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_rcu_node(rnp); /* interrupts 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_rcu_node(rnp, 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_rcu_node(rnp, 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_rcu_node(rnp, 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; 810 811 /* 812 * Tell them what RCU they are running. 813 */ 814 static void __init rcu_bootup_announce(void) 815 { 816 pr_info("Hierarchical RCU implementation.\n"); 817 rcu_bootup_announce_oddness(); 818 } 819 820 /* 821 * Because preemptible RCU does not exist, we never have to check for 822 * CPUs being in quiescent states. 823 */ 824 static void rcu_preempt_note_context_switch(void) 825 { 826 } 827 828 /* 829 * Because preemptible RCU does not exist, there are never any preempted 830 * RCU readers. 831 */ 832 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) 833 { 834 return 0; 835 } 836 837 /* 838 * Because there is no preemptible RCU, there can be no readers blocked. 839 */ 840 static bool rcu_preempt_has_tasks(struct rcu_node *rnp) 841 { 842 return false; 843 } 844 845 /* 846 * Because preemptible RCU does not exist, we never have to check for 847 * tasks blocked within RCU read-side critical sections. 848 */ 849 static void rcu_print_detail_task_stall(struct rcu_state *rsp) 850 { 851 } 852 853 /* 854 * Because preemptible RCU does not exist, we never have to check for 855 * tasks blocked within RCU read-side critical sections. 856 */ 857 static int rcu_print_task_stall(struct rcu_node *rnp) 858 { 859 return 0; 860 } 861 862 /* 863 * Because preemptible RCU does not exist, we never have to check for 864 * tasks blocked within RCU read-side critical sections that are 865 * blocking the current expedited grace period. 866 */ 867 static int rcu_print_task_exp_stall(struct rcu_node *rnp) 868 { 869 return 0; 870 } 871 872 /* 873 * Because there is no preemptible RCU, there can be no readers blocked, 874 * so there is no need to check for blocked tasks. So check only for 875 * bogus qsmask values. 876 */ 877 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) 878 { 879 WARN_ON_ONCE(rnp->qsmask); 880 } 881 882 /* 883 * Because preemptible RCU does not exist, it never has any callbacks 884 * to check. 885 */ 886 static void rcu_preempt_check_callbacks(void) 887 { 888 } 889 890 /* 891 * Wait for an rcu-preempt grace period, but make it happen quickly. 892 * But because preemptible RCU does not exist, map to rcu-sched. 893 */ 894 void synchronize_rcu_expedited(void) 895 { 896 synchronize_sched_expedited(); 897 } 898 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); 899 900 /* 901 * Because preemptible RCU does not exist, rcu_barrier() is just 902 * another name for rcu_barrier_sched(). 903 */ 904 void rcu_barrier(void) 905 { 906 rcu_barrier_sched(); 907 } 908 EXPORT_SYMBOL_GPL(rcu_barrier); 909 910 /* 911 * Because preemptible RCU does not exist, it need not be initialized. 912 */ 913 static void __init __rcu_init_preempt(void) 914 { 915 } 916 917 /* 918 * Because preemptible RCU does not exist, tasks cannot possibly exit 919 * while in preemptible RCU read-side critical sections. 920 */ 921 void exit_rcu(void) 922 { 923 } 924 925 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ 926 927 #ifdef CONFIG_RCU_BOOST 928 929 #include "../locking/rtmutex_common.h" 930 931 #ifdef CONFIG_RCU_TRACE 932 933 static void rcu_initiate_boost_trace(struct rcu_node *rnp) 934 { 935 if (!rcu_preempt_has_tasks(rnp)) 936 rnp->n_balk_blkd_tasks++; 937 else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL) 938 rnp->n_balk_exp_gp_tasks++; 939 else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL) 940 rnp->n_balk_boost_tasks++; 941 else if (rnp->gp_tasks != NULL && rnp->qsmask != 0) 942 rnp->n_balk_notblocked++; 943 else if (rnp->gp_tasks != NULL && 944 ULONG_CMP_LT(jiffies, rnp->boost_time)) 945 rnp->n_balk_notyet++; 946 else 947 rnp->n_balk_nos++; 948 } 949 950 #else /* #ifdef CONFIG_RCU_TRACE */ 951 952 static void rcu_initiate_boost_trace(struct rcu_node *rnp) 953 { 954 } 955 956 #endif /* #else #ifdef CONFIG_RCU_TRACE */ 957 958 static void rcu_wake_cond(struct task_struct *t, int status) 959 { 960 /* 961 * If the thread is yielding, only wake it when this 962 * is invoked from idle 963 */ 964 if (status != RCU_KTHREAD_YIELDING || is_idle_task(current)) 965 wake_up_process(t); 966 } 967 968 /* 969 * Carry out RCU priority boosting on the task indicated by ->exp_tasks 970 * or ->boost_tasks, advancing the pointer to the next task in the 971 * ->blkd_tasks list. 972 * 973 * Note that irqs must be enabled: boosting the task can block. 974 * Returns 1 if there are more tasks needing to be boosted. 975 */ 976 static int rcu_boost(struct rcu_node *rnp) 977 { 978 unsigned long flags; 979 struct task_struct *t; 980 struct list_head *tb; 981 982 if (READ_ONCE(rnp->exp_tasks) == NULL && 983 READ_ONCE(rnp->boost_tasks) == NULL) 984 return 0; /* Nothing left to boost. */ 985 986 raw_spin_lock_irqsave_rcu_node(rnp, flags); 987 988 /* 989 * Recheck under the lock: all tasks in need of boosting 990 * might exit their RCU read-side critical sections on their own. 991 */ 992 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) { 993 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 994 return 0; 995 } 996 997 /* 998 * Preferentially boost tasks blocking expedited grace periods. 999 * This cannot starve the normal grace periods because a second 1000 * expedited grace period must boost all blocked tasks, including 1001 * those blocking the pre-existing normal grace period. 1002 */ 1003 if (rnp->exp_tasks != NULL) { 1004 tb = rnp->exp_tasks; 1005 rnp->n_exp_boosts++; 1006 } else { 1007 tb = rnp->boost_tasks; 1008 rnp->n_normal_boosts++; 1009 } 1010 rnp->n_tasks_boosted++; 1011 1012 /* 1013 * We boost task t by manufacturing an rt_mutex that appears to 1014 * be held by task t. We leave a pointer to that rt_mutex where 1015 * task t can find it, and task t will release the mutex when it 1016 * exits its outermost RCU read-side critical section. Then 1017 * simply acquiring this artificial rt_mutex will boost task 1018 * t's priority. (Thanks to tglx for suggesting this approach!) 1019 * 1020 * Note that task t must acquire rnp->lock to remove itself from 1021 * the ->blkd_tasks list, which it will do from exit() if from 1022 * nowhere else. We therefore are guaranteed that task t will 1023 * stay around at least until we drop rnp->lock. Note that 1024 * rnp->lock also resolves races between our priority boosting 1025 * and task t's exiting its outermost RCU read-side critical 1026 * section. 1027 */ 1028 t = container_of(tb, struct task_struct, rcu_node_entry); 1029 rt_mutex_init_proxy_locked(&rnp->boost_mtx, t); 1030 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 1031 /* Lock only for side effect: boosts task t's priority. */ 1032 rt_mutex_lock(&rnp->boost_mtx); 1033 rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */ 1034 1035 return READ_ONCE(rnp->exp_tasks) != NULL || 1036 READ_ONCE(rnp->boost_tasks) != NULL; 1037 } 1038 1039 /* 1040 * Priority-boosting kthread, one per leaf rcu_node. 1041 */ 1042 static int rcu_boost_kthread(void *arg) 1043 { 1044 struct rcu_node *rnp = (struct rcu_node *)arg; 1045 int spincnt = 0; 1046 int more2boost; 1047 1048 trace_rcu_utilization(TPS("Start boost kthread@init")); 1049 for (;;) { 1050 rnp->boost_kthread_status = RCU_KTHREAD_WAITING; 1051 trace_rcu_utilization(TPS("End boost kthread@rcu_wait")); 1052 rcu_wait(rnp->boost_tasks || rnp->exp_tasks); 1053 trace_rcu_utilization(TPS("Start boost kthread@rcu_wait")); 1054 rnp->boost_kthread_status = RCU_KTHREAD_RUNNING; 1055 more2boost = rcu_boost(rnp); 1056 if (more2boost) 1057 spincnt++; 1058 else 1059 spincnt = 0; 1060 if (spincnt > 10) { 1061 rnp->boost_kthread_status = RCU_KTHREAD_YIELDING; 1062 trace_rcu_utilization(TPS("End boost kthread@rcu_yield")); 1063 schedule_timeout_interruptible(2); 1064 trace_rcu_utilization(TPS("Start boost kthread@rcu_yield")); 1065 spincnt = 0; 1066 } 1067 } 1068 /* NOTREACHED */ 1069 trace_rcu_utilization(TPS("End boost kthread@notreached")); 1070 return 0; 1071 } 1072 1073 /* 1074 * Check to see if it is time to start boosting RCU readers that are 1075 * blocking the current grace period, and, if so, tell the per-rcu_node 1076 * kthread to start boosting them. If there is an expedited grace 1077 * period in progress, it is always time to boost. 1078 * 1079 * The caller must hold rnp->lock, which this function releases. 1080 * The ->boost_kthread_task is immortal, so we don't need to worry 1081 * about it going away. 1082 */ 1083 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) 1084 __releases(rnp->lock) 1085 { 1086 struct task_struct *t; 1087 1088 if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) { 1089 rnp->n_balk_exp_gp_tasks++; 1090 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 1091 return; 1092 } 1093 if (rnp->exp_tasks != NULL || 1094 (rnp->gp_tasks != NULL && 1095 rnp->boost_tasks == NULL && 1096 rnp->qsmask == 0 && 1097 ULONG_CMP_GE(jiffies, rnp->boost_time))) { 1098 if (rnp->exp_tasks == NULL) 1099 rnp->boost_tasks = rnp->gp_tasks; 1100 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 1101 t = rnp->boost_kthread_task; 1102 if (t) 1103 rcu_wake_cond(t, rnp->boost_kthread_status); 1104 } else { 1105 rcu_initiate_boost_trace(rnp); 1106 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 1107 } 1108 } 1109 1110 /* 1111 * Wake up the per-CPU kthread to invoke RCU callbacks. 