tree_plugin.h 88.8 KB
Newer Older
1 2 3
/*
 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
 * Internal non-public definitions that provide either classic
P
Paul E. McKenney 已提交
4
 * or preemptible semantics.
5 6 7 8 9 10 11 12 13 14 15 16
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
17 18
 * along with this program; if not, you can access it online at
 * http://www.gnu.org/licenses/gpl-2.0.html.
19 20 21 22 23 24 25 26
 *
 * Copyright Red Hat, 2009
 * Copyright IBM Corporation, 2009
 *
 * Author: Ingo Molnar <mingo@elte.hu>
 *	   Paul E. McKenney <paulmck@linux.vnet.ibm.com>
 */

27
#include <linux/delay.h>
P
Paul E. McKenney 已提交
28
#include <linux/gfp.h>
29
#include <linux/oom.h>
30
#include <linux/smpboot.h>
31
#include "../time/tick-internal.h"
32

33 34 35
#define RCU_KTHREAD_PRIO 1

#ifdef CONFIG_RCU_BOOST
36
#include "../locking/rtmutex_common.h"
37 38 39 40 41
#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
#else
#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
#endif

P
Paul E. McKenney 已提交
42 43 44
#ifdef CONFIG_RCU_NOCB_CPU
static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
static bool have_rcu_nocb_mask;	    /* Was rcu_nocb_mask allocated? */
45
static bool __read_mostly rcu_nocb_poll;    /* Offload kthread are to poll. */
P
Paul E. McKenney 已提交
46 47 48
static char __initdata nocb_buf[NR_CPUS * 5];
#endif /* #ifdef CONFIG_RCU_NOCB_CPU */

49 50 51 52 53 54 55 56
/*
 * Check the RCU kernel configuration parameters and print informative
 * messages about anything out of the ordinary.  If you like #ifdef, you
 * will love this function.
 */
static void __init rcu_bootup_announce_oddness(void)
{
#ifdef CONFIG_RCU_TRACE
57
	pr_info("\tRCU debugfs-based tracing is enabled.\n");
58 59
#endif
#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
60
	pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
61 62 63
	       CONFIG_RCU_FANOUT);
#endif
#ifdef CONFIG_RCU_FANOUT_EXACT
64
	pr_info("\tHierarchical RCU autobalancing is disabled.\n");
65 66
#endif
#ifdef CONFIG_RCU_FAST_NO_HZ
67
	pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
68 69
#endif
#ifdef CONFIG_PROVE_RCU
70
	pr_info("\tRCU lockdep checking is enabled.\n");
71 72
#endif
#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
73
	pr_info("\tRCU torture testing starts during boot.\n");
74
#endif
75
#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
76
	pr_info("\tDump stacks of tasks blocking RCU-preempt GP.\n");
77 78
#endif
#if defined(CONFIG_RCU_CPU_STALL_INFO)
79
	pr_info("\tAdditional per-CPU info printed with stalls.\n");
80 81
#endif
#if NUM_RCU_LVL_4 != 0
82
	pr_info("\tFour-level hierarchy is enabled.\n");
83
#endif
84
	if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
85
		pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
86
	if (nr_cpu_ids != NR_CPUS)
87
		pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
P
Paul E. McKenney 已提交
88
#ifdef CONFIG_RCU_NOCB_CPU
89 90
#ifndef CONFIG_RCU_NOCB_CPU_NONE
	if (!have_rcu_nocb_mask) {
91
		zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL);
92 93 94
		have_rcu_nocb_mask = true;
	}
#ifdef CONFIG_RCU_NOCB_CPU_ZERO
95
	pr_info("\tOffload RCU callbacks from CPU 0\n");
96 97 98
	cpumask_set_cpu(0, rcu_nocb_mask);
#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
#ifdef CONFIG_RCU_NOCB_CPU_ALL
99
	pr_info("\tOffload RCU callbacks from all CPUs\n");
100
	cpumask_copy(rcu_nocb_mask, cpu_possible_mask);
101 102
#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
P
Paul E. McKenney 已提交
103
	if (have_rcu_nocb_mask) {
104 105 106 107 108
		if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
			pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
			cpumask_and(rcu_nocb_mask, cpu_possible_mask,
				    rcu_nocb_mask);
		}
P
Paul E. McKenney 已提交
109
		cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
110
		pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf);
P
Paul E. McKenney 已提交
111
		if (rcu_nocb_poll)
112
			pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
P
Paul E. McKenney 已提交
113 114
	}
#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
115 116
}

117 118
#ifdef CONFIG_TREE_PREEMPT_RCU

119
RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
120
static struct rcu_state *rcu_state_p = &rcu_preempt_state;
121

122 123
static int rcu_preempted_readers_exp(struct rcu_node *rnp);

124 125 126
/*
 * Tell them what RCU they are running.
 */
127
static void __init rcu_bootup_announce(void)
128
{
129
	pr_info("Preemptible hierarchical RCU implementation.\n");
130
	rcu_bootup_announce_oddness();
131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152
}

/*
 * Return the number of RCU-preempt batches processed thus far
 * for debug and statistics.
 */
long rcu_batches_completed_preempt(void)
{
	return rcu_preempt_state.completed;
}
EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);

/*
 * Return the number of RCU batches processed thus far for debug & stats.
 */
long rcu_batches_completed(void)
{
	return rcu_batches_completed_preempt();
}
EXPORT_SYMBOL_GPL(rcu_batches_completed);

/*
P
Paul E. McKenney 已提交
153
 * Record a preemptible-RCU quiescent state for the specified CPU.  Note
154 155 156
 * that this just means that the task currently running on the CPU is
 * not in a quiescent state.  There might be any number of tasks blocked
 * while in an RCU read-side critical section.
157 158 159 160
 *
 * Unlike the other rcu_*_qs() functions, callers to this function
 * must disable irqs in order to protect the assignment to
 * ->rcu_read_unlock_special.
161
 */
162
static void rcu_preempt_qs(int cpu)
163 164
{
	struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
165

166
	if (rdp->passed_quiesce == 0)
167
		trace_rcu_grace_period(TPS("rcu_preempt"), rdp->gpnum, TPS("cpuqs"));
168
	rdp->passed_quiesce = 1;
169
	current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
170 171 172
}

/*
173 174 175
 * We have entered the scheduler, and the current task might soon be
 * context-switched away from.  If this task is in an RCU read-side
 * critical section, we will no longer be able to rely on the CPU to
176 177 178 179 180 181
 * record that fact, so we enqueue the task on the blkd_tasks list.
 * The task will dequeue itself when it exits the outermost enclosing
 * RCU read-side critical section.  Therefore, the current grace period
 * cannot be permitted to complete until the blkd_tasks list entries
 * predating the current grace period drain, in other words, until
 * rnp->gp_tasks becomes NULL.
182 183
 *
 * Caller must disable preemption.
184
 */
185
static void rcu_preempt_note_context_switch(int cpu)
186 187
{
	struct task_struct *t = current;
188
	unsigned long flags;
189 190 191
	struct rcu_data *rdp;
	struct rcu_node *rnp;

192
	if (t->rcu_read_lock_nesting > 0 &&
193 194 195
	    (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {

		/* Possibly blocking in an RCU read-side critical section. */
196
		rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
197
		rnp = rdp->mynode;
P
Paul E. McKenney 已提交
198
		raw_spin_lock_irqsave(&rnp->lock, flags);
199
		smp_mb__after_unlock_lock();
200
		t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
201
		t->rcu_blocked_node = rnp;
202 203 204 205 206 207 208 209 210

		/*
		 * If this CPU has already checked in, then this task
		 * will hold up the next grace period rather than the
		 * current grace period.  Queue the task accordingly.
		 * If the task is queued for the current grace period
		 * (i.e., this CPU has not yet passed through a quiescent
		 * state for the current grace period), then as long
		 * as that task remains queued, the current grace period
211 212 213 214 215 216
		 * cannot end.  Note that there is some uncertainty as
		 * to exactly when the current grace period started.
		 * We take a conservative approach, which can result
		 * in unnecessarily waiting on tasks that started very
		 * slightly after the current grace period began.  C'est
		 * la vie!!!
217 218 219
		 *
		 * But first, note that the current CPU must still be
		 * on line!
220
		 */
221
		WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
222
		WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
223 224 225
		if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
			list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
			rnp->gp_tasks = &t->rcu_node_entry;
226 227 228 229
#ifdef CONFIG_RCU_BOOST
			if (rnp->boost_tasks != NULL)
				rnp->boost_tasks = rnp->gp_tasks;
#endif /* #ifdef CONFIG_RCU_BOOST */
230 231 232 233 234
		} else {
			list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
			if (rnp->qsmask & rdp->grpmask)
				rnp->gp_tasks = &t->rcu_node_entry;
		}
235 236 237 238 239
		trace_rcu_preempt_task(rdp->rsp->name,
				       t->pid,
				       (rnp->qsmask & rdp->grpmask)
				       ? rnp->gpnum
				       : rnp->gpnum + 1);
P
Paul E. McKenney 已提交
240
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
241 242 243 244 245 246 247 248
	} else if (t->rcu_read_lock_nesting < 0 &&
		   t->rcu_read_unlock_special) {

		/*
		 * Complete exit from RCU read-side critical section on
		 * behalf of preempted instance of __rcu_read_unlock().
		 */
		rcu_read_unlock_special(t);
249 250 251 252 253 254 255 256 257 258 259
	}

	/*
	 * Either we were not in an RCU read-side critical section to
	 * begin with, or we have now recorded that critical section
	 * globally.  Either way, we can now note a quiescent state
	 * for this CPU.  Again, if we were in an RCU read-side critical
	 * section, and if that critical section was blocking the current
	 * grace period, then the fact that the task has been enqueued
	 * means that we continue to block the current grace period.
	 */
260
	local_irq_save(flags);
261
	rcu_preempt_qs(cpu);
262
	local_irq_restore(flags);
263 264
}

265 266 267 268 269
/*
 * Check for preempted RCU readers blocking the current grace period
 * for the specified rcu_node structure.  If the caller needs a reliable
 * answer, it must hold the rcu_node's ->lock.
 */
270
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
271
{
272
	return rnp->gp_tasks != NULL;
273 274
}

275 276 277 278 279 280 281
/*
 * Record a quiescent state for all tasks that were previously queued
 * on the specified rcu_node structure and that were blocking the current
 * RCU grace period.  The caller must hold the specified rnp->lock with
 * irqs disabled, and this lock is released upon return, but irqs remain
 * disabled.
 */
P
Paul E. McKenney 已提交
282
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
283 284 285 286 287
	__releases(rnp->lock)
{
	unsigned long mask;
	struct rcu_node *rnp_p;

288
	if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
P
Paul E. McKenney 已提交
289
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
290 291 292 293 294 295 296 297 298 299
		return;  /* Still need more quiescent states! */
	}

	rnp_p = rnp->parent;
	if (rnp_p == NULL) {
		/*
		 * Either there is only one rcu_node in the tree,
		 * or tasks were kicked up to root rcu_node due to
		 * CPUs going offline.
		 */
P
Paul E. McKenney 已提交
300
		rcu_report_qs_rsp(&rcu_preempt_state, flags);
301 302 303 304 305
		return;
	}

	/* Report up the rest of the hierarchy. */
	mask = rnp->grpmask;
P
Paul E. McKenney 已提交
306 307
	raw_spin_unlock(&rnp->lock);	/* irqs remain disabled. */
	raw_spin_lock(&rnp_p->lock);	/* irqs already disabled. */
308
	smp_mb__after_unlock_lock();
P
Paul E. McKenney 已提交
309
	rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
310 311
}

312 313 314 315 316 317 318 319 320 321 322 323 324 325 326
/*
 * Advance a ->blkd_tasks-list pointer to the next entry, instead
 * returning NULL if at the end of the list.
 */
static struct list_head *rcu_next_node_entry(struct task_struct *t,
					     struct rcu_node *rnp)
{
	struct list_head *np;

	np = t->rcu_node_entry.next;
	if (np == &rnp->blkd_tasks)
		np = NULL;
	return np;
}

327 328 329 330 331
/*
 * Handle special cases during rcu_read_unlock(), such as needing to
 * notify RCU core processing or task having blocked during the RCU
 * read-side critical section.
 */
332
void rcu_read_unlock_special(struct task_struct *t)
333 334
{
	int empty;
335
	int empty_exp;
336
	int empty_exp_now;
337
	unsigned long flags;
338
	struct list_head *np;
339
#ifdef CONFIG_RCU_BOOST
340
	bool drop_boost_mutex = false;
341
#endif /* #ifdef CONFIG_RCU_BOOST */
342 343 344 345 346 347 348 349 350 351 352 353 354 355 356
	struct rcu_node *rnp;
	int special;

	/* NMI handlers cannot block and cannot safely manipulate state. */
	if (in_nmi())
		return;

	local_irq_save(flags);

	/*
	 * If RCU core is waiting for this CPU to exit critical section,
	 * let it know that we have done so.
	 */
	special = t->rcu_read_unlock_special;
	if (special & RCU_READ_UNLOCK_NEED_QS) {
357
		rcu_preempt_qs(smp_processor_id());
358 359 360 361
		if (!t->rcu_read_unlock_special) {
			local_irq_restore(flags);
			return;
		}
362 363
	}

364 365
	/* Hardware IRQ handlers cannot block, complain if they get here. */
	if (WARN_ON_ONCE(in_irq() || in_serving_softirq())) {
366 367 368 369 370 371 372 373
		local_irq_restore(flags);
		return;
	}

	/* Clean up if blocked during RCU read-side critical section. */
	if (special & RCU_READ_UNLOCK_BLOCKED) {
		t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;

