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1 : : /*
2 : : * Read-Copy Update mechanism for mutual exclusion (tree-based version)
3 : : * Internal non-public definitions that provide either classic
4 : : * or preemptible semantics.
5 : : *
6 : : * This program is free software; you can redistribute it and/or modify
7 : : * it under the terms of the GNU General Public License as published by
8 : : * the Free Software Foundation; either version 2 of the License, or
9 : : * (at your option) any later version.
10 : : *
11 : : * This program is distributed in the hope that it will be useful,
12 : : * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 : : * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 : : * GNU General Public License for more details.
15 : : *
16 : : * You should have received a copy of the GNU General Public License
17 : : * along with this program; if not, write to the Free Software
18 : : * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
19 : : *
20 : : * Copyright Red Hat, 2009
21 : : * Copyright IBM Corporation, 2009
22 : : *
23 : : * Author: Ingo Molnar <mingo@elte.hu>
24 : : * Paul E. McKenney <paulmck@linux.vnet.ibm.com>
25 : : */
26 : :
27 : : #include <linux/delay.h>
28 : : #include <linux/gfp.h>
29 : : #include <linux/oom.h>
30 : : #include <linux/smpboot.h>
31 : : #include "../time/tick-internal.h"
32 : :
33 : : #define RCU_KTHREAD_PRIO 1
34 : :
35 : : #ifdef CONFIG_RCU_BOOST
36 : : #define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
37 : : #else
38 : : #define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
39 : : #endif
40 : :
41 : : #ifdef CONFIG_RCU_NOCB_CPU
42 : : static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
43 : : static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */
44 : : static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
45 : : static char __initdata nocb_buf[NR_CPUS * 5];
46 : : #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
47 : :
48 : : /*
49 : : * Check the RCU kernel configuration parameters and print informative
50 : : * messages about anything out of the ordinary. If you like #ifdef, you
51 : : * will love this function.
52 : : */
53 : 0 : static void __init rcu_bootup_announce_oddness(void)
54 : : {
55 : : #ifdef CONFIG_RCU_TRACE
56 : : pr_info("\tRCU debugfs-based tracing is enabled.\n");
57 : : #endif
58 : : #if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
59 : : pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
60 : : CONFIG_RCU_FANOUT);
61 : : #endif
62 : : #ifdef CONFIG_RCU_FANOUT_EXACT
63 : : pr_info("\tHierarchical RCU autobalancing is disabled.\n");
64 : : #endif
65 : : #ifdef CONFIG_RCU_FAST_NO_HZ
66 : : pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
67 : : #endif
68 : : #ifdef CONFIG_PROVE_RCU
69 : : pr_info("\tRCU lockdep checking is enabled.\n");
70 : : #endif
71 : : #ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
72 : : pr_info("\tRCU torture testing starts during boot.\n");
73 : : #endif
74 : : #if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
75 : : pr_info("\tDump stacks of tasks blocking RCU-preempt GP.\n");
76 : : #endif
77 : : #if defined(CONFIG_RCU_CPU_STALL_INFO)
78 : : pr_info("\tAdditional per-CPU info printed with stalls.\n");
79 : : #endif
80 : : #if NUM_RCU_LVL_4 != 0
81 : : pr_info("\tFour-level hierarchy is enabled.\n");
82 : : #endif
83 [ # # ]: 0 : if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
84 : 0 : pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
85 [ # # ]: 0 : if (nr_cpu_ids != NR_CPUS)
86 : 0 : pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
87 : : #ifdef CONFIG_RCU_NOCB_CPU
88 : : #ifndef CONFIG_RCU_NOCB_CPU_NONE
89 : : if (!have_rcu_nocb_mask) {
90 : : zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL);
91 : : have_rcu_nocb_mask = true;
92 : : }
93 : : #ifdef CONFIG_RCU_NOCB_CPU_ZERO
94 : : pr_info("\tOffload RCU callbacks from CPU 0\n");
95 : : cpumask_set_cpu(0, rcu_nocb_mask);
96 : : #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
97 : : #ifdef CONFIG_RCU_NOCB_CPU_ALL
98 : : pr_info("\tOffload RCU callbacks from all CPUs\n");
99 : : cpumask_copy(rcu_nocb_mask, cpu_possible_mask);
100 : : #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
101 : : #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
102 : : if (have_rcu_nocb_mask) {
103 : : if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
104 : : pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
105 : : cpumask_and(rcu_nocb_mask, cpu_possible_mask,
106 : : rcu_nocb_mask);
107 : : }
108 : : cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
109 : : pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf);
110 : : if (rcu_nocb_poll)
111 : : pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
112 : : }
113 : : #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
114 : 0 : }
115 : :
116 : : #ifdef CONFIG_TREE_PREEMPT_RCU
117 : :
118 : : RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
119 : : static struct rcu_state *rcu_state = &rcu_preempt_state;
120 : :
121 : : static int rcu_preempted_readers_exp(struct rcu_node *rnp);
122 : :
123 : : /*
124 : : * Tell them what RCU they are running.
125 : : */
126 : : static void __init rcu_bootup_announce(void)
127 : : {
128 : : pr_info("Preemptible hierarchical RCU implementation.\n");
129 : : rcu_bootup_announce_oddness();
130 : : }
131 : :
132 : : /*
133 : : * Return the number of RCU-preempt batches processed thus far
134 : : * for debug and statistics.
135 : : */
136 : : long rcu_batches_completed_preempt(void)
137 : : {
138 : : return rcu_preempt_state.completed;
139 : : }
140 : : EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);
141 : :
142 : : /*
143 : : * Return the number of RCU batches processed thus far for debug & stats.
144 : : */
145 : : long rcu_batches_completed(void)
146 : : {
147 : : return rcu_batches_completed_preempt();
148 : : }
149 : : EXPORT_SYMBOL_GPL(rcu_batches_completed);
150 : :
151 : : /*
152 : : * Force a quiescent state for preemptible RCU.
153 : : */
154 : : void rcu_force_quiescent_state(void)
155 : : {
156 : : force_quiescent_state(&rcu_preempt_state);
157 : : }
158 : : EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
159 : :
160 : : /*
161 : : * Record a preemptible-RCU quiescent state for the specified CPU. Note
162 : : * that this just means that the task currently running on the CPU is
163 : : * not in a quiescent state. There might be any number of tasks blocked
164 : : * while in an RCU read-side critical section.
165 : : *
166 : : * Unlike the other rcu_*_qs() functions, callers to this function
167 : : * must disable irqs in order to protect the assignment to
168 : : * ->rcu_read_unlock_special.
169 : : */
170 : : static void rcu_preempt_qs(int cpu)
171 : : {
172 : : struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
173 : :
174 : : if (rdp->passed_quiesce == 0)
175 : : trace_rcu_grace_period(TPS("rcu_preempt"), rdp->gpnum, TPS("cpuqs"));
176 : : rdp->passed_quiesce = 1;
177 : : current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
178 : : }
179 : :
180 : : /*
181 : : * We have entered the scheduler, and the current task might soon be
182 : : * context-switched away from. If this task is in an RCU read-side
183 : : * critical section, we will no longer be able to rely on the CPU to
184 : : * record that fact, so we enqueue the task on the blkd_tasks list.
185 : : * The task will dequeue itself when it exits the outermost enclosing
186 : : * RCU read-side critical section. Therefore, the current grace period
187 : : * cannot be permitted to complete until the blkd_tasks list entries
188 : : * predating the current grace period drain, in other words, until
189 : : * rnp->gp_tasks becomes NULL.
190 : : *
191 : : * Caller must disable preemption.
192 : : */
193 : : static void rcu_preempt_note_context_switch(int cpu)
194 : : {
195 : : struct task_struct *t = current;
196 : : unsigned long flags;
197 : : struct rcu_data *rdp;
198 : : struct rcu_node *rnp;
199 : :
200 : : if (t->rcu_read_lock_nesting > 0 &&
201 : : (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
202 : :
203 : : /* Possibly blocking in an RCU read-side critical section. */
204 : : rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
205 : : rnp = rdp->mynode;
206 : : raw_spin_lock_irqsave(&rnp->lock, flags);
207 : : t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
208 : : t->rcu_blocked_node = rnp;
209 : :
210 : : /*
211 : : * If this CPU has already checked in, then this task
212 : : * will hold up the next grace period rather than the
213 : : * current grace period. Queue the task accordingly.
214 : : * If the task is queued for the current grace period
215 : : * (i.e., this CPU has not yet passed through a quiescent
216 : : * state for the current grace period), then as long
217 : : * as that task remains queued, the current grace period
218 : : * cannot end. Note that there is some uncertainty as
219 : : * to exactly when the current grace period started.
220 : : * We take a conservative approach, which can result
221 : : * in unnecessarily waiting on tasks that started very
222 : : * slightly after the current grace period began. C'est
223 : : * la vie!!!
224 : : *
225 : : * But first, note that the current CPU must still be
226 : : * on line!
227 : : */
228 : : WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
229 : : WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
230 : : if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
231 : : list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
232 : : rnp->gp_tasks = &t->rcu_node_entry;
233 : : #ifdef CONFIG_RCU_BOOST
234 : : if (rnp->boost_tasks != NULL)
235 : : rnp->boost_tasks = rnp->gp_tasks;
236 : : #endif /* #ifdef CONFIG_RCU_BOOST */
237 : : } else {
238 : : list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
239 : : if (rnp->qsmask & rdp->grpmask)
240 : : rnp->gp_tasks = &t->rcu_node_entry;
241 : : }
242 : : trace_rcu_preempt_task(rdp->rsp->name,
243 : : t->pid,
244 : : (rnp->qsmask & rdp->grpmask)
245 : : ? rnp->gpnum
246 : : : rnp->gpnum + 1);
247 : : raw_spin_unlock_irqrestore(&rnp->lock, flags);
248 : : } else if (t->rcu_read_lock_nesting < 0 &&
249 : : t->rcu_read_unlock_special) {
250 : :
251 : : /*
252 : : * Complete exit from RCU read-side critical section on
253 : : * behalf of preempted instance of __rcu_read_unlock().
254 : : */
255 : : rcu_read_unlock_special(t);
256 : : }
257 : :
258 : : /*
259 : : * Either we were not in an RCU read-side critical section to
260 : : * begin with, or we have now recorded that critical section
261 : : * globally. Either way, we can now note a quiescent state
262 : : * for this CPU. Again, if we were in an RCU read-side critical
263 : : * section, and if that critical section was blocking the current
264 : : * grace period, then the fact that the task has been enqueued
265 : : * means that we continue to block the current grace period.
266 : : */
267 : : local_irq_save(flags);
268 : : rcu_preempt_qs(cpu);
269 : : local_irq_restore(flags);
270 : : }
271 : :
272 : : /*
273 : : * Check for preempted RCU readers blocking the current grace period
274 : : * for the specified rcu_node structure. If the caller needs a reliable
275 : : * answer, it must hold the rcu_node's ->lock.
276 : : */
277 : : static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
278 : : {
279 : : return rnp->gp_tasks != NULL;
280 : : }
281 : :
282 : : /*
283 : : * Record a quiescent state for all tasks that were previously queued
284 : : * on the specified rcu_node structure and that were blocking the current
285 : : * RCU grace period. The caller must hold the specified rnp->lock with
286 : : * irqs disabled, and this lock is released upon return, but irqs remain
287 : : * disabled.
288 : : */
289 : : static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
290 : : __releases(rnp->lock)
291 : : {
292 : : unsigned long mask;
293 : : struct rcu_node *rnp_p;
294 : :
295 : : if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
296 : : raw_spin_unlock_irqrestore(&rnp->lock, flags);
297 : : return; /* Still need more quiescent states! */
298 : : }
299 : :
300 : : rnp_p = rnp->parent;
301 : : if (rnp_p == NULL) {
302 : : /*
303 : : * Either there is only one rcu_node in the tree,
304 : : * or tasks were kicked up to root rcu_node due to
305 : : * CPUs going offline.
306 : : */
307 : : rcu_report_qs_rsp(&rcu_preempt_state, flags);
308 : : return;
309 : : }
310 : :
311 : : /* Report up the rest of the hierarchy. */
312 : : mask = rnp->grpmask;
313 : : raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
314 : : raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */
315 : : rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
316 : : }
317 : :
318 : : /*
319 : : * Advance a ->blkd_tasks-list pointer to the next entry, instead
320 : : * returning NULL if at the end of the list.
321 : : */
322 : : static struct list_head *rcu_next_node_entry(struct task_struct *t,
323 : : struct rcu_node *rnp)
324 : : {
325 : : struct list_head *np;
326 : :
327 : : np = t->rcu_node_entry.next;
328 : : if (np == &rnp->blkd_tasks)
329 : : np = NULL;
330 : : return np;
331 : : }
332 : :
333 : : /*
334 : : * Handle special cases during rcu_read_unlock(), such as needing to
335 : : * notify RCU core processing or task having blocked during the RCU
336 : : * read-side critical section.
337 : : */
338 : : void rcu_read_unlock_special(struct task_struct *t)
339 : : {
340 : : int empty;
341 : : int empty_exp;
342 : : int empty_exp_now;
343 : : unsigned long flags;
344 : : struct list_head *np;
345 : : #ifdef CONFIG_RCU_BOOST
346 : : struct rt_mutex *rbmp = NULL;
347 : : #endif /* #ifdef CONFIG_RCU_BOOST */
348 : : struct rcu_node *rnp;
349 : : int special;
350 : :
351 : : /* NMI handlers cannot block and cannot safely manipulate state. */
352 : : if (in_nmi())
353 : : return;
354 : :
355 : : local_irq_save(flags);
356 : :
357 : : /*
358 : : * If RCU core is waiting for this CPU to exit critical section,
359 : : * let it know that we have done so.
