Root/
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/stop_machine.h> |
29 | |
30 | #define RCU_KTHREAD_PRIO 1 |
31 | |
32 | #ifdef CONFIG_RCU_BOOST |
33 | #define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO |
34 | #else |
35 | #define RCU_BOOST_PRIO RCU_KTHREAD_PRIO |
36 | #endif |
37 | |
38 | /* |
39 | * Check the RCU kernel configuration parameters and print informative |
40 | * messages about anything out of the ordinary. If you like #ifdef, you |
41 | * will love this function. |
42 | */ |
43 | static void __init rcu_bootup_announce_oddness(void) |
44 | { |
45 | #ifdef CONFIG_RCU_TRACE |
46 | printk(KERN_INFO "\tRCU debugfs-based tracing is enabled.\n"); |
47 | #endif |
48 | #if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32) |
49 | printk(KERN_INFO "\tCONFIG_RCU_FANOUT set to non-default value of %d\n", |
50 | CONFIG_RCU_FANOUT); |
51 | #endif |
52 | #ifdef CONFIG_RCU_FANOUT_EXACT |
53 | printk(KERN_INFO "\tHierarchical RCU autobalancing is disabled.\n"); |
54 | #endif |
55 | #ifdef CONFIG_RCU_FAST_NO_HZ |
56 | printk(KERN_INFO |
57 | "\tRCU dyntick-idle grace-period acceleration is enabled.\n"); |
58 | #endif |
59 | #ifdef CONFIG_PROVE_RCU |
60 | printk(KERN_INFO "\tRCU lockdep checking is enabled.\n"); |
61 | #endif |
62 | #ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE |
63 | printk(KERN_INFO "\tRCU torture testing starts during boot.\n"); |
64 | #endif |
65 | #if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE) |
66 | printk(KERN_INFO "\tVerbose stalled-CPUs detection is disabled.\n"); |
67 | #endif |
68 | #if NUM_RCU_LVL_4 != 0 |
69 | printk(KERN_INFO "\tExperimental four-level hierarchy is enabled.\n"); |
70 | #endif |
71 | } |
72 | |
73 | #ifdef CONFIG_TREE_PREEMPT_RCU |
74 | |
75 | struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt); |
76 | DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data); |
77 | static struct rcu_state *rcu_state = &rcu_preempt_state; |
78 | |
79 | static void rcu_read_unlock_special(struct task_struct *t); |
80 | static int rcu_preempted_readers_exp(struct rcu_node *rnp); |
81 | |
82 | /* |
83 | * Tell them what RCU they are running. |
84 | */ |
85 | static void __init rcu_bootup_announce(void) |
86 | { |
87 | printk(KERN_INFO "Preemptible hierarchical RCU implementation.\n"); |
88 | rcu_bootup_announce_oddness(); |
89 | } |
90 | |
91 | /* |
92 | * Return the number of RCU-preempt batches processed thus far |
93 | * for debug and statistics. |
94 | */ |
95 | long rcu_batches_completed_preempt(void) |
96 | { |
97 | return rcu_preempt_state.completed; |
98 | } |
99 | EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt); |
100 | |
101 | /* |
102 | * Return the number of RCU batches processed thus far for debug & stats. |
103 | */ |
104 | long rcu_batches_completed(void) |
105 | { |
106 | return rcu_batches_completed_preempt(); |
107 | } |
108 | EXPORT_SYMBOL_GPL(rcu_batches_completed); |
109 | |
110 | /* |
111 | * Force a quiescent state for preemptible RCU. |
112 | */ |
113 | void rcu_force_quiescent_state(void) |
114 | { |
115 | force_quiescent_state(&rcu_preempt_state, 0); |
116 | } |
117 | EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); |
118 | |
119 | /* |
120 | * Record a preemptible-RCU quiescent state for the specified CPU. Note |
121 | * that this just means that the task currently running on the CPU is |
122 | * not in a quiescent state. There might be any number of tasks blocked |
123 | * while in an RCU read-side critical section. |
124 | * |
125 | * Unlike the other rcu_*_qs() functions, callers to this function |
126 | * must disable irqs in order to protect the assignment to |
127 | * ->rcu_read_unlock_special. |
128 | */ |
129 | static void rcu_preempt_qs(int cpu) |
130 | { |
131 | struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu); |
132 | |
133 | rdp->passed_quiesce_gpnum = rdp->gpnum; |
134 | barrier(); |