374 375 376 377 378 379
		/*
		 * Remove this task from the list it blocked on.  The
		 * task can migrate while we acquire the lock, but at
		 * most one time.  So at most two passes through loop.
		 */
		for (;;) {
380
			rnp = t->rcu_blocked_node;
P
Paul E. McKenney 已提交
381
			raw_spin_lock(&rnp->lock);  /* irqs already disabled. */
382
			smp_mb__after_unlock_lock();
383
			if (rnp == t->rcu_blocked_node)
384
				break;
P
Paul E. McKenney 已提交
385
			raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
386
		}
387
		empty = !rcu_preempt_blocked_readers_cgp(rnp);
388 389
		empty_exp = !rcu_preempted_readers_exp(rnp);
		smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
390
		np = rcu_next_node_entry(t, rnp);
391
		list_del_init(&t->rcu_node_entry);
392
		t->rcu_blocked_node = NULL;
393
		trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
394
						rnp->gpnum, t->pid);
395 396 397 398
		if (&t->rcu_node_entry == rnp->gp_tasks)
			rnp->gp_tasks = np;
		if (&t->rcu_node_entry == rnp->exp_tasks)
			rnp->exp_tasks = np;
399 400 401
#ifdef CONFIG_RCU_BOOST
		if (&t->rcu_node_entry == rnp->boost_tasks)
			rnp->boost_tasks = np;
402 403
		/* Snapshot ->boost_mtx ownership with rcu_node lock held. */
		drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
404
#endif /* #ifdef CONFIG_RCU_BOOST */
405 406 407 408

		/*
		 * If this was the last task on the current list, and if
		 * we aren't waiting on any CPUs, report the quiescent state.
409 410
		 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
		 * so we must take a snapshot of the expedited state.
411
		 */
412
		empty_exp_now = !rcu_preempted_readers_exp(rnp);
413
		if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) {
414
			trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
415 416 417 418 419 420
							 rnp->gpnum,
							 0, rnp->qsmask,
							 rnp->level,
							 rnp->grplo,
							 rnp->grphi,
							 !!rnp->gp_tasks);
P
Paul E. McKenney 已提交
421
			rcu_report_unblock_qs_rnp(rnp, flags);
422
		} else {
423
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
424
		}
425

426 427
#ifdef CONFIG_RCU_BOOST
		/* Unboost if we were boosted. */
428 429
		if (drop_boost_mutex) {
			rt_mutex_unlock(&rnp->boost_mtx);
430 431
			complete(&rnp->boost_completion);
		}
432 433
#endif /* #ifdef CONFIG_RCU_BOOST */

434 435 436 437
		/*
		 * If this was the last task on the expedited lists,
		 * then we need to report up the rcu_node hierarchy.
		 */
438
		if (!empty_exp && empty_exp_now)
439
			rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);
440 441
	} else {
		local_irq_restore(flags);
442 443 444
	}
}

445 446 447 448 449 450 451 452 453 454 455
#ifdef CONFIG_RCU_CPU_STALL_VERBOSE

/*
 * Dump detailed information for all tasks blocking the current RCU
 * grace period on the specified rcu_node structure.
 */
static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
{
	unsigned long flags;
	struct task_struct *t;

456
	raw_spin_lock_irqsave(&rnp->lock, flags);
457 458 459 460
	if (!rcu_preempt_blocked_readers_cgp(rnp)) {
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
		return;
	}
461 462 463 464 465
	t = list_entry(rnp->gp_tasks,
		       struct task_struct, rcu_node_entry);
	list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
		sched_show_task(t);
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488
}

/*
 * Dump detailed information for all tasks blocking the current RCU
 * grace period.
 */
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
{
	struct rcu_node *rnp = rcu_get_root(rsp);

	rcu_print_detail_task_stall_rnp(rnp);
	rcu_for_each_leaf_node(rsp, rnp)
		rcu_print_detail_task_stall_rnp(rnp);
}

#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */

static void rcu_print_detail_task_stall(struct rcu_state *rsp)
{
}

#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */

489 490 491 492
#ifdef CONFIG_RCU_CPU_STALL_INFO

static void rcu_print_task_stall_begin(struct rcu_node *rnp)
{
493
	pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
494 495 496 497 498
	       rnp->level, rnp->grplo, rnp->grphi);
}

static void rcu_print_task_stall_end(void)
{
499
	pr_cont("\n");
500 501 502 503 504 505 506 507 508 509 510 511 512 513
}

#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */

static void rcu_print_task_stall_begin(struct rcu_node *rnp)
{
}

static void rcu_print_task_stall_end(void)
{
}

#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */

514 515 516 517
/*
 * Scan the current list of tasks blocked within RCU read-side critical
 * sections, printing out the tid of each.
 */
518
static int rcu_print_task_stall(struct rcu_node *rnp)
519 520
{
	struct task_struct *t;
521
	int ndetected = 0;
522

523
	if (!rcu_preempt_blocked_readers_cgp(rnp))
524
		return 0;
525
	rcu_print_task_stall_begin(rnp);
526 527
	t = list_entry(rnp->gp_tasks,
		       struct task_struct, rcu_node_entry);
528
	list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
529
		pr_cont(" P%d", t->pid);
530 531
		ndetected++;
	}
532
	rcu_print_task_stall_end();
533
	return ndetected;
534 535
}

536 537 538 539 540 541
/*
 * Check that the list of blocked tasks for the newly completed grace
 * period is in fact empty.  It is a serious bug to complete a grace
 * period that still has RCU readers blocked!  This function must be
 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
 * must be held by the caller.
542 543 544
 *
 * Also, if there are blocked tasks on the list, they automatically
 * block the newly created grace period, so set up ->gp_tasks accordingly.
545 546 547
 */
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
{
548
	WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
549 550
	if (!list_empty(&rnp->blkd_tasks))
		rnp->gp_tasks = rnp->blkd_tasks.next;
551
	WARN_ON_ONCE(rnp->qsmask);
552 553
}

554 555
#ifdef CONFIG_HOTPLUG_CPU

556 557 558 559 560 561
/*
 * Handle tasklist migration for case in which all CPUs covered by the
 * specified rcu_node have gone offline.  Move them up to the root
 * rcu_node.  The reason for not just moving them to the immediate
 * parent is to remove the need for rcu_read_unlock_special() to
 * make more than two attempts to acquire the target rcu_node's lock.
562 563
 * Returns true if there were tasks blocking the current RCU grace
 * period.
564
 *
565 566 567
 * Returns 1 if there was previously a task blocking the current grace
 * period on the specified rcu_node structure.
 *
568 569
 * The caller must hold rnp->lock with irqs disabled.
 */
570 571 572
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
				     struct rcu_node *rnp,
				     struct rcu_data *rdp)
573 574 575
{
	struct list_head *lp;
	struct list_head *lp_root;
576
	int retval = 0;
577
	struct rcu_node *rnp_root = rcu_get_root(rsp);
578
	struct task_struct *t;
579

580 581
	if (rnp == rnp_root) {
		WARN_ONCE(1, "Last CPU thought to be offlined?");
582
		return 0;  /* Shouldn't happen: at least one CPU online. */
583
	}
584 585 586

	/* If we are on an internal node, complain bitterly. */
	WARN_ON_ONCE(rnp != rdp->mynode);
587 588

	/*
589 590 591 592 593 594 595
	 * Move tasks up to root rcu_node.  Don't try to get fancy for
	 * this corner-case operation -- just put this node's tasks
	 * at the head of the root node's list, and update the root node's
	 * ->gp_tasks and ->exp_tasks pointers to those of this node's,
	 * if non-NULL.  This might result in waiting for more tasks than
	 * absolutely necessary, but this is a good performance/complexity
	 * tradeoff.
596
	 */
597
	if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
598 599 600
		retval |= RCU_OFL_TASKS_NORM_GP;
	if (rcu_preempted_readers_exp(rnp))
		retval |= RCU_OFL_TASKS_EXP_GP;
601 602 603 604 605
	lp = &rnp->blkd_tasks;
	lp_root = &rnp_root->blkd_tasks;
	while (!list_empty(lp)) {
		t = list_entry(lp->next, typeof(*t), rcu_node_entry);
		raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
606
		smp_mb__after_unlock_lock();
607 608 609 610 611 612 613
		list_del(&t->rcu_node_entry);
		t->rcu_blocked_node = rnp_root;
		list_add(&t->rcu_node_entry, lp_root);
		if (&t->rcu_node_entry == rnp->gp_tasks)
			rnp_root->gp_tasks = rnp->gp_tasks;
		if (&t->rcu_node_entry == rnp->exp_tasks)
			rnp_root->exp_tasks = rnp->exp_tasks;
614 615 616 617
#ifdef CONFIG_RCU_BOOST
		if (&t->rcu_node_entry == rnp->boost_tasks)
			rnp_root->boost_tasks = rnp->boost_tasks;
#endif /* #ifdef CONFIG_RCU_BOOST */
618
		raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
619
	}
620

621 622
	rnp->gp_tasks = NULL;
	rnp->exp_tasks = NULL;
623
#ifdef CONFIG_RCU_BOOST
624
	rnp->boost_tasks = NULL;
625 626 627 628 629
	/*
	 * In case root is being boosted and leaf was not.  Make sure
	 * that we boost the tasks blocking the current grace period
	 * in this case.
	 */
630
	raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
631
	smp_mb__after_unlock_lock();
632
	if (rnp_root->boost_tasks != NULL &&
633 634
	    rnp_root->boost_tasks != rnp_root->gp_tasks &&
	    rnp_root->boost_tasks != rnp_root->exp_tasks)
635 636 637 638
		rnp_root->boost_tasks = rnp_root->gp_tasks;
	raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
#endif /* #ifdef CONFIG_RCU_BOOST */

639
	return retval;
640 641
}

642 643
#endif /* #ifdef CONFIG_HOTPLUG_CPU */

644 645 646 647 648 649 650 651 652 653 654 655
/*
 * Check for a quiescent state from the current CPU.  When a task blocks,
 * the task is recorded in the corresponding CPU's rcu_node structure,
 * which is checked elsewhere.
 *
 * Caller must disable hard irqs.
 */
static void rcu_preempt_check_callbacks(int cpu)
{
	struct task_struct *t = current;

	if (t->rcu_read_lock_nesting == 0) {
656
		rcu_preempt_qs(cpu);
657 658
		return;
	}
659 660
	if (t->rcu_read_lock_nesting > 0 &&
	    per_cpu(rcu_preempt_data, cpu).qs_pending)
661
		t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
662 663
}

664 665
#ifdef CONFIG_RCU_BOOST

666 667
static void rcu_preempt_do_callbacks(void)
{
668
	rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data));
669 670
}

671 672
#endif /* #ifdef CONFIG_RCU_BOOST */

673
/*
P
Paul E. McKenney 已提交
674
 * Queue a preemptible-RCU callback for invocation after a grace period.
675 676 677
 */
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
P
Paul E. McKenney 已提交
678
	__call_rcu(head, func, &rcu_preempt_state, -1, 0);
679 680 681
}
EXPORT_SYMBOL_GPL(call_rcu);

682 683 684 685 686
/**
 * synchronize_rcu - wait until a grace period has elapsed.
 *
 * Control will return to the caller some time after a full grace
 * period has elapsed, in other words after all currently executing RCU
687 688 689 690 691
 * read-side critical sections have completed.  Note, however, that
 * upon return from synchronize_rcu(), the caller might well be executing
 * concurrently with new RCU read-side critical sections that began while
 * synchronize_rcu() was waiting.  RCU read-side critical sections are
 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
692 693 694
 *
 * See the description of synchronize_sched() for more detailed information
 * on memory ordering guarantees.
695 696 697
 */
void synchronize_rcu(void)
{
698 699 700 701
	rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
			   !lock_is_held(&rcu_lock_map) &&
			   !lock_is_held(&rcu_sched_lock_map),
			   "Illegal synchronize_rcu() in RCU read-side critical section");
702 703
	if (!rcu_scheduler_active)
		return;
704 705 706 707
	if (rcu_expedited)
		synchronize_rcu_expedited();
	else
		wait_rcu_gp(call_rcu);
708 709 710
}
EXPORT_SYMBOL_GPL(synchronize_rcu);

711
static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
712
static unsigned long sync_rcu_preempt_exp_count;
713 714 715 716 717 718 719 720 721 722
static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);

/*
 * Return non-zero if there are any tasks in RCU read-side critical
 * sections blocking the current preemptible-RCU expedited grace period.
 * If there is no preemptible-RCU expedited grace period currently in
 * progress, returns zero unconditionally.
 */
static int rcu_preempted_readers_exp(struct rcu_node *rnp)
{
723
	return rnp->exp_tasks != NULL;
724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748
}

/*
 * return non-zero if there is no RCU expedited grace period in progress
 * for the specified rcu_node structure, in other words, if all CPUs and
 * tasks covered by the specified rcu_node structure have done their bit
 * for the current expedited grace period.  Works only for preemptible
 * RCU -- other RCU implementation use other means.
 *
 * Caller must hold sync_rcu_preempt_exp_mutex.
 */
static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
{
	return !rcu_preempted_readers_exp(rnp) &&
	       ACCESS_ONCE(rnp->expmask) == 0;
}

/*
 * Report the exit from RCU read-side critical section for the last task
 * that queued itself during or before the current expedited preemptible-RCU
 * grace period.  This event is reported either to the rcu_node structure on
 * which the task was queued or to one of that rcu_node structure's ancestors,
 * recursively up the tree.  (Calm down, calm down, we do the recursion
 * iteratively!)
 *
749 750 751
 * Most callers will set the "wake" flag, but the task initiating the
 * expedited grace period need not wake itself.
 *
752 753
 * Caller must hold sync_rcu_preempt_exp_mutex.
 */
754 755
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
			       bool wake)
756 757 758 759
{
	unsigned long flags;
	unsigned long mask;