360 : : */
361 : : special = t->rcu_read_unlock_special;
362 : : if (special & RCU_READ_UNLOCK_NEED_QS) {
363 : : rcu_preempt_qs(smp_processor_id());
364 : : }
365 : :
366 : : /* Hardware IRQ handlers cannot block. */
367 : : if (in_irq() || in_serving_softirq()) {
368 : : local_irq_restore(flags);
369 : : return;
370 : : }
371 : :
372 : : /* Clean up if blocked during RCU read-side critical section. */
373 : : if (special & RCU_READ_UNLOCK_BLOCKED) {
374 : : t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
375 : :
376 : : /*
377 : : * Remove this task from the list it blocked on. The
378 : : * task can migrate while we acquire the lock, but at
379 : : * most one time. So at most two passes through loop.
380 : : */
381 : : for (;;) {
382 : : rnp = t->rcu_blocked_node;
383 : : raw_spin_lock(&rnp->lock); /* irqs already disabled. */
384 : : if (rnp == t->rcu_blocked_node)
385 : : break;
386 : : raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
387 : : }
388 : : empty = !rcu_preempt_blocked_readers_cgp(rnp);
389 : : empty_exp = !rcu_preempted_readers_exp(rnp);
390 : : smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
391 : : np = rcu_next_node_entry(t, rnp);
392 : : list_del_init(&t->rcu_node_entry);
393 : : t->rcu_blocked_node = NULL;
394 : : trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
395 : : rnp->gpnum, t->pid);
396 : : if (&t->rcu_node_entry == rnp->gp_tasks)
397 : : rnp->gp_tasks = np;
398 : : if (&t->rcu_node_entry == rnp->exp_tasks)
399 : : rnp->exp_tasks = np;
400 : : #ifdef CONFIG_RCU_BOOST
401 : : if (&t->rcu_node_entry == rnp->boost_tasks)
402 : : rnp->boost_tasks = np;
403 : : /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */
404 : : if (t->rcu_boost_mutex) {
405 : : rbmp = t->rcu_boost_mutex;
406 : : t->rcu_boost_mutex = NULL;
407 : : }
408 : : #endif /* #ifdef CONFIG_RCU_BOOST */
409 : :
410 : : /*
411 : : * If this was the last task on the current list, and if
412 : : * we aren't waiting on any CPUs, report the quiescent state.
413 : : * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
414 : : * so we must take a snapshot of the expedited state.
415 : : */
416 : : empty_exp_now = !rcu_preempted_readers_exp(rnp);
417 : : if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) {
418 : : trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
419 : : rnp->gpnum,
420 : : 0, rnp->qsmask,
421 : : rnp->level,
422 : : rnp->grplo,
423 : : rnp->grphi,
424 : : !!rnp->gp_tasks);
425 : : rcu_report_unblock_qs_rnp(rnp, flags);
426 : : } else {
427 : : raw_spin_unlock_irqrestore(&rnp->lock, flags);
428 : : }
429 : :
430 : : #ifdef CONFIG_RCU_BOOST
431 : : /* Unboost if we were boosted. */
432 : : if (rbmp)
433 : : rt_mutex_unlock(rbmp);
434 : : #endif /* #ifdef CONFIG_RCU_BOOST */
435 : :
436 : : /*
437 : : * If this was the last task on the expedited lists,
438 : : * then we need to report up the rcu_node hierarchy.
439 : : */
440 : : if (!empty_exp && empty_exp_now)
441 : : rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);
442 : : } else {
443 : : local_irq_restore(flags);
444 : : }
445 : : }
446 : :
447 : : #ifdef CONFIG_RCU_CPU_STALL_VERBOSE
448 : :
449 : : /*
450 : : * Dump detailed information for all tasks blocking the current RCU
451 : : * grace period on the specified rcu_node structure.
452 : : */
453 : : static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
454 : : {
455 : : unsigned long flags;
456 : : struct task_struct *t;
457 : :
458 : : raw_spin_lock_irqsave(&rnp->lock, flags);
459 : : if (!rcu_preempt_blocked_readers_cgp(rnp)) {
460 : : raw_spin_unlock_irqrestore(&rnp->lock, flags);
461 : : return;
462 : : }
463 : : t = list_entry(rnp->gp_tasks,
464 : : struct task_struct, rcu_node_entry);
465 : : list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
466 : : sched_show_task(t);
467 : : raw_spin_unlock_irqrestore(&rnp->lock, flags);
468 : : }
469 : :
470 : : /*
471 : : * Dump detailed information for all tasks blocking the current RCU
472 : : * grace period.
473 : : */
474 : : static void rcu_print_detail_task_stall(struct rcu_state *rsp)
475 : : {
476 : : struct rcu_node *rnp = rcu_get_root(rsp);
477 : :
478 : : rcu_print_detail_task_stall_rnp(rnp);
479 : : rcu_for_each_leaf_node(rsp, rnp)
480 : : rcu_print_detail_task_stall_rnp(rnp);
481 : : }
482 : :
483 : : #else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
484 : :
485 : : static void rcu_print_detail_task_stall(struct rcu_state *rsp)
486 : : {
487 : : }
488 : :
489 : : #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
490 : :
491 : : #ifdef CONFIG_RCU_CPU_STALL_INFO
492 : :
493 : : static void rcu_print_task_stall_begin(struct rcu_node *rnp)
494 : : {
495 : : pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
496 : : rnp->level, rnp->grplo, rnp->grphi);
497 : : }
498 : :
499 : : static void rcu_print_task_stall_end(void)
500 : : {
501 : : pr_cont("\n");
502 : : }
503 : :
504 : : #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
505 : :
506 : : static void rcu_print_task_stall_begin(struct rcu_node *rnp)
507 : : {
508 : : }
509 : :
510 : : static void rcu_print_task_stall_end(void)
511 : : {
512 : : }
513 : :
514 : : #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
515 : :
516 : : /*
517 : : * Scan the current list of tasks blocked within RCU read-side critical
518 : : * sections, printing out the tid of each.
519 : : */
520 : : static int rcu_print_task_stall(struct rcu_node *rnp)
521 : : {
522 : : struct task_struct *t;
523 : : int ndetected = 0;
524 : :
525 : : if (!rcu_preempt_blocked_readers_cgp(rnp))
526 : : return 0;
527 : : rcu_print_task_stall_begin(rnp);
528 : : t = list_entry(rnp->gp_tasks,
529 : : struct task_struct, rcu_node_entry);
530 : : list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
531 : : pr_cont(" P%d", t->pid);
532 : : ndetected++;
533 : : }
534 : : rcu_print_task_stall_end();
535 : : return ndetected;
536 : : }
537 : :
538 : : /*
539 : : * Check that the list of blocked tasks for the newly completed grace
540 : : * period is in fact empty. It is a serious bug to complete a grace
541 : : * period that still has RCU readers blocked! This function must be
542 : : * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
543 : : * must be held by the caller.
544 : : *
545 : : * Also, if there are blocked tasks on the list, they automatically
546 : : * block the newly created grace period, so set up ->gp_tasks accordingly.
547 : : */
548 : : static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
549 : : {
550 : : WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
551 : : if (!list_empty(&rnp->blkd_tasks))
552 : : rnp->gp_tasks = rnp->blkd_tasks.next;
553 : : WARN_ON_ONCE(rnp->qsmask);
554 : : }
555 : :
556 : : #ifdef CONFIG_HOTPLUG_CPU
557 : :
558 : : /*
559 : : * Handle tasklist migration for case in which all CPUs covered by the
560 : : * specified rcu_node have gone offline. Move them up to the root
561 : : * rcu_node. The reason for not just moving them to the immediate
562 : : * parent is to remove the need for rcu_read_unlock_special() to
563 : : * make more than two attempts to acquire the target rcu_node's lock.
564 : : * Returns true if there were tasks blocking the current RCU grace
565 : : * period.
566 : : *
567 : : * Returns 1 if there was previously a task blocking the current grace
568 : : * period on the specified rcu_node structure.
569 : : *
570 : : * The caller must hold rnp->lock with irqs disabled.
571 : : */
572 : : static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
573 : : struct rcu_node *rnp,
574 : : struct rcu_data *rdp)
575 : : {
576 : : struct list_head *lp;
577 : : struct list_head *lp_root;
578 : : int retval = 0;
579 : : struct rcu_node *rnp_root = rcu_get_root(rsp);
580 : : struct task_struct *t;
581 : :
582 : : if (rnp == rnp_root) {
583 : : WARN_ONCE(1, "Last CPU thought to be offlined?");
584 : : return 0; /* Shouldn't happen: at least one CPU online. */
585 : : }
586 : :
587 : : /* If we are on an internal node, complain bitterly. */
588 : : WARN_ON_ONCE(rnp != rdp->mynode);
589 : :
590 : : /*
591 : : * Move tasks up to root rcu_node. Don't try to get fancy for
592 : : * this corner-case operation -- just put this node's tasks
593 : : * at the head of the root node's list, and update the root node's
594 : : * ->gp_tasks and ->exp_tasks pointers to those of this node's,
595 : : * if non-NULL. This might result in waiting for more tasks than
596 : : * absolutely necessary, but this is a good performance/complexity
597 : : * tradeoff.
598 : : */
599 : : if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
600 : : retval |= RCU_OFL_TASKS_NORM_GP;
601 : : if (rcu_preempted_readers_exp(rnp))
602 : : retval |= RCU_OFL_TASKS_EXP_GP;
603 : : lp = &rnp->blkd_tasks;
604 : : lp_root = &rnp_root->blkd_tasks;
605 : : while (!list_empty(lp)) {
606 : : t = list_entry(lp->next, typeof(*t), rcu_node_entry);
607 : : raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
608 : : list_del(&t->rcu_node_entry);
609 : : t->rcu_blocked_node = rnp_root;
610 : : list_add(&t->rcu_node_entry, lp_root);
611 : : if (&t->rcu_node_entry == rnp->gp_tasks)
612 : : rnp_root->gp_tasks = rnp->gp_tasks;
613 : : if (&t->rcu_node_entry == rnp->exp_tasks)
614 : : rnp_root->exp_tasks = rnp->exp_tasks;
615 : : #ifdef CONFIG_RCU_BOOST
616 : : if (&t->rcu_node_entry == rnp->boost_tasks)
617 : : rnp_root->boost_tasks = rnp->boost_tasks;
618 : : #endif /* #ifdef CONFIG_RCU_BOOST */
619 : : raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
620 : : }
621 : :
622 : : rnp->gp_tasks = NULL;
623 : : rnp->exp_tasks = NULL;
624 : : #ifdef CONFIG_RCU_BOOST
625 : : rnp->boost_tasks = NULL;
626 : : /*
627 : : * In case root is being boosted and leaf was not. Make sure
628 : : * that we boost the tasks blocking the current grace period
629 : : * in this case.
630 : : */
631 : : raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
632 : : if (rnp_root->boost_tasks != NULL &&
633 : : rnp_root->boost_tasks != rnp_root->gp_tasks &&
634 : : rnp_root->boost_tasks != rnp_root->exp_tasks)
635 : : rnp_root->boost_tasks = rnp_root->gp_tasks;
636 : : raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
637 : : #endif /* #ifdef CONFIG_RCU_BOOST */
638 : :
639 : : return retval;
640 : : }
641 : :
642 : : #endif /* #ifdef CONFIG_HOTPLUG_CPU */
643 : :
644 : : /*
645 : : * Check for a quiescent state from the current CPU. When a task blocks,
646 : : * the task is recorded in the corresponding CPU's rcu_node structure,
647 : : * which is checked elsewhere.
648 : : *
649 : : * Caller must disable hard irqs.
650 : : */
651 : : static void rcu_preempt_check_callbacks(int cpu)
652 : : {
653 : : struct task_struct *t = current;
654 : :
655 : : if (t->rcu_read_lock_nesting == 0) {
656 : : rcu_preempt_qs(cpu);
657 : : return;
658 : : }
659 : : if (t->rcu_read_lock_nesting > 0 &&
660 : : per_cpu(rcu_preempt_data, cpu).qs_pending)
661 : : t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
662 : : }
663 : :
664 : : #ifdef CONFIG_RCU_BOOST
665 : :
666 : : static void rcu_preempt_do_callbacks(void)
667 : : {
668 : : rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data));
669 : : }
670 : :
671 : : #endif /* #ifdef CONFIG_RCU_BOOST */
672 : :
673 : : /*
674 : : * Queue a preemptible-RCU callback for invocation after a grace period.
675 : : */
676 : : void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
677 : : {
678 : : __call_rcu(head, func, &rcu_preempt_state, -1, 0);
679 : : }
680 : : EXPORT_SYMBOL_GPL(call_rcu);
681 : :
682 : : /*
683 : : * Queue an RCU callback for lazy invocation after a grace period.
684 : : * This will likely be later named something like "call_rcu_lazy()",
685 : : * but this change will require some way of tagging the lazy RCU
686 : : * callbacks in the list of pending callbacks. Until then, this
687 : : * function may only be called from __kfree_rcu().
688 : : */
689 : : void kfree_call_rcu(struct rcu_head *head,
690 : : void (*func)(struct rcu_head *rcu))
691 : : {
692 : : __call_rcu(head, func, &rcu_preempt_state, -1, 1);
693 : : }
694 : : EXPORT_SYMBOL_GPL(kfree_call_rcu);
695 : :
696 : : /**
697 : : * synchronize_rcu - wait until a grace period has elapsed.