1112 */ 1113 static void invoke_rcu_callbacks_kthread(void) 1114 { 1115 unsigned long flags; 1116 1117 local_irq_save(flags); 1118 __this_cpu_write(rcu_cpu_has_work, 1); 1119 if (__this_cpu_read(rcu_cpu_kthread_task) != NULL && 1120 current != __this_cpu_read(rcu_cpu_kthread_task)) { 1121 rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task), 1122 __this_cpu_read(rcu_cpu_kthread_status)); 1123 } 1124 local_irq_restore(flags); 1125 } 1126 1127 /* 1128 * Is the current CPU running the RCU-callbacks kthread? 1129 * Caller must have preemption disabled. 1130 */ 1131 static bool rcu_is_callbacks_kthread(void) 1132 { 1133 return __this_cpu_read(rcu_cpu_kthread_task) == current; 1134 } 1135 1136 #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) 1137 1138 /* 1139 * Do priority-boost accounting for the start of a new grace period. 1140 */ 1141 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) 1142 { 1143 rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; 1144 } 1145 1146 /* 1147 * Create an RCU-boost kthread for the specified node if one does not 1148 * already exist. We only create this kthread for preemptible RCU. 1149 * Returns zero if all is well, a negated errno otherwise. 1150 */ 1151 static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp, 1152 struct rcu_node *rnp) 1153 { 1154 int rnp_index = rnp - &rsp->node[0]; 1155 unsigned long flags; 1156 struct sched_param sp; 1157 struct task_struct *t; 1158 1159 if (rcu_state_p != rsp) 1160 return 0; 1161 1162 if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0) 1163 return 0; 1164 1165 rsp->boost = 1; 1166 if (rnp->boost_kthread_task != NULL) 1167 return 0; 1168 t = kthread_create(rcu_boost_kthread, (void *)rnp, 1169 "rcub/%d", rnp_index); 1170 if (IS_ERR(t)) 1171 return PTR_ERR(t); 1172 raw_spin_lock_irqsave_rcu_node(rnp, flags); 1173 rnp->boost_kthread_task = t; 1174 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 1175 sp.sched_priority = kthread_prio; 1176 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); 1177 wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ 1178 return 0; 1179 } 1180 1181 static void rcu_kthread_do_work(void) 1182 { 1183 rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data)); 1184 rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data)); 1185 rcu_preempt_do_callbacks(); 1186 } 1187 1188 static void rcu_cpu_kthread_setup(unsigned int cpu) 1189 { 1190 struct sched_param sp; 1191 1192 sp.sched_priority = kthread_prio; 1193 sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); 1194 } 1195 1196 static void rcu_cpu_kthread_park(unsigned int cpu) 1197 { 1198 per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; 1199 } 1200 1201 static int rcu_cpu_kthread_should_run(unsigned int cpu) 1202 { 1203 return __this_cpu_read(rcu_cpu_has_work); 1204 } 1205 1206 /* 1207 * Per-CPU kernel thread that invokes RCU callbacks. This replaces the 1208 * RCU softirq used in flavors and configurations of RCU that do not 1209 * support RCU priority boosting. 1210 */ 1211 static void rcu_cpu_kthread(unsigned int cpu) 1212 { 1213 unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status); 1214 char work, *workp = this_cpu_ptr(&rcu_cpu_has_work); 1215 int spincnt; 1216 1217 for (spincnt = 0; spincnt < 10; spincnt++) { 1218 trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait")); 1219 local_bh_disable(); 1220 *statusp = RCU_KTHREAD_RUNNING; 1221 this_cpu_inc(rcu_cpu_kthread_loops); 1222 local_irq_disable(); 1223 work = *workp; 1224 *workp = 0; 1225 local_irq_enable(); 1226 if (work) 1227 rcu_kthread_do_work(); 1228 local_bh_enable(); 1229 if (*workp == 0) { 1230 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait")); 1231 *statusp = RCU_KTHREAD_WAITING; 1232 return; 1233 } 1234 } 1235 *statusp = RCU_KTHREAD_YIELDING; 1236 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield")); 1237 schedule_timeout_interruptible(2); 1238 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield")); 1239 *statusp = RCU_KTHREAD_WAITING; 1240 } 1241 1242 /* 1243 * Set the per-rcu_node kthread's affinity to cover all CPUs that are 1244 * served by the rcu_node in question. The CPU hotplug lock is still 1245 * held, so the value of rnp->qsmaskinit will be stable. 1246 * 1247 * We don't include outgoingcpu in the affinity set, use -1 if there is 1248 * no outgoing CPU. If there are no CPUs left in the affinity set, 1249 * this function allows the kthread to execute on any CPU. 1250 */ 1251 static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) 1252 { 1253 struct task_struct *t = rnp->boost_kthread_task; 1254 unsigned long mask = rcu_rnp_online_cpus(rnp); 1255 cpumask_var_t cm; 1256 int cpu; 1257 1258 if (!t) 1259 return; 1260 if (!zalloc_cpumask_var(&cm, GFP_KERNEL)) 1261 return; 1262 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) 1263 if ((mask & 0x1) && cpu != outgoingcpu) 1264 cpumask_set_cpu(cpu, cm); 1265 if (cpumask_weight(cm) == 0) 1266 cpumask_setall(cm); 1267 set_cpus_allowed_ptr(t, cm); 1268 free_cpumask_var(cm); 1269 } 1270 1271 static struct smp_hotplug_thread rcu_cpu_thread_spec = { 1272 .store = &rcu_cpu_kthread_task, 1273 .thread_should_run = rcu_cpu_kthread_should_run, 1274 .thread_fn = rcu_cpu_kthread, 1275 .thread_comm = "rcuc/%u", 1276 .setup = rcu_cpu_kthread_setup, 1277 .park = rcu_cpu_kthread_park, 1278 }; 1279 1280 /* 1281 * Spawn boost kthreads -- called as soon as the scheduler is running. 1282 */ 1283 static void __init rcu_spawn_boost_kthreads(void) 1284 { 1285 struct rcu_node *rnp; 1286 int cpu; 1287 1288 for_each_possible_cpu(cpu) 1289 per_cpu(rcu_cpu_has_work, cpu) = 0; 1290 BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec)); 1291 rcu_for_each_leaf_node(rcu_state_p, rnp) 1292 (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp); 1293 } 1294 1295 static void rcu_prepare_kthreads(int cpu) 1296 { 1297 struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu); 1298 struct rcu_node *rnp = rdp->mynode; 1299 1300 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */ 1301 if (rcu_scheduler_fully_active) 1302 (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp); 1303 } 1304 1305 #else /* #ifdef CONFIG_RCU_BOOST */ 1306 1307 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) 1308 __releases(rnp->lock) 1309 { 1310 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 1311 } 1312 1313 static void invoke_rcu_callbacks_kthread(void) 1314 { 1315 WARN_ON_ONCE(1); 1316 } 1317 1318 static bool rcu_is_callbacks_kthread(void) 1319 { 1320 return false; 1321 } 1322 1323 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) 1324 { 1325 } 1326 1327 static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) 1328 { 1329 } 1330 1331 static void __init rcu_spawn_boost_kthreads(void) 1332 { 1333 } 1334 1335 static void rcu_prepare_kthreads(int cpu) 1336 { 1337 } 1338 1339 #endif /* #else #ifdef CONFIG_RCU_BOOST */ 1340 1341 #if !defined(CONFIG_RCU_FAST_NO_HZ) 1342 1343 /* 1344 * Check to see if any future RCU-related work will need to be done 1345 * by the current CPU, even if none need be done immediately, returning 1346 * 1 if so. This function is part of the RCU implementation; it is -not- 1347 * an exported member of the RCU API. 1348 * 1349 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs 1350 * any flavor of RCU. 1351 */ 1352 int rcu_needs_cpu(u64 basemono, u64 *nextevt) 1353 { 1354 *nextevt = KTIME_MAX; 1355 return IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL) 1356 ? 0 : rcu_cpu_has_callbacks(NULL); 1357 } 1358 1359 /* 1360 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up 1361 * after it. 1362 */ 1363 static void rcu_cleanup_after_idle(void) 1364 { 1365 } 1366 1367 /* 1368 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n, 1369 * is nothing. 1370 */ 1371 static void rcu_prepare_for_idle(void) 1372 { 1373 } 1374 1375 /* 1376 * Don't bother keeping a running count of the number of RCU callbacks 1377 * posted because CONFIG_RCU_FAST_NO_HZ=n. 1378 */ 1379 static void rcu_idle_count_callbacks_posted(void) 1380 { 1381 } 1382 1383 #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ 1384 1385 /* 1386 * This code is invoked when a CPU goes idle, at which point we want 1387 * to have the CPU do everything required for RCU so that it can enter 1388 * the energy-efficient dyntick-idle mode. This is handled by a 1389 * state machine implemented by rcu_prepare_for_idle() below. 1390 * 1391 * The following three proprocessor symbols control this state machine: 1392 * 1393 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted 1394 * to sleep in dyntick-idle mode with RCU callbacks pending. This 1395 * is sized to be roughly one RCU grace period. Those energy-efficiency 1396 * benchmarkers who might otherwise be tempted to set this to a large 1397 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your 1398 * system. And if you are -that- concerned about energy efficiency, 1399 * just power the system down and be done with it! 1400 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is 1401 * permitted to sleep in dyntick-idle mode with only lazy RCU 1402 * callbacks pending. Setting this too high can OOM your system. 