135 | if (rdp->passed_quiesce == 0) |
136 | trace_rcu_grace_period("rcu_preempt", rdp->gpnum, "cpuqs"); |
137 | rdp->passed_quiesce = 1; |
138 | current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; |
139 | } |
140 | |
141 | /* |
142 | * We have entered the scheduler, and the current task might soon be |
143 | * context-switched away from. If this task is in an RCU read-side |
144 | * critical section, we will no longer be able to rely on the CPU to |
145 | * record that fact, so we enqueue the task on the blkd_tasks list. |
146 | * The task will dequeue itself when it exits the outermost enclosing |
147 | * RCU read-side critical section. Therefore, the current grace period |
148 | * cannot be permitted to complete until the blkd_tasks list entries |
149 | * predating the current grace period drain, in other words, until |
150 | * rnp->gp_tasks becomes NULL. |
151 | * |
152 | * Caller must disable preemption. |
153 | */ |
154 | static void rcu_preempt_note_context_switch(int cpu) |
155 | { |
156 | struct task_struct *t = current; |
157 | unsigned long flags; |
158 | struct rcu_data *rdp; |
159 | struct rcu_node *rnp; |
160 | |
161 | if (t->rcu_read_lock_nesting > 0 && |
162 | (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { |
163 | |
164 | /* Possibly blocking in an RCU read-side critical section. */ |
165 | rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu); |
166 | rnp = rdp->mynode; |
167 | raw_spin_lock_irqsave(&rnp->lock, flags); |
168 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; |
169 | t->rcu_blocked_node = rnp; |
170 | |
171 | /* |
172 | * If this CPU has already checked in, then this task |
173 | * will hold up the next grace period rather than the |
174 | * current grace period. Queue the task accordingly. |
175 | * If the task is queued for the current grace period |
176 | * (i.e., this CPU has not yet passed through a quiescent |
177 | * state for the current grace period), then as long |
178 | * as that task remains queued, the current grace period |
179 | * cannot end. Note that there is some uncertainty as |
180 | * to exactly when the current grace period started. |
181 | * We take a conservative approach, which can result |
182 | * in unnecessarily waiting on tasks that started very |
183 | * slightly after the current grace period began. C'est |
184 | * la vie!!! |
185 | * |
186 | * But first, note that the current CPU must still be |
187 | * on line! |
188 | */ |
189 | WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0); |
190 | WARN_ON_ONCE(!list_empty(&t->rcu_node_entry)); |
191 | if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) { |
192 | list_add(&t->rcu_node_entry, rnp->gp_tasks->prev); |
193 | rnp->gp_tasks = &t->rcu_node_entry; |
194 | #ifdef CONFIG_RCU_BOOST |
195 | if (rnp->boost_tasks != NULL) |
196 | rnp->boost_tasks = rnp->gp_tasks; |
197 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
198 | } else { |
199 | list_add(&t->rcu_node_entry, &rnp->blkd_tasks); |
200 | if (rnp->qsmask & rdp->grpmask) |
201 | rnp->gp_tasks = &t->rcu_node_entry; |
202 | } |
203 | trace_rcu_preempt_task(rdp->rsp->name, |
204 | t->pid, |
205 | (rnp->qsmask & rdp->grpmask) |
206 | ? rnp->gpnum |
207 | : rnp->gpnum + 1); |
208 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
209 | } else if (t->rcu_read_lock_nesting < 0 && |
210 | t->rcu_read_unlock_special) { |
211 | |
212 | /* |
213 | * Complete exit from RCU read-side critical section on |
214 | * behalf of preempted instance of __rcu_read_unlock(). |
215 | */ |
216 | rcu_read_unlock_special(t); |
217 | } |
218 | |
219 | /* |
220 | * Either we were not in an RCU read-side critical section to |
221 | * begin with, or we have now recorded that critical section |
222 | * globally. Either way, we can now note a quiescent state |
223 | * for this CPU. Again, if we were in an RCU read-side critical |