698 : : *
699 : : * Control will return to the caller some time after a full grace
700 : : * period has elapsed, in other words after all currently executing RCU
701 : : * read-side critical sections have completed. Note, however, that
702 : : * upon return from synchronize_rcu(), the caller might well be executing
703 : : * concurrently with new RCU read-side critical sections that began while
704 : : * synchronize_rcu() was waiting. RCU read-side critical sections are
705 : : * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
706 : : *
707 : : * See the description of synchronize_sched() for more detailed information
708 : : * on memory ordering guarantees.
709 : : */
710 : : void synchronize_rcu(void)
711 : : {
712 : : rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
713 : : !lock_is_held(&rcu_lock_map) &&
714 : : !lock_is_held(&rcu_sched_lock_map),
715 : : "Illegal synchronize_rcu() in RCU read-side critical section");
716 : : if (!rcu_scheduler_active)
717 : : return;
718 : : if (rcu_expedited)
719 : : synchronize_rcu_expedited();
720 : : else
721 : : wait_rcu_gp(call_rcu);
722 : : }
723 : : EXPORT_SYMBOL_GPL(synchronize_rcu);
724 : :
725 : : static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
726 : : static unsigned long sync_rcu_preempt_exp_count;
727 : : static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
728 : :
729 : : /*
730 : : * Return non-zero if there are any tasks in RCU read-side critical
731 : : * sections blocking the current preemptible-RCU expedited grace period.
732 : : * If there is no preemptible-RCU expedited grace period currently in
733 : : * progress, returns zero unconditionally.
734 : : */
735 : : static int rcu_preempted_readers_exp(struct rcu_node *rnp)
736 : : {
737 : : return rnp->exp_tasks != NULL;
738 : : }
739 : :
740 : : /*
741 : : * return non-zero if there is no RCU expedited grace period in progress
742 : : * for the specified rcu_node structure, in other words, if all CPUs and
743 : : * tasks covered by the specified rcu_node structure have done their bit
744 : : * for the current expedited grace period. Works only for preemptible
745 : : * RCU -- other RCU implementation use other means.
746 : : *
747 : : * Caller must hold sync_rcu_preempt_exp_mutex.
748 : : */
749 : : static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
750 : : {
751 : : return !rcu_preempted_readers_exp(rnp) &&
752 : : ACCESS_ONCE(rnp->expmask) == 0;
753 : : }
754 : :
755 : : /*
756 : : * Report the exit from RCU read-side critical section for the last task
757 : : * that queued itself during or before the current expedited preemptible-RCU
758 : : * grace period. This event is reported either to the rcu_node structure on
759 : : * which the task was queued or to one of that rcu_node structure's ancestors,
760 : : * recursively up the tree. (Calm down, calm down, we do the recursion
761 : : * iteratively!)
762 : : *
763 : : * Most callers will set the "wake" flag, but the task initiating the
764 : : * expedited grace period need not wake itself.
765 : : *
766 : : * Caller must hold sync_rcu_preempt_exp_mutex.
767 : : */
768 : : static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
769 : : bool wake)
770 : : {
771 : : unsigned long flags;
772 : : unsigned long mask;
773 : :
774 : : raw_spin_lock_irqsave(&rnp->lock, flags);
775 : : for (;;) {
776 : : if (!sync_rcu_preempt_exp_done(rnp)) {
777 : : raw_spin_unlock_irqrestore(&rnp->lock, flags);
778 : : break;
779 : : }
780 : : if (rnp->parent == NULL) {
781 : : raw_spin_unlock_irqrestore(&rnp->lock, flags);
782 : : if (wake)
783 : : wake_up(&sync_rcu_preempt_exp_wq);
784 : : break;
785 : : }
786 : : mask = rnp->grpmask;
787 : : raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
788 : : rnp = rnp->parent;
789 : : raw_spin_lock(&rnp->lock); /* irqs already disabled */
790 : : rnp->expmask &= ~mask;
791 : : }
792 : : }
793 : :
794 : : /*
795 : : * Snapshot the tasks blocking the newly started preemptible-RCU expedited
796 : : * grace period for the specified rcu_node structure. If there are no such
797 : : * tasks, report it up the rcu_node hierarchy.
798 : : *
799 : : * Caller must hold sync_rcu_preempt_exp_mutex and must exclude
800 : : * CPU hotplug operations.
801 : : */
802 : : static void
803 : : sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
804 : : {
805 : : unsigned long flags;
806 : : int must_wait = 0;
807 : :
808 : : raw_spin_lock_irqsave(&rnp->lock, flags);
809 : : if (list_empty(&rnp->blkd_tasks)) {
810 : : raw_spin_unlock_irqrestore(&rnp->lock, flags);
811 : : } else {
812 : : rnp->exp_tasks = rnp->blkd_tasks.next;
813 : : rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
814 : : must_wait = 1;
815 : : }
816 : : if (!must_wait)
817 : : rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
818 : : }
819 : :
820 : : /**
821 : : * synchronize_rcu_expedited - Brute-force RCU grace period
822 : : *
823 : : * Wait for an RCU-preempt grace period, but expedite it. The basic
824 : : * idea is to invoke synchronize_sched_expedited() to push all the tasks to
825 : : * the ->blkd_tasks lists and wait for this list to drain. This consumes
826 : : * significant time on all CPUs and is unfriendly to real-time workloads,
827 : : * so is thus not recommended for any sort of common-case code.
828 : : * In fact, if you are using synchronize_rcu_expedited() in a loop,
829 : : * please restructure your code to batch your updates, and then Use a
830 : : * single synchronize_rcu() instead.
831 : : *
832 : : * Note that it is illegal to call this function while holding any lock
833 : : * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
834 : : * to call this function from a CPU-hotplug notifier. Failing to observe
835 : : * these restriction will result in deadlock.
836 : : */
837 : : void synchronize_rcu_expedited(void)
838 : : {
839 : : unsigned long flags;
840 : : struct rcu_node *rnp;
841 : : struct rcu_state *rsp = &rcu_preempt_state;
842 : : unsigned long snap;
843 : : int trycount = 0;
844 : :
845 : : smp_mb(); /* Caller's modifications seen first by other CPUs. */
846 : : snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
847 : : smp_mb(); /* Above access cannot bleed into critical section. */
848 : :
849 : : /*
850 : : * Block CPU-hotplug operations. This means that any CPU-hotplug
851 : : * operation that finds an rcu_node structure with tasks in the
852 : : * process of being boosted will know that all tasks blocking
853 : : * this expedited grace period will already be in the process of
854 : : * being boosted. This simplifies the process of moving tasks
855 : : * from leaf to root rcu_node structures.
856 : : */
857 : : get_online_cpus();
858 : :
859 : : /*
860 : : * Acquire lock, falling back to synchronize_rcu() if too many
861 : : * lock-acquisition failures. Of course, if someone does the
862 : : * expedited grace period for us, just leave.
863 : : */
864 : : while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
865 : : if (ULONG_CMP_LT(snap,
866 : : ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
867 : : put_online_cpus();
868 : : goto mb_ret; /* Others did our work for us. */
869 : : }
870 : : if (trycount++ < 10) {
871 : : udelay(trycount * num_online_cpus());
872 : : } else {
873 : : put_online_cpus();
874 : : wait_rcu_gp(call_rcu);
875 : : return;
876 : : }
877 : : }
878 : : if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
879 : : put_online_cpus();
880 : : goto unlock_mb_ret; /* Others did our work for us. */
881 : : }
882 : :
883 : : /* force all RCU readers onto ->blkd_tasks lists. */
884 : : synchronize_sched_expedited();
885 : :
886 : : /* Initialize ->expmask for all non-leaf rcu_node structures. */
887 : : rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
888 : : raw_spin_lock_irqsave(&rnp->lock, flags);
889 : : rnp->expmask = rnp->qsmaskinit;
890 : : raw_spin_unlock_irqrestore(&rnp->lock, flags);
891 : : }
892 : :
893 : : /* Snapshot current state of ->blkd_tasks lists. */
894 : : rcu_for_each_leaf_node(rsp, rnp)
895 : : sync_rcu_preempt_exp_init(rsp, rnp);
896 : : if (NUM_RCU_NODES > 1)
897 : : sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
898 : :
899 : : put_online_cpus();
900 : :
901 : : /* Wait for snapshotted ->blkd_tasks lists to drain. */
902 : : rnp = rcu_get_root(rsp);
903 : : wait_event(sync_rcu_preempt_exp_wq,
904 : : sync_rcu_preempt_exp_done(rnp));
905 : :
906 : : /* Clean up and exit. */
907 : : smp_mb(); /* ensure expedited GP seen before counter increment. */
908 : : ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
909 : : unlock_mb_ret:
910 : : mutex_unlock(&sync_rcu_preempt_exp_mutex);
911 : : mb_ret:
912 : : smp_mb(); /* ensure subsequent action seen after grace period. */
913 : : }
914 : : EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
915 : :
916 : : /**
917 : : * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
918 : : *
919 : : * Note that this primitive does not necessarily wait for an RCU grace period
920 : : * to complete. For example, if there are no RCU callbacks queued anywhere
921 : : * in the system, then rcu_barrier() is within its rights to return
922 : : * immediately, without waiting for anything, much less an RCU grace period.
923 : : */
924 : : void rcu_barrier(void)
925 : : {
926 : : _rcu_barrier(&rcu_preempt_state);
927 : : }
928 : : EXPORT_SYMBOL_GPL(rcu_barrier);
929 : :
930 : : /*
931 : : * Initialize preemptible RCU's state structures.
932 : : */
933 : : static void __init __rcu_init_preempt(void)
934 : : {
935 : : rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
936 : : }
937 : :
938 : : /*
939 : : * Check for a task exiting while in a preemptible-RCU read-side
940 : : * critical section, clean up if so. No need to issue warnings,
941 : : * as debug_check_no_locks_held() already does this if lockdep
942 : : * is enabled.
943 : : */
944 : : void exit_rcu(void)
945 : : {
946 : : struct task_struct *t = current;
947 : :
948 : : if (likely(list_empty(¤t->rcu_node_entry)))
949 : : return;
950 : : t->rcu_read_lock_nesting = 1;
951 : : barrier();
952 : : t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
953 : : __rcu_read_unlock();
954 : : }
955 : :
956 : : #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
957 : :
958 : : static struct rcu_state *rcu_state = &rcu_sched_state;
959 : :
960 : : /*
961 : : * Tell them what RCU they are running.
962 : : */
963 : 0 : static void __init rcu_bootup_announce(void)
964 : : {
965 : 0 : pr_info("Hierarchical RCU implementation.\n");
966 : 0 : rcu_bootup_announce_oddness();
967 : 0 : }
968 : :
969 : : /*
970 : : * Return the number of RCU batches processed thus far for debug & stats.
971 : : */
972 : 0 : long rcu_batches_completed(void)
973 : : {
974 : 0 : return rcu_batches_completed_sched();
975 : : }
976 : : EXPORT_SYMBOL_GPL(rcu_batches_completed);
977 : :
978 : : /*
979 : : * Force a quiescent state for RCU, which, because there is no preemptible
980 : : * RCU, becomes the same as rcu-sched.
981 : : */
982 : 0 : void rcu_force_quiescent_state(void)
983 : : {
984 : : rcu_sched_force_quiescent_state();
985 : 0 : }
986 : : EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
987 : :
988 : : /*
989 : : * Because preemptible RCU does not exist, we never have to check for
990 : : * CPUs being in quiescent states.
991 : : */
992 : : static void rcu_preempt_note_context_switch(int cpu)
993 : : {
994 : : }
995 : :
996 : : /*
997 : : * Because preemptible RCU does not exist, there are never any preempted
998 : : * RCU readers.
999 : : */
1000 : : static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
1001 : : {
1002 : : return 0;
1003 : : }
1004 : :
1005 : : #ifdef CONFIG_HOTPLUG_CPU
1006 : :
1007 : : /* Because preemptible RCU does not exist, no quieting of tasks. */
1008 : : static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
1009 : : {
1010 : : raw_spin_unlock_irqrestore(&rnp->lock, flags);
1011 : : }
1012 : :
1013 : : #endif /* #ifdef CONFIG_HOTPLUG_CPU */
1014 : :
1015 : : /*
1016 : : * Because preemptible RCU does not exist, we never have to check for
1017 : : * tasks blocked within RCU read-side critical sections.
1018 : : */
1019 : : static void rcu_print_detail_task_stall(struct rcu_state *rsp)
1020 : : {
1021 : : }
1022 : :
1023 : : /*
1024 : : * Because preemptible RCU does not exist, we never have to check for
1025 : : * tasks blocked within RCU read-side critical sections.
1026 : : */
1027 : : static int rcu_print_task_stall(struct rcu_node *rnp)
1028 : : {
1029 : : return 0;
1030 : : }
1031 : :
1032 : : /*
1033 : : * Because there is no preemptible RCU, there can be no readers blocked,
1034 : : * so there is no need to check for blocked tasks. So check only for
1035 : : * bogus qsmask values.
1036 : : */
1037 : 0 : static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
1038 : : {
1039 [ - + ][ # # ]: 202052 : WARN_ON_ONCE(rnp->qsmask);
[ # # ]
1040 : 202052 : }
1041 : :
1042 : : #ifdef CONFIG_HOTPLUG_CPU
1043 : :
1044 : : /*
1045 : : * Because preemptible RCU does not exist, it never needs to migrate
1046 : : * tasks that were blocked within RCU read-side critical sections, and
1047 : : * such non-existent tasks cannot possibly have been blocking the current
1048 : : * grace period.
1049 : : */
1050 : : static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
1051 : : struct rcu_node *rnp,
1052 : : struct rcu_data *rdp)
1053 : : {
1054 : : return 0;
1055 : : }
1056 : :
1057 : : #endif /* #ifdef CONFIG_HOTPLUG_CPU */
1058 : :
1059 : : /*
1060 : : * Because preemptible RCU does not exist, it never has any callbacks
1061 : : * to check.