1403 * 1404 * The values below work well in practice. If future workloads require 1405 * adjustment, they can be converted into kernel config parameters, though 1406 * making the state machine smarter might be a better option. 1407 */ 1408 #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */ 1409 #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */ 1410 1411 static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY; 1412 module_param(rcu_idle_gp_delay, int, 0644); 1413 static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY; 1414 module_param(rcu_idle_lazy_gp_delay, int, 0644); 1415 1416 /* 1417 * Try to advance callbacks for all flavors of RCU on the current CPU, but 1418 * only if it has been awhile since the last time we did so. Afterwards, 1419 * if there are any callbacks ready for immediate invocation, return true. 1420 */ 1421 static bool __maybe_unused rcu_try_advance_all_cbs(void) 1422 { 1423 bool cbs_ready = false; 1424 struct rcu_data *rdp; 1425 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); 1426 struct rcu_node *rnp; 1427 struct rcu_state *rsp; 1428 1429 /* Exit early if we advanced recently. */ 1430 if (jiffies == rdtp->last_advance_all) 1431 return false; 1432 rdtp->last_advance_all = jiffies; 1433 1434 for_each_rcu_flavor(rsp) { 1435 rdp = this_cpu_ptr(rsp->rda); 1436 rnp = rdp->mynode; 1437 1438 /* 1439 * Don't bother checking unless a grace period has 1440 * completed since we last checked and there are 1441 * callbacks not yet ready to invoke. 1442 */ 1443 if ((rdp->completed != rnp->completed || 1444 unlikely(READ_ONCE(rdp->gpwrap))) && 1445 rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL]) 1446 note_gp_changes(rsp, rdp); 1447 1448 if (cpu_has_callbacks_ready_to_invoke(rdp)) 1449 cbs_ready = true; 1450 } 1451 return cbs_ready; 1452 } 1453 1454 /* 1455 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready 1456 * to invoke. If the CPU has callbacks, try to advance them. Tell the 1457 * caller to set the timeout based on whether or not there are non-lazy 1458 * callbacks. 1459 * 1460 * The caller must have disabled interrupts. 1461 */ 1462 int rcu_needs_cpu(u64 basemono, u64 *nextevt) 1463 { 1464 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); 1465 unsigned long dj; 1466 1467 if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL)) { 1468 *nextevt = KTIME_MAX; 1469 return 0; 1470 } 1471 1472 /* Snapshot to detect later posting of non-lazy callback. */ 1473 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; 1474 1475 /* If no callbacks, RCU doesn't need the CPU. */ 1476 if (!rcu_cpu_has_callbacks(&rdtp->all_lazy)) { 1477 *nextevt = KTIME_MAX; 1478 return 0; 1479 } 1480 1481 /* Attempt to advance callbacks. */ 1482 if (rcu_try_advance_all_cbs()) { 1483 /* Some ready to invoke, so initiate later invocation. */ 1484 invoke_rcu_core(); 1485 return 1; 1486 } 1487 rdtp->last_accelerate = jiffies; 1488 1489 /* Request timer delay depending on laziness, and round. */ 1490 if (!rdtp->all_lazy) { 1491 dj = round_up(rcu_idle_gp_delay + jiffies, 1492 rcu_idle_gp_delay) - jiffies; 1493 } else { 1494 dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies; 1495 } 1496 *nextevt = basemono + dj * TICK_NSEC; 1497 return 0; 1498 } 1499 1500 /* 1501 * Prepare a CPU for idle from an RCU perspective. The first major task 1502 * is to sense whether nohz mode has been enabled or disabled via sysfs. 1503 * The second major task is to check to see if a non-lazy callback has 1504 * arrived at a CPU that previously had only lazy callbacks. The third 1505 * major task is to accelerate (that is, assign grace-period numbers to) 1506 * any recently arrived callbacks. 1507 * 1508 * The caller must have disabled interrupts. 1509 */ 1510 static void rcu_prepare_for_idle(void) 1511 { 1512 bool needwake; 1513 struct rcu_data *rdp; 1514 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); 1515 struct rcu_node *rnp; 1516 struct rcu_state *rsp; 1517 int tne; 1518 1519 if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL) || 1520 rcu_is_nocb_cpu(smp_processor_id())) 1521 return; 1522 1523 /* Handle nohz enablement switches conservatively. */ 1524 tne = READ_ONCE(tick_nohz_active); 1525 if (tne != rdtp->tick_nohz_enabled_snap) { 1526 if (rcu_cpu_has_callbacks(NULL)) 1527 invoke_rcu_core(); /* force nohz to see update. */ 1528 rdtp->tick_nohz_enabled_snap = tne; 1529 return; 1530 } 1531 if (!tne) 1532 return; 1533 1534 /* 1535 * If a non-lazy callback arrived at a CPU having only lazy 1536 * callbacks, invoke RCU core for the side-effect of recalculating 1537 * idle duration on re-entry to idle. 1538 */ 1539 if (rdtp->all_lazy && 1540 rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) { 1541 rdtp->all_lazy = false; 1542 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; 1543 invoke_rcu_core(); 1544 return; 1545 } 1546 1547 /* 1548 * If we have not yet accelerated this jiffy, accelerate all 1549 * callbacks on this CPU. 1550 */ 1551 if (rdtp->last_accelerate == jiffies) 1552 return; 1553 rdtp->last_accelerate = jiffies; 1554 for_each_rcu_flavor(rsp) { 1555 rdp = this_cpu_ptr(rsp->rda); 1556 if (!*rdp->nxttail[RCU_DONE_TAIL]) 1557 continue; 1558 rnp = rdp->mynode; 1559 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ 1560 needwake = rcu_accelerate_cbs(rsp, rnp, rdp); 1561 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ 1562 if (needwake) 1563 rcu_gp_kthread_wake(rsp); 1564 } 1565 } 1566 1567 /* 1568 * Clean up for exit from idle. Attempt to advance callbacks based on 1569 * any grace periods that elapsed while the CPU was idle, and if any 1570 * callbacks are now ready to invoke, initiate invocation. 1571 */ 1572 static void rcu_cleanup_after_idle(void) 1573 { 1574 if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL) || 1575 rcu_is_nocb_cpu(smp_processor_id())) 1576 return; 1577 if (rcu_try_advance_all_cbs()) 1578 invoke_rcu_core(); 1579 } 1580 1581 /* 1582 * Keep a running count of the number of non-lazy callbacks posted 1583 * on this CPU. This running counter (which is never decremented) allows 1584 * rcu_prepare_for_idle() to detect when something out of the idle loop 1585 * posts a callback, even if an equal number of callbacks are invoked. 1586 * Of course, callbacks should only be posted from within a trace event 1587 * designed to be called from idle or from within RCU_NONIDLE(). 1588 */ 1589 static void rcu_idle_count_callbacks_posted(void) 1590 { 1591 __this_cpu_add(rcu_dynticks.nonlazy_posted, 1); 1592 } 1593 1594 /* 1595 * Data for flushing lazy RCU callbacks at OOM time. 1596 */ 1597 static atomic_t oom_callback_count; 1598 static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq); 1599 1600 /* 1601 * RCU OOM callback -- decrement the outstanding count and deliver the 1602 * wake-up if we are the last one. 1603 */ 1604 static void rcu_oom_callback(struct rcu_head *rhp) 1605 { 1606 if (atomic_dec_and_test(&oom_callback_count)) 1607 wake_up(&oom_callback_wq); 1608 } 1609 1610 /* 1611 * Post an rcu_oom_notify callback on the current CPU if it has at 1612 * least one lazy callback. This will unnecessarily post callbacks 1613 * to CPUs that already have a non-lazy callback at the end of their 1614 * callback list, but this is an infrequent operation, so accept some 1615 * extra overhead to keep things simple. 1616 */ 1617 static void rcu_oom_notify_cpu(void *unused) 1618 { 1619 struct rcu_state *rsp; 1620 struct rcu_data *rdp; 1621 1622 for_each_rcu_flavor(rsp) { 1623 rdp = raw_cpu_ptr(rsp->rda); 1624 if (rdp->qlen_lazy != 0) { 1625 atomic_inc(&oom_callback_count); 1626 rsp->call(&rdp->oom_head, rcu_oom_callback); 1627 } 1628 } 1629 } 1630 1631 /* 1632 * If low on memory, ensure that each CPU has a non-lazy callback. 1633 * This will wake up CPUs that have only lazy callbacks, in turn 1634 * ensuring that they free up the corresponding memory in a timely manner. 1635 * Because an uncertain amount of memory will be freed in some uncertain 1636 * timeframe, we do not claim to have freed anything. 1637 */ 1638 static int rcu_oom_notify(struct notifier_block *self, 1639 unsigned long notused, void *nfreed) 1640 { 1641 int cpu; 1642 1643 /* Wait for callbacks from earlier instance to complete. */ 1644 wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0); 1645 smp_mb(); /* Ensure callback reuse happens after callback invocation. */ 1646 1647 /* 1648 * Prevent premature wakeup: ensure that all increments happen 1649 * before there is a chance of the counter reaching zero. 1650 */ 1651 atomic_set(&oom_callback_count, 1); 1652 1653 for_each_online_cpu(cpu) { 1654 smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1); 1655 cond_resched_rcu_qs(); 1656 } 1657 1658 /* Unconditionally decrement: no need to wake ourselves up. */ 1659 atomic_dec(&oom_callback_count); 1660 1661 return NOTIFY_OK; 1662 } 1663 1664 static struct notifier_block rcu_oom_nb = { 1665 .notifier_call = rcu_oom_notify 1666 }; 1667 1668 static int __init rcu_register_oom_notifier(void) 1669 { 1670 register_oom_notifier(&rcu_oom_nb); 1671 return 0; 1672 } 1673 early_initcall(rcu_register_oom_notifier); 1674 1675 #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ 1676 1677 #ifdef CONFIG_RCU_FAST_NO_HZ 1678 1679 static void print_cpu_stall_fast_no_hz(char *cp, int cpu) 1680 { 1681 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); 1682 unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap; 1683 1684 sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c", 1685 rdtp->last_accelerate & 0xffff, jiffies & 0xffff, 1686 ulong2long(nlpd), 1687 rdtp->all_lazy ? 