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-rw-r--r--kernel/rcupreempt.c1539
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diff --git a/kernel/rcupreempt.c b/kernel/rcupreempt.c
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1/*
2 * Read-Copy Update mechanism for mutual exclusion, realtime implementation
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
17 *
18 * Copyright IBM Corporation, 2006
19 *
20 * Authors: Paul E. McKenney <paulmck@us.ibm.com>
21 * With thanks to Esben Nielsen, Bill Huey, and Ingo Molnar
22 * for pushing me away from locks and towards counters, and
23 * to Suparna Bhattacharya for pushing me completely away
24 * from atomic instructions on the read side.
25 *
26 * - Added handling of Dynamic Ticks
27 * Copyright 2007 - Paul E. Mckenney <paulmck@us.ibm.com>
28 * - Steven Rostedt <srostedt@redhat.com>
29 *
30 * Papers: http://www.rdrop.com/users/paulmck/RCU
31 *
32 * Design Document: http://lwn.net/Articles/253651/
33 *
34 * For detailed explanation of Read-Copy Update mechanism see -
35 * Documentation/RCU/ *.txt
36 *
37 */
38#include <linux/types.h>
39#include <linux/kernel.h>
40#include <linux/init.h>
41#include <linux/spinlock.h>
42#include <linux/smp.h>
43#include <linux/rcupdate.h>
44#include <linux/interrupt.h>
45#include <linux/sched.h>
46#include <asm/atomic.h>
47#include <linux/bitops.h>
48#include <linux/module.h>
49#include <linux/kthread.h>
50#include <linux/completion.h>
51#include <linux/moduleparam.h>
52#include <linux/percpu.h>
53#include <linux/notifier.h>
54#include <linux/cpu.h>
55#include <linux/random.h>
56#include <linux/delay.h>
57#include <linux/cpumask.h>
58#include <linux/rcupreempt_trace.h>
59#include <asm/byteorder.h>
60
61/*
62 * PREEMPT_RCU data structures.
63 */
64
65/*
66 * GP_STAGES specifies the number of times the state machine has
67 * to go through the all the rcu_try_flip_states (see below)
68 * in a single Grace Period.
69 *
70 * GP in GP_STAGES stands for Grace Period ;)
71 */
72#define GP_STAGES 2
73struct rcu_data {
74 spinlock_t lock; /* Protect rcu_data fields. */
75 long completed; /* Number of last completed batch. */
76 int waitlistcount;
77 struct rcu_head *nextlist;
78 struct rcu_head **nexttail;
79 struct rcu_head *waitlist[GP_STAGES];
80 struct rcu_head **waittail[GP_STAGES];
81 struct rcu_head *donelist; /* from waitlist & waitschedlist */
82 struct rcu_head **donetail;
83 long rcu_flipctr[2];
84 struct rcu_head *nextschedlist;
85 struct rcu_head **nextschedtail;
86 struct rcu_head *waitschedlist;
87 struct rcu_head **waitschedtail;
88 int rcu_sched_sleeping;
89#ifdef CONFIG_RCU_TRACE
90 struct rcupreempt_trace trace;
91#endif /* #ifdef CONFIG_RCU_TRACE */
92};
93
94/*
95 * States for rcu_try_flip() and friends.
96 */
97
98enum rcu_try_flip_states {
99
100 /*
101 * Stay here if nothing is happening. Flip the counter if somthing
102 * starts happening. Denoted by "I"
103 */
104 rcu_try_flip_idle_state,
105
106 /*
107 * Wait here for all CPUs to notice that the counter has flipped. This
108 * prevents the old set of counters from ever being incremented once
109 * we leave this state, which in turn is necessary because we cannot
110 * test any individual counter for zero -- we can only check the sum.
111 * Denoted by "A".
112 */
113 rcu_try_flip_waitack_state,
114
115 /*
116 * Wait here for the sum of the old per-CPU counters to reach zero.
117 * Denoted by "Z".
118 */
119 rcu_try_flip_waitzero_state,
120
121 /*
122 * Wait here for each of the other CPUs to execute a memory barrier.
123 * This is necessary to ensure that these other CPUs really have
124 * completed executing their RCU read-side critical sections, despite
125 * their CPUs wildly reordering memory. Denoted by "M".
126 */
127 rcu_try_flip_waitmb_state,
128};
129
130/*
131 * States for rcu_ctrlblk.rcu_sched_sleep.
132 */
133
134enum rcu_sched_sleep_states {
135 rcu_sched_not_sleeping, /* Not sleeping, callbacks need GP. */
136 rcu_sched_sleep_prep, /* Thinking of sleeping, rechecking. */
137 rcu_sched_sleeping, /* Sleeping, awaken if GP needed. */
138};
139
140struct rcu_ctrlblk {
141 spinlock_t fliplock; /* Protect state-machine transitions. */
142 long completed; /* Number of last completed batch. */
143 enum rcu_try_flip_states rcu_try_flip_state; /* The current state of
144 the rcu state machine */
145 spinlock_t schedlock; /* Protect rcu_sched sleep state. */
146 enum rcu_sched_sleep_states sched_sleep; /* rcu_sched state. */
147 wait_queue_head_t sched_wq; /* Place for rcu_sched to sleep. */
148};
149
150struct rcu_dyntick_sched {
151 int dynticks;
152 int dynticks_snap;
153 int sched_qs;
154 int sched_qs_snap;
155 int sched_dynticks_snap;
156};
157
158static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_dyntick_sched, rcu_dyntick_sched) = {
159 .dynticks = 1,
160};
161
162void rcu_qsctr_inc(int cpu)
163{
164 struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
165
166 rdssp->sched_qs++;
167}
168
169#ifdef CONFIG_NO_HZ
170
171void rcu_enter_nohz(void)
172{
173 static DEFINE_RATELIMIT_STATE(rs, 10 * HZ, 1);
174
175 smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
176 __get_cpu_var(rcu_dyntick_sched).dynticks++;
177 WARN_ON_RATELIMIT(__get_cpu_var(rcu_dyntick_sched).dynticks & 0x1, &rs);
178}
179
180void rcu_exit_nohz(void)
181{
182 static DEFINE_RATELIMIT_STATE(rs, 10 * HZ, 1);
183
184 __get_cpu_var(rcu_dyntick_sched).dynticks++;
185 smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
186 WARN_ON_RATELIMIT(!(__get_cpu_var(rcu_dyntick_sched).dynticks & 0x1),
187 &rs);
188}
189
190#endif /* CONFIG_NO_HZ */
191
192
193static DEFINE_PER_CPU(struct rcu_data, rcu_data);
194
195static struct rcu_ctrlblk rcu_ctrlblk = {
196 .fliplock = __SPIN_LOCK_UNLOCKED(rcu_ctrlblk.fliplock),
197 .completed = 0,
198 .rcu_try_flip_state = rcu_try_flip_idle_state,
199 .schedlock = __SPIN_LOCK_UNLOCKED(rcu_ctrlblk.schedlock),
200 .sched_sleep = rcu_sched_not_sleeping,
201 .sched_wq = __WAIT_QUEUE_HEAD_INITIALIZER(rcu_ctrlblk.sched_wq),
202};
203
204static struct task_struct *rcu_sched_grace_period_task;
205
206#ifdef CONFIG_RCU_TRACE
207static char *rcu_try_flip_state_names[] =
208 { "idle", "waitack", "waitzero", "waitmb" };
209#endif /* #ifdef CONFIG_RCU_TRACE */
210
211static DECLARE_BITMAP(rcu_cpu_online_map, NR_CPUS) __read_mostly
212 = CPU_BITS_NONE;
213
214/*
215 * Enum and per-CPU flag to determine when each CPU has seen
216 * the most recent counter flip.