1062 : : */
1063 : : static void rcu_preempt_check_callbacks(int cpu)
1064 : : {
1065 : : }
1066 : :
1067 : : /*
1068 : : * Queue an RCU callback for lazy invocation after a grace period.
1069 : : * This will likely be later named something like "call_rcu_lazy()",
1070 : : * but this change will require some way of tagging the lazy RCU
1071 : : * callbacks in the list of pending callbacks. Until then, this
1072 : : * function may only be called from __kfree_rcu().
1073 : : *
1074 : : * Because there is no preemptible RCU, we use RCU-sched instead.
1075 : : */
1076 : 0 : void kfree_call_rcu(struct rcu_head *head,
1077 : : void (*func)(struct rcu_head *rcu))
1078 : : {
1079 : 698326 : __call_rcu(head, func, &rcu_sched_state, -1, 1);
1080 : 698327 : }
1081 : : EXPORT_SYMBOL_GPL(kfree_call_rcu);
1082 : :
1083 : : /*
1084 : : * Wait for an rcu-preempt grace period, but make it happen quickly.
1085 : : * But because preemptible RCU does not exist, map to rcu-sched.
1086 : : */
1087 : 0 : void synchronize_rcu_expedited(void)
1088 : : {
1089 : 0 : synchronize_sched_expedited();
1090 : 0 : }
1091 : : EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
1092 : :
1093 : : #ifdef CONFIG_HOTPLUG_CPU
1094 : :
1095 : : /*
1096 : : * Because preemptible RCU does not exist, there is never any need to
1097 : : * report on tasks preempted in RCU read-side critical sections during
1098 : : * expedited RCU grace periods.
1099 : : */
1100 : : static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
1101 : : bool wake)
1102 : : {
1103 : : }
1104 : :
1105 : : #endif /* #ifdef CONFIG_HOTPLUG_CPU */
1106 : :
1107 : : /*
1108 : : * Because preemptible RCU does not exist, rcu_barrier() is just
1109 : : * another name for rcu_barrier_sched().
1110 : : */
1111 : 0 : void rcu_barrier(void)
1112 : : {
1113 : : rcu_barrier_sched();
1114 : 0 : }
1115 : : EXPORT_SYMBOL_GPL(rcu_barrier);
1116 : :
1117 : : /*
1118 : : * Because preemptible RCU does not exist, it need not be initialized.
1119 : : */
1120 : : static void __init __rcu_init_preempt(void)
1121 : : {
1122 : : }
1123 : :
1124 : : /*
1125 : : * Because preemptible RCU does not exist, tasks cannot possibly exit
1126 : : * while in preemptible RCU read-side critical sections.
1127 : : */
1128 : 0 : void exit_rcu(void)
1129 : : {
1130 : 1151924 : }
1131 : :
1132 : : #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
1133 : :
1134 : : #ifdef CONFIG_RCU_BOOST
1135 : :
1136 : : #include "../locking/rtmutex_common.h"
1137 : :
1138 : : #ifdef CONFIG_RCU_TRACE
1139 : :
1140 : : static void rcu_initiate_boost_trace(struct rcu_node *rnp)
1141 : : {
1142 : : if (list_empty(&rnp->blkd_tasks))
1143 : : rnp->n_balk_blkd_tasks++;
1144 : : else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
1145 : : rnp->n_balk_exp_gp_tasks++;
1146 : : else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
1147 : : rnp->n_balk_boost_tasks++;
1148 : : else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
1149 : : rnp->n_balk_notblocked++;
1150 : : else if (rnp->gp_tasks != NULL &&
1151 : : ULONG_CMP_LT(jiffies, rnp->boost_time))
1152 : : rnp->n_balk_notyet++;
1153 : : else
1154 : : rnp->n_balk_nos++;
1155 : : }
1156 : :
1157 : : #else /* #ifdef CONFIG_RCU_TRACE */
1158 : :
1159 : : static void rcu_initiate_boost_trace(struct rcu_node *rnp)
1160 : : {
1161 : : }
1162 : :
1163 : : #endif /* #else #ifdef CONFIG_RCU_TRACE */
1164 : :
1165 : : static void rcu_wake_cond(struct task_struct *t, int status)
1166 : : {
1167 : : /*
1168 : : * If the thread is yielding, only wake it when this
1169 : : * is invoked from idle
1170 : : */
1171 : : if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
1172 : : wake_up_process(t);
1173 : : }
1174 : :
1175 : : /*
1176 : : * Carry out RCU priority boosting on the task indicated by ->exp_tasks
1177 : : * or ->boost_tasks, advancing the pointer to the next task in the
1178 : : * ->blkd_tasks list.
1179 : : *
1180 : : * Note that irqs must be enabled: boosting the task can block.
1181 : : * Returns 1 if there are more tasks needing to be boosted.
1182 : : */
1183 : : static int rcu_boost(struct rcu_node *rnp)
1184 : : {
1185 : : unsigned long flags;
1186 : : struct rt_mutex mtx;
1187 : : struct task_struct *t;
1188 : : struct list_head *tb;
1189 : :
1190 : : if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
1191 : : return 0; /* Nothing left to boost. */
1192 : :
1193 : : raw_spin_lock_irqsave(&rnp->lock, flags);
1194 : :
1195 : : /*
1196 : : * Recheck under the lock: all tasks in need of boosting
1197 : : * might exit their RCU read-side critical sections on their own.
1198 : : */
1199 : : if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
1200 : : raw_spin_unlock_irqrestore(&rnp->lock, flags);
1201 : : return 0;
1202 : : }
1203 : :
1204 : : /*
1205 : : * Preferentially boost tasks blocking expedited grace periods.
1206 : : * This cannot starve the normal grace periods because a second
1207 : : * expedited grace period must boost all blocked tasks, including
1208 : : * those blocking the pre-existing normal grace period.
1209 : : */
1210 : : if (rnp->exp_tasks != NULL) {
1211 : : tb = rnp->exp_tasks;
1212 : : rnp->n_exp_boosts++;
1213 : : } else {
1214 : : tb = rnp->boost_tasks;
1215 : : rnp->n_normal_boosts++;
1216 : : }
1217 : : rnp->n_tasks_boosted++;
1218 : :
1219 : : /*
1220 : : * We boost task t by manufacturing an rt_mutex that appears to
1221 : : * be held by task t. We leave a pointer to that rt_mutex where
1222 : : * task t can find it, and task t will release the mutex when it
1223 : : * exits its outermost RCU read-side critical section. Then
1224 : : * simply acquiring this artificial rt_mutex will boost task
1225 : : * t's priority. (Thanks to tglx for suggesting this approach!)
1226 : : *
1227 : : * Note that task t must acquire rnp->lock to remove itself from
1228 : : * the ->blkd_tasks list, which it will do from exit() if from
1229 : : * nowhere else. We therefore are guaranteed that task t will
1230 : : * stay around at least until we drop rnp->lock. Note that
1231 : : * rnp->lock also resolves races between our priority boosting
1232 : : * and task t's exiting its outermost RCU read-side critical
1233 : : * section.
1234 : : */
1235 : : t = container_of(tb, struct task_struct, rcu_node_entry);
1236 : : rt_mutex_init_proxy_locked(&mtx, t);
1237 : : t->rcu_boost_mutex = &mtx;
1238 : : raw_spin_unlock_irqrestore(&rnp->lock, flags);
1239 : : rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */
1240 : : rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
1241 : :
1242 : : return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
1243 : : ACCESS_ONCE(rnp->boost_tasks) != NULL;
1244 : : }
1245 : :
1246 : : /*
1247 : : * Priority-boosting kthread. One per leaf rcu_node and one for the
1248 : : * root rcu_node.
1249 : : */
1250 : : static int rcu_boost_kthread(void *arg)
1251 : : {
1252 : : struct rcu_node *rnp = (struct rcu_node *)arg;
1253 : : int spincnt = 0;
1254 : : int more2boost;
1255 : :
1256 : : trace_rcu_utilization(TPS("Start boost kthread@init"));
1257 : : for (;;) {
1258 : : rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1259 : : trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1260 : : rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1261 : : trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1262 : : rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1263 : : more2boost = rcu_boost(rnp);
1264 : : if (more2boost)
1265 : : spincnt++;
1266 : : else
1267 : : spincnt = 0;
1268 : : if (spincnt > 10) {
1269 : : rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
1270 : : trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
1271 : : schedule_timeout_interruptible(2);
1272 : : trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1273 : : spincnt = 0;
1274 : : }
1275 : : }
1276 : : /* NOTREACHED */
1277 : : trace_rcu_utilization(TPS("End boost kthread@notreached"));
1278 : : return 0;
1279 : : }
1280 : :
1281 : : /*
1282 : : * Check to see if it is time to start boosting RCU readers that are
1283 : : * blocking the current grace period, and, if so, tell the per-rcu_node
1284 : : * kthread to start boosting them. If there is an expedited grace
1285 : : * period in progress, it is always time to boost.
1286 : : *
1287 : : * The caller must hold rnp->lock, which this function releases.
1288 : : * The ->boost_kthread_task is immortal, so we don't need to worry
1289 : : * about it going away.
1290 : : */
1291 : : static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1292 : : {
1293 : : struct task_struct *t;
1294 : :
1295 : : if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
1296 : : rnp->n_balk_exp_gp_tasks++;
1297 : : raw_spin_unlock_irqrestore(&rnp->lock, flags);
1298 : : return;
1299 : : }
1300 : : if (rnp->exp_tasks != NULL ||
1301 : : (rnp->gp_tasks != NULL &&
1302 : : rnp->boost_tasks == NULL &&
1303 : : rnp->qsmask == 0 &&
1304 : : ULONG_CMP_GE(jiffies, rnp->boost_time))) {
1305 : : if (rnp->exp_tasks == NULL)
1306 : : rnp->boost_tasks = rnp->gp_tasks;
1307 : : raw_spin_unlock_irqrestore(&rnp->lock, flags);
1308 : : t = rnp->boost_kthread_task;
1309 : : if (t)
1310 : : rcu_wake_cond(t, rnp->boost_kthread_status);
1311 : : } else {
1312 : : rcu_initiate_boost_trace(rnp);
1313 : : raw_spin_unlock_irqrestore(&rnp->lock, flags);
1314 : : }
1315 : : }
1316 : :
1317 : : /*
1318 : : * Wake up the per-CPU kthread to invoke RCU callbacks.
1319 : : */
1320 : : static void invoke_rcu_callbacks_kthread(void)
1321 : : {
1322 : : unsigned long flags;
1323 : :
1324 : : local_irq_save(flags);
1325 : : __this_cpu_write(rcu_cpu_has_work, 1);
1326 : : if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
1327 : : current != __this_cpu_read(rcu_cpu_kthread_task)) {
1328 : : rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
1329 : : __this_cpu_read(rcu_cpu_kthread_status));
1330 : : }
1331 : : local_irq_restore(flags);
1332 : : }
1333 : :
1334 : : /*
1335 : : * Is the current CPU running the RCU-callbacks kthread?
1336 : : * Caller must have preemption disabled.
1337 : : */
1338 : : static bool rcu_is_callbacks_kthread(void)
1339 : : {
1340 : : return __this_cpu_read(rcu_cpu_kthread_task) == current;
1341 : : }
1342 : :
1343 : : #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1344 : :
1345 : : /*
1346 : : * Do priority-boost accounting for the start of a new grace period.
1347 : : */
1348 : : static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1349 : : {
1350 : : rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
1351 : : }
1352 : :
1353 : : /*
1354 : : * Create an RCU-boost kthread for the specified node if one does not
1355 : : * already exist. We only create this kthread for preemptible RCU.
1356 : : * Returns zero if all is well, a negated errno otherwise.
1357 : : */
1358 : : static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
1359 : : struct rcu_node *rnp)
1360 : : {
1361 : : int rnp_index = rnp - &rsp->node[0];
1362 : : unsigned long flags;
1363 : : struct sched_param sp;
1364 : : struct task_struct *t;
1365 : :
1366 : : if (&rcu_preempt_state != rsp)
1367 : : return 0;
1368 : :
1369 : : if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0)
1370 : : return 0;
1371 : :
1372 : : rsp->boost = 1;
1373 : : if (rnp->boost_kthread_task != NULL)
1374 : : return 0;
1375 : : t = kthread_create(rcu_boost_kthread, (void *)rnp,
1376 : : "rcub/%d", rnp_index);
1377 : : if (IS_ERR(t))
1378 : : return PTR_ERR(t);
1379 : : raw_spin_lock_irqsave(&rnp->lock, flags);
1380 : : rnp->boost_kthread_task = t;
1381 : : raw_spin_unlock_irqrestore(&rnp->lock, flags);
1382 : : sp.sched_priority = RCU_BOOST_PRIO;
1383 : : sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1384 : : wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1385 : : return 0;
1386 : : }
1387 : :
1388 : : static void rcu_kthread_do_work(void)
1389 : : {
1390 : : rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
1391 : : rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
1392 : : rcu_preempt_do_callbacks();
1393 : : }
1394 : :
1395 : : static void rcu_cpu_kthread_setup(unsigned int cpu)
1396 : : {
1397 : : struct sched_param sp;
1398 : :
1399 : : sp.sched_priority = RCU_KTHREAD_PRIO;
1400 : : sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
1401 : : }
1402 : :
1403 : : static void rcu_cpu_kthread_park(unsigned int cpu)
1404 : : {
1405 : : per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
1406 : : }
1407 : :
1408 : : static int rcu_cpu_kthread_should_run(unsigned int cpu)
1409 : : {
1410 : : return __this_cpu_read(rcu_cpu_has_work);
1411 : : }
1412 : :
1413 : : /*
1414 : : * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
1415 : : * RCU softirq used in flavors and configurations of RCU that do not
1416 : : * support RCU priority boosting.