'L' : '.', 1688 rdtp->tick_nohz_enabled_snap ? '.' : 'D'); 1689 } 1690 1691 #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ 1692 1693 static void print_cpu_stall_fast_no_hz(char *cp, int cpu) 1694 { 1695 *cp = '\0'; 1696 } 1697 1698 #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */ 1699 1700 /* Initiate the stall-info list. */ 1701 static void print_cpu_stall_info_begin(void) 1702 { 1703 pr_cont("\n"); 1704 } 1705 1706 /* 1707 * Print out diagnostic information for the specified stalled CPU. 1708 * 1709 * If the specified CPU is aware of the current RCU grace period 1710 * (flavor specified by rsp), then print the number of scheduling 1711 * clock interrupts the CPU has taken during the time that it has 1712 * been aware. Otherwise, print the number of RCU grace periods 1713 * that this CPU is ignorant of, for example, "1" if the CPU was 1714 * aware of the previous grace period. 1715 * 1716 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info. 1717 */ 1718 static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) 1719 { 1720 char fast_no_hz[72]; 1721 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); 1722 struct rcu_dynticks *rdtp = rdp->dynticks; 1723 char *ticks_title; 1724 unsigned long ticks_value; 1725 1726 if (rsp->gpnum == rdp->gpnum) { 1727 ticks_title = "ticks this GP"; 1728 ticks_value = rdp->ticks_this_gp; 1729 } else { 1730 ticks_title = "GPs behind"; 1731 ticks_value = rsp->gpnum - rdp->gpnum; 1732 } 1733 print_cpu_stall_fast_no_hz(fast_no_hz, cpu); 1734 pr_err("\t%d-%c%c%c: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u fqs=%ld %s\n", 1735 cpu, 1736 "O."[!!cpu_online(cpu)], 1737 "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)], 1738 "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)], 1739 ticks_value, ticks_title, 1740 atomic_read(&rdtp->dynticks) & 0xfff, 1741 rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting, 1742 rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu), 1743 READ_ONCE(rsp->n_force_qs) - rsp->n_force_qs_gpstart, 1744 fast_no_hz); 1745 } 1746 1747 /* Terminate the stall-info list. */ 1748 static void print_cpu_stall_info_end(void) 1749 { 1750 pr_err("\t"); 1751 } 1752 1753 /* Zero ->ticks_this_gp for all flavors of RCU. */ 1754 static void zero_cpu_stall_ticks(struct rcu_data *rdp) 1755 { 1756 rdp->ticks_this_gp = 0; 1757 rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id()); 1758 } 1759 1760 /* Increment ->ticks_this_gp for all flavors of RCU. */ 1761 static void increment_cpu_stall_ticks(void) 1762 { 1763 struct rcu_state *rsp; 1764 1765 for_each_rcu_flavor(rsp) 1766 raw_cpu_inc(rsp->rda->ticks_this_gp); 1767 } 1768 1769 #ifdef CONFIG_RCU_NOCB_CPU 1770 1771 /* 1772 * Offload callback processing from the boot-time-specified set of CPUs 1773 * specified by rcu_nocb_mask. For each CPU in the set, there is a 1774 * kthread created that pulls the callbacks from the corresponding CPU, 1775 * waits for a grace period to elapse, and invokes the callbacks. 1776 * The no-CBs CPUs do a wake_up() on their kthread when they insert 1777 * a callback into any empty list, unless the rcu_nocb_poll boot parameter 1778 * has been specified, in which case each kthread actively polls its 1779 * CPU. (Which isn't so great for energy efficiency, but which does 1780 * reduce RCU's overhead on that CPU.) 1781 * 1782 * This is intended to be used in conjunction with Frederic Weisbecker's 1783 * adaptive-idle work, which would seriously reduce OS jitter on CPUs 1784 * running CPU-bound user-mode computations. 1785 * 1786 * Offloading of callback processing could also in theory be used as 1787 * an energy-efficiency measure because CPUs with no RCU callbacks 1788 * queued are more aggressive about entering dyntick-idle mode. 1789 */ 1790 1791 1792 /* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */ 1793 static int __init rcu_nocb_setup(char *str) 1794 { 1795 alloc_bootmem_cpumask_var(&rcu_nocb_mask); 1796 have_rcu_nocb_mask = true; 1797 cpulist_parse(str, rcu_nocb_mask); 1798 return 1; 1799 } 1800 __setup("rcu_nocbs=", rcu_nocb_setup); 1801 1802 static int __init parse_rcu_nocb_poll(char *arg) 1803 { 1804 rcu_nocb_poll = 1; 1805 return 0; 1806 } 1807 early_param("rcu_nocb_poll", parse_rcu_nocb_poll); 1808 1809 /* 1810 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended 1811 * grace period. 1812 */ 1813 static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq) 1814 { 1815 swake_up_all(sq); 1816 } 1817 1818 /* 1819 * Set the root rcu_node structure's ->need_future_gp field 1820 * based on the sum of those of all rcu_node structures. This does 1821 * double-count the root rcu_node structure's requests, but this 1822 * is necessary to handle the possibility of a rcu_nocb_kthread() 1823 * having awakened during the time that the rcu_node structures 1824 * were being updated for the end of the previous grace period. 1825 */ 1826 static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) 1827 { 1828 rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq; 1829 } 1830 1831 static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp) 1832 { 1833 return &rnp->nocb_gp_wq[rnp->completed & 0x1]; 1834 } 1835 1836 static void rcu_init_one_nocb(struct rcu_node *rnp) 1837 { 1838 init_swait_queue_head(&rnp->nocb_gp_wq[0]); 1839 init_swait_queue_head(&rnp->nocb_gp_wq[1]); 1840 } 1841 1842 #ifndef CONFIG_RCU_NOCB_CPU_ALL 1843 /* Is the specified CPU a no-CBs CPU? */ 1844 bool rcu_is_nocb_cpu(int cpu) 1845 { 1846 if (have_rcu_nocb_mask) 1847 return cpumask_test_cpu(cpu, rcu_nocb_mask); 1848 return false; 1849 } 1850 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */ 1851 1852 /* 1853 * Kick the leader kthread for this NOCB group. 1854 */ 1855 static void wake_nocb_leader(struct rcu_data *rdp, bool force) 1856 { 1857 struct rcu_data *rdp_leader = rdp->nocb_leader; 1858 1859 if (!READ_ONCE(rdp_leader->nocb_kthread)) 1860 return; 1861 if (READ_ONCE(rdp_leader->nocb_leader_sleep) || force) { 1862 /* Prior smp_mb__after_atomic() orders against prior enqueue. */ 1863 WRITE_ONCE(rdp_leader->nocb_leader_sleep, false); 1864 swake_up(&rdp_leader->nocb_wq); 1865 } 1866 } 1867 1868 /* 1869 * Does the specified CPU need an RCU callback for the specified flavor 1870 * of rcu_barrier()? 1871 */ 1872 static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu) 1873 { 1874 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); 1875 unsigned long ret; 1876 #ifdef CONFIG_PROVE_RCU 1877 struct rcu_head *rhp; 1878 #endif /* #ifdef CONFIG_PROVE_RCU */ 1879 1880 /* 1881 * Check count of all no-CBs callbacks awaiting invocation. 1882 * There needs to be a barrier before this function is called, 1883 * but associated with a prior determination that no more 1884 * callbacks would be posted. In the worst case, the first 1885 * barrier in _rcu_barrier() suffices (but the caller cannot 1886 * necessarily rely on this, not a substitute for the caller 1887 * getting the concurrency design right!). There must also be 1888 * a barrier between the following load an posting of a callback 1889 * (if a callback is in fact needed). This is associated with an 1890 * atomic_inc() in the caller. 1891 */ 1892 ret = atomic_long_read(&rdp->nocb_q_count); 1893 1894 #ifdef CONFIG_PROVE_RCU 1895 rhp = READ_ONCE(rdp->nocb_head); 1896 if (!rhp) 1897 rhp = READ_ONCE(rdp->nocb_gp_head); 1898 if (!rhp) 1899 rhp = READ_ONCE(rdp->nocb_follower_head); 1900 1901 /* Having no rcuo kthread but CBs after scheduler starts is bad! */ 1902 if (!READ_ONCE(rdp->nocb_kthread) && rhp && 1903 rcu_scheduler_fully_active) { 1904 /* RCU callback enqueued before CPU first came online??? */ 1905 pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n", 1906 cpu, rhp->func); 1907 WARN_ON_ONCE(1); 1908 } 1909 #endif /* #ifdef CONFIG_PROVE_RCU */ 1910 1911 return !!ret; 1912 } 1913 1914 /* 1915 * Enqueue the specified string of rcu_head structures onto the specified 1916 * CPU's no-CBs lists. The CPU is specified by rdp, the head of the 1917 * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy 1918 * counts are supplied by rhcount and rhcount_lazy. 1919 * 1920 * If warranted, also wake up the kthread servicing this CPUs queues. 