217 */
218
219enum rcu_flip_flag_values {
220 rcu_flip_seen, /* Steady/initial state, last flip seen. */
221 /* Only GP detector can update. */
222 rcu_flipped /* Flip just completed, need confirmation. */
223 /* Only corresponding CPU can update. */
224};
225static DEFINE_PER_CPU_SHARED_ALIGNED(enum rcu_flip_flag_values, rcu_flip_flag)
226 = rcu_flip_seen;
227
228/*
229 * Enum and per-CPU flag to determine when each CPU has executed the
230 * needed memory barrier to fence in memory references from its last RCU
231 * read-side critical section in the just-completed grace period.
232 */
233
234enum rcu_mb_flag_values {
235 rcu_mb_done, /* Steady/initial state, no mb()s required. */
236 /* Only GP detector can update. */
237 rcu_mb_needed /* Flip just completed, need an mb(). */
238 /* Only corresponding CPU can update. */
239};
240static DEFINE_PER_CPU_SHARED_ALIGNED(enum rcu_mb_flag_values, rcu_mb_flag)
241 = rcu_mb_done;
242
243/*
244 * RCU_DATA_ME: find the current CPU's rcu_data structure.
245 * RCU_DATA_CPU: find the specified CPU's rcu_data structure.
246 */
247#define RCU_DATA_ME() (&__get_cpu_var(rcu_data))
248#define RCU_DATA_CPU(cpu) (&per_cpu(rcu_data, cpu))
249
250/*
251 * Helper macro for tracing when the appropriate rcu_data is not
252 * cached in a local variable, but where the CPU number is so cached.
253 */
254#define RCU_TRACE_CPU(f, cpu) RCU_TRACE(f, &(RCU_DATA_CPU(cpu)->trace));
255
256/*
257 * Helper macro for tracing when the appropriate rcu_data is not
258 * cached in a local variable.
259 */
260#define RCU_TRACE_ME(f) RCU_TRACE(f, &(RCU_DATA_ME()->trace));
261
262/*
263 * Helper macro for tracing when the appropriate rcu_data is pointed
264 * to by a local variable.
265 */
266#define RCU_TRACE_RDP(f, rdp) RCU_TRACE(f, &((rdp)->trace));
267
268#define RCU_SCHED_BATCH_TIME (HZ / 50)
269
270/*
271 * Return the number of RCU batches processed thus far. Useful
272 * for debug and statistics.
273 */
274long rcu_batches_completed(void)
275{
276 return rcu_ctrlblk.completed;
277}
278EXPORT_SYMBOL_GPL(rcu_batches_completed);
279
280void __rcu_read_lock(void)
281{
282 int idx;
283 struct task_struct *t = current;
284 int nesting;
285
286 nesting = ACCESS_ONCE(t->rcu_read_lock_nesting);
287 if (nesting != 0) {
288
289 /* An earlier rcu_read_lock() covers us, just count it. */
290
291 t->rcu_read_lock_nesting = nesting + 1;
292
293 } else {
294 unsigned long flags;
295
296 /*
297 * We disable interrupts for the following reasons:
298 * - If we get scheduling clock interrupt here, and we
299 * end up acking the counter flip, it's like a promise
300 * that we will never increment the old counter again.
301 * Thus we will break that promise if that
302 * scheduling clock interrupt happens between the time
303 * we pick the .completed field and the time that we
304 * increment our counter.
305 *
306 * - We don't want to be preempted out here.
307 *
308 * NMIs can still occur, of course, and might themselves
309 * contain rcu_read_lock().
310 */
311
312 local_irq_save(flags);
313
314 /*
315 * Outermost nesting of rcu_read_lock(), so increment
316 * the current counter for the current CPU. Use volatile
317 * casts to prevent the compiler from reordering.
318 */
319
320 idx = ACCESS_ONCE(rcu_ctrlblk.completed) & 0x1;
321 ACCESS_ONCE(RCU_DATA_ME()->rcu_flipctr[idx])++;
322
323 /*
324 * Now that the per-CPU counter has been incremented, we
325 * are protected from races with rcu_read_lock() invoked
326 * from NMI handlers on this CPU. We can therefore safely
327 * increment the nesting counter, relieving further NMIs
328 * of the need to increment the per-CPU counter.
329 */
330
331 ACCESS_ONCE(t->rcu_read_lock_nesting) = nesting + 1;
332
333 /*
334 * Now that we have preventing any NMIs from storing
335 * to the ->rcu_flipctr_idx, we can safely use it to
336 * remember which counter to decrement in the matching
337 * rcu_read_unlock().
338 */
339
340 ACCESS_ONCE(t->rcu_flipctr_idx) = idx;
341 local_irq_restore(flags);
342 }
343}
344EXPORT_SYMBOL_GPL(__rcu_read_lock);
345
346void __rcu_read_unlock(void)
347{
348 int idx;
349 struct task_struct *t = current;
350 int nesting;
351
352 nesting = ACCESS_ONCE(t->rcu_read_lock_nesting);
353 if (nesting > 1) {
354
355 /*
356 * We are still protected by the enclosing rcu_read_lock(),
357 * so simply decrement the counter.
358 */
359
360 t->rcu_read_lock_nesting = nesting - 1;
361
362 } else {
363 unsigned long flags;
364
365 /*
366 * Disable local interrupts to prevent the grace-period
367 * detection state machine from seeing us half-done.
368 * NMIs can still occur, of course, and might themselves
369 * contain rcu_read_lock() and rcu_read_unlock().
370 */
371
372 local_irq_save(flags);
373
374 /*
375 * Outermost nesting of rcu_read_unlock(), so we must
376 * decrement the current counter for the current CPU.
377 * This must be done carefully, because NMIs can
378 * occur at any point in this code, and any rcu_read_lock()
379 * and rcu_read_unlock() pairs in the NMI handlers
380 * must interact non-destructively with this code.
381 * Lots of volatile casts, and -very- careful ordering.
382 *
383 * Changes to this code, including this one, must be
384 * inspected, validated, and tested extremely carefully!!!
385 */
386
387 /*
388 * First, pick up the index.
389 */
390
391 idx = ACCESS_ONCE(t->rcu_flipctr_idx);
392
393 /*
394 * Now that we have fetched the counter index, it is
395 * safe to decrement the per-task RCU nesting counter.