224 | * section, and if that critical section was blocking the current |
225 | * grace period, then the fact that the task has been enqueued |
226 | * means that we continue to block the current grace period. |
227 | */ |
228 | local_irq_save(flags); |
229 | rcu_preempt_qs(cpu); |
230 | local_irq_restore(flags); |
231 | } |
232 | |
233 | /* |
234 | * Tree-preemptible RCU implementation for rcu_read_lock(). |
235 | * Just increment ->rcu_read_lock_nesting, shared state will be updated |
236 | * if we block. |
237 | */ |
238 | void __rcu_read_lock(void) |
239 | { |
240 | current->rcu_read_lock_nesting++; |
241 | barrier(); /* needed if we ever invoke rcu_read_lock in rcutree.c */ |
242 | } |
243 | EXPORT_SYMBOL_GPL(__rcu_read_lock); |
244 | |
245 | /* |
246 | * Check for preempted RCU readers blocking the current grace period |
247 | * for the specified rcu_node structure. If the caller needs a reliable |
248 | * answer, it must hold the rcu_node's ->lock. |
249 | */ |
250 | static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
251 | { |
252 | return rnp->gp_tasks != NULL; |
253 | } |
254 | |
255 | /* |
256 | * Record a quiescent state for all tasks that were previously queued |
257 | * on the specified rcu_node structure and that were blocking the current |
258 | * RCU grace period. The caller must hold the specified rnp->lock with |
259 | * irqs disabled, and this lock is released upon return, but irqs remain |
260 | * disabled. |
261 | */ |
262 | static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) |
263 | __releases(rnp->lock) |
264 | { |
265 | unsigned long mask; |
266 | struct rcu_node *rnp_p; |
267 | |
268 | if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) { |
269 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
270 | return; /* Still need more quiescent states! */ |
271 | } |
272 | |
273 | rnp_p = rnp->parent; |
274 | if (rnp_p == NULL) { |
275 | /* |
276 | * Either there is only one rcu_node in the tree, |
277 | * or tasks were kicked up to root rcu_node due to |
278 | * CPUs going offline. |
279 | */ |
280 | rcu_report_qs_rsp(&rcu_preempt_state, flags); |
281 | return; |
282 | } |
283 | |
284 | /* Report up the rest of the hierarchy. */ |
285 | mask = rnp->grpmask; |
286 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
287 | raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */ |
288 | rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags); |
289 | } |
290 | |
291 | /* |
292 | * Advance a ->blkd_tasks-list pointer to the next entry, instead |
293 | * returning NULL if at the end of the list. |
294 | */ |
295 | static struct list_head *rcu_next_node_entry(struct task_struct *t, |
296 | struct rcu_node *rnp) |
297 | { |
298 | struct list_head *np; |
299 | |
300 | np = t->rcu_node_entry.next; |
301 | if (np == &rnp->blkd_tasks) |
302 | np = NULL; |
303 | return np; |
304 | } |
305 | |
306 | /* |
307 | * Handle special cases during rcu_read_unlock(), such as needing to |
308 | * notify RCU core processing or task having blocked during the RCU |
309 | * read-side critical section. |
310 | */ |
311 | static noinline void rcu_read_unlock_special(struct task_struct *t) |
312 | { |
313 | int empty; |
314 | int empty_exp; |
315 | unsigned long flags; |
316 | struct list_head *np; |
317 | #ifdef CONFIG_RCU_BOOST |
318 | struct rt_mutex *rbmp = NULL; |
319 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
320 | struct rcu_node *rnp; |
321 | int special; |
322 | |
323 | /* NMI handlers cannot block and cannot safely manipulate state. */ |
324 | if (in_nmi()) |
325 | return; |
326 | |
327 | local_irq_save(flags); |
328 | |
329 | /* |
330 | * If RCU core is waiting for this CPU to exit critical section, |
331 | * let it know that we have done so. |
332 | */ |
333 | special = t->rcu_read_unlock_special; |
334 | if (special & RCU_READ_UNLOCK_NEED_QS) { |
335 | rcu_preempt_qs(smp_processor_id()); |
336 | } |