P
Paul E. McKenney 已提交
760
	raw_spin_lock_irqsave(&rnp->lock, flags);
761
	smp_mb__after_unlock_lock();
762
	for (;;) {
763 764
		if (!sync_rcu_preempt_exp_done(rnp)) {
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
765
			break;
766
		}
767
		if (rnp->parent == NULL) {
768
			raw_spin_unlock_irqrestore(&rnp->lock, flags);
769 770
			if (wake) {
				smp_mb(); /* EGP done before wake_up(). */
771
				wake_up(&sync_rcu_preempt_exp_wq);
772
			}
773 774 775
			break;
		}
		mask = rnp->grpmask;
P
Paul E. McKenney 已提交
776
		raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
777
		rnp = rnp->parent;
P
Paul E. McKenney 已提交
778
		raw_spin_lock(&rnp->lock); /* irqs already disabled */
779
		smp_mb__after_unlock_lock();
780 781 782 783 784 785 786 787 788
		rnp->expmask &= ~mask;
	}
}

/*
 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
 * grace period for the specified rcu_node structure.  If there are no such
 * tasks, report it up the rcu_node hierarchy.
 *
789 790
 * Caller must hold sync_rcu_preempt_exp_mutex and must exclude
 * CPU hotplug operations.
791 792 793 794
 */
static void
sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
{
795
	unsigned long flags;
796
	int must_wait = 0;
797

798
	raw_spin_lock_irqsave(&rnp->lock, flags);
799
	smp_mb__after_unlock_lock();
800
	if (list_empty(&rnp->blkd_tasks)) {
801
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
802
	} else {
803
		rnp->exp_tasks = rnp->blkd_tasks.next;
804
		rcu_initiate_boost(rnp, flags);  /* releases rnp->lock */
805 806
		must_wait = 1;
	}
807
	if (!must_wait)
808
		rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
809 810
}

811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826
/**
 * synchronize_rcu_expedited - Brute-force RCU grace period
 *
 * Wait for an RCU-preempt grace period, but expedite it.  The basic
 * idea is to invoke synchronize_sched_expedited() to push all the tasks to
 * the ->blkd_tasks lists and wait for this list to drain.  This consumes
 * significant time on all CPUs and is unfriendly to real-time workloads,
 * so is thus not recommended for any sort of common-case code.
 * In fact, if you are using synchronize_rcu_expedited() in a loop,
 * please restructure your code to batch your updates, and then Use a
 * single synchronize_rcu() instead.
 *
 * Note that it is illegal to call this function while holding any lock
 * that is acquired by a CPU-hotplug notifier.  And yes, it is also illegal
 * to call this function from a CPU-hotplug notifier.  Failing to observe
 * these restriction will result in deadlock.
827 828 829
 */
void synchronize_rcu_expedited(void)
{
830 831 832
	unsigned long flags;
	struct rcu_node *rnp;
	struct rcu_state *rsp = &rcu_preempt_state;
833
	unsigned long snap;
834 835 836 837 838 839
	int trycount = 0;

	smp_mb(); /* Caller's modifications seen first by other CPUs. */
	snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
	smp_mb(); /* Above access cannot bleed into critical section. */

840 841 842 843 844 845 846 847 848 849
	/*
	 * Block CPU-hotplug operations.  This means that any CPU-hotplug
	 * operation that finds an rcu_node structure with tasks in the
	 * process of being boosted will know that all tasks blocking
	 * this expedited grace period will already be in the process of
	 * being boosted.  This simplifies the process of moving tasks
	 * from leaf to root rcu_node structures.
	 */
	get_online_cpus();

850 851 852 853 854 855
	/*
	 * Acquire lock, falling back to synchronize_rcu() if too many
	 * lock-acquisition failures.  Of course, if someone does the
	 * expedited grace period for us, just leave.
	 */
	while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
856 857 858 859 860
		if (ULONG_CMP_LT(snap,
		    ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
			put_online_cpus();
			goto mb_ret; /* Others did our work for us. */
		}
861
		if (trycount++ < 10) {
862
			udelay(trycount * num_online_cpus());
863
		} else {
864
			put_online_cpus();
865
			wait_rcu_gp(call_rcu);
866 867 868
			return;
		}
	}
869 870
	if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
		put_online_cpus();
871
		goto unlock_mb_ret; /* Others did our work for us. */
872
	}
873

874
	/* force all RCU readers onto ->blkd_tasks lists. */
875 876 877 878
	synchronize_sched_expedited();

	/* Initialize ->expmask for all non-leaf rcu_node structures. */
	rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
879
		raw_spin_lock_irqsave(&rnp->lock, flags);
880
		smp_mb__after_unlock_lock();
881
		rnp->expmask = rnp->qsmaskinit;
882
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
883 884
	}

885
	/* Snapshot current state of ->blkd_tasks lists. */
886 887 888 889 890
	rcu_for_each_leaf_node(rsp, rnp)
		sync_rcu_preempt_exp_init(rsp, rnp);
	if (NUM_RCU_NODES > 1)
		sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));

891
	put_online_cpus();
892

893
	/* Wait for snapshotted ->blkd_tasks lists to drain. */
894 895 896 897 898 899 900 901 902 903 904
	rnp = rcu_get_root(rsp);
	wait_event(sync_rcu_preempt_exp_wq,
		   sync_rcu_preempt_exp_done(rnp));

	/* Clean up and exit. */
	smp_mb(); /* ensure expedited GP seen before counter increment. */
	ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
unlock_mb_ret:
	mutex_unlock(&sync_rcu_preempt_exp_mutex);
mb_ret:
	smp_mb(); /* ensure subsequent action seen after grace period. */
905 906 907
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);

908 909
/**
 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
910 911 912 913 914
 *
 * Note that this primitive does not necessarily wait for an RCU grace period
 * to complete.  For example, if there are no RCU callbacks queued anywhere
 * in the system, then rcu_barrier() is within its rights to return
 * immediately, without waiting for anything, much less an RCU grace period.
915 916 917
 */
void rcu_barrier(void)
{
918
	_rcu_barrier(&rcu_preempt_state);
919 920 921
}
EXPORT_SYMBOL_GPL(rcu_barrier);

922
/*
P
Paul E. McKenney 已提交
923
 * Initialize preemptible RCU's state structures.
924 925 926
 */
static void __init __rcu_init_preempt(void)
{
927
	rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
928 929
}

930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947
/*
 * Check for a task exiting while in a preemptible-RCU read-side
 * critical section, clean up if so.  No need to issue warnings,
 * as debug_check_no_locks_held() already does this if lockdep
 * is enabled.
 */
void exit_rcu(void)
{
	struct task_struct *t = current;

	if (likely(list_empty(&current->rcu_node_entry)))
		return;
	t->rcu_read_lock_nesting = 1;
	barrier();
	t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
	__rcu_read_unlock();
}

948 949
#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */

950
static struct rcu_state *rcu_state_p = &rcu_sched_state;
951

952 953 954
/*
 * Tell them what RCU they are running.
 */
955
static void __init rcu_bootup_announce(void)
956
{
957
	pr_info("Hierarchical RCU implementation.\n");
958
	rcu_bootup_announce_oddness();
959 960 961 962 963 964 965 966 967 968 969
}

/*
 * Return the number of RCU batches processed thus far for debug & stats.
 */
long rcu_batches_completed(void)
{
	return rcu_batches_completed_sched();
}
EXPORT_SYMBOL_GPL(rcu_batches_completed);

970 971 972 973 974 975 976 977
/*
 * Because preemptible RCU does not exist, we never have to check for
 * CPUs being in quiescent states.
 */
static void rcu_preempt_note_context_switch(int cpu)
{
}

978
/*
P
Paul E. McKenney 已提交
979
 * Because preemptible RCU does not exist, there are never any preempted
980 981
 * RCU readers.
 */
982
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
983 984 985 986
{
	return 0;
}

987 988 989
#ifdef CONFIG_HOTPLUG_CPU

/* Because preemptible RCU does not exist, no quieting of tasks. */
P
Paul E. McKenney 已提交
990
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
991
	__releases(rnp->lock)
992
{
P
Paul E. McKenney 已提交
993
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
994 995 996 997
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

998
/*
P
Paul E. McKenney 已提交
999
 * Because preemptible RCU does not exist, we never have to check for
1000 1001 1002 1003 1004 1005
 * tasks blocked within RCU read-side critical sections.
 */
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
{
}

1006
/*
P
Paul E. McKenney 已提交
1007
 * Because preemptible RCU does not exist, we never have to check for
1008 1009
 * tasks blocked within RCU read-side critical sections.
 */
1010
static int rcu_print_task_stall(struct rcu_node *rnp)
1011
{
1012
	return 0;
1013 1014
}

1015
/*
P
Paul E. McKenney 已提交
1016
 * Because there is no preemptible RCU, there can be no readers blocked,
1017 1018
 * so there is no need to check for blocked tasks.  So check only for
 * bogus qsmask values.
1019 1020 1021
 */
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
{
1022
	WARN_ON_ONCE(rnp->qsmask);
1023 1024
}

1025 1026
#ifdef CONFIG_HOTPLUG_CPU

1027
/*
P
Paul E. McKenney 已提交
1028
 * Because preemptible RCU does not exist, it never needs to migrate
1029 1030 1031
 * tasks that were blocked within RCU read-side critical sections, and
 * such non-existent tasks cannot possibly have been blocking the current
 * grace period.
1032
 */
1033 1034 1035
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
				     struct rcu_node *rnp,
				     struct rcu_data *rdp)
1036
{
1037
	return 0;
1038 1039
}

1040 1041
#endif /* #ifdef CONFIG_HOTPLUG_CPU */

1042
/*
P
Paul E. McKenney 已提交
1043
 * Because preemptible RCU does not exist, it never has any callbacks
1044 1045
 * to check.
 */
1046
static void rcu_preempt_check_callbacks(int cpu)
1047 1048 1049
{
}

1050 1051
/*
 * Wait for an rcu-preempt grace period, but make it happen quickly.
P
Paul E. McKenney 已提交
1052
 * But because preemptible RCU does not exist, map to rcu-sched.
1053 1054 1055 1056 1057 1058 1059
 */
void synchronize_rcu_expedited(void)
{
	synchronize_sched_expedited();
}
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);

1060 1061 1062
#ifdef CONFIG_HOTPLUG_CPU

/*
P
Paul E. McKenney 已提交
1063
 * Because preemptible RCU does not exist, there is never any need to
1064 1065 1066
 * report on tasks preempted in RCU read-side critical sections during
 * expedited RCU grace periods.
 */
1067 1068
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
			       bool wake)
1069 1070 1071 1072 1073
{
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */

1074
/*
P
Paul E. McKenney 已提交
1075
 * Because preemptible RCU does not exist, rcu_barrier() is just
1076 1077 1078 1079 1080 1081 1082 1083
 * another name for rcu_barrier_sched().
 */
void rcu_barrier(void)
{
	rcu_barrier_sched();
}
EXPORT_SYMBOL_GPL(rcu_barrier);

1084
/*
P
Paul E. McKenney 已提交
1085
 * Because preemptible RCU does not exist, it need not be initialized.
1086 1087 1088 1089 1090
 */
static void __init __rcu_init_preempt(void)
{
}

1091 1092 1093 1094 1095 1096 1097 1098
/*
 * Because preemptible RCU does not exist, tasks cannot possibly exit
 * while in preemptible RCU read-side critical sections.
 */
void exit_rcu(void)
{
}

1099
#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
1100

1101 1102
#ifdef CONFIG_RCU_BOOST

1103
#include "../locking/rtmutex_common.h"
1104

1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117
#ifdef CONFIG_RCU_TRACE

static void rcu_initiate_boost_trace(struct rcu_node *rnp)
{
	if (list_empty(&rnp->blkd_tasks))
		rnp->n_balk_blkd_tasks++;
	else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
		rnp->n_balk_exp_gp_tasks++;
	else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
		rnp->n_balk_boost_tasks++;
	else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
		rnp->n_balk_notblocked++;
	else if (rnp->gp_tasks != NULL &&
1118
		 ULONG_CMP_LT(jiffies, rnp->boost_time))
1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131
		rnp->n_balk_notyet++;
	else
		rnp->n_balk_nos++;
}

#else /* #ifdef CONFIG_RCU_TRACE */

static void rcu_initiate_boost_trace(struct rcu_node *rnp)
{
}

#endif /* #else #ifdef CONFIG_RCU_TRACE */

T
Thomas Gleixner 已提交
1132 1133 1134 1135 1136 1137 1138 1139 1140 1141
static void rcu_wake_cond(struct task_struct *t, int status)
{
	/*
	 * If the thread is yielding, only wake it when this
	 * is invoked from idle
	 */
	if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
		wake_up_process(t);
}

1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159
/*
 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
 * or ->boost_tasks, advancing the pointer to the next task in the
 * ->blkd_tasks list.
 *
 * Note that irqs must be enabled: boosting the task can block.
 * Returns 1 if there are more tasks needing to be boosted.
 */
static int rcu_boost(struct rcu_node *rnp)
{
	unsigned long flags;
	struct task_struct *t;
	struct list_head *tb;

	if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
		return 0;  /* Nothing left to boost. */

	raw_spin_lock_irqsave(&rnp->lock, flags);
1160
	smp_mb__after_unlock_lock();
1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176

	/*
	 * Recheck under the lock: all tasks in need of boosting
	 * might exit their RCU read-side critical sections on their own.
	 */
	if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
		return 0;
	}

	/*
	 * Preferentially boost tasks blocking expedited grace periods.
	 * This cannot starve the normal grace periods because a second
	 * expedited grace period must boost all blocked tasks, including
	 * those blocking the pre-existing normal grace period.
	 */
1177
	if (rnp->exp_tasks != NULL) {
1178
		tb = rnp->exp_tasks;
1179 1180
		rnp->n_exp_boosts++;
	} else {
1181
		tb = rnp->boost_tasks;
1182 1183 1184
		rnp->n_normal_boosts++;
	}
	rnp->n_tasks_boosted++;
1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202