396 * After this, any interrupts or NMIs will increment and
397 * decrement the per-CPU counters.
398 */
399 ACCESS_ONCE(t->rcu_read_lock_nesting) = nesting - 1;
400
401 /*
402 * It is now safe to decrement this task's nesting count.
403 * NMIs that occur after this statement will route their
404 * rcu_read_lock() calls through this "else" clause, and
405 * will thus start incrementing the per-CPU counter on
406 * their own. They will also clobber ->rcu_flipctr_idx,
407 * but that is OK, since we have already fetched it.
408 */
409
410 ACCESS_ONCE(RCU_DATA_ME()->rcu_flipctr[idx])--;
411 local_irq_restore(flags);
412 }
413}
414EXPORT_SYMBOL_GPL(__rcu_read_unlock);
415
416/*
417 * If a global counter flip has occurred since the last time that we
418 * advanced callbacks, advance them. Hardware interrupts must be
419 * disabled when calling this function.
420 */
421static void __rcu_advance_callbacks(struct rcu_data *rdp)
422{
423 int cpu;
424 int i;
425 int wlc = 0;
426
427 if (rdp->completed != rcu_ctrlblk.completed) {
428 if (rdp->waitlist[GP_STAGES - 1] != NULL) {
429 *rdp->donetail = rdp->waitlist[GP_STAGES - 1];
430 rdp->donetail = rdp->waittail[GP_STAGES - 1];
431 RCU_TRACE_RDP(rcupreempt_trace_move2done, rdp);
432 }
433 for (i = GP_STAGES - 2; i >= 0; i--) {
434 if (rdp->waitlist[i] != NULL) {
435 rdp->waitlist[i + 1] = rdp->waitlist[i];
436 rdp->waittail[i + 1] = rdp->waittail[i];
437 wlc++;
438 } else {
439 rdp->waitlist[i + 1] = NULL;
440 rdp->waittail[i + 1] =
441 &rdp->waitlist[i + 1];
442 }
443 }
444 if (rdp->nextlist != NULL) {
445 rdp->waitlist[0] = rdp->nextlist;
446 rdp->waittail[0] = rdp->nexttail;
447 wlc++;
448 rdp->nextlist = NULL;
449 rdp->nexttail = &rdp->nextlist;
450 RCU_TRACE_RDP(rcupreempt_trace_move2wait, rdp);
451 } else {
452 rdp->waitlist[0] = NULL;
453 rdp->waittail[0] = &rdp->waitlist[0];
454 }
455 rdp->waitlistcount = wlc;
456 rdp->completed = rcu_ctrlblk.completed;
457 }
458
459 /*
460 * Check to see if this CPU needs to report that it has seen
461 * the most recent counter flip, thereby declaring that all
462 * subsequent rcu_read_lock() invocations will respect this flip.
463 */
464
465 cpu = raw_smp_processor_id();
466 if (per_cpu(rcu_flip_flag, cpu) == rcu_flipped) {
467 smp_mb(); /* Subsequent counter accesses must see new value */
468 per_cpu(rcu_flip_flag, cpu) = rcu_flip_seen;
469 smp_mb(); /* Subsequent RCU read-side critical sections */
470 /* seen -after- acknowledgement. */
471 }
472}
473
474#ifdef CONFIG_NO_HZ
475static DEFINE_PER_CPU(int, rcu_update_flag);
476
477/**
478 * rcu_irq_enter - Called from Hard irq handlers and NMI/SMI.
479 *
480 * If the CPU was idle with dynamic ticks active, this updates the
481 * rcu_dyntick_sched.dynticks to let the RCU handling know that the
482 * CPU is active.
483 */
484void rcu_irq_enter(void)
485{
486 int cpu = smp_processor_id();
487 struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
488
489 if (per_cpu(rcu_update_flag, cpu))
490 per_cpu(rcu_update_flag, cpu)++;
491
492 /*
493 * Only update if we are coming from a stopped ticks mode
494 * (rcu_dyntick_sched.dynticks is even).
495 */
496 if (!in_interrupt() &&
497 (rdssp->dynticks & 0x1) == 0) {
498 /*
499 * The following might seem like we could have a race
500 * with NMI/SMIs. But this really isn't a problem.
501 * Here we do a read/modify/write, and the race happens
502 * when an NMI/SMI comes in after the read and before
503 * the write. But NMI/SMIs will increment this counter
504 * twice before returning, so the zero bit will not
505 * be corrupted by the NMI/SMI which is the most important
506 * part.
507 *
508 * The only thing is that we would bring back the counter
509 * to a postion that it was in during the NMI/SMI.
510 * But the zero bit would be set, so the rest of the
511 * counter would again be ignored.
512 *
513 * On return from the IRQ, the counter may have the zero
514 * bit be 0 and the counter the same as the return from
515 * the NMI/SMI. If the state machine was so unlucky to
516 * see that, it still doesn't matter, since all
517 * RCU read-side critical sections on this CPU would
518 * have already completed.
519 */
520 rdssp->dynticks++;
521 /*
522 * The following memory barrier ensures that any
523 * rcu_read_lock() primitives in the irq handler
524 * are seen by other CPUs to follow the above
525 * increment to rcu_dyntick_sched.dynticks. This is
526 * required in order for other CPUs to correctly
527 * determine when it is safe to advance the RCU
528 * grace-period state machine.
529 */
530 smp_mb(); /* see above block comment. */
531 /*
532 * Since we can't determine the dynamic tick mode from
533 * the rcu_dyntick_sched.dynticks after this routine,
534 * we use a second flag to acknowledge that we came
535 * from an idle state with ticks stopped.
536 */
537 per_cpu(rcu_update_flag, cpu)++;
538 /*
539 * If we take an NMI/SMI now, they will also increment
540 * the rcu_update_flag, and will not update the
541 * rcu_dyntick_sched.dynticks on exit. That is for
542 * this IRQ to do.
543 */
544 }
545}
546
547/**
548 * rcu_irq_exit - Called from exiting Hard irq context.
549 *
550 * If the CPU was idle with dynamic ticks active, update the
551 * rcu_dyntick_sched.dynticks to put let the RCU handling be
552 * aware that the CPU is going back to idle with no ticks.
553 */
554void rcu_irq_exit(void)
555{
556 int cpu = smp_processor_id();
557 struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
558
559 /*
560 * rcu_update_flag is set if we interrupted the CPU
561 * when it was idle with ticks stopped.
562 * Once this occurs, we keep track of interrupt nesting
563 * because a NMI/SMI could also come in, and we still
564 * only want the IRQ that started the increment of the
565 * rcu_dyntick_sched.dynticks to be the one that modifies
566 * it on exit.
567 */
568 if (per_cpu(rcu_update_flag, cpu)) {
569 if (--per_cpu(rcu_update_flag, cpu))
570 return;
571
572 /* This must match the interrupt nesting */
573 WARN_ON(in_interrupt());
574
575 /*
576 * If an NMI/SMI happens now we are still
577 * protected by the rcu_dyntick_sched.dynticks being odd.