1921 */ 1922 static void __call_rcu_nocb_enqueue(struct rcu_data *rdp, 1923 struct rcu_head *rhp, 1924 struct rcu_head **rhtp, 1925 int rhcount, int rhcount_lazy, 1926 unsigned long flags) 1927 { 1928 int len; 1929 struct rcu_head **old_rhpp; 1930 struct task_struct *t; 1931 1932 /* Enqueue the callback on the nocb list and update counts. */ 1933 atomic_long_add(rhcount, &rdp->nocb_q_count); 1934 /* rcu_barrier() relies on ->nocb_q_count add before xchg. */ 1935 old_rhpp = xchg(&rdp->nocb_tail, rhtp); 1936 WRITE_ONCE(*old_rhpp, rhp); 1937 atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy); 1938 smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */ 1939 1940 /* If we are not being polled and there is a kthread, awaken it ... */ 1941 t = READ_ONCE(rdp->nocb_kthread); 1942 if (rcu_nocb_poll || !t) { 1943 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 1944 TPS("WakeNotPoll")); 1945 return; 1946 } 1947 len = atomic_long_read(&rdp->nocb_q_count); 1948 if (old_rhpp == &rdp->nocb_head) { 1949 if (!irqs_disabled_flags(flags)) { 1950 /* ... if queue was empty ... */ 1951 wake_nocb_leader(rdp, false); 1952 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 1953 TPS("WakeEmpty")); 1954 } else { 1955 rdp->nocb_defer_wakeup = RCU_NOGP_WAKE; 1956 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 1957 TPS("WakeEmptyIsDeferred")); 1958 } 1959 rdp->qlen_last_fqs_check = 0; 1960 } else if (len > rdp->qlen_last_fqs_check + qhimark) { 1961 /* ... or if many callbacks queued. */ 1962 if (!irqs_disabled_flags(flags)) { 1963 wake_nocb_leader(rdp, true); 1964 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 1965 TPS("WakeOvf")); 1966 } else { 1967 rdp->nocb_defer_wakeup = RCU_NOGP_WAKE_FORCE; 1968 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 1969 TPS("WakeOvfIsDeferred")); 1970 } 1971 rdp->qlen_last_fqs_check = LONG_MAX / 2; 1972 } else { 1973 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot")); 1974 } 1975 return; 1976 } 1977 1978 /* 1979 * This is a helper for __call_rcu(), which invokes this when the normal 1980 * callback queue is inoperable. If this is not a no-CBs CPU, this 1981 * function returns failure back to __call_rcu(), which can complain 1982 * appropriately. 1983 * 1984 * Otherwise, this function queues the callback where the corresponding 1985 * "rcuo" kthread can find it. 1986 */ 1987 static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, 1988 bool lazy, unsigned long flags) 1989 { 1990 1991 if (!rcu_is_nocb_cpu(rdp->cpu)) 1992 return false; 1993 __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags); 1994 if (__is_kfree_rcu_offset((unsigned long)rhp->func)) 1995 trace_rcu_kfree_callback(rdp->rsp->name, rhp, 1996 (unsigned long)rhp->func, 1997 -atomic_long_read(&rdp->nocb_q_count_lazy), 1998 -atomic_long_read(&rdp->nocb_q_count)); 1999 else 2000 trace_rcu_callback(rdp->rsp->name, rhp, 2001 -atomic_long_read(&rdp->nocb_q_count_lazy), 2002 -atomic_long_read(&rdp->nocb_q_count)); 2003 2004 /* 2005 * If called from an extended quiescent state with interrupts 2006 * disabled, invoke the RCU core in order to allow the idle-entry 2007 * deferred-wakeup check to function. 2008 */ 2009 if (irqs_disabled_flags(flags) && 2010 !rcu_is_watching() && 2011 cpu_online(smp_processor_id())) 2012 invoke_rcu_core(); 2013 2014 return true; 2015 } 2016 2017 /* 2018 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is 2019 * not a no-CBs CPU. 2020 */ 2021 static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, 2022 struct rcu_data *rdp, 2023 unsigned long flags) 2024 { 2025 long ql = rsp->qlen; 2026 long qll = rsp->qlen_lazy; 2027 2028 /* If this is not a no-CBs CPU, tell the caller to do it the old way. */ 2029 if (!rcu_is_nocb_cpu(smp_processor_id())) 2030 return false; 2031 rsp->qlen = 0; 2032 rsp->qlen_lazy = 0; 2033 2034 /* First, enqueue the donelist, if any. This preserves CB ordering. */ 2035 if (rsp->orphan_donelist != NULL) { 2036 __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist, 2037 rsp->orphan_donetail, ql, qll, flags); 2038 ql = qll = 0; 2039 rsp->orphan_donelist = NULL; 2040 rsp->orphan_donetail = &rsp->orphan_donelist; 2041 } 2042 if (rsp->orphan_nxtlist != NULL) { 2043 __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist, 2044 rsp->orphan_nxttail, ql, qll, flags); 2045 ql = qll = 0; 2046 rsp->orphan_nxtlist = NULL; 2047 rsp->orphan_nxttail = &rsp->orphan_nxtlist; 2048 } 2049 return true; 2050 } 2051 2052 /* 2053 * If necessary, kick off a new grace period, and either way wait 2054 * for a subsequent grace period to complete. 2055 */ 2056 static void rcu_nocb_wait_gp(struct rcu_data *rdp) 2057 { 2058 unsigned long c; 2059 bool d; 2060 unsigned long flags; 2061 bool needwake; 2062 struct rcu_node *rnp = rdp->mynode; 2063 2064 raw_spin_lock_irqsave_rcu_node(rnp, flags); 2065 needwake = rcu_start_future_gp(rnp, rdp, &c); 2066 raw_spin_unlock_irqrestore_rcu_node(rnp, flags); 2067 if (needwake) 2068 rcu_gp_kthread_wake(rdp->rsp); 2069 2070 /* 2071 * Wait for the grace period. Do so interruptibly to avoid messing 2072 * up the load average. 2073 */ 2074 trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait")); 2075 for (;;) { 2076 swait_event_interruptible( 2077 rnp->nocb_gp_wq[c & 0x1], 2078 (d = ULONG_CMP_GE(READ_ONCE(rnp->completed), c))); 2079 if (likely(d)) 2080 break; 2081 WARN_ON(signal_pending(current)); 2082 trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait")); 2083 } 2084 trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait")); 2085 smp_mb(); /* Ensure that CB invocation happens after GP end. */ 2086 } 2087 2088 /* 2089 * Leaders come here to wait for additional callbacks to show up. 2090 * This function does not return until callbacks appear. 2091 */ 2092 static void nocb_leader_wait(struct rcu_data *my_rdp) 2093 { 2094 bool firsttime = true; 2095 bool gotcbs; 2096 struct rcu_data *rdp; 2097 struct rcu_head **tail; 2098 2099 wait_again: 2100 2101 /* Wait for callbacks to appear. */ 2102 if (!rcu_nocb_poll) { 2103 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Sleep"); 2104 swait_event_interruptible(my_rdp->nocb_wq, 2105 !READ_ONCE(my_rdp->nocb_leader_sleep)); 2106 /* Memory barrier handled by smp_mb() calls below and repoll. */ 2107 } else if (firsttime) { 2108 firsttime = false; /* Don't drown trace log with "Poll"! */ 2109 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Poll"); 2110 } 2111 2112 /* 2113 * Each pass through the following loop checks a follower for CBs. 2114 * We are our own first follower. Any CBs found are moved to 2115 * nocb_gp_head, where they await a grace period. 2116 */ 2117 gotcbs = false; 2118 for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) { 2119 rdp->nocb_gp_head = READ_ONCE(rdp->nocb_head); 2120 if (!rdp->nocb_gp_head) 2121 continue; /* No CBs here, try next follower. */ 2122 2123 /* Move callbacks to wait-for-GP list, which is empty. */ 2124 WRITE_ONCE(rdp->nocb_head, NULL); 2125 rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head); 2126 gotcbs = true; 2127 } 2128 2129 /* 2130 * If there were no callbacks, sleep a bit, rescan after a 2131 * memory barrier, and go retry. 2132 */ 2133 if (unlikely(!gotcbs)) { 2134 if (!rcu_nocb_poll) 2135 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, 2136 "WokeEmpty"); 2137 WARN_ON(signal_pending(current)); 2138 schedule_timeout_interruptible(1); 2139 2140 /* Rescan in case we were a victim of memory ordering. */ 2141 my_rdp->nocb_leader_sleep = true; 2142 smp_mb(); /* Ensure _sleep true before scan. */ 2143 for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) 2144 if (READ_ONCE(rdp->nocb_head)) { 2145 /* Found CB, so short-circuit next wait. */ 2146 my_rdp->nocb_leader_sleep = false; 2147 break; 2148 } 2149 goto wait_again; 2150 } 2151 2152 /* Wait for one grace period. */ 2153 rcu_nocb_wait_gp(my_rdp); 2154 2155 /* 2156 * We left ->nocb_leader_sleep unset to reduce cache thrashing. 2157 * We set it now, but recheck for new callbacks while 2158 * traversing our follower list. 2159 */ 2160 my_rdp->nocb_leader_sleep = true; 2161 smp_mb(); /* Ensure _sleep true before scan of ->nocb_head. */ 2162 2163 /* Each pass through the following loop wakes a follower, if needed. */ 2164 for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) { 2165 if (READ_ONCE(rdp->nocb_head)) 2166 my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/ 2167 if (!rdp->nocb_gp_head) 2168 continue; /* No CBs, so no need to wake follower. */ 2169 2170 /* Append callbacks to follower's "done" list. */ 2171 tail = xchg(&rdp->nocb_follower_tail, rdp->nocb_gp_tail); 2172 *tail = rdp->nocb_gp_head; 2173 smp_mb__after_atomic(); /* Store *tail before wakeup. */ 2174 if (rdp != my_rdp && tail == &rdp->nocb_follower_head) { 2175 /* 2176 * List was empty, wake up the follower. 2177 * Memory barriers supplied by atomic_long_add(). 2178 */ 2179 swake_up(&rdp->nocb_wq); 2180 } 2181 } 2182 2183 /* If we (the leader) don't have CBs, go wait some more. */ 2184 if (!my_rdp->nocb_follower_head) 2185 goto wait_again; 2186 } 2187 2188 /* 2189 * Followers come here to wait for additional callbacks to show up. 2190 * This function does not return until callbacks appear. 