1417 : : */
1418 : : static void rcu_cpu_kthread(unsigned int cpu)
1419 : : {
1420 : : unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
1421 : : char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
1422 : : int spincnt;
1423 : :
1424 : : for (spincnt = 0; spincnt < 10; spincnt++) {
1425 : : trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
1426 : : local_bh_disable();
1427 : : *statusp = RCU_KTHREAD_RUNNING;
1428 : : this_cpu_inc(rcu_cpu_kthread_loops);
1429 : : local_irq_disable();
1430 : : work = *workp;
1431 : : *workp = 0;
1432 : : local_irq_enable();
1433 : : if (work)
1434 : : rcu_kthread_do_work();
1435 : : local_bh_enable();
1436 : : if (*workp == 0) {
1437 : : trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
1438 : : *statusp = RCU_KTHREAD_WAITING;
1439 : : return;
1440 : : }
1441 : : }
1442 : : *statusp = RCU_KTHREAD_YIELDING;
1443 : : trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
1444 : : schedule_timeout_interruptible(2);
1445 : : trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
1446 : : *statusp = RCU_KTHREAD_WAITING;
1447 : : }
1448 : :
1449 : : /*
1450 : : * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1451 : : * served by the rcu_node in question. The CPU hotplug lock is still
1452 : : * held, so the value of rnp->qsmaskinit will be stable.
1453 : : *
1454 : : * We don't include outgoingcpu in the affinity set, use -1 if there is
1455 : : * no outgoing CPU. If there are no CPUs left in the affinity set,
1456 : : * this function allows the kthread to execute on any CPU.
1457 : : */
1458 : : static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1459 : : {
1460 : : struct task_struct *t = rnp->boost_kthread_task;
1461 : : unsigned long mask = rnp->qsmaskinit;
1462 : : cpumask_var_t cm;
1463 : : int cpu;
1464 : :
1465 : : if (!t)
1466 : : return;
1467 : : if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
1468 : : return;
1469 : : for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
1470 : : if ((mask & 0x1) && cpu != outgoingcpu)
1471 : : cpumask_set_cpu(cpu, cm);
1472 : : if (cpumask_weight(cm) == 0) {
1473 : : cpumask_setall(cm);
1474 : : for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
1475 : : cpumask_clear_cpu(cpu, cm);
1476 : : WARN_ON_ONCE(cpumask_weight(cm) == 0);
1477 : : }
1478 : : set_cpus_allowed_ptr(t, cm);
1479 : : free_cpumask_var(cm);
1480 : : }
1481 : :
1482 : : static struct smp_hotplug_thread rcu_cpu_thread_spec = {
1483 : : .store = &rcu_cpu_kthread_task,
1484 : : .thread_should_run = rcu_cpu_kthread_should_run,
1485 : : .thread_fn = rcu_cpu_kthread,
1486 : : .thread_comm = "rcuc/%u",
1487 : : .setup = rcu_cpu_kthread_setup,
1488 : : .park = rcu_cpu_kthread_park,
1489 : : };
1490 : :
1491 : : /*
1492 : : * Spawn all kthreads -- called as soon as the scheduler is running.
1493 : : */
1494 : : static int __init rcu_spawn_kthreads(void)
1495 : : {
1496 : : struct rcu_node *rnp;
1497 : : int cpu;
1498 : :
1499 : : rcu_scheduler_fully_active = 1;
1500 : : for_each_possible_cpu(cpu)
1501 : : per_cpu(rcu_cpu_has_work, cpu) = 0;
1502 : : BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
1503 : : rnp = rcu_get_root(rcu_state);
1504 : : (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
1505 : : if (NUM_RCU_NODES > 1) {
1506 : : rcu_for_each_leaf_node(rcu_state, rnp)
1507 : : (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
1508 : : }
1509 : : return 0;
1510 : : }
1511 : : early_initcall(rcu_spawn_kthreads);
1512 : :
1513 : : static void rcu_prepare_kthreads(int cpu)
1514 : : {
1515 : : struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
1516 : : struct rcu_node *rnp = rdp->mynode;
1517 : :
1518 : : /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1519 : : if (rcu_scheduler_fully_active)
1520 : : (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
1521 : : }
1522 : :
1523 : : #else /* #ifdef CONFIG_RCU_BOOST */
1524 : :
1525 : : static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1526 : : {
1527 : 26430 : raw_spin_unlock_irqrestore(&rnp->lock, flags);
1528 : : }
1529 : :
1530 : 0 : static void invoke_rcu_callbacks_kthread(void)
1531 : : {
1532 [ # # ][ # # ]: 0 : WARN_ON_ONCE(1);
1533 : 0 : }
1534 : :
1535 : : static bool rcu_is_callbacks_kthread(void)
1536 : : {
1537 : : return false;
1538 : : }
1539 : :
1540 : : static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1541 : : {
1542 : : }
1543 : :
1544 : : static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1545 : : {
1546 : : }
1547 : :
1548 : 0 : static int __init rcu_scheduler_really_started(void)
1549 : : {
1550 : 0 : rcu_scheduler_fully_active = 1;
1551 : 0 : return 0;
1552 : : }
1553 : : early_initcall(rcu_scheduler_really_started);
1554 : :
1555 : : static void rcu_prepare_kthreads(int cpu)
1556 : : {
1557 : : }
1558 : :
1559 : : #endif /* #else #ifdef CONFIG_RCU_BOOST */
1560 : :
1561 : : #if !defined(CONFIG_RCU_FAST_NO_HZ)
1562 : :
1563 : : /*
1564 : : * Check to see if any future RCU-related work will need to be done
1565 : : * by the current CPU, even if none need be done immediately, returning
1566 : : * 1 if so. This function is part of the RCU implementation; it is -not-
1567 : : * an exported member of the RCU API.
1568 : : *
1569 : : * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
1570 : : * any flavor of RCU.
1571 : : */
1572 : 0 : int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
1573 : : {
1574 : 6166722 : *delta_jiffies = ULONG_MAX;
1575 : 6166722 : return rcu_cpu_has_callbacks(cpu, NULL);
1576 : : }
1577 : :
1578 : : /*
1579 : : * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1580 : : * after it.
1581 : : */
1582 : : static void rcu_cleanup_after_idle(int cpu)
1583 : : {
1584 : : }
1585 : :
1586 : : /*
1587 : : * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1588 : : * is nothing.
1589 : : */
1590 : : static void rcu_prepare_for_idle(int cpu)
1591 : : {
1592 : : }
1593 : :
1594 : : /*
1595 : : * Don't bother keeping a running count of the number of RCU callbacks
1596 : : * posted because CONFIG_RCU_FAST_NO_HZ=n.
1597 : : */
1598 : : static void rcu_idle_count_callbacks_posted(void)
1599 : : {
1600 : : }
1601 : :
1602 : : #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1603 : :
1604 : : /*
1605 : : * This code is invoked when a CPU goes idle, at which point we want
1606 : : * to have the CPU do everything required for RCU so that it can enter
1607 : : * the energy-efficient dyntick-idle mode. This is handled by a
1608 : : * state machine implemented by rcu_prepare_for_idle() below.
1609 : : *
1610 : : * The following three proprocessor symbols control this state machine:
1611 : : *
1612 : : * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1613 : : * to sleep in dyntick-idle mode with RCU callbacks pending. This
1614 : : * is sized to be roughly one RCU grace period. Those energy-efficiency
1615 : : * benchmarkers who might otherwise be tempted to set this to a large
1616 : : * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1617 : : * system. And if you are -that- concerned about energy efficiency,
1618 : : * just power the system down and be done with it!
1619 : : * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1620 : : * permitted to sleep in dyntick-idle mode with only lazy RCU
1621 : : * callbacks pending. Setting this too high can OOM your system.
1622 : : *
1623 : : * The values below work well in practice. If future workloads require
1624 : : * adjustment, they can be converted into kernel config parameters, though
1625 : : * making the state machine smarter might be a better option.
1626 : : */
1627 : : #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
1628 : : #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
1629 : :
1630 : : static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
1631 : : module_param(rcu_idle_gp_delay, int, 0644);
1632 : : static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
1633 : : module_param(rcu_idle_lazy_gp_delay, int, 0644);
1634 : :
1635 : : extern int tick_nohz_active;
1636 : :
1637 : : /*
1638 : : * Try to advance callbacks for all flavors of RCU on the current CPU, but
1639 : : * only if it has been awhile since the last time we did so. Afterwards,
1640 : : * if there are any callbacks ready for immediate invocation, return true.
1641 : : */
1642 : : static bool rcu_try_advance_all_cbs(void)
1643 : : {
1644 : : bool cbs_ready = false;
1645 : : struct rcu_data *rdp;
1646 : : struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1647 : : struct rcu_node *rnp;
1648 : : struct rcu_state *rsp;
1649 : :
1650 : : /* Exit early if we advanced recently. */
1651 : : if (jiffies == rdtp->last_advance_all)
1652 : : return 0;
1653 : : rdtp->last_advance_all = jiffies;
1654 : :
1655 : : for_each_rcu_flavor(rsp) {
1656 : : rdp = this_cpu_ptr(rsp->rda);
1657 : : rnp = rdp->mynode;
1658 : :
1659 : : /*
1660 : : * Don't bother checking unless a grace period has
1661 : : * completed since we last checked and there are
1662 : : * callbacks not yet ready to invoke.
1663 : : */
1664 : : if (rdp->completed != rnp->completed &&
1665 : : rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
1666 : : note_gp_changes(rsp, rdp);
1667 : :
1668 : : if (cpu_has_callbacks_ready_to_invoke(rdp))
1669 : : cbs_ready = true;
1670 : : }
1671 : : return cbs_ready;
1672 : : }
1673 : :
1674 : : /*
1675 : : * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1676 : : * to invoke. If the CPU has callbacks, try to advance them. Tell the
1677 : : * caller to set the timeout based on whether or not there are non-lazy
1678 : : * callbacks.
1679 : : *
1680 : : * The caller must have disabled interrupts.
1681 : : */
1682 : : int rcu_needs_cpu(int cpu, unsigned long *dj)
1683 : : {
1684 : : struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1685 : :
1686 : : /* Snapshot to detect later posting of non-lazy callback. */
1687 : : rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1688 : :
1689 : : /* If no callbacks, RCU doesn't need the CPU. */
1690 : : if (!rcu_cpu_has_callbacks(cpu, &rdtp->all_lazy)) {
1691 : : *dj = ULONG_MAX;
1692 : : return 0;
1693 : : }
1694 : :
1695 : : /* Attempt to advance callbacks. */
1696 : : if (rcu_try_advance_all_cbs()) {
1697 : : /* Some ready to invoke, so initiate later invocation. */
1698 : : invoke_rcu_core();
1699 : : return 1;
1700 : : }
1701 : : rdtp->last_accelerate = jiffies;
1702 : :
1703 : : /* Request timer delay depending on laziness, and round. */
1704 : : if (!rdtp->all_lazy) {
1705 : : *dj = round_up(rcu_idle_gp_delay + jiffies,
1706 : : rcu_idle_gp_delay) - jiffies;
1707 : : } else {
1708 : : *dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
1709 : : }
1710 : : return 0;
1711 : : }
1712 : :
1713 : : /*
1714 : : * Prepare a CPU for idle from an RCU perspective. The first major task
1715 : : * is to sense whether nohz mode has been enabled or disabled via sysfs.
1716 : : * The second major task is to check to see if a non-lazy callback has
1717 : : * arrived at a CPU that previously had only lazy callbacks. The third
1718 : : * major task is to accelerate (that is, assign grace-period numbers to)
1719 : : * any recently arrived callbacks.
1720 : : *
1721 : : * The caller must have disabled interrupts.
1722 : : */
1723 : : static void rcu_prepare_for_idle(int cpu)
1724 : : {
1725 : : struct rcu_data *rdp;
1726 : : struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1727 : : struct rcu_node *rnp;
1728 : : struct rcu_state *rsp;
1729 : : int tne;
1730 : :
1731 : : /* Handle nohz enablement switches conservatively. */
1732 : : tne = ACCESS_ONCE(tick_nohz_active);
1733 : : if (tne != rdtp->tick_nohz_enabled_snap) {
1734 : : if (rcu_cpu_has_callbacks(cpu, NULL))
1735 : : invoke_rcu_core(); /* force nohz to see update. */
1736 : : rdtp->tick_nohz_enabled_snap = tne;
1737 : : return;
1738 : : }
1739 : : if (!tne)
1740 : : return;
1741 : :
1742 : : /* If this is a no-CBs CPU, no callbacks, just return. */
1743 : : if (rcu_is_nocb_cpu(cpu))
1744 : : return;
1745 : :
1746 : : /*
1747 : : * If a non-lazy callback arrived at a CPU having only lazy
1748 : : * callbacks, invoke RCU core for the side-effect of recalculating
1749 : : * idle duration on re-entry to idle.
1750 : : */
1751 : : if (rdtp->all_lazy &&
1752 : : rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
1753 : : rdtp->all_lazy = false;
1754 : : rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1755 : : invoke_rcu_core();
1756 : : return;
1757 : : }
1758 : :
1759 : : /*
1760 : : * If we have not yet accelerated this jiffy, accelerate all
1761 : : * callbacks on this CPU.