578 */
579
580 /*
581 * The following memory barrier ensures that any
582 * rcu_read_unlock() primitives in the irq handler
583 * are seen by other CPUs to preceed the following
584 * increment to rcu_dyntick_sched.dynticks. This
585 * is required in order for other CPUs to determine
586 * when it is safe to advance the RCU grace-period
587 * state machine.
588 */
589 smp_mb(); /* see above block comment. */
590 rdssp->dynticks++;
591 WARN_ON(rdssp->dynticks & 0x1);
592 }
593}
594
595void rcu_nmi_enter(void)
596{
597 rcu_irq_enter();
598}
599
600void rcu_nmi_exit(void)
601{
602 rcu_irq_exit();
603}
604
605static void dyntick_save_progress_counter(int cpu)
606{
607 struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
608
609 rdssp->dynticks_snap = rdssp->dynticks;
610}
611
612static inline int
613rcu_try_flip_waitack_needed(int cpu)
614{
615 long curr;
616 long snap;
617 struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
618
619 curr = rdssp->dynticks;
620 snap = rdssp->dynticks_snap;
621 smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
622
623 /*
624 * If the CPU remained in dynticks mode for the entire time
625 * and didn't take any interrupts, NMIs, SMIs, or whatever,
626 * then it cannot be in the middle of an rcu_read_lock(), so
627 * the next rcu_read_lock() it executes must use the new value
628 * of the counter. So we can safely pretend that this CPU
629 * already acknowledged the counter.
630 */
631
632 if ((curr == snap) && ((curr & 0x1) == 0))
633 return 0;
634
635 /*
636 * If the CPU passed through or entered a dynticks idle phase with
637 * no active irq handlers, then, as above, we can safely pretend
638 * that this CPU already acknowledged the counter.
639 */
640
641 if ((curr - snap) > 2 || (curr & 0x1) == 0)
642 return 0;
643
644 /* We need this CPU to explicitly acknowledge the counter flip. */
645
646 return 1;
647}
648
649static inline int
650rcu_try_flip_waitmb_needed(int cpu)
651{
652 long curr;
653 long snap;
654 struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
655
656 curr = rdssp->dynticks;
657 snap = rdssp->dynticks_snap;
658 smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
659
660 /*
661 * If the CPU remained in dynticks mode for the entire time
662 * and didn't take any interrupts, NMIs, SMIs, or whatever,
663 * then it cannot have executed an RCU read-side critical section
664 * during that time, so there is no need for it to execute a
665 * memory barrier.
666 */
667
668 if ((curr == snap) && ((curr & 0x1) == 0))
669 return 0;
670
671 /*
672 * If the CPU either entered or exited an outermost interrupt,
673 * SMI, NMI, or whatever handler, then we know that it executed
674 * a memory barrier when doing so. So we don't need another one.
675 */
676 if (curr != snap)
677 return 0;
678
679 /* We need the CPU to execute a memory barrier. */
680
681 return 1;
682}
683
684static void dyntick_save_progress_counter_sched(int cpu)
685{
686 struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
687
688 rdssp->sched_dynticks_snap = rdssp->dynticks;
689}
690
691static int rcu_qsctr_inc_needed_dyntick(int cpu)
692{
693 long curr;
694 long snap;
695 struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
696
697 curr = rdssp->dynticks;
698 snap = rdssp->sched_dynticks_snap;
699 smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
700
701 /*
702 * If the CPU remained in dynticks mode for the entire time
703 * and didn't take any interrupts, NMIs, SMIs, or whatever,
704 * then it cannot be in the middle of an rcu_read_lock(), so
705 * the next rcu_read_lock() it executes must use the new value
706 * of the counter. Therefore, this CPU has been in a quiescent
707 * state the entire time, and we don't need to wait for it.
708 */
709
710 if ((curr == snap) && ((curr & 0x1) == 0))
711 return 0;
712
713 /*
714 * If the CPU passed through or entered a dynticks idle phase with
715 * no active irq handlers, then, as above, this CPU has already
716 * passed through a quiescent state.
717 */
718
719 if ((curr - snap) > 2 || (snap & 0x1) == 0)
720 return 0;
721
722 /* We need this CPU to go through a quiescent state. */
723
724 return 1;
725}
726
727#else /* !CONFIG_NO_HZ */
728
729# define dyntick_save_progress_counter(cpu) do { } while (0)
730# define rcu_try_flip_waitack_needed(cpu) (1)
731# define rcu_try_flip_waitmb_needed(cpu) (1)
732
733# define dyntick_save_progress_counter_sched(cpu) do { } while (0)
734# define rcu_qsctr_inc_needed_dyntick(cpu) (1)
735
736#endif /* CONFIG_NO_HZ */
737
738static void save_qsctr_sched(int cpu)
739{
740 struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
741
742 rdssp->sched_qs_snap = rdssp->sched_qs;
743}
744
745static inline int rcu_qsctr_inc_needed(int cpu)
746{
747 struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
748
749 /*
750 * If there has been a quiescent state, no more need to wait
751 * on this CPU.
752 */
753
754 if (rdssp->sched_qs != rdssp->sched_qs_snap) {
755 smp_mb(); /* force ordering with cpu entering schedule(). */
756 return 0;
757 }
758
759 /* We need this CPU to go through a quiescent state. */
760
761 return 1;
762}
763
764/*
765 * Get here when RCU is idle. Decide whether we need to
766 * move out of idle state, and return non-zero if so.
767 * "Straightforward" approach for the moment, might later
768 * use callback-list lengths, grace-period duration, or
769 * some such to determine when to exit idle state.
770 * Might also need a pre-idle test that does not acquire
771 * the lock, but let's get the simple case working first...
772 */
773
774static int
775rcu_try_flip_idle(void)
776{
777 int cpu;
778
779 RCU_TRACE_ME(rcupreempt_trace_try_flip_i1);
780 if (!rcu_pending(smp_processor_id())) {
781 RCU_TRACE_ME(rcupreempt_trace_try_flip_ie1);
782 return 0;
783 }
784
785 /*
786 * Do the flip.
787 */
788
789 RCU_TRACE_ME(rcupreempt_trace_try_flip_g1);
790 rcu_ctrlblk.completed++; /* stands in for rcu_try_flip_g2 */
791
792 /*
793 * Need a memory barrier so that other CPUs see the new
794 * counter value before they see the subsequent change of all
795 * the rcu_flip_flag instances to rcu_flipped.
796 */
797
798 smp_mb(); /* see above block comment. */
799
800 /* Now ask each CPU for acknowledgement of the flip. */
801
802 for_each_cpu(cpu, to_cpumask(rcu_cpu_online_map)) {
803 per_cpu(rcu_flip_flag, cpu) = rcu_flipped;
804 dyntick_save_progress_counter(cpu);
805 }
806
807 return 1;
808}
809
810/*
811 * Wait for CPUs to acknowledge the flip.