337 | |
338 | /* Hardware IRQ handlers cannot block. */ |
339 | if (in_irq() || in_serving_softirq()) { |
340 | local_irq_restore(flags); |
341 | return; |
342 | } |
343 | |
344 | /* Clean up if blocked during RCU read-side critical section. */ |
345 | if (special & RCU_READ_UNLOCK_BLOCKED) { |
346 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; |
347 | |
348 | /* |
349 | * Remove this task from the list it blocked on. The |
350 | * task can migrate while we acquire the lock, but at |
351 | * most one time. So at most two passes through loop. |
352 | */ |
353 | for (;;) { |
354 | rnp = t->rcu_blocked_node; |
355 | raw_spin_lock(&rnp->lock); /* irqs already disabled. */ |
356 | if (rnp == t->rcu_blocked_node) |
357 | break; |
358 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
359 | } |
360 | empty = !rcu_preempt_blocked_readers_cgp(rnp); |
361 | empty_exp = !rcu_preempted_readers_exp(rnp); |
362 | smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */ |
363 | np = rcu_next_node_entry(t, rnp); |
364 | list_del_init(&t->rcu_node_entry); |
365 | t->rcu_blocked_node = NULL; |
366 | trace_rcu_unlock_preempted_task("rcu_preempt", |
367 | rnp->gpnum, t->pid); |
368 | if (&t->rcu_node_entry == rnp->gp_tasks) |
369 | rnp->gp_tasks = np; |
370 | if (&t->rcu_node_entry == rnp->exp_tasks) |
371 | rnp->exp_tasks = np; |
372 | #ifdef CONFIG_RCU_BOOST |
373 | if (&t->rcu_node_entry == rnp->boost_tasks) |
374 | rnp->boost_tasks = np; |
375 | /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */ |
376 | if (t->rcu_boost_mutex) { |
377 | rbmp = t->rcu_boost_mutex; |
378 | t->rcu_boost_mutex = NULL; |
379 | } |
380 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
381 | |
382 | /* |
383 | * If this was the last task on the current list, and if |
384 | * we aren't waiting on any CPUs, report the quiescent state. |
385 | * Note that rcu_report_unblock_qs_rnp() releases rnp->lock. |
386 | */ |
387 | if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) { |
388 | trace_rcu_quiescent_state_report("preempt_rcu", |
389 | rnp->gpnum, |
390 | 0, rnp->qsmask, |
391 | rnp->level, |
392 | rnp->grplo, |
393 | rnp->grphi, |
394 | !!rnp->gp_tasks); |
395 | rcu_report_unblock_qs_rnp(rnp, flags); |
396 | } else |
397 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
398 | |
399 | #ifdef CONFIG_RCU_BOOST |
400 | /* Unboost if we were boosted. */ |
401 | if (rbmp) |
402 | rt_mutex_unlock(rbmp); |
403 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
404 | |
405 | /* |
406 | * If this was the last task on the expedited lists, |
407 | * then we need to report up the rcu_node hierarchy. |
408 | */ |
409 | if (!empty_exp && !rcu_preempted_readers_exp(rnp)) |
410 | rcu_report_exp_rnp(&rcu_preempt_state, rnp); |
411 | } else { |
412 | local_irq_restore(flags); |
413 | } |
414 | } |
415 | |
416 | /* |
417 | * Tree-preemptible RCU implementation for rcu_read_unlock(). |
418 | * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost |
419 | * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then |
420 | * invoke rcu_read_unlock_special() to clean up after a context switch |
421 | * in an RCU read-side critical section and other special cases. |
422 | */ |
423 | void __rcu_read_unlock(void) |
424 | { |
425 | struct task_struct *t = current; |
426 | |
427 | if (t->rcu_read_lock_nesting != 1) |
428 | --t->rcu_read_lock_nesting; |
429 | else { |
430 | barrier(); /* critical section before exit code. */ |
431 | t->rcu_read_lock_nesting = INT_MIN; |
432 | barrier(); /* assign before ->rcu_read_unlock_special load */ |
433 | if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) |
434 | rcu_read_unlock_special(t); |
435 | barrier(); /* ->rcu_read_unlock_special load before assign */ |
436 | t->rcu_read_lock_nesting = 0; |
437 | } |
438 | #ifdef CONFIG_PROVE_LOCKING |
439 | { |
440 | int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting); |