1762 : : */
1763 : : if (rdtp->last_accelerate == jiffies)
1764 : : return;
1765 : : rdtp->last_accelerate = jiffies;
1766 : : for_each_rcu_flavor(rsp) {
1767 : : rdp = per_cpu_ptr(rsp->rda, cpu);
1768 : : if (!*rdp->nxttail[RCU_DONE_TAIL])
1769 : : continue;
1770 : : rnp = rdp->mynode;
1771 : : raw_spin_lock(&rnp->lock); /* irqs already disabled. */
1772 : : rcu_accelerate_cbs(rsp, rnp, rdp);
1773 : : raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1774 : : }
1775 : : }
1776 : :
1777 : : /*
1778 : : * Clean up for exit from idle. Attempt to advance callbacks based on
1779 : : * any grace periods that elapsed while the CPU was idle, and if any
1780 : : * callbacks are now ready to invoke, initiate invocation.
1781 : : */
1782 : : static void rcu_cleanup_after_idle(int cpu)
1783 : : {
1784 : :
1785 : : if (rcu_is_nocb_cpu(cpu))
1786 : : return;
1787 : : if (rcu_try_advance_all_cbs())
1788 : : invoke_rcu_core();
1789 : : }
1790 : :
1791 : : /*
1792 : : * Keep a running count of the number of non-lazy callbacks posted
1793 : : * on this CPU. This running counter (which is never decremented) allows
1794 : : * rcu_prepare_for_idle() to detect when something out of the idle loop
1795 : : * posts a callback, even if an equal number of callbacks are invoked.
1796 : : * Of course, callbacks should only be posted from within a trace event
1797 : : * designed to be called from idle or from within RCU_NONIDLE().
1798 : : */
1799 : : static void rcu_idle_count_callbacks_posted(void)
1800 : : {
1801 : : __this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
1802 : : }
1803 : :
1804 : : /*
1805 : : * Data for flushing lazy RCU callbacks at OOM time.
1806 : : */
1807 : : static atomic_t oom_callback_count;
1808 : : static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
1809 : :
1810 : : /*
1811 : : * RCU OOM callback -- decrement the outstanding count and deliver the
1812 : : * wake-up if we are the last one.
1813 : : */
1814 : : static void rcu_oom_callback(struct rcu_head *rhp)
1815 : : {
1816 : : if (atomic_dec_and_test(&oom_callback_count))
1817 : : wake_up(&oom_callback_wq);
1818 : : }
1819 : :
1820 : : /*
1821 : : * Post an rcu_oom_notify callback on the current CPU if it has at
1822 : : * least one lazy callback. This will unnecessarily post callbacks
1823 : : * to CPUs that already have a non-lazy callback at the end of their
1824 : : * callback list, but this is an infrequent operation, so accept some
1825 : : * extra overhead to keep things simple.
1826 : : */
1827 : : static void rcu_oom_notify_cpu(void *unused)
1828 : : {
1829 : : struct rcu_state *rsp;
1830 : : struct rcu_data *rdp;
1831 : :
1832 : : for_each_rcu_flavor(rsp) {
1833 : : rdp = __this_cpu_ptr(rsp->rda);
1834 : : if (rdp->qlen_lazy != 0) {
1835 : : atomic_inc(&oom_callback_count);
1836 : : rsp->call(&rdp->oom_head, rcu_oom_callback);
1837 : : }
1838 : : }
1839 : : }
1840 : :
1841 : : /*
1842 : : * If low on memory, ensure that each CPU has a non-lazy callback.
1843 : : * This will wake up CPUs that have only lazy callbacks, in turn
1844 : : * ensuring that they free up the corresponding memory in a timely manner.
1845 : : * Because an uncertain amount of memory will be freed in some uncertain
1846 : : * timeframe, we do not claim to have freed anything.
1847 : : */
1848 : : static int rcu_oom_notify(struct notifier_block *self,
1849 : : unsigned long notused, void *nfreed)
1850 : : {
1851 : : int cpu;
1852 : :
1853 : : /* Wait for callbacks from earlier instance to complete. */
1854 : : wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
1855 : :
1856 : : /*
1857 : : * Prevent premature wakeup: ensure that all increments happen
1858 : : * before there is a chance of the counter reaching zero.
1859 : : */
1860 : : atomic_set(&oom_callback_count, 1);
1861 : :
1862 : : get_online_cpus();
1863 : : for_each_online_cpu(cpu) {
1864 : : smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
1865 : : cond_resched();
1866 : : }
1867 : : put_online_cpus();
1868 : :
1869 : : /* Unconditionally decrement: no need to wake ourselves up. */
1870 : : atomic_dec(&oom_callback_count);
1871 : :
1872 : : return NOTIFY_OK;
1873 : : }
1874 : :
1875 : : static struct notifier_block rcu_oom_nb = {
1876 : : .notifier_call = rcu_oom_notify
1877 : : };
1878 : :
1879 : : static int __init rcu_register_oom_notifier(void)
1880 : : {
1881 : : register_oom_notifier(&rcu_oom_nb);
1882 : : return 0;
1883 : : }
1884 : : early_initcall(rcu_register_oom_notifier);
1885 : :
1886 : : #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1887 : :
1888 : : #ifdef CONFIG_RCU_CPU_STALL_INFO
1889 : :
1890 : : #ifdef CONFIG_RCU_FAST_NO_HZ
1891 : :
1892 : : static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1893 : : {
1894 : : struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1895 : : unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
1896 : :
1897 : : sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
1898 : : rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
1899 : : ulong2long(nlpd),
1900 : : rdtp->all_lazy ? 'L' : '.',
1901 : : rdtp->tick_nohz_enabled_snap ? '.' : 'D');
1902 : : }
1903 : :
1904 : : #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
1905 : :
1906 : : static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1907 : : {
1908 : : *cp = '\0';
1909 : : }
1910 : :
1911 : : #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
1912 : :
1913 : : /* Initiate the stall-info list. */
1914 : : static void print_cpu_stall_info_begin(void)
1915 : : {
1916 : : pr_cont("\n");
1917 : : }
1918 : :
1919 : : /*
1920 : : * Print out diagnostic information for the specified stalled CPU.
1921 : : *
1922 : : * If the specified CPU is aware of the current RCU grace period
1923 : : * (flavor specified by rsp), then print the number of scheduling
1924 : : * clock interrupts the CPU has taken during the time that it has
1925 : : * been aware. Otherwise, print the number of RCU grace periods
1926 : : * that this CPU is ignorant of, for example, "1" if the CPU was
1927 : : * aware of the previous grace period.
1928 : : *
1929 : : * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
1930 : : */
1931 : : static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
1932 : : {
1933 : : char fast_no_hz[72];
1934 : : struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1935 : : struct rcu_dynticks *rdtp = rdp->dynticks;
1936 : : char *ticks_title;
1937 : : unsigned long ticks_value;
1938 : :
1939 : : if (rsp->gpnum == rdp->gpnum) {
1940 : : ticks_title = "ticks this GP";
1941 : : ticks_value = rdp->ticks_this_gp;
1942 : : } else {
1943 : : ticks_title = "GPs behind";
1944 : : ticks_value = rsp->gpnum - rdp->gpnum;
1945 : : }
1946 : : print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
1947 : : pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
1948 : : cpu, ticks_value, ticks_title,
1949 : : atomic_read(&rdtp->dynticks) & 0xfff,
1950 : : rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
1951 : : rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
1952 : : fast_no_hz);
1953 : : }
1954 : :
1955 : : /* Terminate the stall-info list. */
1956 : : static void print_cpu_stall_info_end(void)
1957 : : {
1958 : : pr_err("\t");
1959 : : }
1960 : :
1961 : : /* Zero ->ticks_this_gp for all flavors of RCU. */
1962 : : static void zero_cpu_stall_ticks(struct rcu_data *rdp)
1963 : : {
1964 : : rdp->ticks_this_gp = 0;
1965 : : rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
1966 : : }
1967 : :
1968 : : /* Increment ->ticks_this_gp for all flavors of RCU. */
1969 : : static void increment_cpu_stall_ticks(void)
1970 : : {
1971 : : struct rcu_state *rsp;
1972 : :
1973 : : for_each_rcu_flavor(rsp)
1974 : : __this_cpu_ptr(rsp->rda)->ticks_this_gp++;
1975 : : }
1976 : :
1977 : : #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
1978 : :
1979 : : static void print_cpu_stall_info_begin(void)
1980 : : {
1981 : 0 : pr_cont(" {");
1982 : : }
1983 : :
1984 : : static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
1985 : : {
1986 : 0 : pr_cont(" %d", cpu);
1987 : : }
1988 : :
1989 : : static void print_cpu_stall_info_end(void)
1990 : : {
1991 : 0 : pr_cont("} ");
1992 : : }
1993 : :
1994 : : static void zero_cpu_stall_ticks(struct rcu_data *rdp)
1995 : : {
1996 : : }
1997 : :
1998 : : static void increment_cpu_stall_ticks(void)
1999 : : {
2000 : : }
2001 : :
2002 : : #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
2003 : :
2004 : : #ifdef CONFIG_RCU_NOCB_CPU
2005 : :
2006 : : /*
2007 : : * Offload callback processing from the boot-time-specified set of CPUs
2008 : : * specified by rcu_nocb_mask. For each CPU in the set, there is a
2009 : : * kthread created that pulls the callbacks from the corresponding CPU,
2010 : : * waits for a grace period to elapse, and invokes the callbacks.
2011 : : * The no-CBs CPUs do a wake_up() on their kthread when they insert
2012 : : * a callback into any empty list, unless the rcu_nocb_poll boot parameter
2013 : : * has been specified, in which case each kthread actively polls its
2014 : : * CPU. (Which isn't so great for energy efficiency, but which does
2015 : : * reduce RCU's overhead on that CPU.)
2016 : : *
2017 : : * This is intended to be used in conjunction with Frederic Weisbecker's
2018 : : * adaptive-idle work, which would seriously reduce OS jitter on CPUs
2019 : : * running CPU-bound user-mode computations.
2020 : : *
2021 : : * Offloading of callback processing could also in theory be used as
2022 : : * an energy-efficiency measure because CPUs with no RCU callbacks
2023 : : * queued are more aggressive about entering dyntick-idle mode.
2024 : : */
2025 : :
2026 : :
2027 : : /* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
2028 : : static int __init rcu_nocb_setup(char *str)
2029 : : {
2030 : : alloc_bootmem_cpumask_var(&rcu_nocb_mask);
2031 : : have_rcu_nocb_mask = true;
2032 : : cpulist_parse(str, rcu_nocb_mask);
2033 : : return 1;
2034 : : }
2035 : : __setup("rcu_nocbs=", rcu_nocb_setup);
2036 : :
2037 : : static int __init parse_rcu_nocb_poll(char *arg)
2038 : : {
2039 : : rcu_nocb_poll = 1;
2040 : : return 0;
2041 : : }
2042 : : early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
2043 : :
2044 : : /*
2045 : : * Do any no-CBs CPUs need another grace period?
2046 : : *
2047 : : * Interrupts must be disabled. If the caller does not hold the root
2048 : : * rnp_node structure's ->lock, the results are advisory only.
2049 : : */
2050 : : static int rcu_nocb_needs_gp(struct rcu_state *rsp)
2051 : : {
2052 : : struct rcu_node *rnp = rcu_get_root(rsp);
2053 : :
2054 : : return rnp->need_future_gp[(ACCESS_ONCE(rnp->completed) + 1) & 0x1];
2055 : : }
2056 : :
2057 : : /*
2058 : : * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
2059 : : * grace period.
2060 : : */
2061 : : static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
2062 : : {
2063 : : wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]);
2064 : : }
2065 : :
2066 : : /*
2067 : : * Set the root rcu_node structure's ->need_future_gp field
2068 : : * based on the sum of those of all rcu_node structures. This does
2069 : : * double-count the root rcu_node structure's requests, but this
2070 : : * is necessary to handle the possibility of a rcu_nocb_kthread()
2071 : : * having awakened during the time that the rcu_node structures
2072 : : * were being updated for the end of the previous grace period.
2073 : : */
2074 : : static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
2075 : : {
2076 : : rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
2077 : : }
2078 : :
2079 : : static void rcu_init_one_nocb(struct rcu_node *rnp)
2080 : : {
2081 : : init_waitqueue_head(&rnp->nocb_gp_wq[0]);
2082 : : init_waitqueue_head(&rnp->nocb_gp_wq[1]);
2083 : : }
2084 : :
2085 : : /* Is the specified CPU a no-CPUs CPU? */
2086 : : bool rcu_is_nocb_cpu(int cpu)
2087 : : {
2088 : : if (have_rcu_nocb_mask)
2089 : : return cpumask_test_cpu(cpu, rcu_nocb_mask);
2090 : : return false;
2091 : : }
2092 : :
2093 : : /*
2094 : : * Enqueue the specified string of rcu_head structures onto the specified
2095 : : * CPU's no-CBs lists. The CPU is specified by rdp, the head of the
2096 : : * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
2097 : : * counts are supplied by rhcount and rhcount_lazy.
2098 : : *
2099 : : * If warranted, also wake up the kthread servicing this CPUs queues.