812 */
813
814static int
815rcu_try_flip_waitack(void)
816{
817 int cpu;
818
819 RCU_TRACE_ME(rcupreempt_trace_try_flip_a1);
820 for_each_cpu(cpu, to_cpumask(rcu_cpu_online_map))
821 if (rcu_try_flip_waitack_needed(cpu) &&
822 per_cpu(rcu_flip_flag, cpu) != rcu_flip_seen) {
823 RCU_TRACE_ME(rcupreempt_trace_try_flip_ae1);
824 return 0;
825 }
826
827 /*
828 * Make sure our checks above don't bleed into subsequent
829 * waiting for the sum of the counters to reach zero.
830 */
831
832 smp_mb(); /* see above block comment. */
833 RCU_TRACE_ME(rcupreempt_trace_try_flip_a2);
834 return 1;
835}
836
837/*
838 * Wait for collective ``last'' counter to reach zero,
839 * then tell all CPUs to do an end-of-grace-period memory barrier.
840 */
841
842static int
843rcu_try_flip_waitzero(void)
844{
845 int cpu;
846 int lastidx = !(rcu_ctrlblk.completed & 0x1);
847 int sum = 0;
848
849 /* Check to see if the sum of the "last" counters is zero. */
850
851 RCU_TRACE_ME(rcupreempt_trace_try_flip_z1);
852 for_each_cpu(cpu, to_cpumask(rcu_cpu_online_map))
853 sum += RCU_DATA_CPU(cpu)->rcu_flipctr[lastidx];
854 if (sum != 0) {
855 RCU_TRACE_ME(rcupreempt_trace_try_flip_ze1);
856 return 0;
857 }
858
859 /*
860 * This ensures that the other CPUs see the call for
861 * memory barriers -after- the sum to zero has been
862 * detected here
863 */
864 smp_mb(); /* ^^^^^^^^^^^^ */
865
866 /* Call for a memory barrier from each CPU. */
867 for_each_cpu(cpu, to_cpumask(rcu_cpu_online_map)) {
868 per_cpu(rcu_mb_flag, cpu) = rcu_mb_needed;
869 dyntick_save_progress_counter(cpu);
870 }
871
872 RCU_TRACE_ME(rcupreempt_trace_try_flip_z2);
873 return 1;
874}
875
876/*
877 * Wait for all CPUs to do their end-of-grace-period memory barrier.
878 * Return 0 once all CPUs have done so.
879 */
880
881static int
882rcu_try_flip_waitmb(void)
883{
884 int cpu;
885
886 RCU_TRACE_ME(rcupreempt_trace_try_flip_m1);
887 for_each_cpu(cpu, to_cpumask(rcu_cpu_online_map))
888 if (rcu_try_flip_waitmb_needed(cpu) &&
889 per_cpu(rcu_mb_flag, cpu) != rcu_mb_done) {
890 RCU_TRACE_ME(rcupreempt_trace_try_flip_me1);
891 return 0;
892 }
893
894 smp_mb(); /* Ensure that the above checks precede any following flip. */
895 RCU_TRACE_ME(rcupreempt_trace_try_flip_m2);
896 return 1;
897}
898
899/*
900 * Attempt a single flip of the counters. Remember, a single flip does
901 * -not- constitute a grace period. Instead, the interval between
902 * at least GP_STAGES consecutive flips is a grace period.
903 *
904 * If anyone is nuts enough to run this CONFIG_PREEMPT_RCU implementation
905 * on a large SMP, they might want to use a hierarchical organization of
906 * the per-CPU-counter pairs.
907 */
908static void rcu_try_flip(void)
909{
910 unsigned long flags;
911
912 RCU_TRACE_ME(rcupreempt_trace_try_flip_1);
913 if (unlikely(!spin_trylock_irqsave(&rcu_ctrlblk.fliplock, flags))) {
914 RCU_TRACE_ME(rcupreempt_trace_try_flip_e1);
915 return;
916 }
917
918 /*
919 * Take the next transition(s) through the RCU grace-period
920 * flip-counter state machine.
921 */
922
923 switch (rcu_ctrlblk.rcu_try_flip_state) {
924 case rcu_try_flip_idle_state:
925 if (rcu_try_flip_idle())
926 rcu_ctrlblk.rcu_try_flip_state =
927 rcu_try_flip_waitack_state;
928 break;
929 case rcu_try_flip_waitack_state:
930 if (rcu_try_flip_waitack())
931 rcu_ctrlblk.rcu_try_flip_state =
932 rcu_try_flip_waitzero_state;
933 break;
934 case rcu_try_flip_waitzero_state:
935 if (rcu_try_flip_waitzero())
936 rcu_ctrlblk.rcu_try_flip_state =
937 rcu_try_flip_waitmb_state;
938 break;
939 case rcu_try_flip_waitmb_state:
940 if (rcu_try_flip_waitmb())
941 rcu_ctrlblk.rcu_try_flip_state =
942 rcu_try_flip_idle_state;
943 }
944 spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
945}
946
947/*
948 * Check to see if this CPU needs to do a memory barrier in order to
949 * ensure that any prior RCU read-side critical sections have committed
950 * their counter manipulations and critical-section memory references
951 * before declaring the grace period to be completed.
952 */
953static void rcu_check_mb(int cpu)
954{
955 if (per_cpu(rcu_mb_flag, cpu) == rcu_mb_needed) {
956 smp_mb(); /* Ensure RCU read-side accesses are visible. */
957 per_cpu(rcu_mb_flag, cpu) = rcu_mb_done;
958 }
959}
960
961void rcu_check_callbacks(int cpu, int user)
962{
963 unsigned long flags;
964 struct rcu_data *rdp = RCU_DATA_CPU(cpu);
965
966 /*
967 * If this CPU took its interrupt from user mode or from the
968 * idle loop, and this is not a nested interrupt, then
969 * this CPU has to have exited all prior preept-disable
970 * sections of code. So increment the counter to note this.
971 *
972 * The memory barrier is needed to handle the case where
973 * writes from a preempt-disable section of code get reordered
974 * into schedule() by this CPU's write buffer. So the memory
975 * barrier makes sure that the rcu_qsctr_inc() is seen by other
976 * CPUs to happen after any such write.