	/*
	 * We boost task t by manufacturing an rt_mutex that appears to
	 * be held by task t.  We leave a pointer to that rt_mutex where
	 * task t can find it, and task t will release the mutex when it
	 * exits its outermost RCU read-side critical section.  Then
	 * simply acquiring this artificial rt_mutex will boost task
	 * t's priority.  (Thanks to tglx for suggesting this approach!)
	 *
	 * Note that task t must acquire rnp->lock to remove itself from
	 * the ->blkd_tasks list, which it will do from exit() if from
	 * nowhere else.  We therefore are guaranteed that task t will
	 * stay around at least until we drop rnp->lock.  Note that
	 * rnp->lock also resolves races between our priority boosting
	 * and task t's exiting its outermost RCU read-side critical
	 * section.
	 */
	t = container_of(tb, struct task_struct, rcu_node_entry);
1203
	rt_mutex_init_proxy_locked(&rnp->boost_mtx, t);
1204
	init_completion(&rnp->boost_completion);
1205
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1206 1207 1208
	/* Lock only for side effect: boosts task t's priority. */
	rt_mutex_lock(&rnp->boost_mtx);
	rt_mutex_unlock(&rnp->boost_mtx);  /* Then keep lockdep happy. */
1209

1210
	/* Wait for boostee to be done w/boost_mtx before reinitializing. */
1211
	wait_for_completion(&rnp->boost_completion);
1212

1213 1214
	return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
	       ACCESS_ONCE(rnp->boost_tasks) != NULL;
1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226
}

/*
 * Priority-boosting kthread.  One per leaf rcu_node and one for the
 * root rcu_node.
 */
static int rcu_boost_kthread(void *arg)
{
	struct rcu_node *rnp = (struct rcu_node *)arg;
	int spincnt = 0;
	int more2boost;

1227
	trace_rcu_utilization(TPS("Start boost kthread@init"));
1228
	for (;;) {
1229
		rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1230
		trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1231
		rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1232
		trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1233
		rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1234 1235 1236 1237 1238 1239
		more2boost = rcu_boost(rnp);
		if (more2boost)
			spincnt++;
		else
			spincnt = 0;
		if (spincnt > 10) {
T
Thomas Gleixner 已提交
1240
			rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
1241
			trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
T
Thomas Gleixner 已提交
1242
			schedule_timeout_interruptible(2);
1243
			trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1244 1245 1246
			spincnt = 0;
		}
	}
1247
	/* NOTREACHED */
1248
	trace_rcu_utilization(TPS("End boost kthread@notreached"));
1249 1250 1251 1252 1253 1254 1255 1256 1257
	return 0;
}

/*
 * Check to see if it is time to start boosting RCU readers that are
 * blocking the current grace period, and, if so, tell the per-rcu_node
 * kthread to start boosting them.  If there is an expedited grace
 * period in progress, it is always time to boost.
 *
1258 1259 1260
 * The caller must hold rnp->lock, which this function releases.
 * The ->boost_kthread_task is immortal, so we don't need to worry
 * about it going away.
1261
 */
1262
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1263
	__releases(rnp->lock)
1264 1265 1266
{
	struct task_struct *t;

1267 1268
	if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
		rnp->n_balk_exp_gp_tasks++;
1269
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1270
		return;
1271
	}
1272 1273 1274 1275 1276 1277 1278
	if (rnp->exp_tasks != NULL ||
	    (rnp->gp_tasks != NULL &&
	     rnp->boost_tasks == NULL &&
	     rnp->qsmask == 0 &&
	     ULONG_CMP_GE(jiffies, rnp->boost_time))) {
		if (rnp->exp_tasks == NULL)
			rnp->boost_tasks = rnp->gp_tasks;
1279
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1280
		t = rnp->boost_kthread_task;
T
Thomas Gleixner 已提交
1281 1282
		if (t)
			rcu_wake_cond(t, rnp->boost_kthread_status);
1283
	} else {
1284
		rcu_initiate_boost_trace(rnp);
1285 1286
		raw_spin_unlock_irqrestore(&rnp->lock, flags);
	}
1287 1288
}

1289 1290 1291 1292 1293 1294 1295 1296 1297
/*
 * Wake up the per-CPU kthread to invoke RCU callbacks.
 */
static void invoke_rcu_callbacks_kthread(void)
{
	unsigned long flags;

	local_irq_save(flags);
	__this_cpu_write(rcu_cpu_has_work, 1);
1298
	if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
T
Thomas Gleixner 已提交
1299 1300 1301 1302
	    current != __this_cpu_read(rcu_cpu_kthread_task)) {
		rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
			      __this_cpu_read(rcu_cpu_kthread_status));
	}
1303 1304 1305
	local_irq_restore(flags);
}

1306 1307 1308 1309 1310 1311
/*
 * Is the current CPU running the RCU-callbacks kthread?
 * Caller must have preemption disabled.
 */
static bool rcu_is_callbacks_kthread(void)
{
1312
	return __this_cpu_read(rcu_cpu_kthread_task) == current;
1313 1314
}

1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329
#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)

/*
 * Do priority-boost accounting for the start of a new grace period.
 */
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
{
	rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
}

/*
 * Create an RCU-boost kthread for the specified node if one does not
 * already exist.  We only create this kthread for preemptible RCU.
 * Returns zero if all is well, a negated errno otherwise.
 */
1330
static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
T
Thomas Gleixner 已提交
1331
						 struct rcu_node *rnp)
1332
{
T
Thomas Gleixner 已提交
1333
	int rnp_index = rnp - &rsp->node[0];
1334 1335 1336 1337 1338 1339
	unsigned long flags;
	struct sched_param sp;
	struct task_struct *t;

	if (&rcu_preempt_state != rsp)
		return 0;
T
Thomas Gleixner 已提交
1340 1341 1342 1343

	if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0)
		return 0;

1344
	rsp->boost = 1;
1345 1346 1347
	if (rnp->boost_kthread_task != NULL)
		return 0;
	t = kthread_create(rcu_boost_kthread, (void *)rnp,
1348
			   "rcub/%d", rnp_index);
1349 1350 1351
	if (IS_ERR(t))
		return PTR_ERR(t);
	raw_spin_lock_irqsave(&rnp->lock, flags);
1352
	smp_mb__after_unlock_lock();
1353 1354
	rnp->boost_kthread_task = t;
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1355
	sp.sched_priority = RCU_BOOST_PRIO;
1356
	sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1357
	wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1358 1359 1360
	return 0;
}

1361 1362
static void rcu_kthread_do_work(void)
{
1363 1364
	rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
	rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
1365 1366 1367
	rcu_preempt_do_callbacks();
}

1368
static void rcu_cpu_kthread_setup(unsigned int cpu)
1369 1370 1371
{
	struct sched_param sp;

1372 1373
	sp.sched_priority = RCU_KTHREAD_PRIO;
	sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
1374 1375
}

1376
static void rcu_cpu_kthread_park(unsigned int cpu)
1377
{
1378
	per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
1379 1380
}

1381
static int rcu_cpu_kthread_should_run(unsigned int cpu)
1382
{
1383
	return __this_cpu_read(rcu_cpu_has_work);
1384 1385 1386 1387
}

/*
 * Per-CPU kernel thread that invokes RCU callbacks.  This replaces the
1388 1389
 * RCU softirq used in flavors and configurations of RCU that do not
 * support RCU priority boosting.
1390
 */
1391
static void rcu_cpu_kthread(unsigned int cpu)
1392
{
1393 1394
	unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
	char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
1395
	int spincnt;
1396

1397
	for (spincnt = 0; spincnt < 10; spincnt++) {
1398
		trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
1399 1400
		local_bh_disable();
		*statusp = RCU_KTHREAD_RUNNING;
1401 1402
		this_cpu_inc(rcu_cpu_kthread_loops);
		local_irq_disable();
1403 1404
		work = *workp;
		*workp = 0;
1405
		local_irq_enable();
1406 1407 1408
		if (work)
			rcu_kthread_do_work();
		local_bh_enable();
1409
		if (*workp == 0) {
1410
			trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
1411 1412
			*statusp = RCU_KTHREAD_WAITING;
			return;
1413 1414
		}
	}
1415
	*statusp = RCU_KTHREAD_YIELDING;
1416
	trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
1417
	schedule_timeout_interruptible(2);
1418
	trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
1419
	*statusp = RCU_KTHREAD_WAITING;
1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430
}

/*
 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
 * served by the rcu_node in question.  The CPU hotplug lock is still
 * held, so the value of rnp->qsmaskinit will be stable.
 *
 * We don't include outgoingcpu in the affinity set, use -1 if there is
 * no outgoing CPU.  If there are no CPUs left in the affinity set,
 * this function allows the kthread to execute on any CPU.
 */
T
Thomas Gleixner 已提交
1431
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1432
{
T
Thomas Gleixner 已提交
1433 1434
	struct task_struct *t = rnp->boost_kthread_task;
	unsigned long mask = rnp->qsmaskinit;
1435 1436 1437
	cpumask_var_t cm;
	int cpu;

T
Thomas Gleixner 已提交
1438
	if (!t)
1439
		return;
T
Thomas Gleixner 已提交
1440
	if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
1441 1442 1443 1444 1445 1446 1447 1448 1449 1450
		return;
	for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
		if ((mask & 0x1) && cpu != outgoingcpu)
			cpumask_set_cpu(cpu, cm);
	if (cpumask_weight(cm) == 0) {
		cpumask_setall(cm);
		for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
			cpumask_clear_cpu(cpu, cm);
		WARN_ON_ONCE(cpumask_weight(cm) == 0);
	}
T
Thomas Gleixner 已提交
1451
	set_cpus_allowed_ptr(t, cm);
1452 1453 1454
	free_cpumask_var(cm);
}

1455 1456 1457 1458 1459 1460 1461 1462
static struct smp_hotplug_thread rcu_cpu_thread_spec = {
	.store			= &rcu_cpu_kthread_task,
	.thread_should_run	= rcu_cpu_kthread_should_run,
	.thread_fn		= rcu_cpu_kthread,
	.thread_comm		= "rcuc/%u",
	.setup			= rcu_cpu_kthread_setup,
	.park			= rcu_cpu_kthread_park,
};
1463 1464 1465 1466 1467 1468 1469

/*
 * Spawn all kthreads -- called as soon as the scheduler is running.
 */
static int __init rcu_spawn_kthreads(void)
{
	struct rcu_node *rnp;
T
Thomas Gleixner 已提交
1470
	int cpu;
1471

1472
	rcu_scheduler_fully_active = 1;
1473
	for_each_possible_cpu(cpu)
1474
		per_cpu(rcu_cpu_has_work, cpu) = 0;
1475
	BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
1476 1477
	rnp = rcu_get_root(rcu_state_p);
	(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
1478
	if (NUM_RCU_NODES > 1) {
1479 1480
		rcu_for_each_leaf_node(rcu_state_p, rnp)
			(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
1481 1482 1483 1484 1485
	}
	return 0;
}
early_initcall(rcu_spawn_kthreads);

1486
static void rcu_prepare_kthreads(int cpu)
1487
{
1488
	struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
1489 1490 1491
	struct rcu_node *rnp = rdp->mynode;

	/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1492
	if (rcu_scheduler_fully_active)
1493
		(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
1494 1495
}

1496 1497
#else /* #ifdef CONFIG_RCU_BOOST */

1498
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1499
	__releases(rnp->lock)
1500
{
1501
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1502 1503
}

1504
static void invoke_rcu_callbacks_kthread(void)
1505
{
1506
	WARN_ON_ONCE(1);
1507 1508
}

1509 1510 1511 1512 1513
static bool rcu_is_callbacks_kthread(void)
{
	return false;
}

1514 1515 1516 1517
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
{
}

T
Thomas Gleixner 已提交
1518
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1519 1520 1521
{
}

1522 1523 1524 1525 1526 1527 1528
static int __init rcu_scheduler_really_started(void)
{
	rcu_scheduler_fully_active = 1;
	return 0;
}
early_initcall(rcu_scheduler_really_started);

1529
static void rcu_prepare_kthreads(int cpu)
1530 1531 1532
{
}

1533 1534
#endif /* #else #ifdef CONFIG_RCU_BOOST */

1535 1536 1537 1538 1539 1540 1541 1542
#if !defined(CONFIG_RCU_FAST_NO_HZ)

/*
 * Check to see if any future RCU-related work will need to be done
 * by the current CPU, even if none need be done immediately, returning
 * 1 if so.  This function is part of the RCU implementation; it is -not-
 * an exported member of the RCU API.
 *
1543 1544
 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
 * any flavor of RCU.
1545
 */
1546
#ifndef CONFIG_RCU_NOCB_CPU_ALL
1547
int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
1548
{
1549
	*delta_jiffies = ULONG_MAX;
1550
	return rcu_cpu_has_callbacks(cpu, NULL);
1551
}
1552
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1553 1554 1555 1556 1557 1558 1559 1560 1561

/*
 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
 * after it.
 */
static void rcu_cleanup_after_idle(int cpu)
{
}

1562
/*
1563
 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1564 1565 1566 1567 1568 1569
 * is nothing.
 */
static void rcu_prepare_for_idle(int cpu)
{
}

1570 1571 1572 1573 1574 1575 1576 1577
/*
 * Don't bother keeping a running count of the number of RCU callbacks
 * posted because CONFIG_RCU_FAST_NO_HZ=n.
 */
static void rcu_idle_count_callbacks_posted(void)
{
}