2191 */ 2192 static void nocb_follower_wait(struct rcu_data *rdp) 2193 { 2194 bool firsttime = true; 2195 2196 for (;;) { 2197 if (!rcu_nocb_poll) { 2198 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 2199 "FollowerSleep"); 2200 swait_event_interruptible(rdp->nocb_wq, 2201 READ_ONCE(rdp->nocb_follower_head)); 2202 } else if (firsttime) { 2203 /* Don't drown trace log with "Poll"! */ 2204 firsttime = false; 2205 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "Poll"); 2206 } 2207 if (smp_load_acquire(&rdp->nocb_follower_head)) { 2208 /* ^^^ Ensure CB invocation follows _head test. */ 2209 return; 2210 } 2211 if (!rcu_nocb_poll) 2212 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 2213 "WokeEmpty"); 2214 WARN_ON(signal_pending(current)); 2215 schedule_timeout_interruptible(1); 2216 } 2217 } 2218 2219 /* 2220 * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes 2221 * callbacks queued by the corresponding no-CBs CPU, however, there is 2222 * an optional leader-follower relationship so that the grace-period 2223 * kthreads don't have to do quite so many wakeups. 2224 */ 2225 static int rcu_nocb_kthread(void *arg) 2226 { 2227 int c, cl; 2228 struct rcu_head *list; 2229 struct rcu_head *next; 2230 struct rcu_head **tail; 2231 struct rcu_data *rdp = arg; 2232 2233 /* Each pass through this loop invokes one batch of callbacks */ 2234 for (;;) { 2235 /* Wait for callbacks. */ 2236 if (rdp->nocb_leader == rdp) 2237 nocb_leader_wait(rdp); 2238 else 2239 nocb_follower_wait(rdp); 2240 2241 /* Pull the ready-to-invoke callbacks onto local list. */ 2242 list = READ_ONCE(rdp->nocb_follower_head); 2243 BUG_ON(!list); 2244 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "WokeNonEmpty"); 2245 WRITE_ONCE(rdp->nocb_follower_head, NULL); 2246 tail = xchg(&rdp->nocb_follower_tail, &rdp->nocb_follower_head); 2247 2248 /* Each pass through the following loop invokes a callback. */ 2249 trace_rcu_batch_start(rdp->rsp->name, 2250 atomic_long_read(&rdp->nocb_q_count_lazy), 2251 atomic_long_read(&rdp->nocb_q_count), -1); 2252 c = cl = 0; 2253 while (list) { 2254 next = list->next; 2255 /* Wait for enqueuing to complete, if needed. */ 2256 while (next == NULL && &list->next != tail) { 2257 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 2258 TPS("WaitQueue")); 2259 schedule_timeout_interruptible(1); 2260 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, 2261 TPS("WokeQueue")); 2262 next = list->next; 2263 } 2264 debug_rcu_head_unqueue(list); 2265 local_bh_disable(); 2266 if (__rcu_reclaim(rdp->rsp->name, list)) 2267 cl++; 2268 c++; 2269 local_bh_enable(); 2270 list = next; 2271 } 2272 trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1); 2273 smp_mb__before_atomic(); /* _add after CB invocation. */ 2274 atomic_long_add(-c, &rdp->nocb_q_count); 2275 atomic_long_add(-cl, &rdp->nocb_q_count_lazy); 2276 rdp->n_nocbs_invoked += c; 2277 } 2278 return 0; 2279 } 2280 2281 /* Is a deferred wakeup of rcu_nocb_kthread() required? */ 2282 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) 2283 { 2284 return READ_ONCE(rdp->nocb_defer_wakeup); 2285 } 2286 2287 /* Do a deferred wakeup of rcu_nocb_kthread(). */ 2288 static void do_nocb_deferred_wakeup(struct rcu_data *rdp) 2289 { 2290 int ndw; 2291 2292 if (!rcu_nocb_need_deferred_wakeup(rdp)) 2293 return; 2294 ndw = READ_ONCE(rdp->nocb_defer_wakeup); 2295 WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOGP_WAKE_NOT); 2296 wake_nocb_leader(rdp, ndw == RCU_NOGP_WAKE_FORCE); 2297 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWake")); 2298 } 2299 2300 void __init rcu_init_nohz(void) 2301 { 2302 int cpu; 2303 bool need_rcu_nocb_mask = true; 2304 struct rcu_state *rsp; 2305 2306 #ifdef CONFIG_RCU_NOCB_CPU_NONE 2307 need_rcu_nocb_mask = false; 2308 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */ 2309 2310 #if defined(CONFIG_NO_HZ_FULL) 2311 if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask)) 2312 need_rcu_nocb_mask = true; 2313 #endif /* #if defined(CONFIG_NO_HZ_FULL) */ 2314 2315 if (!have_rcu_nocb_mask && need_rcu_nocb_mask) { 2316 if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) { 2317 pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n"); 2318 return; 2319 } 2320 have_rcu_nocb_mask = true; 2321 } 2322 if (!have_rcu_nocb_mask) 2323 return; 2324 2325 #ifdef CONFIG_RCU_NOCB_CPU_ZERO 2326 pr_info("\tOffload RCU callbacks from CPU 0\n"); 2327 cpumask_set_cpu(0, rcu_nocb_mask); 2328 #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */ 2329 #ifdef CONFIG_RCU_NOCB_CPU_ALL 2330 pr_info("\tOffload RCU callbacks from all CPUs\n"); 2331 cpumask_copy(rcu_nocb_mask, cpu_possible_mask); 2332 #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */ 2333 #if defined(CONFIG_NO_HZ_FULL) 2334 if (tick_nohz_full_running) 2335 cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask); 2336 #endif /* #if defined(CONFIG_NO_HZ_FULL) */ 2337 2338 if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) { 2339 pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n"); 2340 cpumask_and(rcu_nocb_mask, cpu_possible_mask, 2341 rcu_nocb_mask); 2342 } 2343 pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n", 2344 cpumask_pr_args(rcu_nocb_mask)); 2345 if (rcu_nocb_poll) 2346 pr_info("\tPoll for callbacks from no-CBs CPUs.\n"); 2347 2348 for_each_rcu_flavor(rsp) { 2349 for_each_cpu(cpu, rcu_nocb_mask) 2350 init_nocb_callback_list(per_cpu_ptr(rsp->rda, cpu)); 2351 rcu_organize_nocb_kthreads(rsp); 2352 } 2353 } 2354 2355 /* Initialize per-rcu_data variables for no-CBs CPUs. */ 2356 static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) 2357 { 2358 rdp->nocb_tail = &rdp->nocb_head; 2359 init_swait_queue_head(&rdp->nocb_wq); 2360 rdp->nocb_follower_tail = &rdp->nocb_follower_head; 2361 } 2362 2363 /* 2364 * If the specified CPU is a no-CBs CPU that does not already have its 2365 * rcuo kthread for the specified RCU flavor, spawn it. If the CPUs are 2366 * brought online out of order, this can require re-organizing the 2367 * leader-follower relationships. 2368 */ 2369 static void rcu_spawn_one_nocb_kthread(struct rcu_state *rsp, int cpu) 2370 { 2371 struct rcu_data *rdp; 2372 struct rcu_data *rdp_last; 2373 struct rcu_data *rdp_old_leader; 2374 struct rcu_data *rdp_spawn = per_cpu_ptr(rsp->rda, cpu); 2375 struct task_struct *t; 2376 2377 /* 2378 * If this isn't a no-CBs CPU or if it already has an rcuo kthread, 2379 * then nothing to do. 2380 */ 2381 if (!rcu_is_nocb_cpu(cpu) || rdp_spawn->nocb_kthread) 2382 return; 2383 2384 /* If we didn't spawn the leader first, reorganize! */ 2385 rdp_old_leader = rdp_spawn->nocb_leader; 2386 if (rdp_old_leader != rdp_spawn && !rdp_old_leader->nocb_kthread) { 2387 rdp_last = NULL; 2388 rdp = rdp_old_leader; 2389 do { 2390 rdp->nocb_leader = rdp_spawn; 2391 if (rdp_last && rdp != rdp_spawn) 2392 rdp_last->nocb_next_follower = rdp; 2393 if (rdp == rdp_spawn) { 2394 rdp = rdp->nocb_next_follower; 2395 } else { 2396 rdp_last = rdp; 2397 rdp = rdp->nocb_next_follower; 2398 rdp_last->nocb_next_follower = NULL; 2399 } 2400 } while (rdp); 2401 rdp_spawn->nocb_next_follower = rdp_old_leader; 2402 } 2403 2404 /* Spawn the kthread for this CPU and RCU flavor. */ 2405 t = kthread_run(rcu_nocb_kthread, rdp_spawn, 2406 "rcuo%c/%d", rsp->abbr, cpu); 2407 BUG_ON(IS_ERR(t)); 2408 WRITE_ONCE(rdp_spawn->nocb_kthread, t); 2409 } 2410 2411 /* 2412 * If the specified CPU is a no-CBs CPU that does not already have its 2413 * rcuo kthreads, spawn them. 2414 */ 2415 static void rcu_spawn_all_nocb_kthreads(int cpu) 2416 { 2417 struct rcu_state *rsp; 2418 2419 if (rcu_scheduler_fully_active) 2420 for_each_rcu_flavor(rsp) 2421 rcu_spawn_one_nocb_kthread(rsp, cpu); 2422 } 2423 2424 /* 2425 * Once the scheduler is running, spawn rcuo kthreads for all online 2426 * no-CBs CPUs. This assumes that the early_initcall()s happen before 2427 * non-boot CPUs come online -- if this changes, we will need to add 2428 * some mutual exclusion. 2429 */ 2430 static void __init rcu_spawn_nocb_kthreads(void) 2431 { 2432 int cpu; 2433 2434 for_each_online_cpu(cpu) 2435 rcu_spawn_all_nocb_kthreads(cpu); 2436 } 2437 2438 /* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */ 2439 static int rcu_nocb_leader_stride = -1; 2440 module_param(rcu_nocb_leader_stride, int, 0444); 2441 2442 /* 2443 * Initialize leader-follower relationships for all no-CBs CPU. 2444 */ 2445 static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp) 2446 { 2447 int cpu; 2448 int ls = rcu_nocb_leader_stride; 2449 int nl = 0; /* Next leader. */ 2450 struct rcu_data *rdp; 2451 struct rcu_data *rdp_leader = NULL; /* Suppress misguided gcc warn. */ 2452 struct rcu_data *rdp_prev = NULL; 2453 2454 if (!have_rcu_nocb_mask) 2455 return; 2456 if (ls == -1) { 2457 ls = int_sqrt(nr_cpu_ids); 2458 rcu_nocb_leader_stride = ls; 2459 } 2460 2461 /* 2462 * Each pass through this loop sets up one rcu_data structure and 2463 * spawns one rcu_nocb_kthread(). 