977 */
978
979 if (user ||
980 (idle_cpu(cpu) && !in_softirq() &&
981 hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
982 smp_mb(); /* Guard against aggressive schedule(). */
983 rcu_qsctr_inc(cpu);
984 }
985
986 rcu_check_mb(cpu);
987 if (rcu_ctrlblk.completed == rdp->completed)
988 rcu_try_flip();
989 spin_lock_irqsave(&rdp->lock, flags);
990 RCU_TRACE_RDP(rcupreempt_trace_check_callbacks, rdp);
991 __rcu_advance_callbacks(rdp);
992 if (rdp->donelist == NULL) {
993 spin_unlock_irqrestore(&rdp->lock, flags);
994 } else {
995 spin_unlock_irqrestore(&rdp->lock, flags);
996 raise_softirq(RCU_SOFTIRQ);
997 }
998}
999
1000/*
1001 * Needed by dynticks, to make sure all RCU processing has finished
1002 * when we go idle:
1003 */
1004void rcu_advance_callbacks(int cpu, int user)
1005{
1006 unsigned long flags;
1007 struct rcu_data *rdp = RCU_DATA_CPU(cpu);
1008
1009 if (rcu_ctrlblk.completed == rdp->completed) {
1010 rcu_try_flip();
1011 if (rcu_ctrlblk.completed == rdp->completed)
1012 return;
1013 }
1014 spin_lock_irqsave(&rdp->lock, flags);
1015 RCU_TRACE_RDP(rcupreempt_trace_check_callbacks, rdp);
1016 __rcu_advance_callbacks(rdp);
1017 spin_unlock_irqrestore(&rdp->lock, flags);
1018}
1019
1020#ifdef CONFIG_HOTPLUG_CPU
1021#define rcu_offline_cpu_enqueue(srclist, srctail, dstlist, dsttail) do { \
1022 *dsttail = srclist; \
1023 if (srclist != NULL) { \
1024 dsttail = srctail; \
1025 srclist = NULL; \
1026 srctail = &srclist;\
1027 } \
1028 } while (0)
1029
1030void rcu_offline_cpu(int cpu)
1031{
1032 int i;
1033 struct rcu_head *list = NULL;
1034 unsigned long flags;
1035 struct rcu_data *rdp = RCU_DATA_CPU(cpu);
1036 struct rcu_head *schedlist = NULL;
1037 struct rcu_head **schedtail = &schedlist;
1038 struct rcu_head **tail = &list;
1039
1040 /*
1041 * Remove all callbacks from the newly dead CPU, retaining order.
1042 * Otherwise rcu_barrier() will fail
1043 */
1044
1045 spin_lock_irqsave(&rdp->lock, flags);
1046 rcu_offline_cpu_enqueue(rdp->donelist, rdp->donetail, list, tail);
1047 for (i = GP_STAGES - 1; i >= 0; i--)
1048 rcu_offline_cpu_enqueue(rdp->waitlist[i], rdp->waittail[i],
1049 list, tail);
1050 rcu_offline_cpu_enqueue(rdp->nextlist, rdp->nexttail, list, tail);
1051 rcu_offline_cpu_enqueue(rdp->waitschedlist, rdp->waitschedtail,
1052 schedlist, schedtail);
1053 rcu_offline_cpu_enqueue(rdp->nextschedlist, rdp->nextschedtail,
1054 schedlist, schedtail);
1055 rdp->rcu_sched_sleeping = 0;
1056 spin_unlock_irqrestore(&rdp->lock, flags);
1057 rdp->waitlistcount = 0;
1058
1059 /* Disengage the newly dead CPU from the grace-period computation. */
1060
1061 spin_lock_irqsave(&rcu_ctrlblk.fliplock, flags);
1062 rcu_check_mb(cpu);
1063 if (per_cpu(rcu_flip_flag, cpu) == rcu_flipped) {
1064 smp_mb(); /* Subsequent counter accesses must see new value */
1065 per_cpu(rcu_flip_flag, cpu) = rcu_flip_seen;
1066 smp_mb(); /* Subsequent RCU read-side critical sections */
1067 /* seen -after- acknowledgement. */
1068 }
1069
1070 RCU_DATA_ME()->rcu_flipctr[0] += RCU_DATA_CPU(cpu)->rcu_flipctr[0];
1071 RCU_DATA_ME()->rcu_flipctr[1] += RCU_DATA_CPU(cpu)->rcu_flipctr[1];
1072
1073 RCU_DATA_CPU(cpu)->rcu_flipctr[0] = 0;
1074 RCU_DATA_CPU(cpu)->rcu_flipctr[1] = 0;
1075
1076 cpumask_clear_cpu(cpu, to_cpumask(rcu_cpu_online_map));
1077
1078 spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
1079
1080 /*
1081 * Place the removed callbacks on the current CPU's queue.
1082 * Make them all start a new grace period: simple approach,
1083 * in theory could starve a given set of callbacks, but
1084 * you would need to be doing some serious CPU hotplugging
1085 * to make this happen. If this becomes a problem, adding
1086 * a synchronize_rcu() to the hotplug path would be a simple
1087 * fix.
1088 */
1089
1090 local_irq_save(flags); /* disable preempt till we know what lock. */
1091 rdp = RCU_DATA_ME();
1092 spin_lock(&rdp->lock);
1093 *rdp->nexttail = list;
1094 if (list)
1095 rdp->nexttail = tail;
1096 *rdp->nextschedtail = schedlist;
1097 if (schedlist)
1098 rdp->nextschedtail = schedtail;
1099 spin_unlock_irqrestore(&rdp->lock, flags);
1100}
1101
1102#else /* #ifdef CONFIG_HOTPLUG_CPU */
1103
1104void rcu_offline_cpu(int cpu)
1105{
1106}
1107
1108#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
1109
1110void __cpuinit rcu_online_cpu(int cpu)
1111{
1112 unsigned long flags;
1113 struct rcu_data *rdp;
1114
1115 spin_lock_irqsave(&rcu_ctrlblk.fliplock, flags);
1116 cpumask_set_cpu(cpu, to_cpumask(rcu_cpu_online_map));
1117 spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
1118
1119 /*
1120 * The rcu_sched grace-period processing might have bypassed
1121 * this CPU, given that it was not in the rcu_cpu_online_map
1122 * when the grace-period scan started. This means that the
1123 * grace-period task might sleep. So make sure that if this
1124 * should happen, the first callback posted to this CPU will
1125 * wake up the grace-period task if need be.