1578 1579
#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */

1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594
/*
 * This code is invoked when a CPU goes idle, at which point we want
 * to have the CPU do everything required for RCU so that it can enter
 * the energy-efficient dyntick-idle mode.  This is handled by a
 * state machine implemented by rcu_prepare_for_idle() below.
 *
 * The following three proprocessor symbols control this state machine:
 *
 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
 *	to sleep in dyntick-idle mode with RCU callbacks pending.  This
 *	is sized to be roughly one RCU grace period.  Those energy-efficiency
 *	benchmarkers who might otherwise be tempted to set this to a large
 *	number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
 *	system.  And if you are -that- concerned about energy efficiency,
 *	just power the system down and be done with it!
1595 1596 1597
 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
 *	permitted to sleep in dyntick-idle mode with only lazy RCU
 *	callbacks pending.  Setting this too high can OOM your system.
1598 1599 1600 1601 1602
 *
 * The values below work well in practice.  If future workloads require
 * adjustment, they can be converted into kernel config parameters, though
 * making the state machine smarter might be a better option.
 */
1603
#define RCU_IDLE_GP_DELAY 4		/* Roughly one grace period. */
1604
#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ)	/* Roughly six seconds. */
1605

1606 1607 1608 1609
static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
module_param(rcu_idle_gp_delay, int, 0644);
static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
module_param(rcu_idle_lazy_gp_delay, int, 0644);
1610

1611
extern int tick_nohz_active;
1612 1613

/*
1614 1615 1616
 * Try to advance callbacks for all flavors of RCU on the current CPU, but
 * only if it has been awhile since the last time we did so.  Afterwards,
 * if there are any callbacks ready for immediate invocation, return true.
1617
 */
1618
static bool __maybe_unused rcu_try_advance_all_cbs(void)
1619
{
1620 1621
	bool cbs_ready = false;
	struct rcu_data *rdp;
1622
	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1623 1624
	struct rcu_node *rnp;
	struct rcu_state *rsp;
1625

1626 1627 1628 1629 1630
	/* Exit early if we advanced recently. */
	if (jiffies == rdtp->last_advance_all)
		return 0;
	rdtp->last_advance_all = jiffies;

1631 1632 1633
	for_each_rcu_flavor(rsp) {
		rdp = this_cpu_ptr(rsp->rda);
		rnp = rdp->mynode;
1634

1635 1636 1637 1638 1639 1640 1641
		/*
		 * Don't bother checking unless a grace period has
		 * completed since we last checked and there are
		 * callbacks not yet ready to invoke.
		 */
		if (rdp->completed != rnp->completed &&
		    rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
1642
			note_gp_changes(rsp, rdp);
1643

1644 1645 1646 1647
		if (cpu_has_callbacks_ready_to_invoke(rdp))
			cbs_ready = true;
	}
	return cbs_ready;
1648 1649
}

1650
/*
1651 1652 1653 1654
 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
 * to invoke.  If the CPU has callbacks, try to advance them.  Tell the
 * caller to set the timeout based on whether or not there are non-lazy
 * callbacks.
1655
 *
1656
 * The caller must have disabled interrupts.
1657
 */
1658
#ifndef CONFIG_RCU_NOCB_CPU_ALL
1659
int rcu_needs_cpu(int cpu, unsigned long *dj)
1660 1661 1662
{
	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);

1663 1664 1665
	/* Snapshot to detect later posting of non-lazy callback. */
	rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;

1666
	/* If no callbacks, RCU doesn't need the CPU. */
1667 1668
	if (!rcu_cpu_has_callbacks(cpu, &rdtp->all_lazy)) {
		*dj = ULONG_MAX;
1669 1670
		return 0;
	}
1671 1672 1673 1674 1675

	/* Attempt to advance callbacks. */
	if (rcu_try_advance_all_cbs()) {
		/* Some ready to invoke, so initiate later invocation. */
		invoke_rcu_core();
1676 1677
		return 1;
	}
1678 1679 1680
	rdtp->last_accelerate = jiffies;

	/* Request timer delay depending on laziness, and round. */
1681
	if (!rdtp->all_lazy) {
1682 1683
		*dj = round_up(rcu_idle_gp_delay + jiffies,
			       rcu_idle_gp_delay) - jiffies;
1684
	} else {
1685
		*dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
1686
	}
1687 1688
	return 0;
}
1689
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1690

1691
/*
1692 1693 1694 1695 1696 1697
 * Prepare a CPU for idle from an RCU perspective.  The first major task
 * is to sense whether nohz mode has been enabled or disabled via sysfs.
 * The second major task is to check to see if a non-lazy callback has
 * arrived at a CPU that previously had only lazy callbacks.  The third
 * major task is to accelerate (that is, assign grace-period numbers to)
 * any recently arrived callbacks.
1698 1699
 *
 * The caller must have disabled interrupts.
1700
 */
1701
static void rcu_prepare_for_idle(int cpu)
1702
{
1703
#ifndef CONFIG_RCU_NOCB_CPU_ALL
1704
	bool needwake;
1705
	struct rcu_data *rdp;
1706
	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1707 1708
	struct rcu_node *rnp;
	struct rcu_state *rsp;
1709 1710 1711
	int tne;

	/* Handle nohz enablement switches conservatively. */
1712
	tne = ACCESS_ONCE(tick_nohz_active);
1713
	if (tne != rdtp->tick_nohz_enabled_snap) {
1714
		if (rcu_cpu_has_callbacks(cpu, NULL))
1715 1716 1717 1718 1719 1720
			invoke_rcu_core(); /* force nohz to see update. */
		rdtp->tick_nohz_enabled_snap = tne;
		return;
	}
	if (!tne)
		return;
1721

1722
	/* If this is a no-CBs CPU, no callbacks, just return. */
1723
	if (rcu_is_nocb_cpu(cpu))
1724 1725
		return;

1726
	/*
1727 1728 1729
	 * If a non-lazy callback arrived at a CPU having only lazy
	 * callbacks, invoke RCU core for the side-effect of recalculating
	 * idle duration on re-entry to idle.
1730
	 */
1731 1732
	if (rdtp->all_lazy &&
	    rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
1733 1734
		rdtp->all_lazy = false;
		rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1735
		invoke_rcu_core();
1736 1737 1738
		return;
	}

1739
	/*
1740 1741
	 * If we have not yet accelerated this jiffy, accelerate all
	 * callbacks on this CPU.
1742
	 */
1743
	if (rdtp->last_accelerate == jiffies)
1744
		return;
1745 1746 1747 1748 1749 1750 1751
	rdtp->last_accelerate = jiffies;
	for_each_rcu_flavor(rsp) {
		rdp = per_cpu_ptr(rsp->rda, cpu);
		if (!*rdp->nxttail[RCU_DONE_TAIL])
			continue;
		rnp = rdp->mynode;
		raw_spin_lock(&rnp->lock); /* irqs already disabled. */
1752
		smp_mb__after_unlock_lock();
1753
		needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
1754
		raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1755 1756
		if (needwake)
			rcu_gp_kthread_wake(rsp);
1757
	}
1758
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1759
}
1760

1761 1762 1763 1764 1765 1766 1767
/*
 * Clean up for exit from idle.  Attempt to advance callbacks based on
 * any grace periods that elapsed while the CPU was idle, and if any
 * callbacks are now ready to invoke, initiate invocation.
 */
static void rcu_cleanup_after_idle(int cpu)
{
1768
#ifndef CONFIG_RCU_NOCB_CPU_ALL
1769
	if (rcu_is_nocb_cpu(cpu))
1770
		return;
1771 1772
	if (rcu_try_advance_all_cbs())
		invoke_rcu_core();
1773
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1774 1775
}

1776
/*
1777 1778 1779 1780 1781 1782
 * Keep a running count of the number of non-lazy callbacks posted
 * on this CPU.  This running counter (which is never decremented) allows
 * rcu_prepare_for_idle() to detect when something out of the idle loop
 * posts a callback, even if an equal number of callbacks are invoked.
 * Of course, callbacks should only be posted from within a trace event
 * designed to be called from idle or from within RCU_NONIDLE().
1783 1784 1785
 */
static void rcu_idle_count_callbacks_posted(void)
{
1786
	__this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
1787 1788
}

1789 1790 1791 1792 1793 1794 1795 1796 1797 1798 1799 1800 1801 1802 1803 1804 1805 1806 1807 1808 1809 1810 1811 1812 1813 1814 1815 1816 1817
/*
 * Data for flushing lazy RCU callbacks at OOM time.
 */
static atomic_t oom_callback_count;
static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);

/*
 * RCU OOM callback -- decrement the outstanding count and deliver the
 * wake-up if we are the last one.
 */
static void rcu_oom_callback(struct rcu_head *rhp)
{
	if (atomic_dec_and_test(&oom_callback_count))
		wake_up(&oom_callback_wq);
}

/*
 * Post an rcu_oom_notify callback on the current CPU if it has at
 * least one lazy callback.  This will unnecessarily post callbacks
 * to CPUs that already have a non-lazy callback at the end of their
 * callback list, but this is an infrequent operation, so accept some
 * extra overhead to keep things simple.
 */
static void rcu_oom_notify_cpu(void *unused)
{
	struct rcu_state *rsp;
	struct rcu_data *rdp;

	for_each_rcu_flavor(rsp) {
1818
		rdp = raw_cpu_ptr(rsp->rda);
1819 1820 1821 1822 1823 1824 1825 1826 1827 1828 1829 1830 1831 1832 1833 1834 1835 1836 1837 1838 1839
		if (rdp->qlen_lazy != 0) {
			atomic_inc(&oom_callback_count);
			rsp->call(&rdp->oom_head, rcu_oom_callback);
		}
	}
}

/*
 * If low on memory, ensure that each CPU has a non-lazy callback.
 * This will wake up CPUs that have only lazy callbacks, in turn
 * ensuring that they free up the corresponding memory in a timely manner.
 * Because an uncertain amount of memory will be freed in some uncertain
 * timeframe, we do not claim to have freed anything.
 */
static int rcu_oom_notify(struct notifier_block *self,
			  unsigned long notused, void *nfreed)
{
	int cpu;

	/* Wait for callbacks from earlier instance to complete. */
	wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
1840
	smp_mb(); /* Ensure callback reuse happens after callback invocation. */
1841 1842 1843 1844 1845 1846 1847 1848 1849 1850 1851 1852 1853 1854 1855 1856 1857 1858 1859 1860 1861 1862 1863 1864 1865 1866 1867 1868 1869 1870 1871

	/*
	 * Prevent premature wakeup: ensure that all increments happen
	 * before there is a chance of the counter reaching zero.
	 */
	atomic_set(&oom_callback_count, 1);

	get_online_cpus();
	for_each_online_cpu(cpu) {
		smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
		cond_resched();
	}
	put_online_cpus();

	/* Unconditionally decrement: no need to wake ourselves up. */
	atomic_dec(&oom_callback_count);

	return NOTIFY_OK;
}

static struct notifier_block rcu_oom_nb = {
	.notifier_call = rcu_oom_notify
};

static int __init rcu_register_oom_notifier(void)
{
	register_oom_notifier(&rcu_oom_nb);
	return 0;
}
early_initcall(rcu_register_oom_notifier);

1872
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1873 1874 1875 1876 1877 1878 1879

#ifdef CONFIG_RCU_CPU_STALL_INFO

#ifdef CONFIG_RCU_FAST_NO_HZ

static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
1880
	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1881
	unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
1882

1883 1884 1885 1886 1887
	sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
		rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
		ulong2long(nlpd),
		rdtp->all_lazy ? 'L' : '.',
		rdtp->tick_nohz_enabled_snap ? '.' : 'D');
1888 1889 1890 1891 1892 1893
}

#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */

static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
1894
	*cp = '\0';
1895 1896 1897 1898 1899 1900 1901
}

#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */

/* Initiate the stall-info list. */
static void print_cpu_stall_info_begin(void)
{
1902
	pr_cont("\n");
1903 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932
}

/*
 * Print out diagnostic information for the specified stalled CPU.
 *
 * If the specified CPU is aware of the current RCU grace period
 * (flavor specified by rsp), then print the number of scheduling
 * clock interrupts the CPU has taken during the time that it has
 * been aware.  Otherwise, print the number of RCU grace periods
 * that this CPU is ignorant of, for example, "1" if the CPU was
 * aware of the previous grace period.
 *
 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
 */
static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
{
	char fast_no_hz[72];
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
	struct rcu_dynticks *rdtp = rdp->dynticks;
	char *ticks_title;
	unsigned long ticks_value;

	if (rsp->gpnum == rdp->gpnum) {
		ticks_title = "ticks this GP";
		ticks_value = rdp->ticks_this_gp;
	} else {
		ticks_title = "GPs behind";
		ticks_value = rsp->gpnum - rdp->gpnum;
	}
	print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
1933
	pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
1934 1935 1936
	       cpu, ticks_value, ticks_title,
	       atomic_read(&rdtp->dynticks) & 0xfff,
	       rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
1937
	       rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
1938 1939 1940 1941 1942 1943
	       fast_no_hz);
}

/* Terminate the stall-info list. */
static void print_cpu_stall_info_end(void)
{
1944
	pr_err("\t");
1945 1946 1947 1948 1949 1950
}

/* Zero ->ticks_this_gp for all flavors of RCU. */
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
{
	rdp->ticks_this_gp = 0;
1951
	rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
1952 1953 1954 1955 1956
}

/* Increment ->ticks_this_gp for all flavors of RCU. */
static void increment_cpu_stall_ticks(void)
{
1957 1958 1959
	struct rcu_state *rsp;

	for_each_rcu_flavor(rsp)
1960
		raw_cpu_inc(rsp->rda->ticks_this_gp);
1961 1962 1963 1964 1965 1966
}

#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */

static void print_cpu_stall_info_begin(void)
{
1967
	pr_cont(" {");
1968 1969 1970 1971
}

static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
{
1972
	pr_cont(" %d", cpu);
1973 1974 1975 1976
}

static void print_cpu_stall_info_end(void)
{
1977
	pr_cont("} ");
1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988
}

static void zero_cpu_stall_ticks(struct rcu_data *rdp)
{
}

static void increment_cpu_stall_ticks(void)
{
}

#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
P
Paul E. McKenney 已提交
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022

