 if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL) || 1521 rcu_is_nocb_cpu(smp_processor_id())) 1522 return; 1523 1524 /* Handle nohz enablement switches conservatively. */ 1525 tne = READ_ONCE(tick_nohz_active); 1526 if (tne != rdtp->tick_nohz_enabled_snap) { 1527 if (rcu_cpu_has_callbacks(NULL)) 1528 invoke_rcu_core(); /* force nohz to see update. */ 1529 rdtp->tick_nohz_enabled_snap = tne; 1530 return; 1531 } 1532 if (!tne) 1533 return; 1534 1535 /* 1536 * If a non-lazy callback arrived at a CPU having only lazy 1537 * callbacks, invoke RCU core for the side-effect of recalculating 1538 * idle duration on re-entry to idle. 1539 */ 1540 if (rdtp->all_lazy && 1541 rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) { 1542 rdtp->all_lazy = false; 1543 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; 1544 invoke_rcu_core(); 1545 return; 1546 } 1547 1548 /* 1549 * If we have not yet accelerated this jiffy, accelerate all 1550 * callbacks on this CPU. 1551 */ 1552 if (rdtp->last_accelerate == jiffies) 1553 return; 1554 rdtp->last_accelerate = jiffies; 1555 for_each_rcu_flavor(rsp) { 1556 rdp = this_cpu_ptr(rsp->rda); 1557 if (!*rdp->nxttail[RCU_DONE_TAIL]) 1558 continue; 1559 rnp = rdp->mynode; 1560 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ 1561 needwake = rcu_accelerate_cbs(rsp, rnp, rdp); 1562 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ 1563 if (needwake) 1564 rcu_gp_kthread_wake(rsp); 1565 } 1566 } 1567 1568 /* 1569 * Clean up for exit from idle. Attempt to advance callbacks based on 1570 * any grace periods that elapsed while the CPU was idle, and if any 1571 * callbacks are now ready to invoke, initiate invocation. 1572 */ 1573 static void rcu_cleanup_after_idle(void) 1574 { 1575 if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL) || 1576 rcu_is_nocb_cpu(smp_processor_id())) 1577 return; 1578 if (rcu_try_advance_all_cbs()) 1579 invoke_rcu_core(); 1580 } 1581 1582 /* 1583 * Keep a running count of the number of non-lazy callbacks posted 1584 * on this CPU. This running counter (which is never decremented) allows 1585 * rcu_prepare_for_idle() to detect when something out of the idle loop 1586 * posts a callback, even if an equal number of callbacks are invoked. 1587 * Of course, callbacks should only be posted from within a trace event 1588 * designed to be called from idle or from within RCU_NONIDLE(). 1589 */ 1590 static void rcu_idle_count_callbacks_posted(void) 1591 { 1592 __this_cpu_add(rcu_dynticks.nonlazy_posted, 1); 1593 } 1594 1595 /* 1596 * Data for flushing lazy RCU callbacks at OOM time. 1597 */ 1598 static atomic_t oom_callback_count; 1599 static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq); 1600 1601 /* 1602 * RCU OOM callback -- decrement the outstanding count and deliver the 1603 * wake-up if we are the last one. 1604 */ 1605 static void rcu_oom_callback(struct rcu_head *rhp) 1606 { 1607 if (atomic_dec_and_test(&oom_callback_count)) 1608 wake_up(&oom_callback_wq); 1609 } 1610 1611 /* 1612 * Post an rcu_oom_notify callback on the current CPU if it has at 1613 * least one lazy callback. This will unnecessarily post callbacks 1614 * to CPUs that already have a non-lazy callback at the end of their 1615 * callback list, but this is an infrequent operation, so accept some 1616 * extra overhead to keep things simple. 1617 */ 1618 static void rcu_oom_notify_cpu(void *unused) 1619 { 1620 struct rcu_state *rsp; 1621 struct rcu_data *rdp; 1622 1623 for_each_rcu_flavor(rsp) { 1624 rdp = raw_cpu_ptr(rsp->rda); 1625 if (rdp->qlen_lazy != 0) { 1626 atomic_inc(&oom_callback_count); 1627 rsp->call(&rdp->oom_head, rcu_oom_callback); 1628 } 1629 } 1630 } 1631 1632 /* 1633 * If low on memory, ensure that each CPU has a non-lazy callback. 1634 * This will wake up CPUs that have only lazy callbacks, in turn 1635 * ensuring that they free up the corresponding memory in a timely manner. 1636 * Because an uncertain amount of memory will be freed in some uncertain 1637 * timeframe, we do not claim to have freed anything. 1638 */ 1639 static int rcu_oom_notify(struct notifier_block *self, 1640 unsigned long notused, void *nfreed) 1641 { 1642 int cpu; 1643 1644 /* Wait for callbacks from earlier instance to complete. */ 1645 wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0); 1646 smp_mb(); /* Ensure callback reuse happens after callback invocation. */ 1647 1648 /* 1649 * Prevent premature wakeup: ensure that all increments happen 1650 * before there is a chance of the counter reaching zero. 1651 */ 1652 atomic_set(&oom_callback_count, 1); 1653 1654 for_each_online_cpu(cpu) { 1655 smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1); 1656 cond_resched_rcu_qs(); 1657 } 1658 1659 /* Unconditionally decrement: no need to wake ourselves up. */ 1660 atomic_dec(&oom_callback_count); 1661 1662 return NOTIFY_OK; 1663 } 1664 1665 static struct notifier_block rcu_oom_nb = { 1666 .notifier_call = rcu_oom_notify 1667 }; 1668 1669 static int __init rcu_register_oom_notifier(void) 1670 { 1671 register_oom_notifier(&rcu_oom_nb); 1672 return 0; 1673 } 1674 early_initcall(rcu_register_oom_notifier); 1675 1676 #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ 1677 1678 #ifdef CONFIG_RCU_FAST_NO_HZ 1679 1680 static void print_cpu_stall_fast_no_hz(char *cp, int cpu) 1681 { 1682 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); 1683 unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap; 1684 1685 sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c", 1686 rdtp->last_accelerate & 0xffff, jiffies & 0xffff, 1687 ulong2long(nlpd), 1688 rdtp->all_lazy ? 'L' : '.', 1689 rdtp->tick_nohz_enabled_snap ? '.' : 'D'); 1690 } 1691 1692 #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ 1693 1694 static void print_cpu_stall_fast_no_hz(char *cp, int cpu) 1695 { 1696 *cp = '\0'; 1697 } 1698 1699 #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */ 1700 1701 /* Initiate the stall-info list. */ 1702 static void print_cpu_stall_info_begin(void) 1703 { 1704 pr_cont("\n"); 1705 } 1706 1707 /* 1708 * Print out diagnostic information for the specified stalled CPU. 1709 * 1710 * If the specified CPU is aware of the current RCU grace period 1711 * (flavor specified by rsp), then print the number of scheduling 1712 * clock interrupts the CPU has taken during the time that it has 1713 * been aware. Otherwise, print the number of RCU grace periods 1714 * that this CPU is ignorant of, for example, "1" if the CPU was 1715 * aware of the previous grace period. 