1126 */
1127
1128 rdp = RCU_DATA_CPU(cpu);
1129 spin_lock_irqsave(&rdp->lock, flags);
1130 rdp->rcu_sched_sleeping = 1;
1131 spin_unlock_irqrestore(&rdp->lock, flags);
1132}
1133
1134static void rcu_process_callbacks(struct softirq_action *unused)
1135{
1136 unsigned long flags;
1137 struct rcu_head *next, *list;
1138 struct rcu_data *rdp;
1139
1140 local_irq_save(flags);
1141 rdp = RCU_DATA_ME();
1142 spin_lock(&rdp->lock);
1143 list = rdp->donelist;
1144 if (list == NULL) {
1145 spin_unlock_irqrestore(&rdp->lock, flags);
1146 return;
1147 }
1148 rdp->donelist = NULL;
1149 rdp->donetail = &rdp->donelist;
1150 RCU_TRACE_RDP(rcupreempt_trace_done_remove, rdp);
1151 spin_unlock_irqrestore(&rdp->lock, flags);
1152 while (list) {
1153 next = list->next;
1154 list->func(list);
1155 list = next;
1156 RCU_TRACE_ME(rcupreempt_trace_invoke);
1157 }
1158}
1159
1160void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
1161{
1162 unsigned long flags;
1163 struct rcu_data *rdp;
1164
1165 head->func = func;
1166 head->next = NULL;
1167 local_irq_save(flags);
1168 rdp = RCU_DATA_ME();
1169 spin_lock(&rdp->lock);
1170 __rcu_advance_callbacks(rdp);
1171 *rdp->nexttail = head;
1172 rdp->nexttail = &head->next;
1173 RCU_TRACE_RDP(rcupreempt_trace_next_add, rdp);
1174 spin_unlock_irqrestore(&rdp->lock, flags);
1175}
1176EXPORT_SYMBOL_GPL(call_rcu);
1177
1178void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
1179{
1180 unsigned long flags;
1181 struct rcu_data *rdp;
1182 int wake_gp = 0;
1183
1184 head->func = func;
1185 head->next = NULL;
1186 local_irq_save(flags);
1187 rdp = RCU_DATA_ME();
1188 spin_lock(&rdp->lock);
1189 *rdp->nextschedtail = head;
1190 rdp->nextschedtail = &head->next;
1191 if (rdp->rcu_sched_sleeping) {
1192
1193 /* Grace-period processing might be sleeping... */
1194
1195 rdp->rcu_sched_sleeping = 0;
1196 wake_gp = 1;
1197 }
1198 spin_unlock_irqrestore(&rdp->lock, flags);
1199 if (wake_gp) {
1200
1201 /* Wake up grace-period processing, unless someone beat us. */
1202
1203 spin_lock_irqsave(&rcu_ctrlblk.schedlock, flags);
1204 if (rcu_ctrlblk.sched_sleep != rcu_sched_sleeping)
1205 wake_gp = 0;
1206 rcu_ctrlblk.sched_sleep = rcu_sched_not_sleeping;
1207 spin_unlock_irqrestore(&rcu_ctrlblk.schedlock, flags);
1208 if (wake_gp)
1209 wake_up_interruptible(&rcu_ctrlblk.sched_wq);
1210 }
1211}
1212EXPORT_SYMBOL_GPL(call_rcu_sched);
1213
1214/*
1215 * Wait until all currently running preempt_disable() code segments
1216 * (including hardware-irq-disable segments) complete. Note that
1217 * in -rt this does -not- necessarily result in all currently executing
1218 * interrupt -handlers- having completed.
1219 */
1220void __synchronize_sched(void)
1221{
1222 struct rcu_synchronize rcu;
1223
1224 if (num_online_cpus() == 1)
1225 return; /* blocking is gp if only one CPU! */
1226
1227 init_completion(&rcu.completion);
1228 /* Will wake me after RCU finished. */
1229 call_rcu_sched(&rcu.head, wakeme_after_rcu);
1230 /* Wait for it. */
1231 wait_for_completion(&rcu.completion);
1232}
1233EXPORT_SYMBOL_GPL(__synchronize_sched);
1234
1235/*
1236 * kthread function that manages call_rcu_sched grace periods.
1237 */
1238static int rcu_sched_grace_period(void *arg)
1239{
1240 int couldsleep; /* might sleep after current pass. */
1241 int couldsleepnext = 0; /* might sleep after next pass. */
1242 int cpu;
1243 unsigned long flags;
1244 struct rcu_data *rdp;
1245 int ret;
1246
1247 /*
1248 * Each pass through the following loop handles one
1249 * rcu_sched grace period cycle.
1250 */
1251 do {
1252 /* Save each CPU's current state. */
1253
1254 for_each_online_cpu(cpu) {
1255 dyntick_save_progress_counter_sched(cpu);
1256 save_qsctr_sched(cpu);
1257 }
1258
1259 /*
1260 * Sleep for about an RCU grace-period's worth to
1261 * allow better batching and to consume less CPU.
1262 */
1263 schedule_timeout_interruptible(RCU_SCHED_BATCH_TIME);
1264
1265 /*
1266 * If there was nothing to do last time, prepare to
1267 * sleep at the end of the current grace period cycle.
1268 */
1269 couldsleep = couldsleepnext;
1270 couldsleepnext = 1;
1271 if (couldsleep) {
1272 spin_lock_irqsave(&rcu_ctrlblk.schedlock, flags);
1273 rcu_ctrlblk.sched_sleep = rcu_sched_sleep_prep;
1274 spin_unlock_irqrestore(&rcu_ctrlblk.schedlock, flags);
1275 }
1276
1277 /*
1278 * Wait on each CPU in turn to have either visited
1279 * a quiescent state or been in dynticks-idle mode.
1280 */
1281 for_each_online_cpu(cpu) {
1282 while (rcu_qsctr_inc_needed(cpu) &&
1283 rcu_qsctr_inc_needed_dyntick(cpu)) {
1284 /* resched_cpu(cpu); @@@ */
1285 schedule_timeout_interruptible(1);
1286 }
1287 }
1288
1289 /* Advance callbacks for each CPU. */
1290
1291 for_each_online_cpu(cpu) {
1292
1293 rdp = RCU_DATA_CPU(cpu);
1294 spin_lock_irqsave(&rdp->lock, flags);
1295
1296 /*
1297 * We are running on this CPU irq-disabled, so no
1298 * CPU can go offline until we re-enable irqs.
1299 * The current CPU might have already gone
1300 * offline (between the for_each_offline_cpu and
1301 * the spin_lock_irqsave), but in that case all its
1302 * callback lists will be empty, so no harm done.
1303 *
1304 * Advance the callbacks! We share normal RCU's
1305 * donelist, since callbacks are invoked the
1306 * same way in either case.
1307 */
1308 if (rdp->waitschedlist != NULL) {
1309 *rdp->donetail = rdp->waitschedlist;
1310 rdp->donetail = rdp->waitschedtail;
1311
1312 /*
1313 * Next rcu_check_callbacks() will
1314 * do the required raise_softirq().
1315 */
1316 }
1317 if (rdp->nextschedlist != NULL) {
1318 rdp->waitschedlist = rdp->nextschedlist;
1319 rdp->waitschedtail = rdp->nextschedtail;
1320 couldsleep = 0;
1321 couldsleepnext = 0;
1322 } else {
1323 rdp->waitschedlist = NULL;
1324 rdp->waitschedtail = &rdp->waitschedlist;
1325 }
1326 rdp->nextschedlist = NULL;
1327 rdp->nextschedtail = &rdp->nextschedlist;
1328
1329 /* Mark sleep intention. */
1330
1331 rdp->rcu_sched_sleeping = couldsleep;
1332
1333 spin_unlock_irqrestore(&rdp->lock, flags);
1334 }
1335
1336 /* If we saw callbacks on the last scan, go deal with them. */
1337
1338 if (!couldsleep)
1339 continue;
1340
1341 /* Attempt to block... */
1342
1343 spin_lock_irqsave(&rcu_ctrlblk.schedlock, flags);
1344 if (rcu_ctrlblk.sched_sleep != rcu_sched_sleep_prep) {
1345
1346 /*
1347 * Someone posted a callback after we scanned.
1348 * Go take care of it.