441 | |
442 | WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2); |
443 | } |
444 | #endif /* #ifdef CONFIG_PROVE_LOCKING */ |
445 | } |
446 | EXPORT_SYMBOL_GPL(__rcu_read_unlock); |
447 | |
448 | #ifdef CONFIG_RCU_CPU_STALL_VERBOSE |
449 | |
450 | /* |
451 | * Dump detailed information for all tasks blocking the current RCU |
452 | * grace period on the specified rcu_node structure. |
453 | */ |
454 | static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) |
455 | { |
456 | unsigned long flags; |
457 | struct task_struct *t; |
458 | |
459 | if (!rcu_preempt_blocked_readers_cgp(rnp)) |
460 | return; |
461 | raw_spin_lock_irqsave(&rnp->lock, flags); |
462 | t = list_entry(rnp->gp_tasks, |
463 | struct task_struct, rcu_node_entry); |
464 | list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) |
465 | sched_show_task(t); |
466 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
467 | } |
468 | |
469 | /* |
470 | * Dump detailed information for all tasks blocking the current RCU |
471 | * grace period. |
472 | */ |
473 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) |
474 | { |
475 | struct rcu_node *rnp = rcu_get_root(rsp); |
476 | |
477 | rcu_print_detail_task_stall_rnp(rnp); |
478 | rcu_for_each_leaf_node(rsp, rnp) |
479 | rcu_print_detail_task_stall_rnp(rnp); |
480 | } |
481 | |
482 | #else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ |
483 | |
484 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) |
485 | { |
486 | } |
487 | |
488 | #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ |
489 | |
490 | /* |
491 | * Scan the current list of tasks blocked within RCU read-side critical |
492 | * sections, printing out the tid of each. |
493 | */ |
494 | static int rcu_print_task_stall(struct rcu_node *rnp) |
495 | { |
496 | struct task_struct *t; |
497 | int ndetected = 0; |
498 | |
499 | if (!rcu_preempt_blocked_readers_cgp(rnp)) |
500 | return 0; |
501 | t = list_entry(rnp->gp_tasks, |
502 | struct task_struct, rcu_node_entry); |
503 | list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { |
504 | printk(" P%d", t->pid); |
505 | ndetected++; |
506 | } |
507 | return ndetected; |
508 | } |
509 | |
510 | /* |
511 | * Suppress preemptible RCU's CPU stall warnings by pushing the |
512 | * time of the next stall-warning message comfortably far into the |
513 | * future. |
514 | */ |
515 | static void rcu_preempt_stall_reset(void) |
516 | { |
517 | rcu_preempt_state.jiffies_stall = jiffies + ULONG_MAX / 2; |
518 | } |
519 | |
520 | /* |
521 | * Check that the list of blocked tasks for the newly completed grace |
522 | * period is in fact empty. It is a serious bug to complete a grace |
523 | * period that still has RCU readers blocked! This function must be |
524 | * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock |
525 | * must be held by the caller. |
526 | * |
527 | * Also, if there are blocked tasks on the list, they automatically |
528 | * block the newly created grace period, so set up ->gp_tasks accordingly. |
529 | */ |
530 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) |
531 | { |
532 | WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)); |
533 | if (!list_empty(&rnp->blkd_tasks)) |
534 | rnp->gp_tasks = rnp->blkd_tasks.next; |
535 | WARN_ON_ONCE(rnp->qsmask); |
536 | } |
537 | |
538 | #ifdef CONFIG_HOTPLUG_CPU |
539 | |
540 | /* |
541 | * Handle tasklist migration for case in which all CPUs covered by the |
542 | * specified rcu_node have gone offline. Move them up to the root |
543 | * rcu_node. The reason for not just moving them to the immediate |
544 | * parent is to remove the need for rcu_read_unlock_special() to |
545 | * make more than two attempts to acquire the target rcu_node's lock. |
546 | * Returns true if there were tasks blocking the current RCU grace |
547 | * period. |
548 | * |
549 | * Returns 1 if there was previously a task blocking the current grace |