2464 */ 2465 for_each_cpu(cpu, rcu_nocb_mask) { 2466 rdp = per_cpu_ptr(rsp->rda, cpu); 2467 if (rdp->cpu >= nl) { 2468 /* New leader, set up for followers & next leader. */ 2469 nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls; 2470 rdp->nocb_leader = rdp; 2471 rdp_leader = rdp; 2472 } else { 2473 /* Another follower, link to previous leader. */ 2474 rdp->nocb_leader = rdp_leader; 2475 rdp_prev->nocb_next_follower = rdp; 2476 } 2477 rdp_prev = rdp; 2478 } 2479 } 2480 2481 /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */ 2482 static bool init_nocb_callback_list(struct rcu_data *rdp) 2483 { 2484 if (!rcu_is_nocb_cpu(rdp->cpu)) 2485 return false; 2486 2487 /* If there are early-boot callbacks, move them to nocb lists. */ 2488 if (rdp->nxtlist) { 2489 rdp->nocb_head = rdp->nxtlist; 2490 rdp->nocb_tail = rdp->nxttail[RCU_NEXT_TAIL]; 2491 atomic_long_set(&rdp->nocb_q_count, rdp->qlen); 2492 atomic_long_set(&rdp->nocb_q_count_lazy, rdp->qlen_lazy); 2493 rdp->nxtlist = NULL; 2494 rdp->qlen = 0; 2495 rdp->qlen_lazy = 0; 2496 } 2497 rdp->nxttail[RCU_NEXT_TAIL] = NULL; 2498 return true; 2499 } 2500 2501 #else /* #ifdef CONFIG_RCU_NOCB_CPU */ 2502 2503 static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu) 2504 { 2505 WARN_ON_ONCE(1); /* Should be dead code. */ 2506 return false; 2507 } 2508 2509 static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq) 2510 { 2511 } 2512 2513 static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) 2514 { 2515 } 2516 2517 static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp) 2518 { 2519 return NULL; 2520 } 2521 2522 static void rcu_init_one_nocb(struct rcu_node *rnp) 2523 { 2524 } 2525 2526 static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, 2527 bool lazy, unsigned long flags) 2528 { 2529 return false; 2530 } 2531 2532 static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, 2533 struct rcu_data *rdp, 2534 unsigned long flags) 2535 { 2536 return false; 2537 } 2538 2539 static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) 2540 { 2541 } 2542 2543 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) 2544 { 2545 return false; 2546 } 2547 2548 static void do_nocb_deferred_wakeup(struct rcu_data *rdp) 2549 { 2550 } 2551 2552 static void rcu_spawn_all_nocb_kthreads(int cpu) 2553 { 2554 } 2555 2556 static void __init rcu_spawn_nocb_kthreads(void) 2557 { 2558 } 2559 2560 static bool init_nocb_callback_list(struct rcu_data *rdp) 2561 { 2562 return false; 2563 } 2564 2565 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ 2566 2567 /* 2568 * An adaptive-ticks CPU can potentially execute in kernel mode for an 2569 * arbitrarily long period of time with the scheduling-clock tick turned 2570 * off. RCU will be paying attention to this CPU because it is in the 2571 * kernel, but the CPU cannot be guaranteed to be executing the RCU state 2572 * machine because the scheduling-clock tick has been disabled. Therefore, 2573 * if an adaptive-ticks CPU is failing to respond to the current grace 2574 * period and has not be idle from an RCU perspective, kick it. 2575 */ 2576 static void __maybe_unused rcu_kick_nohz_cpu(int cpu) 2577 { 2578 #ifdef CONFIG_NO_HZ_FULL 2579 if (tick_nohz_full_cpu(cpu)) 2580 smp_send_reschedule(cpu); 2581 #endif /* #ifdef CONFIG_NO_HZ_FULL */ 2582 } 2583 2584 2585 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE 2586 2587 static int full_sysidle_state; /* Current system-idle state. */ 2588 #define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */ 2589 #define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */ 2590 #define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */ 2591 #define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */ 2592 #define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */ 2593 2594 /* 2595 * Invoked to note exit from irq or task transition to idle. Note that 2596 * usermode execution does -not- count as idle here! After all, we want 2597 * to detect full-system idle states, not RCU quiescent states and grace 2598 * periods. The caller must have disabled interrupts. 2599 */ 2600 static void rcu_sysidle_enter(int irq) 2601 { 2602 unsigned long j; 2603 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); 2604 2605 /* If there are no nohz_full= CPUs, no need to track this. */ 2606 if (!tick_nohz_full_enabled()) 2607 return; 2608 2609 /* Adjust nesting, check for fully idle. */ 2610 if (irq) { 2611 rdtp->dynticks_idle_nesting--; 2612 WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0); 2613 if (rdtp->dynticks_idle_nesting != 0) 2614 return; /* Still not fully idle. */ 2615 } else { 2616 if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) == 2617 DYNTICK_TASK_NEST_VALUE) { 2618 rdtp->dynticks_idle_nesting = 0; 2619 } else { 2620 rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE; 2621 WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0); 2622 return; /* Still not fully idle. */ 2623 } 2624 } 2625 2626 /* Record start of fully idle period. */ 2627 j = jiffies; 2628 WRITE_ONCE(rdtp->dynticks_idle_jiffies, j); 2629 smp_mb__before_atomic(); 2630 atomic_inc(&rdtp->dynticks_idle); 2631 smp_mb__after_atomic(); 2632 WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1); 2633 } 2634 2635 /* 2636 * Unconditionally force exit from full system-idle state. This is 2637 * invoked when a normal CPU exits idle, but must be called separately 2638 * for the timekeeping CPU (tick_do_timer_cpu). The reason for this 2639 * is that the timekeeping CPU is permitted to take scheduling-clock 2640 * interrupts while the system is in system-idle state, and of course 2641 * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock 2642 * interrupt from any other type of interrupt. 2643 */ 2644 void rcu_sysidle_force_exit(void) 2645 { 2646 int oldstate = READ_ONCE(full_sysidle_state); 2647 int newoldstate; 2648 2649 /* 2650 * Each pass through the following loop attempts to exit full 2651 * system-idle state. If contention proves to be a problem, 2652 * a trylock-based contention tree could be used here. 2653 */ 2654 while (oldstate > RCU_SYSIDLE_SHORT) { 2655 newoldstate = cmpxchg(&full_sysidle_state, 2656 oldstate, RCU_SYSIDLE_NOT); 2657 if (oldstate == newoldstate && 2658 oldstate == RCU_SYSIDLE_FULL_NOTED) { 2659 rcu_kick_nohz_cpu(tick_do_timer_cpu); 2660 return; /* We cleared it, done! */ 2661 } 2662 oldstate = newoldstate; 2663 } 2664 smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */ 2665 } 2666 2667 /* 2668 * Invoked to note entry to irq or task transition from idle. Note that 2669 * usermode execution does -not- count as idle here! The caller must 2670 * have disabled interrupts. 2671 */ 2672 static void rcu_sysidle_exit(int irq) 2673 { 2674 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); 2675 2676 /* If there are no nohz_full= CPUs, no need to track this. */ 2677 if (!tick_nohz_full_enabled()) 2678 return; 2679 2680 /* Adjust nesting, check for already non-idle. */ 2681 if (irq) { 2682 rdtp->dynticks_idle_nesting++; 2683 WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0); 2684 if (rdtp->dynticks_idle_nesting != 1) 2685 return; /* Already non-idle. */ 2686 } else { 2687 /* 2688 * Allow for irq misnesting. Yes, it really is possible 2689 * to enter an irq handler then never leave it, and maybe 2690 * also vice versa. Handle both possibilities. 2691 */ 2692 if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) { 2693 rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE; 2694 WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0); 2695 return; /* Already non-idle. */ 2696 } else { 2697 rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE; 2698 } 2699 } 2700 2701 /* Record end of idle period. */ 2702 smp_mb__before_atomic(); 2703 atomic_inc(&rdtp->dynticks_idle); 2704 smp_mb__after_atomic(); 2705 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1)); 2706 2707 /* 2708 * If we are the timekeeping CPU, we are permitted to be non-idle 2709 * during a system-idle state. This must be the case, because 2710 * the timekeeping CPU has to take scheduling-clock interrupts 2711 * during the time that the system is transitioning to full 2712 * system-idle state. This means that the timekeeping CPU must 2713 * invoke rcu_sysidle_force_exit() directly if it does anything 2714 * more than take a scheduling-clock interrupt. 2715 */ 2716 if (smp_processor_id() == tick_do_timer_cpu) 2717 return; 2718 2719 /* Update system-idle state: We are clearly no longer fully idle! */ 2720 rcu_sysidle_force_exit(); 2721 } 2722 2723 /* 2724 * Check to see if the current CPU is idle. Note that usermode execution 2725 * does not count as idle. The caller must have disabled interrupts, 2726 * and must be running on tick_do_timer_cpu. 2727 */ 2728 static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, 2729 unsigned long *maxj) 2730 { 2731 int cur; 2732 unsigned long j; 2733 struct rcu_dynticks *rdtp = rdp->dynticks; 2734 2735 /* If there are no nohz_full= CPUs, don't check system-wide idleness. */ 2736 if (!tick_nohz_full_enabled()) 2737 return; 2738 2739 /* 2740 * If some other CPU has already reported non-idle, if this is 2741 * not the flavor of RCU that tracks sysidle state, or if this 2742 * is an offline or the timekeeping CPU, nothing to do. 2743 */ 2744 if (!