1716 * 1717 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info. 1718 */ 1719 static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) 1720 { 1721 char fast_no_hz[72]; 1722 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); 1723 struct rcu_dynticks *rdtp = rdp->dynticks; 1724 char *ticks_title; 1725 unsigned long ticks_value; 1726 1727 if (rsp->gpnum == rdp->gpnum) { 1728 ticks_title = "ticks this GP"; 1729 ticks_value = rdp->ticks_this_gp; 1730 } else { 1731 ticks_title = "GPs behind"; 1732 ticks_value = rsp->gpnum - rdp->gpnum; 1733 } 1734 print_cpu_stall_fast_no_hz(fast_no_hz, cpu); 1735 pr_err("\t%d-%c%c%c: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u fqs=%ld %s\n", 1736 cpu, 1737 "O."[!!cpu_online(cpu)], 1738 "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)], 1739 "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)], 1740 ticks_value, ticks_title, 1741 atomic_read(&rdtp->dynticks) & 0xfff, 1742 rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting, 1743 rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu), 1744 READ_ONCE(rsp->n_force_qs) - rsp->n_force_qs_gpstart, 1745 fast_no_hz); 1746 } 1747 1748 /* Terminate the stall-info list. */ 1749 static void print_cpu_stall_info_end(void) 1750 { 1751 pr_err("\t"); 1752 } 1753 1754 /* Zero ->ticks_this_gp for all flavors of RCU. */ 1755 static void zero_cpu_stall_ticks(struct rcu_data *rdp) 1756 { 1757 rdp->ticks_this_gp = 0; 1758 rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id()); 1759 } 1760 1761 /* Increment ->ticks_this_gp for all flavors of RCU. */ 1762 static void increment_cpu_stall_ticks(void) 1763 { 1764 struct rcu_state *rsp; 1765 1766 for_each_rcu_flavor(rsp) 1767 raw_cpu_inc(rsp->rda->ticks_this_gp); 1768 } 1769 1770 #ifdef CONFIG_RCU_NOCB_CPU 1771 1772 /* 1773 * Offload callback processing from the boot-time-specified set of CPUs 1774 * specified by rcu_nocb_mask. For each CPU in the set, there is a 1775 * kthread created that pulls the callbacks from the corresponding CPU, 1776 * waits for a grace period to elapse, and invokes the callbacks. 1777 * The no-CBs CPUs do a wake_up() on their kthread when they insert 1778 * a callback into any empty list, unless the rcu_nocb_poll boot parameter 1779 * has been specified, in which case each kthread actively polls its 1780 * CPU. (Which isn't so great for energy efficiency, but which does 1781 * reduce RCU's overhead on that CPU.) 1782 * 1783 * This is intended to be used in conjunction with Frederic Weisbecker's 1784 * adaptive-idle work, which would seriously reduce OS jitter on CPUs 1785 * running CPU-bound user-mode computations. 1786 * 1787 * Offloading of callback processing could also in theory be used as 1788 * an energy-efficiency measure because CPUs with no RCU callbacks 1789 * queued are more aggressive about entering dyntick-idle mode. 1790 */ 1791 1792 1793 /* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */ 1794 static int __init rcu_nocb_setup(char *str) 1795 { 1796 alloc_bootmem_cpumask_var(&rcu_nocb_mask); 1797 have_rcu_nocb_mask = true; 1798 cpulist_parse(str, rcu_nocb_mask); 1799 return 1; 1800 } 1801 __setup("rcu_nocbs=", rcu_nocb_setup); 1802 1803 static int __init parse_rcu_nocb_poll(char *arg) 1804 { 1805 rcu_nocb_poll = 1; 1806 return 0; 1807 } 1808 early_param("rcu_nocb_poll", parse_rcu_nocb_poll); 1809 1810 /* 1811 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended 1812 * grace period. 1813 */ 1814 static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) 1815 { 1816 wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]); 1817 } 1818 1819 /* 1820 * Set the root rcu_node structure's ->need_future_gp field 1821 * based on the sum of those of all rcu_node structures. This does 1822 * double-count the root rcu_node structure's requests, but this 1823 * is necessary to handle the possibility of a rcu_nocb_kthread() 1824 * having awakened during the time that the rcu_node structures 1825 * were being updated for the end of the previous grace period. 1826 */ 1827 static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) 1828 { 1829 rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq; 1830 } 1831 1832 static void rcu_init_one_nocb(struct rcu_node *rnp) 1833 { 1834 init_waitqueue_head(&rnp->nocb_gp_wq[0]); 1835 init_waitqueue_head(&rnp->nocb_gp_wq[1]); 1836 } 1837 1838 #ifndef CONFIG_RCU_NOCB_CPU_ALL 1839 /* Is the specified CPU a no-CBs CPU? */ 1840 bool rcu_is_nocb_cpu(int cpu) 1841 { 1842 if (have_rcu_nocb_mask) 1843 return cpumask_test_cpu(cpu, rcu_nocb_mask); 1844 return false; 1845 } 1846 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */ 1847 1848 /* 1849 * Kick the leader kthread for this NOCB group. 1850 */ 1851 static void wake_nocb_leader(struct rcu_data *rdp, bool force) 1852 { 1853 struct rcu_data *rdp_leader = rdp->nocb_leader; 1854 1855 if (!READ_ONCE(rdp_leader->nocb_kthread)) 1856 return; 1857 if (READ_ONCE(rdp_leader->nocb_leader_sleep) || force) { 1858 /* Prior smp_mb__after_atomic() orders against prior enqueue. */ 1859 WRITE_ONCE(rdp_leader->nocb_leader_sleep, false); 1860 wake_up(&rdp_leader->nocb_wq); 1861 } 1862 } 1863 1864 /* 1865 * Does the specified CPU need an RCU callback for the specified flavor 1866 * of rcu_barrier()? 1867 */ 1868 static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu) 1869 { 1870 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); 1871 unsigned long ret; 1872 #ifdef CONFIG_PROVE_RCU 1873 struct rcu_head *rhp; 1874 #endif /* #ifdef CONFIG_PROVE_RCU */ 1875 1876 /* 1877 * Check count of all no-CBs callbacks awaiting invocation. 1878 * There needs to be a barrier before this function is called, 1879 * but associated with a prior determination that no more 1880 * callbacks would be posted. In the worst case, the first 1881 * barrier in _rcu_barrier() suffices (but the caller cannot 1882 * necessarily rely on this, not a substitute for the caller 1883 * getting the concurrency design right!). There must also be 1884 * a barrier between the following load an posting of a callback 1885 * (if a callback is in fact needed). This is associated with an 1886 * atomic_inc() in the caller. 