#ifdef CONFIG_RCU_NOCB_CPU

/*
 * Offload callback processing from the boot-time-specified set of CPUs
 * specified by rcu_nocb_mask.  For each CPU in the set, there is a
 * kthread created that pulls the callbacks from the corresponding CPU,
 * waits for a grace period to elapse, and invokes the callbacks.
 * The no-CBs CPUs do a wake_up() on their kthread when they insert
 * a callback into any empty list, unless the rcu_nocb_poll boot parameter
 * has been specified, in which case each kthread actively polls its
 * CPU.  (Which isn't so great for energy efficiency, but which does
 * reduce RCU's overhead on that CPU.)
 *
 * This is intended to be used in conjunction with Frederic Weisbecker's
 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
 * running CPU-bound user-mode computations.
 *
 * Offloading of callback processing could also in theory be used as
 * an energy-efficiency measure because CPUs with no RCU callbacks
 * queued are more aggressive about entering dyntick-idle mode.
 */


/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
static int __init rcu_nocb_setup(char *str)
{
	alloc_bootmem_cpumask_var(&rcu_nocb_mask);
	have_rcu_nocb_mask = true;
	cpulist_parse(str, rcu_nocb_mask);
	return 1;
}
__setup("rcu_nocbs=", rcu_nocb_setup);

2023 2024 2025 2026 2027 2028 2029
static int __init parse_rcu_nocb_poll(char *arg)
{
	rcu_nocb_poll = 1;
	return 0;
}
early_param("rcu_nocb_poll", parse_rcu_nocb_poll);

2030
/*
2031 2032
 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
 * grace period.
2033
 */
2034
static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
2035
{
2036
	wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]);
2037 2038 2039
}

/*
2040
 * Set the root rcu_node structure's ->need_future_gp field
2041 2042 2043 2044 2045
 * based on the sum of those of all rcu_node structures.  This does
 * double-count the root rcu_node structure's requests, but this
 * is necessary to handle the possibility of a rcu_nocb_kthread()
 * having awakened during the time that the rcu_node structures
 * were being updated for the end of the previous grace period.
2046
 */
2047 2048
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
{
2049
	rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
2050 2051 2052
}

static void rcu_init_one_nocb(struct rcu_node *rnp)
2053
{
2054 2055
	init_waitqueue_head(&rnp->nocb_gp_wq[0]);
	init_waitqueue_head(&rnp->nocb_gp_wq[1]);
2056 2057
}

2058
#ifndef CONFIG_RCU_NOCB_CPU_ALL
L
Liu Ping Fan 已提交
2059
/* Is the specified CPU a no-CBs CPU? */
2060
bool rcu_is_nocb_cpu(int cpu)
P
Paul E. McKenney 已提交
2061 2062 2063 2064 2065
{
	if (have_rcu_nocb_mask)
		return cpumask_test_cpu(cpu, rcu_nocb_mask);
	return false;
}
2066
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
P
Paul E. McKenney 已提交
2067

2068 2069 2070 2071 2072 2073 2074 2075 2076
/*
 * Kick the leader kthread for this NOCB group.
 */
static void wake_nocb_leader(struct rcu_data *rdp, bool force)
{
	struct rcu_data *rdp_leader = rdp->nocb_leader;

	if (!ACCESS_ONCE(rdp_leader->nocb_kthread))
		return;
2077
	if (ACCESS_ONCE(rdp_leader->nocb_leader_sleep) || force) {
2078
		/* Prior xchg orders against prior callback enqueue. */
2079
		ACCESS_ONCE(rdp_leader->nocb_leader_sleep) = false;
2080 2081 2082 2083
		wake_up(&rdp_leader->nocb_wq);
	}
}

P
Paul E. McKenney 已提交
2084 2085 2086 2087 2088 2089 2090 2091 2092 2093 2094
/*
 * Enqueue the specified string of rcu_head structures onto the specified
 * CPU's no-CBs lists.  The CPU is specified by rdp, the head of the
 * string by rhp, and the tail of the string by rhtp.  The non-lazy/lazy
 * counts are supplied by rhcount and rhcount_lazy.
 *
 * If warranted, also wake up the kthread servicing this CPUs queues.
 */
static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
				    struct rcu_head *rhp,
				    struct rcu_head **rhtp,
2095 2096
				    int rhcount, int rhcount_lazy,
				    unsigned long flags)
P
Paul E. McKenney 已提交
2097 2098 2099 2100 2101 2102 2103 2104 2105 2106 2107 2108 2109
{
	int len;
	struct rcu_head **old_rhpp;
	struct task_struct *t;

	/* Enqueue the callback on the nocb list and update counts. */
	old_rhpp = xchg(&rdp->nocb_tail, rhtp);
	ACCESS_ONCE(*old_rhpp) = rhp;
	atomic_long_add(rhcount, &rdp->nocb_q_count);
	atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);

	/* If we are not being polled and there is a kthread, awaken it ... */
	t = ACCESS_ONCE(rdp->nocb_kthread);
2110
	if (rcu_nocb_poll || !t) {
2111 2112
		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
				    TPS("WakeNotPoll"));
P
Paul E. McKenney 已提交
2113
		return;
2114
	}
P
Paul E. McKenney 已提交
2115 2116
	len = atomic_long_read(&rdp->nocb_q_count);
	if (old_rhpp == &rdp->nocb_head) {
2117
		if (!irqs_disabled_flags(flags)) {
2118 2119
			/* ... if queue was empty ... */
			wake_nocb_leader(rdp, false);
2120 2121 2122 2123 2124 2125 2126
			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
					    TPS("WakeEmpty"));
		} else {
			rdp->nocb_defer_wakeup = true;
			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
					    TPS("WakeEmptyIsDeferred"));
		}
P
Paul E. McKenney 已提交
2127 2128
		rdp->qlen_last_fqs_check = 0;
	} else if (len > rdp->qlen_last_fqs_check + qhimark) {
2129 2130
		/* ... or if many callbacks queued. */
		wake_nocb_leader(rdp, true);
P
Paul E. McKenney 已提交
2131
		rdp->qlen_last_fqs_check = LONG_MAX / 2;
2132 2133 2134
		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeOvf"));
	} else {
		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
P
Paul E. McKenney 已提交
2135 2136 2137 2138 2139 2140 2141 2142 2143 2144 2145 2146 2147 2148
	}
	return;
}

/*
 * This is a helper for __call_rcu(), which invokes this when the normal
 * callback queue is inoperable.  If this is not a no-CBs CPU, this
 * function returns failure back to __call_rcu(), which can complain
 * appropriately.
 *
 * Otherwise, this function queues the callback where the corresponding
 * "rcuo" kthread can find it.
 */
static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2149
			    bool lazy, unsigned long flags)
P
Paul E. McKenney 已提交
2150 2151
{

2152
	if (!rcu_is_nocb_cpu(rdp->cpu))
P
Paul E. McKenney 已提交
2153
		return 0;
2154
	__call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
2155 2156 2157
	if (__is_kfree_rcu_offset((unsigned long)rhp->func))
		trace_rcu_kfree_callback(rdp->rsp->name, rhp,
					 (unsigned long)rhp->func,
2158 2159
					 -atomic_long_read(&rdp->nocb_q_count_lazy),
					 -atomic_long_read(&rdp->nocb_q_count));
2160 2161
	else
		trace_rcu_callback(rdp->rsp->name, rhp,
2162 2163
				   -atomic_long_read(&rdp->nocb_q_count_lazy),
				   -atomic_long_read(&rdp->nocb_q_count));
P
Paul E. McKenney 已提交
2164 2165 2166 2167 2168 2169 2170 2171
	return 1;
}

/*
 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
 * not a no-CBs CPU.
 */
static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
2172 2173
						     struct rcu_data *rdp,
						     unsigned long flags)
P
Paul E. McKenney 已提交
2174 2175 2176 2177 2178
{
	long ql = rsp->qlen;
	long qll = rsp->qlen_lazy;

	/* If this is not a no-CBs CPU, tell the caller to do it the old way. */
2179
	if (!rcu_is_nocb_cpu(smp_processor_id()))
P
Paul E. McKenney 已提交
2180 2181 2182 2183 2184 2185 2186
		return 0;
	rsp->qlen = 0;
	rsp->qlen_lazy = 0;

	/* First, enqueue the donelist, if any.  This preserves CB ordering. */
	if (rsp->orphan_donelist != NULL) {
		__call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist,
2187
					rsp->orphan_donetail, ql, qll, flags);
P
Paul E. McKenney 已提交
2188 2189 2190 2191 2192 2193
		ql = qll = 0;
		rsp->orphan_donelist = NULL;
		rsp->orphan_donetail = &rsp->orphan_donelist;
	}
	if (rsp->orphan_nxtlist != NULL) {
		__call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist,
2194
					rsp->orphan_nxttail, ql, qll, flags);
P
Paul E. McKenney 已提交
2195 2196 2197 2198 2199 2200 2201 2202
		ql = qll = 0;
		rsp->orphan_nxtlist = NULL;
		rsp->orphan_nxttail = &rsp->orphan_nxtlist;
	}
	return 1;
}

/*
2203 2204
 * If necessary, kick off a new grace period, and either way wait
 * for a subsequent grace period to complete.
P
Paul E. McKenney 已提交
2205
 */
2206
static void rcu_nocb_wait_gp(struct rcu_data *rdp)
P
Paul E. McKenney 已提交
2207
{
2208
	unsigned long c;
2209
	bool d;
2210
	unsigned long flags;
2211
	bool needwake;
2212 2213 2214
	struct rcu_node *rnp = rdp->mynode;

	raw_spin_lock_irqsave(&rnp->lock, flags);
2215
	smp_mb__after_unlock_lock();
2216
	needwake = rcu_start_future_gp(rnp, rdp, &c);
2217
	raw_spin_unlock_irqrestore(&rnp->lock, flags);
2218 2219
	if (needwake)
		rcu_gp_kthread_wake(rdp->rsp);
P
Paul E. McKenney 已提交
2220 2221

	/*
2222 2223
	 * Wait for the grace period.  Do so interruptibly to avoid messing
	 * up the load average.
P
Paul E. McKenney 已提交
2224
	 */
2225
	trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
2226
	for (;;) {
2227 2228 2229 2230
		wait_event_interruptible(
			rnp->nocb_gp_wq[c & 0x1],
			(d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c)));
		if (likely(d))
2231
			break;
2232
		flush_signals(current);
2233
		trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
2234
	}
2235
	trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
2236
	smp_mb(); /* Ensure that CB invocation happens after GP end. */
P
Paul E. McKenney 已提交
2237 2238
}

2239 2240 2241 2242 2243 2244 2245 2246 2247 2248 2249 2250 2251 2252 2253 2254 2255
/*
 * Leaders come here to wait for additional callbacks to show up.
 * This function does not return until callbacks appear.
 */
static void nocb_leader_wait(struct rcu_data *my_rdp)
{
	bool firsttime = true;
	bool gotcbs;
	struct rcu_data *rdp;
	struct rcu_head **tail;

wait_again:

	/* Wait for callbacks to appear. */
	if (!rcu_nocb_poll) {
		trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Sleep");
		wait_event_interruptible(my_rdp->nocb_wq,
2256
				!ACCESS_ONCE(my_rdp->nocb_leader_sleep));
2257 2258 2259 2260 2261 2262 2263 2264 2265 2266 2267 2268 2269 2270 2271 2272 2273 2274 2275 2276 2277 2278 2279 2280 2281 2282 2283 2284 2285 2286 2287 2288 2289 2290 2291 2292 2293 2294
		/* Memory barrier handled by smp_mb() calls below and repoll. */
	} else if (firsttime) {
		firsttime = false; /* Don't drown trace log with "Poll"! */
		trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Poll");
	}

	/*
	 * Each pass through the following loop checks a follower for CBs.
	 * We are our own first follower.  Any CBs found are moved to
	 * nocb_gp_head, where they await a grace period.
	 */
	gotcbs = false;
	for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
		rdp->nocb_gp_head = ACCESS_ONCE(rdp->nocb_head);
		if (!rdp->nocb_gp_head)
			continue;  /* No CBs here, try next follower. */

		/* Move callbacks to wait-for-GP list, which is empty. */
		ACCESS_ONCE(rdp->nocb_head) = NULL;
		rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
		rdp->nocb_gp_count = atomic_long_xchg(&rdp->nocb_q_count, 0);
		rdp->nocb_gp_count_lazy =
			atomic_long_xchg(&rdp->nocb_q_count_lazy, 0);
		gotcbs = true;
	}

	/*
	 * If there were no callbacks, sleep a bit, rescan after a
	 * memory barrier, and go retry.
	 */
	if (unlikely(!gotcbs)) {
		if (!rcu_nocb_poll)
			trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu,
					    "WokeEmpty");
		flush_signals(current);
		schedule_timeout_interruptible(1);

		/* Rescan in case we were a victim of memory ordering. */
2295 2296
		my_rdp->nocb_leader_sleep = true;
		smp_mb();  /* Ensure _sleep true before scan. */
2297 2298 2299
		for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower)
			if (ACCESS_ONCE(rdp->nocb_head)) {
				/* Found CB, so short-circuit next wait. */
2300
				my_rdp->nocb_leader_sleep = false;
2301 2302 2303 2304 2305 2306 2307 2308 2309
				break;
			}
		goto wait_again;
	}

	/* Wait for one grace period. */
	rcu_nocb_wait_gp(my_rdp);

	/*
2310 2311
	 * We left ->nocb_leader_sleep unset to reduce cache thrashing.
	 * We set it now, but recheck for new callbacks while
2312 2313
	 * traversing our follower list.
	 */
2314 2315
	my_rdp->nocb_leader_sleep = true;
	smp_mb(); /* Ensure _sleep true before scan of ->nocb_head. */
2316 2317 2318 2319