*isidle || rdp->rsp != rcu_state_p || 2745 cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu) 2746 return; 2747 /* Verify affinity of current kthread. */ 2748 WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu); 2749 2750 /* Pick up current idle and NMI-nesting counter and check. */ 2751 cur = atomic_read(&rdtp->dynticks_idle); 2752 if (cur & 0x1) { 2753 *isidle = false; /* We are not idle! */ 2754 return; 2755 } 2756 smp_mb(); /* Read counters before timestamps. */ 2757 2758 /* Pick up timestamps. */ 2759 j = READ_ONCE(rdtp->dynticks_idle_jiffies); 2760 /* If this CPU entered idle more recently, update maxj timestamp. */ 2761 if (ULONG_CMP_LT(*maxj, j)) 2762 *maxj = j; 2763 } 2764 2765 /* 2766 * Is this the flavor of RCU that is handling full-system idle? 2767 */ 2768 static bool is_sysidle_rcu_state(struct rcu_state *rsp) 2769 { 2770 return rsp == rcu_state_p; 2771 } 2772 2773 /* 2774 * Return a delay in jiffies based on the number of CPUs, rcu_node 2775 * leaf fanout, and jiffies tick rate. The idea is to allow larger 2776 * systems more time to transition to full-idle state in order to 2777 * avoid the cache thrashing that otherwise occur on the state variable. 2778 * Really small systems (less than a couple of tens of CPUs) should 2779 * instead use a single global atomically incremented counter, and later 2780 * versions of this will automatically reconfigure themselves accordingly. 2781 */ 2782 static unsigned long rcu_sysidle_delay(void) 2783 { 2784 if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) 2785 return 0; 2786 return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000); 2787 } 2788 2789 /* 2790 * Advance the full-system-idle state. This is invoked when all of 2791 * the non-timekeeping CPUs are idle. 2792 */ 2793 static void rcu_sysidle(unsigned long j) 2794 { 2795 /* Check the current state. */ 2796 switch (READ_ONCE(full_sysidle_state)) { 2797 case RCU_SYSIDLE_NOT: 2798 2799 /* First time all are idle, so note a short idle period. */ 2800 WRITE_ONCE(full_sysidle_state, RCU_SYSIDLE_SHORT); 2801 break; 2802 2803 case RCU_SYSIDLE_SHORT: 2804 2805 /* 2806 * Idle for a bit, time to advance to next state? 2807 * cmpxchg failure means race with non-idle, let them win. 2808 */ 2809 if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay())) 2810 (void)cmpxchg(&full_sysidle_state, 2811 RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG); 2812 break; 2813 2814 case RCU_SYSIDLE_LONG: 2815 2816 /* 2817 * Do an additional check pass before advancing to full. 2818 * cmpxchg failure means race with non-idle, let them win. 2819 */ 2820 if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay())) 2821 (void)cmpxchg(&full_sysidle_state, 2822 RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL); 2823 break; 2824 2825 default: 2826 break; 2827 } 2828 } 2829 2830 /* 2831 * Found a non-idle non-timekeeping CPU, so kick the system-idle state 2832 * back to the beginning. 2833 */ 2834 static void rcu_sysidle_cancel(void) 2835 { 2836 smp_mb(); 2837 if (full_sysidle_state > RCU_SYSIDLE_SHORT) 2838 WRITE_ONCE(full_sysidle_state, RCU_SYSIDLE_NOT); 2839 } 2840 2841 /* 2842 * Update the sysidle state based on the results of a force-quiescent-state 2843 * scan of the CPUs' dyntick-idle state. 2844 */ 2845 static void rcu_sysidle_report(struct rcu_state *rsp, int isidle, 2846 unsigned long maxj, bool gpkt) 2847 { 2848 if (rsp != rcu_state_p) 2849 return; /* Wrong flavor, ignore. */ 2850 if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) 2851 return; /* Running state machine from timekeeping CPU. */ 2852 if (isidle) 2853 rcu_sysidle(maxj); /* More idle! */ 2854 else 2855 rcu_sysidle_cancel(); /* Idle is over. */ 2856 } 2857 2858 /* 2859 * Wrapper for rcu_sysidle_report() when called from the grace-period 2860 * kthread's context. 2861 */ 2862 static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle, 2863 unsigned long maxj) 2864 { 2865 /* If there are no nohz_full= CPUs, no need to track this. */ 2866 if (!tick_nohz_full_enabled()) 2867 return; 2868 2869 rcu_sysidle_report(rsp, isidle, maxj, true); 2870 } 2871 2872 /* Callback and function for forcing an RCU grace period. */ 2873 struct rcu_sysidle_head { 2874 struct rcu_head rh; 2875 int inuse; 2876 }; 2877 2878 static void rcu_sysidle_cb(struct rcu_head *rhp) 2879 { 2880 struct rcu_sysidle_head *rshp; 2881 2882 /* 2883 * The following memory barrier is needed to replace the 2884 * memory barriers that would normally be in the memory 2885 * allocator. 2886 */ 2887 smp_mb(); /* grace period precedes setting inuse. */ 2888 2889 rshp = container_of(rhp, struct rcu_sysidle_head, rh); 2890 WRITE_ONCE(rshp->inuse, 0); 2891 } 2892 2893 /* 2894 * Check to see if the system is fully idle, other than the timekeeping CPU. 2895 * The caller must have disabled interrupts. This is not intended to be 2896 * called unless tick_nohz_full_enabled(). 2897 */ 2898 bool rcu_sys_is_idle(void) 2899 { 2900 static struct rcu_sysidle_head rsh; 2901 int rss = READ_ONCE(full_sysidle_state); 2902 2903 if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu)) 2904 return false; 2905 2906 /* Handle small-system case by doing a full scan of CPUs. */ 2907 if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) { 2908 int oldrss = rss - 1; 2909 2910 /* 2911 * One pass to advance to each state up to _FULL. 2912 * Give up if any pass fails to advance the state. 2913 */ 2914 while (rss < RCU_SYSIDLE_FULL && oldrss < rss) { 2915 int cpu; 2916 bool isidle = true; 2917 unsigned long maxj = jiffies - ULONG_MAX / 4; 2918 struct rcu_data *rdp; 2919 2920 /* Scan all the CPUs looking for nonidle CPUs. */ 2921 for_each_possible_cpu(cpu) { 2922 rdp = per_cpu_ptr(rcu_state_p->rda, cpu); 2923 rcu_sysidle_check_cpu(rdp, &isidle, &maxj); 2924 if (!isidle) 2925 break; 2926 } 2927 rcu_sysidle_report(rcu_state_p, isidle, maxj, false); 2928 oldrss = rss; 2929 rss = READ_ONCE(full_sysidle_state); 2930 } 2931 } 2932 2933 /* If this is the first observation of an idle period, record it. */ 2934 if (rss == RCU_SYSIDLE_FULL) { 2935 rss = cmpxchg(&full_sysidle_state, 2936 RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED); 2937 return rss == RCU_SYSIDLE_FULL; 2938 } 2939 2940 smp_mb(); /* ensure rss load happens before later caller actions. */ 2941 2942 /* If already fully idle, tell the caller (in case of races). */ 2943 if (rss == RCU_SYSIDLE_FULL_NOTED) 2944 return true; 2945 2946 /* 2947 * If we aren't there yet, and a grace period is not in flight, 2948 * initiate a grace period. Either way, tell the caller that 2949 * we are not there yet. We use an xchg() rather than an assignment 2950 * to make up for the memory barriers that would otherwise be 2951 * provided by the memory allocator. 2952 */ 2953 if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL && 2954 !rcu_gp_in_progress(rcu_state_p) && 2955 !rsh.inuse && xchg(&rsh.inuse, 1) == 0) 2956 call_rcu(&rsh.rh, rcu_sysidle_cb); 2957 return false; 2958 } 2959 2960 /* 2961 * Initialize dynticks sysidle state for CPUs coming online. 2962 */ 2963 static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp) 2964 { 2965 rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE; 2966 } 2967 2968 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ 2969 2970 static void rcu_sysidle_enter(int irq) 2971 { 2972 } 2973 2974 static void rcu_sysidle_exit(int irq) 2975 { 2976 } 2977 2978 static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, 2979 unsigned long *maxj) 2980 { 2981 } 2982 2983 static bool is_sysidle_rcu_state(struct rcu_state *rsp) 2984 { 2985 return false; 2986 } 2987 2988 static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle, 2989 unsigned long maxj) 2990 { 2991 } 2992 2993 static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp) 2994 { 2995 } 2996 2997 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ 2998 2999 /* 3000 * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the 3001 * grace-period kthread will do force_quiescent_state() processing? 3002 * The idea is to avoid waking up RCU core processing on such a 3003 * CPU unless the grace period has extended for too long. 3004 * 3005 * This code relies on the fact that all NO_HZ_FULL CPUs are also 3006 * CONFIG_RCU_NOCB_CPU CPUs. 3007 */ 3008 static bool rcu_nohz_full_cpu(struct rcu_state *rsp) 3009 { 3010 #ifdef CONFIG_NO_HZ_FULL 3011 if (tick_nohz_full_cpu(smp_processor_id()) && 3012 (!rcu_gp_in_progress(rsp) || 3013 ULONG_CMP_LT(jiffies, READ_ONCE(rsp->gp_start) + HZ))) 3014 return true; 3015 #endif /* #ifdef CONFIG_NO_HZ_FULL */ 3016 return false; 3017 } 3018 3019 /* 3020 * Bind the grace-period kthread for the sysidle flavor of RCU to the 3021 * timekeeping CPU. 3022 */ 3023 static void rcu_bind_gp_kthread(void) 3024 { 3025 int __maybe_unused cpu; 3026 3027 if (!tick_nohz_full_enabled()) 3028 return; 3029 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE 3030 cpu = tick_do_timer_cpu; 3031 if (cpu >= 0 && cpu < nr_cpu_ids) 3032 set_cpus_allowed_ptr(current, cpumask_of(cpu)); 3033 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ 3034 housekeeping_affine(current); 3035 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ 3036 } 3037 3038 /* Record the current task on dyntick-idle entry. */ 3039 static void rcu_dynticks_task_enter(void) 3040 { 3041 #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) 3042 WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id()); 3043 #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */ 3044 } 3045 3046 /* Record no current task on dyntick-idle exit. */ 3047 static void rcu_dynticks_task_exit(void) 3048 { 3049 #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) 3050 WRITE_ONCE(current->rcu_tasks_idle_cpu, -1); 3051 #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */ 3052 } 3053