1887 */ 1888 ret = atomic_long_read(&rdp->nocb_q_count); 1889 1890 #ifdef CONFIG_PROVE_RCU 1891 rhp = READ_ONCE(rdp->nocb_head); 1892 if (!rhp) 1893 rhp = READ_ONCE(rdp->nocb_gp_head); 1894 if (!rhp) 1895 rhp = READ_ONCE(rdp->nocb_follower_head); 1896 1897 /* Having no rcuo kthread but CBs after scheduler starts is bad! */ 1898 if (!READ_ONCE(rdp->nocb_kthread) && rhp && 1899 rcu_scheduler_fully_active) { 1900 /* RCU callback enqueued before CPU first came online??? */ 1901 pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n", 1902 cpu, rhp->func); 1903 WARN_ON_ONCE(1); 1904 } 1905 #endif /* #ifdef CONFIG_PROVE_RCU */ 1906 1907 return !!ret; 1908 } 1909 1910 /* 1911 * Enqueue the specified string of rcu_head structures onto the specified 1912 * CPU's no-CBs lists. The CPU is specified by rdp, the head of the 1913 * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy 1914 * counts are supplied by rhcount and rhcount_lazy. 1915 * 1916 * If warranted, also wake up the kthread servicing this CPUs queues. 1917 */ 1918 static void __call_rcu_nocb_enqueue(struct rcu_data *rdp, 1919 struct rcu_head *rhp, 1920 struct rcu_head **rhtp, 1921 int rhcount, int rhcount_lazy, 1922 unsigned long flags) 1923 { 1924 int len; 1925 struct rcu_head **old_rhpp; 1926 struct task_struct *t; 1927 1928 /* Enqueue the callback on the nocb list and update counts. */ 1929 atomic_long_add(rhcount, &rdp->nocb_q_count); 1930 /* rcu_barrier() relies on ->nocb_q_count add before xchg. */ 1931 old_rhpp = xchg(&rdp->nocb_tail, rhtp); 1932 WRITE_ONCE(*old_rhpp, rhp); 1933 atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy); 1934 smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */ 1935 1936 /* If we are not being polled and there is a kthread, awaken it ... */ 1937 t = READ_ONCE(rdp->nocb_kthread); 1938 if (rcu_nocb_poll || !t) { 1939 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 1940 TPS("WakeNotPoll")); 1941 return; 1942 } 1943 len = atomic_long_read(&rdp->nocb_q_count); 1944 if (old_rhpp == &rdp->nocb_head) { 1945 if (!irqs_disabled_flags(flags)) { 1946 /* ... if queue was empty ... */ 1947 wake_nocb_leader(rdp, false); 1948 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 1949 TPS("WakeEmpty")); 1950 } else { 1951 rdp->nocb_defer_wakeup = RCU_NOGP_WAKE; 1952 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 1953 TPS("WakeEmptyIsDeferred")); 1954 } 1955 rdp->qlen_last_fqs_check = 0; 1956 } else if (len > rdp->qlen_last_fqs_check + qhimark) { 1957 /* ... or if many callbacks queued. */ 1958 if (!irqs_disabled_flags(flags)) { 1959 wake_nocb_leader(rdp, true); 1960 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 1961 TPS("WakeOvf")); 1962 } else { 1963 rdp->nocb_defer_wakeup = RCU_NOGP_WAKE_FORCE; 1964 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 1965 TPS("WakeOvfIsDeferred")); 1966 } 1967 rdp->qlen_last_fqs_check = LONG_MAX / 2; 1968 } else { 1969 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot")); 1970 } 1971 return; 1972 } 1973 1974 /* 1975 * This is a helper for __call_rcu(), which invokes this when the normal 1976 * callback queue is inoperable. If this is not a no-CBs CPU, this 1977 * function returns failure back to __call_rcu(), which can complain 1978 * appropriately. 1979 * 1980 * Otherwise, this function queues the callback where the corresponding 1981 * "rcuo" kthread can find it. 1982 */ 1983 static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, 1984 bool lazy, unsigned long flags) 1985 { 1986 1987 if (!rcu_is_nocb_cpu(rdp->cpu)) 1988 return false; 1989 __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags); 1990 if (__is_kfree_rcu_offset((unsigned long)rhp->func)) 1991 trace_rcu_kfree_callback(rdp->rsp->name, rhp, 1992 (unsigned long)rhp->func, 1993 -atomic_long_read(&rdp->nocb_q_count_lazy), 1994 -atomic_long_read(&rdp->nocb_q_count)); 1995 else 1996 trace_rcu_callback(rdp->rsp->name, rhp, 1997 -atomic_long_read(&rdp->nocb_q_count_lazy), 1998 -atomic_long_read(&rdp->nocb_q_count)); 1999 2000 /* 2001 * If called from an extended quiescent state with interrupts 2002 * disabled, invoke the RCU core in order to allow the idle-entry 2003 * deferred-wakeup check to function. 2004 */ 2005 if (irqs_disabled_flags(flags) && 2006 !rcu_is_watching() && 2007 cpu_online(smp_processor_id())) 2008 invoke_rcu_core(); 2009 2010 return true; 2011 } 2012 2013 /* 2014 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is 2015 * not a no-CBs CPU. 2016 */ 2017 static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, 2018 struct rcu_data *rdp, 2019 unsigned long flags) 2020 { 2021 long ql = rsp->qlen; 2022 long qll = rsp->qlen_lazy; 2023 2024 /* If this is not a no-CBs CPU, tell the caller to do it the old way. */ 2025 if (!rcu_is_nocb_cpu(smp_processor_id())) 2026 return false; 2027 rsp->qlen = 0; 2028 rsp->qlen_lazy = 0; 2029 2030 /* First, enqueue the donelist, if any. This preserves CB ordering. */ 2031 if (rsp->orphan_donelist != NULL) { 2032 __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist, 2033 rsp->orphan_donetail, ql, qll, flags); 2034 ql = qll = 0; 2035 rsp->orphan_donelist = NULL; 2036 rsp->orphan_donetail = &rsp->orphan_donelist; 2037 } 2038 if (rsp->orphan_nxtlist != NULL) { 2039 __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist, 2040 rsp->orphan_nxttail, ql, qll, flags); 2041 ql = qll = 0; 2042 rsp->orphan_nxtlist = NULL; 2043 rsp->orphan_nxttail = &rsp->orphan_nxtlist; 2044 } 2045 return true; 2046 } 2047 2048 /* 2049 * If necessary, kick off a new grace period, and either way wait 2050 * for a subsequent grace period to complete. 2051 */ 2052 static void rcu_nocb_wait_gp(struct rcu_data *rdp) 2053 { 2054 unsigned long c; 2055 bool d; 2056 unsigned long flags; 2057 bool needwake; 2058 struct rcu_node *rnp = rdp->mynode; 2059 2060 raw_spin_lock_irqsave_rcu_node(rnp, flags); 2061 needwake = rcu_start_future_gp(rnp, rdp, &c); 2062 raw_spin_unlock_irqrestore(&rnp->lock, flags); 2063 if (needwake) 2064 rcu_gp_kthread_wake(rdp->rsp); 2065 2066 /* 2067 * Wait for the grace period. Do so interruptibly to avoid messing 2068 * up the load average. 