	/* Each pass through the following loop wakes a follower, if needed. */
	for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
		if (ACCESS_ONCE(rdp->nocb_head))
2320
			my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/
2321 2322 2323 2324 2325 2326 2327 2328 2329 2330 2331 2332 2333 2334 2335 2336 2337 2338 2339 2340 2341 2342 2343 2344 2345 2346 2347 2348 2349 2350 2351 2352 2353 2354 2355 2356 2357 2358 2359 2360 2361 2362 2363 2364 2365 2366 2367 2368 2369 2370 2371 2372 2373 2374
		if (!rdp->nocb_gp_head)
			continue; /* No CBs, so no need to wake follower. */

		/* Append callbacks to follower's "done" list. */
		tail = xchg(&rdp->nocb_follower_tail, rdp->nocb_gp_tail);
		*tail = rdp->nocb_gp_head;
		atomic_long_add(rdp->nocb_gp_count, &rdp->nocb_follower_count);
		atomic_long_add(rdp->nocb_gp_count_lazy,
				&rdp->nocb_follower_count_lazy);
		if (rdp != my_rdp && tail == &rdp->nocb_follower_head) {
			/*
			 * List was empty, wake up the follower.
			 * Memory barriers supplied by atomic_long_add().
			 */
			wake_up(&rdp->nocb_wq);
		}
	}

	/* If we (the leader) don't have CBs, go wait some more. */
	if (!my_rdp->nocb_follower_head)
		goto wait_again;
}

/*
 * Followers come here to wait for additional callbacks to show up.
 * This function does not return until callbacks appear.
 */
static void nocb_follower_wait(struct rcu_data *rdp)
{
	bool firsttime = true;

	for (;;) {
		if (!rcu_nocb_poll) {
			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
					    "FollowerSleep");
			wait_event_interruptible(rdp->nocb_wq,
						 ACCESS_ONCE(rdp->nocb_follower_head));
		} else if (firsttime) {
			/* Don't drown trace log with "Poll"! */
			firsttime = false;
			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "Poll");
		}
		if (smp_load_acquire(&rdp->nocb_follower_head)) {
			/* ^^^ Ensure CB invocation follows _head test. */
			return;
		}
		if (!rcu_nocb_poll)
			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
					    "WokeEmpty");
		flush_signals(current);
		schedule_timeout_interruptible(1);
	}
}

P
Paul E. McKenney 已提交
2375 2376
/*
 * Per-rcu_data kthread, but only for no-CBs CPUs.  Each kthread invokes
2377 2378 2379
 * callbacks queued by the corresponding no-CBs CPU, however, there is
 * an optional leader-follower relationship so that the grace-period
 * kthreads don't have to do quite so many wakeups.
P
Paul E. McKenney 已提交
2380 2381 2382 2383 2384 2385 2386 2387 2388 2389 2390
 */
static int rcu_nocb_kthread(void *arg)
{
	int c, cl;
	struct rcu_head *list;
	struct rcu_head *next;
	struct rcu_head **tail;
	struct rcu_data *rdp = arg;

	/* Each pass through this loop invokes one batch of callbacks */
	for (;;) {
2391 2392 2393 2394 2395 2396 2397 2398 2399 2400 2401 2402 2403 2404 2405 2406
		/* Wait for callbacks. */
		if (rdp->nocb_leader == rdp)
			nocb_leader_wait(rdp);
		else
			nocb_follower_wait(rdp);

		/* Pull the ready-to-invoke callbacks onto local list. */
		list = ACCESS_ONCE(rdp->nocb_follower_head);
		BUG_ON(!list);
		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "WokeNonEmpty");
		ACCESS_ONCE(rdp->nocb_follower_head) = NULL;
		tail = xchg(&rdp->nocb_follower_tail, &rdp->nocb_follower_head);
		c = atomic_long_xchg(&rdp->nocb_follower_count, 0);
		cl = atomic_long_xchg(&rdp->nocb_follower_count_lazy, 0);
		rdp->nocb_p_count += c;
		rdp->nocb_p_count_lazy += cl;
P
Paul E. McKenney 已提交
2407 2408 2409 2410 2411 2412 2413 2414

		/* Each pass through the following loop invokes a callback. */
		trace_rcu_batch_start(rdp->rsp->name, cl, c, -1);
		c = cl = 0;
		while (list) {
			next = list->next;
			/* Wait for enqueuing to complete, if needed. */
			while (next == NULL && &list->next != tail) {
2415 2416
				trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
						    TPS("WaitQueue"));
P
Paul E. McKenney 已提交
2417
				schedule_timeout_interruptible(1);
2418 2419
				trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
						    TPS("WokeQueue"));
P
Paul E. McKenney 已提交
2420 2421 2422 2423 2424 2425 2426 2427 2428 2429 2430 2431 2432
				next = list->next;
			}
			debug_rcu_head_unqueue(list);
			local_bh_disable();
			if (__rcu_reclaim(rdp->rsp->name, list))
				cl++;
			c++;
			local_bh_enable();
			list = next;
		}
		trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
		ACCESS_ONCE(rdp->nocb_p_count) -= c;
		ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl;
2433
		rdp->n_nocbs_invoked += c;
P
Paul E. McKenney 已提交
2434 2435 2436 2437
	}
	return 0;
}

2438 2439 2440 2441 2442 2443 2444 2445 2446 2447 2448 2449
/* Is a deferred wakeup of rcu_nocb_kthread() required? */
static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
{
	return ACCESS_ONCE(rdp->nocb_defer_wakeup);
}

/* Do a deferred wakeup of rcu_nocb_kthread(). */
static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
{
	if (!rcu_nocb_need_deferred_wakeup(rdp))
		return;
	ACCESS_ONCE(rdp->nocb_defer_wakeup) = false;
2450
	wake_nocb_leader(rdp, false);
2451 2452 2453
	trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWakeEmpty"));
}

P
Paul E. McKenney 已提交
2454 2455 2456 2457 2458
/* Initialize per-rcu_data variables for no-CBs CPUs. */
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
{
	rdp->nocb_tail = &rdp->nocb_head;
	init_waitqueue_head(&rdp->nocb_wq);
2459
	rdp->nocb_follower_tail = &rdp->nocb_follower_head;
P
Paul E. McKenney 已提交
2460 2461
}

2462 2463 2464 2465 2466 2467 2468 2469
/* How many follower CPU IDs per leader?  Default of -1 for sqrt(nr_cpu_ids). */
static int rcu_nocb_leader_stride = -1;
module_param(rcu_nocb_leader_stride, int, 0444);

/*
 * Create a kthread for each RCU flavor for each no-CBs CPU.
 * Also initialize leader-follower relationships.
 */
P
Paul E. McKenney 已提交
2470 2471 2472
static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
{
	int cpu;
2473 2474
	int ls = rcu_nocb_leader_stride;
	int nl = 0;  /* Next leader. */
P
Paul E. McKenney 已提交
2475
	struct rcu_data *rdp;
2476 2477
	struct rcu_data *rdp_leader = NULL;  /* Suppress misguided gcc warn. */
	struct rcu_data *rdp_prev = NULL;
P
Paul E. McKenney 已提交
2478 2479 2480 2481
	struct task_struct *t;

	if (rcu_nocb_mask == NULL)
		return;
2482 2483 2484 2485
#if defined(CONFIG_NO_HZ_FULL) && !defined(CONFIG_NO_HZ_FULL_ALL)
	if (tick_nohz_full_running)
		cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
#endif /* #if defined(CONFIG_NO_HZ_FULL) && !defined(CONFIG_NO_HZ_FULL_ALL) */
2486 2487 2488 2489 2490 2491 2492 2493 2494
	if (ls == -1) {
		ls = int_sqrt(nr_cpu_ids);
		rcu_nocb_leader_stride = ls;
	}

	/*
	 * Each pass through this loop sets up one rcu_data structure and
	 * spawns one rcu_nocb_kthread().
	 */
P
Paul E. McKenney 已提交
2495 2496
	for_each_cpu(cpu, rcu_nocb_mask) {
		rdp = per_cpu_ptr(rsp->rda, cpu);
2497 2498 2499 2500 2501 2502 2503 2504 2505 2506 2507 2508 2509
		if (rdp->cpu >= nl) {
			/* New leader, set up for followers & next leader. */
			nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
			rdp->nocb_leader = rdp;
			rdp_leader = rdp;
		} else {
			/* Another follower, link to previous leader. */
			rdp->nocb_leader = rdp_leader;
			rdp_prev->nocb_next_follower = rdp;
		}
		rdp_prev = rdp;

		/* Spawn the kthread for this CPU. */
2510 2511
		t = kthread_run(rcu_nocb_kthread, rdp,
				"rcuo%c/%d", rsp->abbr, cpu);
P
Paul E. McKenney 已提交
2512 2513 2514 2515 2516 2517
		BUG_ON(IS_ERR(t));
		ACCESS_ONCE(rdp->nocb_kthread) = t;
	}
}

/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
2518
static bool init_nocb_callback_list(struct rcu_data *rdp)
P
Paul E. McKenney 已提交
2519 2520 2521
{
	if (rcu_nocb_mask == NULL ||
	    !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask))
2522
		return false;
P
Paul E. McKenney 已提交
2523
	rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2524
	return true;
P
Paul E. McKenney 已提交
2525 2526
}

2527 2528
#else /* #ifdef CONFIG_RCU_NOCB_CPU */

2529
static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
P
Paul E. McKenney 已提交
2530 2531 2532
{
}

2533 2534 2535 2536 2537 2538 2539
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
{
}

static void rcu_init_one_nocb(struct rcu_node *rnp)
{
}
P
Paul E. McKenney 已提交
2540 2541

static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2542
			    bool lazy, unsigned long flags)
P
Paul E. McKenney 已提交
2543 2544 2545 2546 2547
{
	return 0;
}

static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
2548 2549
						     struct rcu_data *rdp,
						     unsigned long flags)
P
Paul E. McKenney 已提交
2550 2551 2552 2553 2554 2555 2556 2557
{
	return 0;
}

static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
{
}

2558 2559 2560 2561 2562 2563 2564 2565 2566
static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
{
	return false;
}

static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
{
}

P
Paul E. McKenney 已提交
2567 2568 2569 2570
static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
{
}

2571
static bool init_nocb_callback_list(struct rcu_data *rdp)
P
Paul E. McKenney 已提交
2572
{
2573
	return false;
P
Paul E. McKenney 已提交
2574 2575 2576
}

#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2577 2578 2579 2580 2581 2582 2583 2584 2585 2586

/*
 * An adaptive-ticks CPU can potentially execute in kernel mode for an
 * arbitrarily long period of time with the scheduling-clock tick turned
 * off.  RCU will be paying attention to this CPU because it is in the
 * kernel, but the CPU cannot be guaranteed to be executing the RCU state
 * machine because the scheduling-clock tick has been disabled.  Therefore,
 * if an adaptive-ticks CPU is failing to respond to the current grace
 * period and has not be idle from an RCU perspective, kick it.
 */
2587
static void __maybe_unused rcu_kick_nohz_cpu(int cpu)
2588 2589 2590 2591 2592 2593
{
#ifdef CONFIG_NO_HZ_FULL
	if (tick_nohz_full_cpu(cpu))
		smp_send_reschedule(cpu);
#endif /* #ifdef CONFIG_NO_HZ_FULL */
}
2594 2595 2596 2597


#ifdef CONFIG_NO_HZ_FULL_SYSIDLE

2598 2599 2600 2601 2602
/*
 * Define RCU flavor that holds sysidle state.  This needs to be the
 * most active flavor of RCU.
 */
#ifdef CONFIG_PREEMPT_RCU
2603
static struct rcu_state *rcu_sysidle_state = &rcu_preempt_state;
2604
#else /* #ifdef CONFIG_PREEMPT_RCU */
2605
static struct rcu_state *rcu_sysidle_state = &rcu_sched_state;
2606 2607
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */

2608
static int full_sysidle_state;		/* Current system-idle state. */
2609 2610 2611 2612 2613 2614
#define RCU_SYSIDLE_NOT		0	/* Some CPU is not idle. */
#define RCU_SYSIDLE_SHORT	1	/* All CPUs idle for brief period. */
#define RCU_SYSIDLE_LONG	2	/* All CPUs idle for long enough. */
#define RCU_SYSIDLE_FULL	3	/* All CPUs idle, ready for sysidle. */
#define RCU_SYSIDLE_FULL_NOTED	4	/* Actually entered sysidle state. */

2615 2616 2617 2618 2619 2620 2621 2622 2623 2624 2625 2626 2627 2628 2629 2630 2631 2632 2633 2634 2635 2636 2637 2638 2639 2640 2641 2642 2643 2644
/*
 * Invoked to note exit from irq or task transition to idle.  Note that
 * usermode execution does -not- count as idle here!  After all, we want
 * to detect full-system idle states, not RCU quiescent states and grace
 * periods.  The caller must have disabled interrupts.
 */
static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
{
	unsigned long j;

	/* Adjust nesting, check for fully idle. */
	if (irq) {
		rdtp->dynticks_idle_nesting--;
		WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
		if (rdtp->dynticks_idle_nesting != 0)
			return;  /* Still not fully idle. */
	} else {
		if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) ==
		    DYNTICK_TASK_NEST_VALUE) {
			rdtp->dynticks_idle_nesting = 0;
		} else {
			rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE;
			WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
			return;  /* Still not fully idle. */
		}
	}

	/* Record start of fully idle period. */
	j = jiffies;
	ACCESS_ONCE(rdtp->dynticks_idle_jiffies) = j;
2645
	smp_mb__before_atomic();
2646
	atomic_inc(&rdtp->dynticks_idle);
2647
	smp_mb__after_atomic();
2648 2649 2650
	WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1);
}