2100 : : */
2101 : : static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
2102 : : struct rcu_head *rhp,
2103 : : struct rcu_head **rhtp,
2104 : : int rhcount, int rhcount_lazy)
2105 : : {
2106 : : int len;
2107 : : struct rcu_head **old_rhpp;
2108 : : struct task_struct *t;
2109 : :
2110 : : /* Enqueue the callback on the nocb list and update counts. */
2111 : : old_rhpp = xchg(&rdp->nocb_tail, rhtp);
2112 : : ACCESS_ONCE(*old_rhpp) = rhp;
2113 : : atomic_long_add(rhcount, &rdp->nocb_q_count);
2114 : : atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
2115 : :
2116 : : /* If we are not being polled and there is a kthread, awaken it ... */
2117 : : t = ACCESS_ONCE(rdp->nocb_kthread);
2118 : : if (rcu_nocb_poll || !t) {
2119 : : trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2120 : : TPS("WakeNotPoll"));
2121 : : return;
2122 : : }
2123 : : len = atomic_long_read(&rdp->nocb_q_count);
2124 : : if (old_rhpp == &rdp->nocb_head) {
2125 : : wake_up(&rdp->nocb_wq); /* ... only if queue was empty ... */
2126 : : rdp->qlen_last_fqs_check = 0;
2127 : : trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeEmpty"));
2128 : : } else if (len > rdp->qlen_last_fqs_check + qhimark) {
2129 : : wake_up_process(t); /* ... or if many callbacks queued. */
2130 : : rdp->qlen_last_fqs_check = LONG_MAX / 2;
2131 : : trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeOvf"));
2132 : : } else {
2133 : : trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
2134 : : }
2135 : : return;
2136 : : }
2137 : :
2138 : : /*
2139 : : * This is a helper for __call_rcu(), which invokes this when the normal
2140 : : * callback queue is inoperable. If this is not a no-CBs CPU, this
2141 : : * function returns failure back to __call_rcu(), which can complain
2142 : : * appropriately.
2143 : : *
2144 : : * Otherwise, this function queues the callback where the corresponding
2145 : : * "rcuo" kthread can find it.
2146 : : */
2147 : : static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2148 : : bool lazy)
2149 : : {
2150 : :
2151 : : if (!rcu_is_nocb_cpu(rdp->cpu))
2152 : : return 0;
2153 : : __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy);
2154 : : if (__is_kfree_rcu_offset((unsigned long)rhp->func))
2155 : : trace_rcu_kfree_callback(rdp->rsp->name, rhp,
2156 : : (unsigned long)rhp->func,
2157 : : -atomic_long_read(&rdp->nocb_q_count_lazy),
2158 : : -atomic_long_read(&rdp->nocb_q_count));
2159 : : else
2160 : : trace_rcu_callback(rdp->rsp->name, rhp,
2161 : : -atomic_long_read(&rdp->nocb_q_count_lazy),
2162 : : -atomic_long_read(&rdp->nocb_q_count));
2163 : : return 1;
2164 : : }
2165 : :
2166 : : /*
2167 : : * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
2168 : : * not a no-CBs CPU.
2169 : : */
2170 : : static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
2171 : : struct rcu_data *rdp)
2172 : : {
2173 : : long ql = rsp->qlen;
2174 : : long qll = rsp->qlen_lazy;
2175 : :
2176 : : /* If this is not a no-CBs CPU, tell the caller to do it the old way. */
2177 : : if (!rcu_is_nocb_cpu(smp_processor_id()))
2178 : : return 0;
2179 : : rsp->qlen = 0;
2180 : : rsp->qlen_lazy = 0;
2181 : :
2182 : : /* First, enqueue the donelist, if any. This preserves CB ordering. */
2183 : : if (rsp->orphan_donelist != NULL) {
2184 : : __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist,
2185 : : rsp->orphan_donetail, ql, qll);
2186 : : ql = qll = 0;
2187 : : rsp->orphan_donelist = NULL;
2188 : : rsp->orphan_donetail = &rsp->orphan_donelist;
2189 : : }
2190 : : if (rsp->orphan_nxtlist != NULL) {
2191 : : __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist,
2192 : : rsp->orphan_nxttail, ql, qll);
2193 : : ql = qll = 0;
2194 : : rsp->orphan_nxtlist = NULL;
2195 : : rsp->orphan_nxttail = &rsp->orphan_nxtlist;
2196 : : }
2197 : : return 1;
2198 : : }
2199 : :
2200 : : /*
2201 : : * If necessary, kick off a new grace period, and either way wait
2202 : : * for a subsequent grace period to complete.
2203 : : */
2204 : : static void rcu_nocb_wait_gp(struct rcu_data *rdp)
2205 : : {
2206 : : unsigned long c;
2207 : : bool d;
2208 : : unsigned long flags;
2209 : : struct rcu_node *rnp = rdp->mynode;
2210 : :
2211 : : raw_spin_lock_irqsave(&rnp->lock, flags);
2212 : : c = rcu_start_future_gp(rnp, rdp);
2213 : : raw_spin_unlock_irqrestore(&rnp->lock, flags);
2214 : :
2215 : : /*
2216 : : * Wait for the grace period. Do so interruptibly to avoid messing
2217 : : * up the load average.
2218 : : */
2219 : : trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
2220 : : for (;;) {
2221 : : wait_event_interruptible(
2222 : : rnp->nocb_gp_wq[c & 0x1],
2223 : : (d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c)));
2224 : : if (likely(d))
2225 : : break;
2226 : : flush_signals(current);
2227 : : trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
2228 : : }
2229 : : trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
2230 : : smp_mb(); /* Ensure that CB invocation happens after GP end. */
2231 : : }
2232 : :
2233 : : /*
2234 : : * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
2235 : : * callbacks queued by the corresponding no-CBs CPU.
2236 : : */
2237 : : static int rcu_nocb_kthread(void *arg)
2238 : : {
2239 : : int c, cl;
2240 : : bool firsttime = 1;
2241 : : struct rcu_head *list;
2242 : : struct rcu_head *next;
2243 : : struct rcu_head **tail;
2244 : : struct rcu_data *rdp = arg;
2245 : :
2246 : : /* Each pass through this loop invokes one batch of callbacks */
2247 : : for (;;) {
2248 : : /* If not polling, wait for next batch of callbacks. */
2249 : : if (!rcu_nocb_poll) {
2250 : : trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2251 : : TPS("Sleep"));
2252 : : wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head);
2253 : : } else if (firsttime) {
2254 : : firsttime = 0;
2255 : : trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2256 : : TPS("Poll"));
2257 : : }
2258 : : list = ACCESS_ONCE(rdp->nocb_head);
2259 : : if (!list) {
2260 : : if (!rcu_nocb_poll)
2261 : : trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2262 : : TPS("WokeEmpty"));
2263 : : schedule_timeout_interruptible(1);
2264 : : flush_signals(current);
2265 : : continue;
2266 : : }
2267 : : firsttime = 1;
2268 : : trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2269 : : TPS("WokeNonEmpty"));
2270 : :
2271 : : /*
2272 : : * Extract queued callbacks, update counts, and wait
2273 : : * for a grace period to elapse.
2274 : : */
2275 : : ACCESS_ONCE(rdp->nocb_head) = NULL;
2276 : : tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
2277 : : c = atomic_long_xchg(&rdp->nocb_q_count, 0);
2278 : : cl = atomic_long_xchg(&rdp->nocb_q_count_lazy, 0);
2279 : : ACCESS_ONCE(rdp->nocb_p_count) += c;
2280 : : ACCESS_ONCE(rdp->nocb_p_count_lazy) += cl;
2281 : : rcu_nocb_wait_gp(rdp);
2282 : :
2283 : : /* Each pass through the following loop invokes a callback. */
2284 : : trace_rcu_batch_start(rdp->rsp->name, cl, c, -1);
2285 : : c = cl = 0;
2286 : : while (list) {
2287 : : next = list->next;
2288 : : /* Wait for enqueuing to complete, if needed. */
2289 : : while (next == NULL && &list->next != tail) {
2290 : : trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2291 : : TPS("WaitQueue"));
2292 : : schedule_timeout_interruptible(1);
2293 : : trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2294 : : TPS("WokeQueue"));
2295 : : next = list->next;
2296 : : }
2297 : : debug_rcu_head_unqueue(list);
2298 : : local_bh_disable();
2299 : : if (__rcu_reclaim(rdp->rsp->name, list))
2300 : : cl++;
2301 : : c++;
2302 : : local_bh_enable();
2303 : : list = next;
2304 : : }
2305 : : trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
2306 : : ACCESS_ONCE(rdp->nocb_p_count) -= c;
2307 : : ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl;
2308 : : rdp->n_nocbs_invoked += c;
2309 : : }
2310 : : return 0;
2311 : : }
2312 : :
2313 : : /* Initialize per-rcu_data variables for no-CBs CPUs. */
2314 : : static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2315 : : {
2316 : : rdp->nocb_tail = &rdp->nocb_head;
2317 : : init_waitqueue_head(&rdp->nocb_wq);
2318 : : }
2319 : :
2320 : : /* Create a kthread for each RCU flavor for each no-CBs CPU. */
2321 : : static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
2322 : : {
2323 : : int cpu;
2324 : : struct rcu_data *rdp;
2325 : : struct task_struct *t;
2326 : :
2327 : : if (rcu_nocb_mask == NULL)
2328 : : return;
2329 : : for_each_cpu(cpu, rcu_nocb_mask) {
2330 : : rdp = per_cpu_ptr(rsp->rda, cpu);
2331 : : t = kthread_run(rcu_nocb_kthread, rdp,
2332 : : "rcuo%c/%d", rsp->abbr, cpu);
2333 : : BUG_ON(IS_ERR(t));
2334 : : ACCESS_ONCE(rdp->nocb_kthread) = t;
2335 : : }
2336 : : }
2337 : :
2338 : : /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
2339 : : static bool init_nocb_callback_list(struct rcu_data *rdp)
2340 : : {
2341 : : if (rcu_nocb_mask == NULL ||
2342 : : !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask))
2343 : : return false;
2344 : : rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2345 : : return true;
2346 : : }
2347 : :
2348 : : #else /* #ifdef CONFIG_RCU_NOCB_CPU */
2349 : :
2350 : : static int rcu_nocb_needs_gp(struct rcu_state *rsp)
2351 : : {
2352 : : return 0;
2353 : : }
2354 : :
2355 : : static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
2356 : : {
2357 : : }
2358 : :
2359 : : static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
2360 : : {
2361 : : }
2362 : :
2363 : : static void rcu_init_one_nocb(struct rcu_node *rnp)
2364 : : {
2365 : : }
2366 : :
2367 : : static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2368 : : bool lazy)
2369 : : {
2370 : : return 0;
2371 : : }
2372 : :
2373 : : static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
2374 : : struct rcu_data *rdp)
2375 : : {
2376 : : return 0;
2377 : : }
2378 : :
2379 : : static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2380 : : {
2381 : : }
2382 : :
2383 : : static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
2384 : : {
2385 : : }
2386 : :
2387 : : static bool init_nocb_callback_list(struct rcu_data *rdp)
2388 : : {
2389 : : return false;
2390 : : }
2391 : :
2392 : : #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2393 : :
2394 : : /*
2395 : : * An adaptive-ticks CPU can potentially execute in kernel mode for an
2396 : : * arbitrarily long period of time with the scheduling-clock tick turned
2397 : : * off. RCU will be paying attention to this CPU because it is in the
2398 : : * kernel, but the CPU cannot be guaranteed to be executing the RCU state
2399 : : * machine because the scheduling-clock tick has been disabled. Therefore,
2400 : : * if an adaptive-ticks CPU is failing to respond to the current grace
2401 : : * period and has not be idle from an RCU perspective, kick it.
2402 : : */
2403 : : static void rcu_kick_nohz_cpu(int cpu)
2404 : : {
2405 : : #ifdef CONFIG_NO_HZ_FULL
2406 : : if (tick_nohz_full_cpu(cpu))
2407 : : smp_send_reschedule(cpu);
2408 : : #endif /* #ifdef CONFIG_NO_HZ_FULL */
2409 : : }
2410 : :
2411 : :
2412 : : #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
2413 : :
2414 : : /*
2415 : : * Define RCU flavor that holds sysidle state. This needs to be the
2416 : : * most active flavor of RCU.
2417 : : */
2418 : : #ifdef CONFIG_PREEMPT_RCU
2419 : : static struct rcu_state *rcu_sysidle_state = &rcu_preempt_state;
2420 : : #else /* #ifdef CONFIG_PREEMPT_RCU */
2421 : : static struct rcu_state *rcu_sysidle_state = &rcu_sched_state;
2422 : : #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
2423 : :
2424 : : static int full_sysidle_state; /* Current system-idle state. */
2425 : : #define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */
2426 : : #define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */
2427 : : #define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */
2428 : : #define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */
2429 : : #define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */
2430 : :
2431 : : /*
2432 : : * Invoked to note exit from irq or task transition to idle. Note that
2433 : : * usermode execution does -not- count as idle here! After all, we want
2434 : : * to detect full-system idle states, not RCU quiescent states and grace
2435 : : * periods. The caller must have disabled interrupts.
2436 : : */
2437 : : static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
2438 : : {
2439 : : unsigned long j;
2440 : :
2441 : : /* Adjust nesting, check for fully idle. */
2442 : : if (irq) {
2443 : : rdtp->dynticks_idle_nesting--;
2444 : : WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
2445 : : if (rdtp->dynticks_idle_nesting != 0)
2446 : : return; /* Still not fully idle. */
2447 : : } else {
2448 : : if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) ==
2449 : : DYNTICK_TASK_NEST_VALUE) {
2450 : : rdtp->dynticks_idle_nesting = 0;
2451 : : } else {
2452 : : rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE;
2453 : : WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
2454 : : return; /* Still not fully idle. */
2455 : : }
2456 : : }
2457 : :
2458 : : /* Record start of fully idle period. */
2459 : : j = jiffies;
2460 : : ACCESS_ONCE(rdtp->dynticks_idle_jiffies) = j;
2461 : : smp_mb__before_atomic_inc();
2462 : : atomic_inc(&rdtp->dynticks_idle);
2463 : : smp_mb__after_atomic_inc();
2464 : : WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1);
2465 : : }
2466 : :
2467 : : /*
2468 : : * Unconditionally force exit from full system-idle state. This is
2469 : : * invoked when a normal CPU exits idle, but must be called separately
2470 : : * for the timekeeping CPU (tick_do_timer_cpu). The reason for this
2471 : : * is that the timekeeping CPU is permitted to take scheduling-clock
2472 : : * interrupts while the system is in system-idle state, and of course
2473 : : * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock
2474 : : * interrupt from any other type of interrupt.