2069 */ 2070 trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait")); 2071 for (;;) { 2072 wait_event_interruptible( 2073 rnp->nocb_gp_wq[c & 0x1], 2074 (d = ULONG_CMP_GE(READ_ONCE(rnp->completed), c))); 2075 if (likely(d)) 2076 break; 2077 WARN_ON(signal_pending(current)); 2078 trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait")); 2079 } 2080 trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait")); 2081 smp_mb(); /* Ensure that CB invocation happens after GP end. */ 2082 } 2083 2084 /* 2085 * Leaders come here to wait for additional callbacks to show up. 2086 * This function does not return until callbacks appear. 2087 */ 2088 static void nocb_leader_wait(struct rcu_data *my_rdp) 2089 { 2090 bool firsttime = true; 2091 bool gotcbs; 2092 struct rcu_data *rdp; 2093 struct rcu_head **tail; 2094 2095 wait_again: 2096 2097 /* Wait for callbacks to appear. */ 2098 if (!rcu_nocb_poll) { 2099 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Sleep"); 2100 wait_event_interruptible(my_rdp->nocb_wq, 2101 !READ_ONCE(my_rdp->nocb_leader_sleep)); 2102 /* Memory barrier handled by smp_mb() calls below and repoll. */ 2103 } else if (firsttime) { 2104 firsttime = false; /* Don't drown trace log with "Poll"! */ 2105 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Poll"); 2106 } 2107 2108 /* 2109 * Each pass through the following loop checks a follower for CBs. 2110 * We are our own first follower. Any CBs found are moved to 2111 * nocb_gp_head, where they await a grace period. 2112 */ 2113 gotcbs = false; 2114 for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) { 2115 rdp->nocb_gp_head = READ_ONCE(rdp->nocb_head); 2116 if (!rdp->nocb_gp_head) 2117 continue; /* No CBs here, try next follower. */ 2118 2119 /* Move callbacks to wait-for-GP list, which is empty. */ 2120 WRITE_ONCE(rdp->nocb_head, NULL); 2121 rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head); 2122 gotcbs = true; 2123 } 2124 2125 /* 2126 * If there were no callbacks, sleep a bit, rescan after a 2127 * memory barrier, and go retry. 2128 */ 2129 if (unlikely(!gotcbs)) { 2130 if (!rcu_nocb_poll) 2131 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, 2132 "WokeEmpty"); 2133 WARN_ON(signal_pending(current)); 2134 schedule_timeout_interruptible(1); 2135 2136 /* Rescan in case we were a victim of memory ordering. */ 2137 my_rdp->nocb_leader_sleep = true; 2138 smp_mb(); /* Ensure _sleep true before scan. */ 2139 for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) 2140 if (READ_ONCE(rdp->nocb_head)) { 2141 /* Found CB, so short-circuit next wait. */ 2142 my_rdp->nocb_leader_sleep = false; 2143 break; 2144 } 2145 goto wait_again; 2146 } 2147 2148 /* Wait for one grace period. */ 2149 rcu_nocb_wait_gp(my_rdp); 2150 2151 /* 2152 * We left ->nocb_leader_sleep unset to reduce cache thrashing. 2153 * We set it now, but recheck for new callbacks while 2154 * traversing our follower list. 2155 */ 2156 my_rdp->nocb_leader_sleep = true; 2157 smp_mb(); /* Ensure _sleep true before scan of ->nocb_head. */ 2158 2159 /* Each pass through the following loop wakes a follower, if needed. */ 2160 for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) { 2161 if (READ_ONCE(rdp->nocb_head)) 2162 my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/ 2163 if (!rdp->nocb_gp_head) 2164 continue; /* No CBs, so no need to wake follower. */ 2165 2166 /* Append callbacks to follower's "done" list. */ 2167 tail = xchg(&rdp->nocb_follower_tail, rdp->nocb_gp_tail); 2168 *tail = rdp->nocb_gp_head; 2169 smp_mb__after_atomic(); /* Store *tail before wakeup. */ 2170 if (rdp != my_rdp && tail == &rdp->nocb_follower_head) { 2171 /* 2172 * List was empty, wake up the follower. 2173 * Memory barriers supplied by atomic_long_add(). 2174 */ 2175 wake_up(&rdp->nocb_wq); 2176 } 2177 } 2178 2179 /* If we (the leader) don't have CBs, go wait some more. */ 2180 if (!my_rdp->nocb_follower_head) 2181 goto wait_again; 2182 } 2183 2184 /* 2185 * Followers come here to wait for additional callbacks to show up. 2186 * This function does not return until callbacks appear. 2187 */ 2188 static void nocb_follower_wait(struct rcu_data *rdp) 2189 { 2190 bool firsttime = true; 2191 2192 for (;;) { 2193 if (!rcu_nocb_poll) { 2194 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 2195 "FollowerSleep"); 2196 wait_event_interruptible(rdp->nocb_wq, 2197 READ_ONCE(rdp->nocb_follower_head)); 2198 } else if (firsttime) { 2199 /* Don't drown trace log with "Poll"! */ 2200 firsttime = false; 2201 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "Poll"); 2202 } 2203 if (smp_load_acquire(&rdp->nocb_follower_head)) { 2204 /* ^^^ Ensure CB invocation follows _head test. */ 2205 return; 2206 } 2207 if (!rcu_nocb_poll) 2208 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 2209 "WokeEmpty"); 2210 WARN_ON(signal_pending(current)); 2211 schedule_timeout_interruptible(1); 2212 } 2213 } 2214 2215 /* 2216 * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes 2217 * callbacks queued by the corresponding no-CBs CPU, however, there is 2218 * an optional leader-follower relationship so that the grace-period 2219 * kthreads don't have to do quite so many wakeups. 2220 */ 2221 static int rcu_nocb_kthread(void *arg) 2222 { 2223 int c, cl; 2224 struct rcu_head *list; 2225 struct rcu_head *next; 2226 struct rcu_head **tail; 2227 struct rcu_data *rdp = arg; 2228 2229 /* Each pass through this loop invokes one batch of callbacks */ 2230 for (;;) { 2231 /* Wait for callbacks. */ 2232 if (rdp->nocb_leader == rdp) 2233 nocb_leader_wait(rdp); 2234 else 2235 nocb_follower_wait(rdp); 2236 2237 /* Pull the ready-to-invoke callbacks onto local list. */ 2238 list = READ_ONCE(rdp->nocb_follower_head); 2239 BUG_ON(!list); 2240 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "WokeNonEmpty"); 2241 WRITE_ONCE(rdp->nocb_follower_head, NULL); 2242 tail = xchg(&rdp->nocb_follower_tail, &rdp->nocb_follower_head); 2243 2244 /* Each pass through the following loop invokes a callback. */ 2245 trace_rcu_batch_start(rdp->rsp->name, 2246 atomic_long_read(&rdp->nocb_q_count_lazy), 2247 atomic_long_read(&rdp->nocb_q_count), -1); 2248 c = cl = 0; 2249 while (list) { 2250 next = list->next; 2251 /* Wait for enqueuing to complete, if needed. */ 2252 while (next == NULL && &list->next != tail) { 2253 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 2254 TPS("WaitQueue")); 2255 schedule_timeout_interruptible(1); 2256 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 2257 TPS("WokeQueue")); 2258 next = list->next; 2259 } 2260 debug_rcu_head_unqueue(list); 2261 local_bh_disable(); 2262 