2651 2652 2653 2654 2655 2656 2657 2658 2659 2660 2661 2662 2663 2664 2665 2666 2667 2668 2669 2670 2671 2672 2673 2674 2675 2676 2677 2678 2679 2680 2681 2682
/*
 * Unconditionally force exit from full system-idle state.  This is
 * invoked when a normal CPU exits idle, but must be called separately
 * for the timekeeping CPU (tick_do_timer_cpu).  The reason for this
 * is that the timekeeping CPU is permitted to take scheduling-clock
 * interrupts while the system is in system-idle state, and of course
 * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock
 * interrupt from any other type of interrupt.
 */
void rcu_sysidle_force_exit(void)
{
	int oldstate = ACCESS_ONCE(full_sysidle_state);
	int newoldstate;

	/*
	 * Each pass through the following loop attempts to exit full
	 * system-idle state.  If contention proves to be a problem,
	 * a trylock-based contention tree could be used here.
	 */
	while (oldstate > RCU_SYSIDLE_SHORT) {
		newoldstate = cmpxchg(&full_sysidle_state,
				      oldstate, RCU_SYSIDLE_NOT);
		if (oldstate == newoldstate &&
		    oldstate == RCU_SYSIDLE_FULL_NOTED) {
			rcu_kick_nohz_cpu(tick_do_timer_cpu);
			return; /* We cleared it, done! */
		}
		oldstate = newoldstate;
	}
	smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */
}

2683 2684 2685 2686 2687 2688 2689 2690 2691 2692 2693 2694 2695 2696 2697 2698 2699 2700 2701 2702 2703 2704 2705 2706 2707 2708 2709 2710 2711
/*
 * Invoked to note entry to irq or task transition from idle.  Note that
 * usermode execution does -not- count as idle here!  The caller must
 * have disabled interrupts.
 */
static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
{
	/* Adjust nesting, check for already non-idle. */
	if (irq) {
		rdtp->dynticks_idle_nesting++;
		WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
		if (rdtp->dynticks_idle_nesting != 1)
			return; /* Already non-idle. */
	} else {
		/*
		 * Allow for irq misnesting.  Yes, it really is possible
		 * to enter an irq handler then never leave it, and maybe
		 * also vice versa.  Handle both possibilities.
		 */
		if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) {
			rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE;
			WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
			return; /* Already non-idle. */
		} else {
			rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE;
		}
	}

	/* Record end of idle period. */
2712
	smp_mb__before_atomic();
2713
	atomic_inc(&rdtp->dynticks_idle);
2714
	smp_mb__after_atomic();
2715
	WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1));
2716 2717 2718 2719 2720 2721 2722 2723 2724 2725 2726 2727 2728 2729 2730 2731 2732 2733 2734 2735 2736 2737 2738 2739 2740 2741 2742 2743 2744 2745 2746 2747 2748 2749 2750 2751

	/*
	 * If we are the timekeeping CPU, we are permitted to be non-idle
	 * during a system-idle state.  This must be the case, because
	 * the timekeeping CPU has to take scheduling-clock interrupts
	 * during the time that the system is transitioning to full
	 * system-idle state.  This means that the timekeeping CPU must
	 * invoke rcu_sysidle_force_exit() directly if it does anything
	 * more than take a scheduling-clock interrupt.
	 */
	if (smp_processor_id() == tick_do_timer_cpu)
		return;

	/* Update system-idle state: We are clearly no longer fully idle! */
	rcu_sysidle_force_exit();
}

/*
 * Check to see if the current CPU is idle.  Note that usermode execution
 * does not count as idle.  The caller must have disabled interrupts.
 */
static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
				  unsigned long *maxj)
{
	int cur;
	unsigned long j;
	struct rcu_dynticks *rdtp = rdp->dynticks;

	/*
	 * If some other CPU has already reported non-idle, if this is
	 * not the flavor of RCU that tracks sysidle state, or if this
	 * is an offline or the timekeeping CPU, nothing to do.
	 */
	if (!*isidle || rdp->rsp != rcu_sysidle_state ||
	    cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
		return;
2752 2753
	if (rcu_gp_in_progress(rdp->rsp))
		WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
2754 2755 2756 2757 2758 2759 2760 2761 2762 2763 2764 2765 2766 2767 2768 2769 2770 2771 2772 2773 2774 2775 2776 2777 2778 2779 2780 2781 2782 2783 2784 2785 2786 2787 2788 2789 2790 2791 2792 2793 2794 2795 2796 2797 2798 2799 2800 2801 2802 2803 2804 2805 2806 2807 2808 2809 2810 2811 2812 2813 2814 2815 2816 2817 2818 2819 2820 2821 2822 2823 2824 2825 2826 2827 2828 2829 2830 2831 2832 2833 2834 2835 2836 2837 2838 2839 2840 2841

	/* Pick up current idle and NMI-nesting counter and check. */
	cur = atomic_read(&rdtp->dynticks_idle);
	if (cur & 0x1) {
		*isidle = false; /* We are not idle! */
		return;
	}
	smp_mb(); /* Read counters before timestamps. */

	/* Pick up timestamps. */
	j = ACCESS_ONCE(rdtp->dynticks_idle_jiffies);
	/* If this CPU entered idle more recently, update maxj timestamp. */
	if (ULONG_CMP_LT(*maxj, j))
		*maxj = j;
}

/*
 * Is this the flavor of RCU that is handling full-system idle?
 */
static bool is_sysidle_rcu_state(struct rcu_state *rsp)
{
	return rsp == rcu_sysidle_state;
}

/*
 * Return a delay in jiffies based on the number of CPUs, rcu_node
 * leaf fanout, and jiffies tick rate.  The idea is to allow larger
 * systems more time to transition to full-idle state in order to
 * avoid the cache thrashing that otherwise occur on the state variable.
 * Really small systems (less than a couple of tens of CPUs) should
 * instead use a single global atomically incremented counter, and later
 * versions of this will automatically reconfigure themselves accordingly.
 */
static unsigned long rcu_sysidle_delay(void)
{
	if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
		return 0;
	return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000);
}

/*
 * Advance the full-system-idle state.  This is invoked when all of
 * the non-timekeeping CPUs are idle.
 */
static void rcu_sysidle(unsigned long j)
{
	/* Check the current state. */
	switch (ACCESS_ONCE(full_sysidle_state)) {
	case RCU_SYSIDLE_NOT:

		/* First time all are idle, so note a short idle period. */
		ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_SHORT;
		break;

	case RCU_SYSIDLE_SHORT:

		/*
		 * Idle for a bit, time to advance to next state?
		 * cmpxchg failure means race with non-idle, let them win.
		 */
		if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
			(void)cmpxchg(&full_sysidle_state,
				      RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG);
		break;

	case RCU_SYSIDLE_LONG:

		/*
		 * Do an additional check pass before advancing to full.
		 * cmpxchg failure means race with non-idle, let them win.
		 */
		if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
			(void)cmpxchg(&full_sysidle_state,
				      RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL);
		break;

	default:
		break;
	}
}

/*
 * Found a non-idle non-timekeeping CPU, so kick the system-idle state
 * back to the beginning.
 */
static void rcu_sysidle_cancel(void)
{
	smp_mb();
2842 2843
	if (full_sysidle_state > RCU_SYSIDLE_SHORT)
		ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT;
2844 2845 2846 2847 2848 2849 2850 2851 2852 2853 2854 2855 2856 2857 2858 2859 2860 2861 2862 2863 2864 2865 2866 2867 2868 2869 2870 2871 2872 2873 2874 2875 2876 2877 2878 2879 2880 2881 2882 2883 2884 2885 2886 2887 2888 2889 2890 2891 2892 2893 2894 2895 2896 2897 2898 2899 2900 2901 2902 2903 2904 2905 2906 2907 2908 2909 2910 2911 2912 2913 2914 2915 2916 2917 2918 2919 2920 2921 2922 2923 2924 2925 2926 2927 2928 2929 2930 2931 2932 2933 2934 2935 2936 2937 2938 2939 2940 2941 2942 2943 2944 2945 2946 2947 2948 2949 2950 2951 2952 2953 2954 2955 2956 2957 2958
}

/*
 * Update the sysidle state based on the results of a force-quiescent-state
 * scan of the CPUs' dyntick-idle state.
 */
static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
			       unsigned long maxj, bool gpkt)
{
	if (rsp != rcu_sysidle_state)
		return;  /* Wrong flavor, ignore. */
	if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
		return;  /* Running state machine from timekeeping CPU. */
	if (isidle)
		rcu_sysidle(maxj);    /* More idle! */
	else
		rcu_sysidle_cancel(); /* Idle is over. */
}

/*
 * Wrapper for rcu_sysidle_report() when called from the grace-period
 * kthread's context.
 */
static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
				  unsigned long maxj)
{
	rcu_sysidle_report(rsp, isidle, maxj, true);
}

/* Callback and function for forcing an RCU grace period. */
struct rcu_sysidle_head {
	struct rcu_head rh;
	int inuse;
};

static void rcu_sysidle_cb(struct rcu_head *rhp)
{
	struct rcu_sysidle_head *rshp;

	/*
	 * The following memory barrier is needed to replace the
	 * memory barriers that would normally be in the memory
	 * allocator.
	 */
	smp_mb();  /* grace period precedes setting inuse. */

	rshp = container_of(rhp, struct rcu_sysidle_head, rh);
	ACCESS_ONCE(rshp->inuse) = 0;
}

/*
 * Check to see if the system is fully idle, other than the timekeeping CPU.
 * The caller must have disabled interrupts.
 */
bool rcu_sys_is_idle(void)
{
	static struct rcu_sysidle_head rsh;
	int rss = ACCESS_ONCE(full_sysidle_state);

	if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu))
		return false;

	/* Handle small-system case by doing a full scan of CPUs. */
	if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) {
		int oldrss = rss - 1;

		/*
		 * One pass to advance to each state up to _FULL.
		 * Give up if any pass fails to advance the state.
		 */
		while (rss < RCU_SYSIDLE_FULL && oldrss < rss) {
			int cpu;
			bool isidle = true;
			unsigned long maxj = jiffies - ULONG_MAX / 4;
			struct rcu_data *rdp;

			/* Scan all the CPUs looking for nonidle CPUs. */
			for_each_possible_cpu(cpu) {
				rdp = per_cpu_ptr(rcu_sysidle_state->rda, cpu);
				rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
				if (!isidle)
					break;
			}
			rcu_sysidle_report(rcu_sysidle_state,
					   isidle, maxj, false);
			oldrss = rss;
			rss = ACCESS_ONCE(full_sysidle_state);
		}
	}

	/* If this is the first observation of an idle period, record it. */
	if (rss == RCU_SYSIDLE_FULL) {
		rss = cmpxchg(&full_sysidle_state,
			      RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED);
		return rss == RCU_SYSIDLE_FULL;
	}

	smp_mb(); /* ensure rss load happens before later caller actions. */

	/* If already fully idle, tell the caller (in case of races). */
	if (rss == RCU_SYSIDLE_FULL_NOTED)
		return true;

	/*
	 * If we aren't there yet, and a grace period is not in flight,
	 * initiate a grace period.  Either way, tell the caller that
	 * we are not there yet.  We use an xchg() rather than an assignment
	 * to make up for the memory barriers that would otherwise be
	 * provided by the memory allocator.
	 */
	if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
	    !rcu_gp_in_progress(rcu_sysidle_state) &&
	    !rsh.inuse && xchg(&rsh.inuse, 1) == 0)
		call_rcu(&rsh.rh, rcu_sysidle_cb);
	return false;
2959 2960
}

2961 2962 2963 2964 2965 2966 2967 2968 2969 2970
/*
 * Initialize dynticks sysidle state for CPUs coming online.
 */
static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
{
	rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE;
}

#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */

2971 2972 2973 2974 2975 2976 2977 2978
static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
{
}

static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
{
}

2979 2980 2981 2982 2983 2984 2985 2986 2987 2988 2989 2990 2991 2992 2993
static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
				  unsigned long *maxj)
{
}

static bool is_sysidle_rcu_state(struct rcu_state *rsp)
{
	return false;
}

static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
				  unsigned long maxj)
{
}

2994 2995 2996 2997 2998
static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
{
}

#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
2999 3000 3001 3002 3003 3004 3005 3006

/*
 * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
 * grace-period kthread will do force_quiescent_state() processing?
 * The idea is to avoid waking up RCU core processing on such a
 * CPU unless the grace period has extended for too long.
 *
 * This code relies on the fact that all NO_HZ_FULL CPUs are also
3007
 * CONFIG_RCU_NOCB_CPU CPUs.
3008 3009 3010 3011 3012 3013 3014 3015 3016 3017 3018
 */
static bool rcu_nohz_full_cpu(struct rcu_state *rsp)
{
#ifdef CONFIG_NO_HZ_FULL
	if (tick_nohz_full_cpu(smp_processor_id()) &&
	    (!rcu_gp_in_progress(rsp) ||
	     ULONG_CMP_LT(jiffies, ACCESS_ONCE(rsp->gp_start) + HZ)))
		return 1;
#endif /* #ifdef CONFIG_NO_HZ_FULL */
	return 0;
}
3019 3020 3021 3022 3023 3024 3025

/*
 * Bind the grace-period kthread for the sysidle flavor of RCU to the
 * timekeeping CPU.
 */
static void rcu_bind_gp_kthread(void)
{
3026
	int __maybe_unused cpu;
3027

3028
	if (!tick_nohz_full_enabled())
3029
		return;
3030 3031 3032
#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
	cpu = tick_do_timer_cpu;
	if (cpu >= 0 && cpu < nr_cpu_ids && raw_smp_processor_id() != cpu)
3033
		set_cpus_allowed_ptr(current, cpumask_of(cpu));
3034 3035 3036 3037
#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
	if (!is_housekeeping_cpu(raw_smp_processor_id()))
		housekeeping_affine(current);
#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3038
}