1349 */
1350 spin_unlock_irqrestore(&rcu_ctrlblk.schedlock, flags);
1351 couldsleepnext = 0;
1352 continue;
1353 }
1354
1355 /* Block until the next person posts a callback. */
1356
1357 rcu_ctrlblk.sched_sleep = rcu_sched_sleeping;
1358 spin_unlock_irqrestore(&rcu_ctrlblk.schedlock, flags);
1359 ret = 0; /* unused */
1360 __wait_event_interruptible(rcu_ctrlblk.sched_wq,
1361 rcu_ctrlblk.sched_sleep != rcu_sched_sleeping,
1362 ret);
1363
1364 couldsleepnext = 0;
1365
1366 } while (!kthread_should_stop());
1367
1368 return (0);
1369}
1370
1371/*
1372 * Check to see if any future RCU-related work will need to be done
1373 * by the current CPU, even if none need be done immediately, returning
1374 * 1 if so. Assumes that notifiers would take care of handling any
1375 * outstanding requests from the RCU core.
1376 *
1377 * This function is part of the RCU implementation; it is -not-
1378 * an exported member of the RCU API.
1379 */
1380int rcu_needs_cpu(int cpu)
1381{
1382 struct rcu_data *rdp = RCU_DATA_CPU(cpu);
1383
1384 return (rdp->donelist != NULL ||
1385 !!rdp->waitlistcount ||
1386 rdp->nextlist != NULL ||
1387 rdp->nextschedlist != NULL ||
1388 rdp->waitschedlist != NULL);
1389}
1390
1391int rcu_pending(int cpu)
1392{
1393 struct rcu_data *rdp = RCU_DATA_CPU(cpu);
1394
1395 /* The CPU has at least one callback queued somewhere. */
1396
1397 if (rdp->donelist != NULL ||
1398 !!rdp->waitlistcount ||
1399 rdp->nextlist != NULL ||
1400 rdp->nextschedlist != NULL ||
1401 rdp->waitschedlist != NULL)
1402 return 1;
1403
1404 /* The RCU core needs an acknowledgement from this CPU. */
1405
1406 if ((per_cpu(rcu_flip_flag, cpu) == rcu_flipped) ||
1407 (per_cpu(rcu_mb_flag, cpu) == rcu_mb_needed))
1408 return 1;
1409
1410 /* This CPU has fallen behind the global grace-period number. */
1411
1412 if (rdp->completed != rcu_ctrlblk.completed)
1413 return 1;
1414
1415 /* Nothing needed from this CPU. */
1416
1417 return 0;
1418}
1419
1420static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
1421 unsigned long action, void *hcpu)
1422{
1423 long cpu = (long)hcpu;
1424
1425 switch (action) {
1426 case CPU_UP_PREPARE:
1427 case CPU_UP_PREPARE_FROZEN:
1428 rcu_online_cpu(cpu);
1429 break;
1430 case CPU_UP_CANCELED:
1431 case CPU_UP_CANCELED_FROZEN:
1432 case CPU_DEAD:
1433 case CPU_DEAD_FROZEN:
1434 rcu_offline_cpu(cpu);
1435 break;
1436 default:
1437 break;
1438 }
1439 return NOTIFY_OK;
1440}
1441
1442static struct notifier_block __cpuinitdata rcu_nb = {
1443 .notifier_call = rcu_cpu_notify,
1444};
1445
1446void __init __rcu_init(void)
1447{
1448 int cpu;
1449 int i;
1450 struct rcu_data *rdp;
1451
1452 printk(KERN_NOTICE "Preemptible RCU implementation.\n");
1453 for_each_possible_cpu(cpu) {
1454 rdp = RCU_DATA_CPU(cpu);
1455 spin_lock_init(&rdp->lock);
1456 rdp->completed = 0;
1457 rdp->waitlistcount = 0;
1458 rdp->nextlist = NULL;
1459 rdp->nexttail = &rdp->nextlist;
1460 for (i = 0; i < GP_STAGES; i++) {
1461 rdp->waitlist[i] = NULL;
1462 rdp->waittail[i] = &rdp->waitlist[i];
1463 }
1464 rdp->donelist = NULL;
1465 rdp->donetail = &rdp->donelist;
1466 rdp->rcu_flipctr[0] = 0;
1467 rdp->rcu_flipctr[1] = 0;
1468 rdp->nextschedlist = NULL;
1469 rdp->nextschedtail = &rdp->nextschedlist;
1470 rdp->waitschedlist = NULL;
1471 rdp->waitschedtail = &rdp->waitschedlist;
1472 rdp->rcu_sched_sleeping = 0;
1473 }
1474 register_cpu_notifier(&rcu_nb);
1475
1476 /*
1477 * We don't need protection against CPU-Hotplug here
1478 * since
1479 * a) If a CPU comes online while we are iterating over the
1480 * cpu_online_mask below, we would only end up making a
1481 * duplicate call to rcu_online_cpu() which sets the corresponding
1482 * CPU's mask in the rcu_cpu_online_map.
1483 *
1484 * b) A CPU cannot go offline at this point in time since the user
1485 * does not have access to the sysfs interface, nor do we
1486 * suspend the system.
1487 */
1488 for_each_online_cpu(cpu)
1489 rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE, (void *)(long) cpu);
1490
1491 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
1492}
1493
1494/*
1495 * Late-boot-time RCU initialization that must wait until after scheduler
1496 * has been initialized.
1497 */
1498void __init rcu_init_sched(void)
1499{
1500 rcu_sched_grace_period_task = kthread_run(rcu_sched_grace_period,
1501 NULL,
1502 "rcu_sched_grace_period");
1503 WARN_ON(IS_ERR(rcu_sched_grace_period_task));
1504}
1505
1506#ifdef CONFIG_RCU_TRACE
1507long *rcupreempt_flipctr(int cpu)
1508{
1509 return &RCU_DATA_CPU(cpu)->rcu_flipctr[0];
1510}
1511EXPORT_SYMBOL_GPL(rcupreempt_flipctr);
1512
1513int rcupreempt_flip_flag(int cpu)
1514{
1515 return per_cpu(rcu_flip_flag, cpu);
1516}
1517EXPORT_SYMBOL_GPL(rcupreempt_flip_flag);
1518
1519int rcupreempt_mb_flag(int cpu)
1520{
1521 return per_cpu(rcu_mb_flag, cpu);
1522}
1523EXPORT_SYMBOL_GPL(rcupreempt_mb_flag);
1524
1525char *rcupreempt_try_flip_state_name(void)
1526{
1527 return rcu_try_flip_state_names[rcu_ctrlblk.rcu_try_flip_state];
1528}
1529EXPORT_SYMBOL_GPL(rcupreempt_try_flip_state_name);
1530
1531struct rcupreempt_trace *rcupreempt_trace_cpu(int cpu)
1532{
1533 struct rcu_data *rdp = RCU_DATA_CPU(cpu);
1534
1535 return &rdp->trace;
1536}
1537EXPORT_SYMBOL_GPL(rcupreempt_trace_cpu);
1538
1539#endif /* #ifdef RCU_TRACE */
generated by cgit v1.2.2 (git 2.25.0) at 2025-12-14 11:44:45 -0500