if (__rcu_reclaim(rdp->rsp->name, list)) 2263 cl++; 2264 c++; 2265 local_bh_enable(); 2266 list = next; 2267 } 2268 trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1); 2269 smp_mb__before_atomic(); /* _add after CB invocation. */ 2270 atomic_long_add(-c, &rdp->nocb_q_count); 2271 atomic_long_add(-cl, &rdp->nocb_q_count_lazy); 2272 rdp->n_nocbs_invoked += c; 2273 } 2274 return 0; 2275 } 2276 2277 /* Is a deferred wakeup of rcu_nocb_kthread() required? */ 2278 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) 2279 { 2280 return READ_ONCE(rdp->nocb_defer_wakeup); 2281 } 2282 2283 /* Do a deferred wakeup of rcu_nocb_kthread(). */ 2284 static void do_nocb_deferred_wakeup(struct rcu_data *rdp) 2285 { 2286 int ndw; 2287 2288 if (!rcu_nocb_need_deferred_wakeup(rdp)) 2289 return; 2290 ndw = READ_ONCE(rdp->nocb_defer_wakeup); 2291 WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOGP_WAKE_NOT); 2292 wake_nocb_leader(rdp, ndw == RCU_NOGP_WAKE_FORCE); 2293 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWake")); 2294 } 2295 2296 void __init rcu_init_nohz(void) 2297 { 2298 int cpu; 2299 bool need_rcu_nocb_mask = true; 2300 struct rcu_state *rsp; 2301 2302 #ifdef CONFIG_RCU_NOCB_CPU_NONE 2303 need_rcu_nocb_mask = false; 2304 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */ 2305 2306 #if defined(CONFIG_NO_HZ_FULL) 2307 if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask)) 2308 need_rcu_nocb_mask = true; 2309 #endif /* #if defined(CONFIG_NO_HZ_FULL) */ 2310 2311 if (!have_rcu_nocb_mask && need_rcu_nocb_mask) { 2312 if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) { 2313 pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n"); 2314 return; 2315 } 2316 have_rcu_nocb_mask = true; 2317 } 2318 if (!have_rcu_nocb_mask) 2319 return; 2320 2321 #ifdef CONFIG_RCU_NOCB_CPU_ZERO 2322 pr_info("\tOffload RCU callbacks from CPU 0\n"); 2323 cpumask_set_cpu(0, rcu_nocb_mask); 2324 #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */ 2325 #ifdef CONFIG_RCU_NOCB_CPU_ALL 2326 pr_info("\tOffload RCU callbacks from all CPUs\n"); 2327 cpumask_copy(rcu_nocb_mask, cpu_possible_mask); 2328 #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */ 2329 #if defined(CONFIG_NO_HZ_FULL) 2330 if (tick_nohz_full_running) 2331 cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask); 2332 #endif /* #if defined(CONFIG_NO_HZ_FULL) */ 2333 2334 if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) { 2335 pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n"); 2336 cpumask_and(rcu_nocb_mask, cpu_possible_mask, 2337 rcu_nocb_mask); 2338 } 2339 pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n", 2340 cpumask_pr_args(rcu_nocb_mask)); 2341 if (rcu_nocb_poll) 2342 pr_info("\tPoll for callbacks from no-CBs CPUs.\n"); 2343 2344 for_each_rcu_flavor(rsp) { 2345 for_each_cpu(cpu, rcu_nocb_mask) 2346 init_nocb_callback_list(per_cpu_ptr(rsp->rda, cpu)); 2347 rcu_organize_nocb_kthreads(rsp); 2348 } 2349 } 2350 2351 /* Initialize per-rcu_data variables for no-CBs CPUs. */ 2352 static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) 2353 { 2354 rdp->nocb_tail = &rdp->nocb_head; 2355 init_waitqueue_head(&rdp->nocb_wq); 2356 rdp->nocb_follower_tail = &rdp->nocb_follower_head; 2357 } 2358 2359 /* 2360 * If the specified CPU is a no-CBs CPU that does not already have its 2361 * rcuo kthread for the specified RCU flavor, spawn it. If the CPUs are 2362 * brought online out of order, this can require re-organizing the 2363 * leader-follower relationships. 2364 */ 2365 static void rcu_spawn_one_nocb_kthread(struct rcu_state *rsp, int cpu) 2366 { 2367 struct rcu_data *rdp; 2368 struct rcu_data *rdp_last; 2369 struct rcu_data *rdp_old_leader; 2370 struct rcu_data *rdp_spawn = per_cpu_ptr(rsp->rda, cpu); 2371 struct task_struct *t; 2372 2373 /* 2374 * If this isn't a no-CBs CPU or if it already has an rcuo kthread, 2375 * then nothing to do. 2376 */ 2377 if (!rcu_is_nocb_cpu(cpu) || rdp_spawn->nocb_kthread) 2378 return; 2379 2380 /* If we didn't spawn the leader first, reorganize! */ 2381 rdp_old_leader = rdp_spawn->nocb_leader; 2382 if (rdp_old_leader != rdp_spawn && !rdp_old_leader->nocb_kthread) { 2383 rdp_last = NULL; 2384 rdp = rdp_old_leader; 2385 do { 2386 rdp->nocb_leader = rdp_spawn; 2387 if (rdp_last && rdp != rdp_spawn) 2388 rdp_last->nocb_next_follower = rdp; 2389 if (rdp == rdp_spawn) { 2390 rdp = rdp->nocb_next_follower; 2391 } else { 2392 rdp_last = rdp; 2393 rdp = rdp->nocb_next_follower; 2394 rdp_last->nocb_next_follower = NULL; 2395 } 2396 } while (rdp); 2397 rdp_spawn->nocb_next_follower = rdp_old_leader; 2398 } 2399 2400 /* Spawn the kthread for this CPU and RCU flavor. */ 2401 t = kthread_run(rcu_nocb_kthread, rdp_spawn, 2402 "rcuo%c/%d", rsp->abbr, cpu); 2403 BUG_ON(IS_ERR(t)); 2404 WRITE_ONCE(rdp_spawn->nocb_kthread, t); 2405 } 2406 2407 /* 2408 * If the specified CPU is a no-CBs CPU that does not already have its 2409 * rcuo kthreads, spawn them. 2410 */ 2411 static void rcu_spawn_all_nocb_kthreads(int cpu) 2412 { 2413 struct rcu_state *rsp; 2414 2415 if (rcu_scheduler_fully_active) 2416 for_each_rcu_flavor(rsp) 2417 rcu_spawn_one_nocb_kthread(rsp, cpu); 2418 } 2419 2420 /* 2421 * Once the scheduler is running, spawn rcuo kthreads for all online 2422 * no-CBs CPUs. This assumes that the early_initcall()s happen before 2423 * non-boot CPUs come online -- if this changes, we will need to add 2424 * some mutual exclusion. 2425 */ 2426 static void __init rcu_spawn_nocb_kthreads(void) 2427 { 2428 int cpu; 2429 2430 for_each_online_cpu(cpu) 2431 rcu_spawn_all_nocb_kthreads(cpu); 2432 } 2433 2434 /* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */ 2435 static int rcu_nocb_leader_stride = -1; 2436 module_param(rcu_nocb_leader_stride, int, 0444); 2437 2438 /* 2439 * Initialize leader-follower relationships for all no-CBs CPU. 2440 */ 2441 static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp) 2442 { 2443 int cpu; 2444 int ls = rcu_nocb_leader_stride; 2445 int nl = 0; /* Next leader. */ 2446 struct rcu_data *rdp; 2447 struct rcu_data *rdp_leader = NULL; /* Suppress misguided gcc warn. */ 2448 struct rcu_data *rdp_prev = NULL; 2449 2450 if (!have_rcu_nocb_mask) 2451 return; 2452 if (ls == -1) { 2453 ls = int_sqrt(nr_cpu_ids); 2454 rcu_nocb_leader_stride = ls; 2455 } 2456 2457 /* 2458 * Each pass through this loop sets up one rcu_data structure and 2459 * spawns one rcu_nocb_kthread(). 