2475 : : */
2476 : : void rcu_sysidle_force_exit(void)
2477 : : {
2478 : : int oldstate = ACCESS_ONCE(full_sysidle_state);
2479 : : int newoldstate;
2480 : :
2481 : : /*
2482 : : * Each pass through the following loop attempts to exit full
2483 : : * system-idle state. If contention proves to be a problem,
2484 : : * a trylock-based contention tree could be used here.
2485 : : */
2486 : : while (oldstate > RCU_SYSIDLE_SHORT) {
2487 : : newoldstate = cmpxchg(&full_sysidle_state,
2488 : : oldstate, RCU_SYSIDLE_NOT);
2489 : : if (oldstate == newoldstate &&
2490 : : oldstate == RCU_SYSIDLE_FULL_NOTED) {
2491 : : rcu_kick_nohz_cpu(tick_do_timer_cpu);
2492 : : return; /* We cleared it, done! */
2493 : : }
2494 : : oldstate = newoldstate;
2495 : : }
2496 : : smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */
2497 : : }
2498 : :
2499 : : /*
2500 : : * Invoked to note entry to irq or task transition from idle. Note that
2501 : : * usermode execution does -not- count as idle here! The caller must
2502 : : * have disabled interrupts.
2503 : : */
2504 : : static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
2505 : : {
2506 : : /* Adjust nesting, check for already non-idle. */
2507 : : if (irq) {
2508 : : rdtp->dynticks_idle_nesting++;
2509 : : WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
2510 : : if (rdtp->dynticks_idle_nesting != 1)
2511 : : return; /* Already non-idle. */
2512 : : } else {
2513 : : /*
2514 : : * Allow for irq misnesting. Yes, it really is possible
2515 : : * to enter an irq handler then never leave it, and maybe
2516 : : * also vice versa. Handle both possibilities.
2517 : : */
2518 : : if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) {
2519 : : rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE;
2520 : : WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
2521 : : return; /* Already non-idle. */
2522 : : } else {
2523 : : rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE;
2524 : : }
2525 : : }
2526 : :
2527 : : /* Record end of idle period. */
2528 : : smp_mb__before_atomic_inc();
2529 : : atomic_inc(&rdtp->dynticks_idle);
2530 : : smp_mb__after_atomic_inc();
2531 : : WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1));
2532 : :
2533 : : /*
2534 : : * If we are the timekeeping CPU, we are permitted to be non-idle
2535 : : * during a system-idle state. This must be the case, because
2536 : : * the timekeeping CPU has to take scheduling-clock interrupts
2537 : : * during the time that the system is transitioning to full
2538 : : * system-idle state. This means that the timekeeping CPU must
2539 : : * invoke rcu_sysidle_force_exit() directly if it does anything
2540 : : * more than take a scheduling-clock interrupt.
2541 : : */
2542 : : if (smp_processor_id() == tick_do_timer_cpu)
2543 : : return;
2544 : :
2545 : : /* Update system-idle state: We are clearly no longer fully idle! */
2546 : : rcu_sysidle_force_exit();
2547 : : }
2548 : :
2549 : : /*
2550 : : * Check to see if the current CPU is idle. Note that usermode execution
2551 : : * does not count as idle. The caller must have disabled interrupts.
2552 : : */
2553 : : static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
2554 : : unsigned long *maxj)
2555 : : {
2556 : : int cur;
2557 : : unsigned long j;
2558 : : struct rcu_dynticks *rdtp = rdp->dynticks;
2559 : :
2560 : : /*
2561 : : * If some other CPU has already reported non-idle, if this is
2562 : : * not the flavor of RCU that tracks sysidle state, or if this
2563 : : * is an offline or the timekeeping CPU, nothing to do.
2564 : : */
2565 : : if (!*isidle || rdp->rsp != rcu_sysidle_state ||
2566 : : cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
2567 : : return;
2568 : : if (rcu_gp_in_progress(rdp->rsp))
2569 : : WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
2570 : :
2571 : : /* Pick up current idle and NMI-nesting counter and check. */
2572 : : cur = atomic_read(&rdtp->dynticks_idle);
2573 : : if (cur & 0x1) {
2574 : : *isidle = false; /* We are not idle! */
2575 : : return;
2576 : : }
2577 : : smp_mb(); /* Read counters before timestamps. */
2578 : :
2579 : : /* Pick up timestamps. */
2580 : : j = ACCESS_ONCE(rdtp->dynticks_idle_jiffies);
2581 : : /* If this CPU entered idle more recently, update maxj timestamp. */
2582 : : if (ULONG_CMP_LT(*maxj, j))
2583 : : *maxj = j;
2584 : : }
2585 : :
2586 : : /*
2587 : : * Is this the flavor of RCU that is handling full-system idle?
2588 : : */
2589 : : static bool is_sysidle_rcu_state(struct rcu_state *rsp)
2590 : : {
2591 : : return rsp == rcu_sysidle_state;
2592 : : }
2593 : :
2594 : : /*
2595 : : * Bind the grace-period kthread for the sysidle flavor of RCU to the
2596 : : * timekeeping CPU.
2597 : : */
2598 : : static void rcu_bind_gp_kthread(void)
2599 : : {
2600 : : int cpu = ACCESS_ONCE(tick_do_timer_cpu);
2601 : :
2602 : : if (cpu < 0 || cpu >= nr_cpu_ids)
2603 : : return;
2604 : : if (raw_smp_processor_id() != cpu)
2605 : : set_cpus_allowed_ptr(current, cpumask_of(cpu));
2606 : : }
2607 : :
2608 : : /*
2609 : : * Return a delay in jiffies based on the number of CPUs, rcu_node
2610 : : * leaf fanout, and jiffies tick rate. The idea is to allow larger
2611 : : * systems more time to transition to full-idle state in order to
2612 : : * avoid the cache thrashing that otherwise occur on the state variable.
2613 : : * Really small systems (less than a couple of tens of CPUs) should
2614 : : * instead use a single global atomically incremented counter, and later
2615 : : * versions of this will automatically reconfigure themselves accordingly.
2616 : : */
2617 : : static unsigned long rcu_sysidle_delay(void)
2618 : : {
2619 : : if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
2620 : : return 0;
2621 : : return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000);
2622 : : }
2623 : :
2624 : : /*
2625 : : * Advance the full-system-idle state. This is invoked when all of
2626 : : * the non-timekeeping CPUs are idle.
2627 : : */
2628 : : static void rcu_sysidle(unsigned long j)
2629 : : {
2630 : : /* Check the current state. */
2631 : : switch (ACCESS_ONCE(full_sysidle_state)) {
2632 : : case RCU_SYSIDLE_NOT:
2633 : :
2634 : : /* First time all are idle, so note a short idle period. */
2635 : : ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_SHORT;
2636 : : break;
2637 : :
2638 : : case RCU_SYSIDLE_SHORT:
2639 : :
2640 : : /*
2641 : : * Idle for a bit, time to advance to next state?
2642 : : * cmpxchg failure means race with non-idle, let them win.
2643 : : */
2644 : : if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
2645 : : (void)cmpxchg(&full_sysidle_state,
2646 : : RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG);
2647 : : break;
2648 : :
2649 : : case RCU_SYSIDLE_LONG:
2650 : :
2651 : : /*
2652 : : * Do an additional check pass before advancing to full.
2653 : : * cmpxchg failure means race with non-idle, let them win.
2654 : : */
2655 : : if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
2656 : : (void)cmpxchg(&full_sysidle_state,
2657 : : RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL);
2658 : : break;
2659 : :
2660 : : default:
2661 : : break;
2662 : : }
2663 : : }
2664 : :
2665 : : /*
2666 : : * Found a non-idle non-timekeeping CPU, so kick the system-idle state
2667 : : * back to the beginning.
2668 : : */
2669 : : static void rcu_sysidle_cancel(void)
2670 : : {
2671 : : smp_mb();
2672 : : ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT;
2673 : : }
2674 : :
2675 : : /*
2676 : : * Update the sysidle state based on the results of a force-quiescent-state
2677 : : * scan of the CPUs' dyntick-idle state.
2678 : : */
2679 : : static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
2680 : : unsigned long maxj, bool gpkt)
2681 : : {
2682 : : if (rsp != rcu_sysidle_state)
2683 : : return; /* Wrong flavor, ignore. */
2684 : : if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
2685 : : return; /* Running state machine from timekeeping CPU. */
2686 : : if (isidle)
2687 : : rcu_sysidle(maxj); /* More idle! */
2688 : : else
2689 : : rcu_sysidle_cancel(); /* Idle is over. */
2690 : : }
2691 : :
2692 : : /*
2693 : : * Wrapper for rcu_sysidle_report() when called from the grace-period
2694 : : * kthread's context.
2695 : : */
2696 : : static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
2697 : : unsigned long maxj)
2698 : : {
2699 : : rcu_sysidle_report(rsp, isidle, maxj, true);
2700 : : }
2701 : :
2702 : : /* Callback and function for forcing an RCU grace period. */
2703 : : struct rcu_sysidle_head {
2704 : : struct rcu_head rh;
2705 : : int inuse;
2706 : : };
2707 : :
2708 : : static void rcu_sysidle_cb(struct rcu_head *rhp)
2709 : : {
2710 : : struct rcu_sysidle_head *rshp;
2711 : :
2712 : : /*
2713 : : * The following memory barrier is needed to replace the
2714 : : * memory barriers that would normally be in the memory
2715 : : * allocator.
2716 : : */
2717 : : smp_mb(); /* grace period precedes setting inuse. */
2718 : :
2719 : : rshp = container_of(rhp, struct rcu_sysidle_head, rh);
2720 : : ACCESS_ONCE(rshp->inuse) = 0;
2721 : : }
2722 : :
2723 : : /*
2724 : : * Check to see if the system is fully idle, other than the timekeeping CPU.
2725 : : * The caller must have disabled interrupts.
2726 : : */
2727 : : bool rcu_sys_is_idle(void)
2728 : : {
2729 : : static struct rcu_sysidle_head rsh;
2730 : : int rss = ACCESS_ONCE(full_sysidle_state);
2731 : :
2732 : : if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu))
2733 : : return false;
2734 : :
2735 : : /* Handle small-system case by doing a full scan of CPUs. */
2736 : : if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) {
2737 : : int oldrss = rss - 1;
2738 : :
2739 : : /*
2740 : : * One pass to advance to each state up to _FULL.
2741 : : * Give up if any pass fails to advance the state.
2742 : : */
2743 : : while (rss < RCU_SYSIDLE_FULL && oldrss < rss) {
2744 : : int cpu;
2745 : : bool isidle = true;
2746 : : unsigned long maxj = jiffies - ULONG_MAX / 4;
2747 : : struct rcu_data *rdp;
2748 : :
2749 : : /* Scan all the CPUs looking for nonidle CPUs. */
2750 : : for_each_possible_cpu(cpu) {
2751 : : rdp = per_cpu_ptr(rcu_sysidle_state->rda, cpu);
2752 : : rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
2753 : : if (!isidle)
2754 : : break;
2755 : : }
2756 : : rcu_sysidle_report(rcu_sysidle_state,
2757 : : isidle, maxj, false);
2758 : : oldrss = rss;
2759 : : rss = ACCESS_ONCE(full_sysidle_state);
2760 : : }
2761 : : }
2762 : :
2763 : : /* If this is the first observation of an idle period, record it. */
2764 : : if (rss == RCU_SYSIDLE_FULL) {
2765 : : rss = cmpxchg(&full_sysidle_state,
2766 : : RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED);
2767 : : return rss == RCU_SYSIDLE_FULL;
2768 : : }
2769 : :
2770 : : smp_mb(); /* ensure rss load happens before later caller actions. */
2771 : :
2772 : : /* If already fully idle, tell the caller (in case of races). */
2773 : : if (rss == RCU_SYSIDLE_FULL_NOTED)
2774 : : return true;
2775 : :
2776 : : /*
2777 : : * If we aren't there yet, and a grace period is not in flight,
2778 : : * initiate a grace period. Either way, tell the caller that
2779 : : * we are not there yet. We use an xchg() rather than an assignment
2780 : : * to make up for the memory barriers that would otherwise be
2781 : : * provided by the memory allocator.
2782 : : */
2783 : : if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
2784 : : !rcu_gp_in_progress(rcu_sysidle_state) &&
2785 : : !rsh.inuse && xchg(&rsh.inuse, 1) == 0)
2786 : : call_rcu(&rsh.rh, rcu_sysidle_cb);
2787 : : return false;
2788 : : }
2789 : :
2790 : : /*
2791 : : * Initialize dynticks sysidle state for CPUs coming online.
2792 : : */
2793 : : static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
2794 : : {
2795 : : rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE;
2796 : : }
2797 : :
2798 : : #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
2799 : :
2800 : : static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
2801 : : {
2802 : : }
2803 : :
2804 : : static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
2805 : : {
2806 : : }
2807 : :
2808 : : static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
2809 : : unsigned long *maxj)
2810 : : {
2811 : : }
2812 : :
2813 : : static bool is_sysidle_rcu_state(struct rcu_state *rsp)
2814 : : {
2815 : : return false;
2816 : : }
2817 : :
2818 : : static void rcu_bind_gp_kthread(void)
2819 : : {
2820 : : }
2821 : :
2822 : : static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
2823 : : unsigned long maxj)
2824 : : {
2825 : : }
2826 : :
2827 : : static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
2828 : : {
2829 : : }
2830 : :
2831 : : #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
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