2460 */ 2461 for_each_cpu(cpu, rcu_nocb_mask) { 2462 rdp = per_cpu_ptr(rsp->rda, cpu); 2463 if (rdp->cpu >= nl) { 2464 /* New leader, set up for followers & next leader. */ 2465 nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls; 2466 rdp->nocb_leader = rdp; 2467 rdp_leader = rdp; 2468 } else { 2469 /* Another follower, link to previous leader. */ 2470 rdp->nocb_leader = rdp_leader; 2471 rdp_prev->nocb_next_follower = rdp; 2472 } 2473 rdp_prev = rdp; 2474 } 2475 } 2476 2477 /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */ 2478 static bool init_nocb_callback_list(struct rcu_data *rdp) 2479 { 2480 if (!rcu_is_nocb_cpu(rdp->cpu)) 2481 return false; 2482 2483 /* If there are early-boot callbacks, move them to nocb lists. */ 2484 if (rdp->nxtlist) { 2485 rdp->nocb_head = rdp->nxtlist; 2486 rdp->nocb_tail = rdp->nxttail[RCU_NEXT_TAIL]; 2487 atomic_long_set(&rdp->nocb_q_count, rdp->qlen); 2488 atomic_long_set(&rdp->nocb_q_count_lazy, rdp->qlen_lazy); 2489 rdp->nxtlist = NULL; 2490 rdp->qlen = 0; 2491 rdp->qlen_lazy = 0; 2492 } 2493 rdp->nxttail[RCU_NEXT_TAIL] = NULL; 2494 return true; 2495 } 2496 2497 #else /* #ifdef CONFIG_RCU_NOCB_CPU */ 2498 2499 static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu) 2500 { 2501 WARN_ON_ONCE(1); /* Should be dead code. */ 2502 return false; 2503 } 2504 2505 static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) 2506 { 2507 } 2508 2509 static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) 2510 { 2511 } 2512 2513 static void rcu_init_one_nocb(struct rcu_node *rnp) 2514 { 2515 } 2516 2517 static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, 2518 bool lazy, unsigned long flags) 2519 { 2520 return false; 2521 } 2522 2523 static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, 2524 struct rcu_data *rdp, 2525 unsigned long flags) 2526 { 2527 return false; 2528 } 2529 2530 static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) 2531 { 2532 } 2533 2534 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) 2535 { 2536 return false; 2537 } 2538 2539 static void do_nocb_deferred_wakeup(struct rcu_data *rdp) 2540 { 2541 } 2542 2543 static void rcu_spawn_all_nocb_kthreads(int cpu) 2544 { 2545 } 2546 2547 static void __init rcu_spawn_nocb_kthreads(void) 2548 { 2549 } 2550 2551 static bool init_nocb_callback_list(struct rcu_data *rdp) 2552 { 2553 return false; 2554 } 2555 2556 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ 2557 2558 /* 2559 * An adaptive-ticks CPU can potentially execute in kernel mode for an 2560 * arbitrarily long period of time with the scheduling-clock tick turned 2561 * off. RCU will be paying attention to this CPU because it is in the 2562 * kernel, but the CPU cannot be guaranteed to be executing the RCU state 2563 * machine because the scheduling-clock tick has been disabled. Therefore, 2564 * if an adaptive-ticks CPU is failing to respond to the current grace 2565 * period and has not be idle from an RCU perspective, kick it. 2566 */ 2567 static void __maybe_unused rcu_kick_nohz_cpu(int cpu) 2568 { 2569 #ifdef CONFIG_NO_HZ_FULL 2570 if (tick_nohz_full_cpu(cpu)) 2571 smp_send_reschedule(cpu); 2572 #endif /* #ifdef CONFIG_NO_HZ_FULL */ 2573 } 2574 2575 2576 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE 2577 2578 static int full_sysidle_state; /* Current system-idle state. */ 2579 #define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */ 2580 #define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */ 2581 #define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */ 2582 #define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */ 2583 #define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */ 2584 2585 /* 2586 * Invoked to note exit from irq or task transition to idle. Note that 2587 * usermode execution does -not- count as idle here! After all, we want 2588 * to detect full-system idle states, not RCU quiescent states and grace 2589 * periods. The caller must have disabled interrupts. 2590 */ 2591 static void rcu_sysidle_enter(int irq) 2592 { 2593 unsigned long j; 2594 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); 2595 2596 /* If there are no nohz_full= CPUs, no need to track this. */ 2597 if (!tick_nohz_full_enabled()) 2598 return; 2599 2600 /* Adjust nesting, check for fully idle. */ 2601 if (irq) { 2602 rdtp->dynticks_idle_nesting--; 2603 WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0); 2604 if (rdtp->dynticks_idle_nesting != 0) 2605 return; /* Still not fully idle. */ 2606 } else { 2607 if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) == 2608 DYNTICK_TASK_NEST_VALUE) { 2609 rdtp->dynticks_idle_nesting = 0; 2610 } else { 2611 rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE; 2612 WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0); 2613 return; /* Still not fully idle. */ 2614 } 2615 } 2616 2617 /* Record start of fully idle period. */ 2618 j = jiffies; 2619 WRITE_ONCE(rdtp->dynticks_idle_jiffies, j); 2620 smp_mb__before_atomic(); 2621 atomic_inc(&rdtp->dynticks_idle); 2622 smp_mb__after_atomic(); 2623 WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1); 2624 } 2625 2626 /* 2627 * Unconditionally force exit from full system-idle state. This is 2628 * invoked when a normal CPU exits idle, but must be called separately 2629 * for the timekeeping CPU (tick_do_timer_cpu). The reason for this 2630 * is that the timekeeping CPU is permitted to take scheduling-clock 2631 * interrupts while the system is in system-idle state, and of course 2632 * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock 2633 * interrupt from any other type of interrupt. 2634 */ 2635 void rcu_sysidle_force_exit(void) 2636 { 2637 int oldstate = READ_ONCE(full_sysidle_state); 2638 int newoldstate; 2639 2640 /* 2641 * Each pass through the following loop attempts to exit full 2642 * system-idle state. If contention proves to be a problem, 2643 * a trylock-based contention tree could be used here. 2644 */ 2645 while (oldstate > RCU_SYSIDLE_SHORT) { 2646 newoldstate = cmpxchg(&full_sysidle_state, 2647 oldstate, RCU_SYSIDLE_NOT); 2648 if (oldstate == newoldstate && 2649 oldstate == RCU_SYSIDLE_FULL_NOTED) { 2650 rcu_kick_nohz_cpu(tick_do_timer_cpu); 2651 return; /* We cleared it, done! */ 2652 } 2653 oldstate = newoldstate; 2654 } 2655 smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */ 2656 } 2657 2658 /* 2659 * Invoked to note entry to irq or task transition from idle. Note that 2660 * usermode execution does -not- count as idle here! The caller must 2661 * have disabled interrupts. 2662 */ 2663 static void rcu_sysidle_exit(int irq) 2664 { 2665 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); 2666 2667 /* If there are no nohz_full= CPUs, no need to track this. */ 2668 if (!tick_nohz_full_enabled()) 2669 return; 2670 2671 /* Adjust nesting, check for already non-idle. */ 2672 if (irq) { 2673 rdtp->dynticks_idle_nesting++; 2674 WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0); 2675 if (rdtp->dynticks_idle_nesting != 1) 2676 return; /* Already non-idle. */ 2677 } else { 2678 /* 2679 * Allow for irq misnesting. Yes, it really is possible 2680 * to enter an irq handler then never leave it, and maybe 2681 * also vice versa. Handle both possibilities. 2682 */ 2683 if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) { 2684 rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE; 2685 WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0); 2686 return; /* Already non-idle. */ 2687 } else { 2688 rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE; 2689 } 2690 } 2691 2692 /* Record end of idle period. */ 2693 smp_mb__before_atomic(); 2694 atomic_inc(&rdtp->dynticks_idle); 2695 smp_mb__after_atomic(); 2696 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1)); 2697 2698 /* 2699 * If we are the timekeeping CPU, we are permitted to be non-idle 2700 * during a system-idle state. This must be the case, because 2701 * the timekeeping CPU has to take scheduling-clock interrupts 2702 * during the time that the system is transitioning to full 2703 * system-idle state. This means that the timekeeping CPU must 2704 * invoke rcu_sysidle_force_exit() directly if it does anything 2705 * more than take a scheduling-clock interrupt. 2706 */ 2707 if (smp_processor_id() == tick_do_timer_cpu) 2708 return; 2709 2710 /* Update system-idle state: We are clearly no longer fully idle! */ 2711 rcu_sysidle_force_exit(); 2712 } 2713 2714 /* 2715 * Check to see if the current CPU is idle. Note that usermode execution 2716 * does not count as idle. The caller must have disabled interrupts, 2717 * and must be running on tick_do_timer_cpu. 2718 */ 2719 static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, 2720 unsigned long *maxj) 2721 { 2722 int cur; 2723 unsigned long j; 2724 struct rcu_dynticks *rdtp = rdp->dynticks; 2725 2726 /* If there are no nohz_full= CPUs, don't check system-wide idleness. */ 2727 if (!tick_nohz_full_enabled()) 2728 return; 2729 2730 /* 2731 * If some other CPU has already reported non-idle, if this is 2732 * not the flavor of RCU that tracks sysidle state, or if this 2733 * is an offline or the timekeeping CPU, nothing to do. 2734 */ 2735 if (!*isidle || rdp->rsp != rcu_state_p || 2736 cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu) 2737 return; 2738 /* Verify affinity of current kthread. */ 2739 WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu); 2740 2741 /* Pick up current idle and NMI-nesting counter and check. */ 2742 cur = atomic_read(&rdtp->dynticks_idle); 2743 if (cur & 0x1) { 2744 *isidle = false; /* We are not idle! */ 2745 return; 2746 } 2747 smp_mb(); /* Read counters before timestamps. */ 2748 2749 /* Pick up timestamps. */ 2750 j = READ_ONCE(rdtp->dynticks_idle_jiffies); 2751 /* If this CPU entered idle more recently, update maxj timestamp. */ 2752 if (ULONG_CMP_LT(*maxj, j)) 2753 *maxj = j; 2754 } 2755 2756 /* 2757 * Is this the flavor of RCU that is handling full-system idle? 2758 */ 2759 static bool is_sysidle_rcu_state(struct rcu_state *rsp) 2760 { 2761 return rsp == rcu_state_p; 2762 } 2763 2764 /* 2765 * Return a delay in jiffies based on the number of CPUs, rcu_node 2766 * leaf fanout, and jiffies tick rate. The idea is to allow larger 2767 * systems more time to transition to full-idle state in order to 2768 * avoid the cache thrashing that otherwise occur on the state variable. 2769 * Really small systems (less than a couple of tens of CPUs) should 2770 * instead use a single global atomically incremented counter, and later 2771 * versions of this will automatically reconfigure themselves accordingly. 2772 */ 2773 static unsigned long rcu_sysidle_delay(void) 2774 { 2775 if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) 2776 return 0; 2777 return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000); 2778 } 2779 2780 /* 2781 * Advance the full-system-idle state. This is invoked when all of 2782 * the non-timekeeping CPUs are idle. 2783 */ 2784 static void rcu_sysidle(unsigned long j) 2785 { 2786 /* Check the current state. */ 2787 switch (READ_ONCE(full_sysidle_state)) { 2788 case RCU_SYSIDLE_NOT: 2789 2790 /* First time all are idle, so note a short idle period. */ 2791 WRITE_ONCE(full_sysidle_state, RCU_SYSIDLE_SHORT); 2792 break; 2793 2794 case RCU_SYSIDLE_SHORT: 2795 2796 /* 2797 * Idle for a bit, time to advance to next state? 2798 * cmpxchg failure means race with non-idle, let them win. 2799 */ 2800 if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay())) 2801 (void)cmpxchg(&full_sysidle_state, 2802 RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG); 2803 break; 2804 2805 case RCU_SYSIDLE_LONG: 2806 2807 /* 2808 * Do an additional check pass before advancing to full. 2809 * cmpxchg failure means race with non-idle, let them win. 2810 */ 2811 if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay())) 2812 (void)cmpxchg(&full_sysidle_state, 2813 RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL); 2814 break; 2815 2816 default: 2817 break; 2818 } 2819 } 2820 2821 /* 2822 * Found a non-idle non-timekeeping CPU, so kick the system-idle state 2823 * back to the beginning. 2824 */ 2825 static void rcu_sysidle_cancel(void) 2826 { 2827 smp_mb(); 2828 if (full_sysidle_state > RCU_SYSIDLE_SHORT) 2829 WRITE_ONCE(full_sysidle_state, RCU_SYSIDLE_NOT); 2830 } 2831 2832 /* 2833 * Update the sysidle state based on the results of a force-quiescent-state 2834 * scan of the CPUs' dyntick-idle state. 2835 */ 2836 static void rcu_sysidle_report(struct rcu_state *rsp, int isidle, 2837 unsigned long maxj, bool gpkt) 2838 { 2839 if (rsp != rcu_state_p) 2840 return; /* Wrong flavor, ignore. */ 2841 if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) 2842 return; /* Running state machine from timekeeping CPU. */ 2843 if (isidle) 2844 rcu_sysidle(maxj); /* More idle! */ 2845 else 2846 rcu_sysidle_cancel(); /* Idle is over. */ 2847 } 2848 2849 /* 2850 * Wrapper for rcu_sysidle_report() when called from the grace-period 2851 * kthread's context. 2852 */ 2853 static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle, 2854 unsigned long maxj) 2855 { 2856 /* If there are no nohz_full= CPUs, no need to track this. */ 2857 if (!tick_nohz_full_enabled()) 2858 return; 2859 2860 rcu_sysidle_report(rsp, isidle, maxj, true); 2861 } 2862 2863 /* Callback and function for forcing an RCU grace period. */ 2864 struct rcu_sysidle_head { 2865 struct rcu_head rh; 2866 int inuse; 2867 }; 2868 2869 static void rcu_sysidle_cb(struct rcu_head *rhp) 2870 { 2871 struct rcu_sysidle_head *rshp; 2872 2873 /* 2874 * The following memory barrier is needed to replace the 2875 * memory barriers that would normally be in the memory 2876 * allocator. 2877 */ 2878 smp_mb(); /* grace period precedes setting inuse. */ 2879 2880 rshp = container_of(rhp, struct rcu_sysidle_head, rh); 2881 WRITE_ONCE(rshp->inuse, 0); 2882 } 2883 2884 /* 2885 * Check to see if the system is fully idle, other than the timekeeping CPU. 2886 * The caller must have disabled interrupts. This is not intended to be 2887 * called unless tick_nohz_full_enabled(). 2888 */ 2889 bool rcu_sys_is_idle(void) 2890 { 2891 static struct rcu_sysidle_head rsh; 2892 int rss = READ_ONCE(full_sysidle_state); 2893 2894 if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu)) 2895 return false; 2896 2897 /* Handle small-system case by doing a full scan of CPUs. */ 2898 if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) { 2899 int oldrss = rss - 1; 2900 2901 /* 2902 * One pass to advance to each state up to _FULL. 2903 * Give up if any pass fails to advance the state. 2904 */ 2905 while (rss < RCU_SYSIDLE_FULL && oldrss < rss) { 2906 int cpu; 2907 bool isidle = true; 2908 unsigned long maxj = jiffies - ULONG_MAX / 4; 2909 struct rcu_data *rdp; 2910 2911 /* Scan all the CPUs looking for nonidle CPUs. */ 2912 for_each_possible_cpu(cpu) { 2913 rdp = per_cpu_ptr(rcu_state_p->rda, cpu); 2914 rcu_sysidle_check_cpu(rdp, &isidle, &maxj); 2915 if (!isidle) 2916 break; 2917 } 2918 rcu_sysidle_report(rcu_state_p, isidle, maxj, false); 2919 oldrss = rss; 2920 rss = READ_ONCE(full_sysidle_state); 2921 } 2922 } 2923 2924 /* If this is the first observation of an idle period, record it. */ 2925 if (rss == RCU_SYSIDLE_FULL) { 2926 rss = cmpxchg(&full_sysidle_state, 2927 RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED); 2928 return rss == RCU_SYSIDLE_FULL; 2929 } 2930 2931 smp_mb(); /* ensure rss load happens before later caller actions. */ 2932 2933 /* If already fully idle, tell the caller (in case of races). */ 2934 if (rss == RCU_SYSIDLE_FULL_NOTED) 2935 return true; 2936 2937 /* 2938 * If we aren't there yet, and a grace period is not in flight, 2939 * initiate a grace period. Either way, tell the caller that 2940 * we are not there yet. We use an xchg() rather than an assignment 2941 * to make up for the memory barriers that would otherwise be 2942 * provided by the memory allocator. 2943 */ 2944 if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL && 2945 !rcu_gp_in_progress(rcu_state_p) && 2946 !rsh.inuse && xchg(&rsh.inuse, 1) == 0) 2947 call_rcu(&rsh.rh, rcu_sysidle_cb); 2948 return false; 2949 } 2950 2951 /* 2952 * Initialize dynticks sysidle state for CPUs coming online. 2953 */ 2954 static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp) 2955 { 2956 rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE; 2957 } 2958 2959 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ 2960 2961 static void rcu_sysidle_enter(int irq) 2962 { 2963 } 2964 2965 static void rcu_sysidle_exit(int irq) 2966 { 2967 } 2968 2969 static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, 2970 unsigned long *maxj) 2971 { 2972 } 2973 2974 static bool is_sysidle_rcu_state(struct rcu_state *rsp) 2975 { 2976 return false; 2977 } 2978 2979 static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle, 2980 unsigned long maxj) 2981 { 2982 } 2983 2984 static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp) 2985 { 2986 } 2987 2988 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ 2989 2990 /* 2991 * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the 2992 * grace-period kthread will do force_quiescent_state() processing? 2993 * The idea is to avoid waking up RCU core processing on such a 2994 * CPU unless the grace period has extended for too long. 2995 * 2996 * This code relies on the fact that all NO_HZ_FULL CPUs are also 2997 * CONFIG_RCU_NOCB_CPU CPUs. 2998 */ 2999 static bool rcu_nohz_full_cpu(struct rcu_state *rsp) 3000 { 3001 #ifdef CONFIG_NO_HZ_FULL 3002 if (tick_nohz_full_cpu(smp_processor_id()) && 3003 (!rcu_gp_in_progress(rsp) || 3004 ULONG_CMP_LT(jiffies, READ_ONCE(rsp->gp_start) + HZ))) 3005 return true; 3006 #endif /* #ifdef CONFIG_NO_HZ_FULL */ 3007 return false; 3008 } 3009 3010 /* 3011 * Bind the grace-period kthread for the sysidle flavor of RCU to the 3012 * timekeeping CPU. 3013 */ 3014 static void rcu_bind_gp_kthread(void) 3015 { 3016 int __maybe_unused cpu; 3017 3018 if (!tick_nohz_full_enabled()) 3019 return; 3020 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE 3021 cpu = tick_do_timer_cpu; 3022 if (cpu >= 0 && cpu < nr_cpu_ids) 3023 set_cpus_allowed_ptr(current, cpumask_of(cpu)); 3024 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ 3025 housekeeping_affine(current); 3026 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ 3027 } 3028 3029 /* Record the current task on dyntick-idle entry. */ 3030 static void rcu_dynticks_task_enter(void) 3031 { 3032 #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) 3033 WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id()); 3034 #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */ 3035 } 3036 3037 /* Record no current task on dyntick-idle exit. */ 3038 static void rcu_dynticks_task_exit(void) 3039 { 3040 #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) 3041 WRITE_ONCE(current->rcu_tasks_idle_cpu, -1); 3042 #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */ 3043 } 3044