550 | * period on the specified rcu_node structure. |
551 | * |
552 | * The caller must hold rnp->lock with irqs disabled. |
553 | */ |
554 | static int rcu_preempt_offline_tasks(struct rcu_state *rsp, |
555 | struct rcu_node *rnp, |
556 | struct rcu_data *rdp) |
557 | { |
558 | struct list_head *lp; |
559 | struct list_head *lp_root; |
560 | int retval = 0; |
561 | struct rcu_node *rnp_root = rcu_get_root(rsp); |
562 | struct task_struct *t; |
563 | |
564 | if (rnp == rnp_root) { |
565 | WARN_ONCE(1, "Last CPU thought to be offlined?"); |
566 | return 0; /* Shouldn't happen: at least one CPU online. */ |
567 | } |
568 | |
569 | /* If we are on an internal node, complain bitterly. */ |
570 | WARN_ON_ONCE(rnp != rdp->mynode); |
571 | |
572 | /* |
573 | * Move tasks up to root rcu_node. Don't try to get fancy for |
574 | * this corner-case operation -- just put this node's tasks |
575 | * at the head of the root node's list, and update the root node's |
576 | * ->gp_tasks and ->exp_tasks pointers to those of this node's, |
577 | * if non-NULL. This might result in waiting for more tasks than |
578 | * absolutely necessary, but this is a good performance/complexity |
579 | * tradeoff. |
580 | */ |
581 | if (rcu_preempt_blocked_readers_cgp(rnp)) |
582 | retval |= RCU_OFL_TASKS_NORM_GP; |
583 | if (rcu_preempted_readers_exp(rnp)) |
584 | retval |= RCU_OFL_TASKS_EXP_GP; |
585 | lp = &rnp->blkd_tasks; |
586 | lp_root = &rnp_root->blkd_tasks; |
587 | while (!list_empty(lp)) { |
588 | t = list_entry(lp->next, typeof(*t), rcu_node_entry); |
589 | raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ |
590 | list_del(&t->rcu_node_entry); |
591 | t->rcu_blocked_node = rnp_root; |
592 | list_add(&t->rcu_node_entry, lp_root); |
593 | if (&t->rcu_node_entry == rnp->gp_tasks) |
594 | rnp_root->gp_tasks = rnp->gp_tasks; |
595 | if (&t->rcu_node_entry == rnp->exp_tasks) |
596 | rnp_root->exp_tasks = rnp->exp_tasks; |
597 | #ifdef CONFIG_RCU_BOOST |
598 | if (&t->rcu_node_entry == rnp->boost_tasks) |
599 | rnp_root->boost_tasks = rnp->boost_tasks; |
600 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
601 | raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ |
602 | } |
603 | |
604 | #ifdef CONFIG_RCU_BOOST |
605 | /* In case root is being boosted and leaf is not. */ |
606 | raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ |
607 | if (rnp_root->boost_tasks != NULL && |
608 | rnp_root->boost_tasks != rnp_root->gp_tasks) |
609 | rnp_root->boost_tasks = rnp_root->gp_tasks; |
610 | raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ |
611 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
612 | |
613 | rnp->gp_tasks = NULL; |
614 | rnp->exp_tasks = NULL; |
615 | return retval; |
616 | } |
617 | |
618 | /* |
619 | * Do CPU-offline processing for preemptible RCU. |
620 | */ |
621 | static void rcu_preempt_offline_cpu(int cpu) |
622 | { |
623 | __rcu_offline_cpu(cpu, &rcu_preempt_state); |
624 | } |
625 | |
626 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
627 | |
628 | /* |
629 | * Check for a quiescent state from the current CPU. When a task blocks, |
630 | * the task is recorded in the corresponding CPU's rcu_node structure, |
631 | * which is checked elsewhere. |
632 | * |
633 | * Caller must disable hard irqs. |
634 | */ |
635 | static void rcu_preempt_check_callbacks(int cpu) |
636 | { |
637 | struct task_struct *t = current; |
638 | |
639 | if (t->rcu_read_lock_nesting == 0) { |
640 | rcu_preempt_qs(cpu); |
641 | return; |
642 | } |
643 | if (t->rcu_read_lock_nesting > 0 && |
644 | per_cpu(rcu_preempt_data, cpu).qs_pending) |
645 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; |
646 | } |
647 | |
648 | /* |
649 | * Process callbacks for preemptible RCU. |
650 | */ |
651 | static void rcu_preempt_process_callbacks(void) |
652 | { |
653 | __rcu_process_callbacks(&rcu_preempt_state, |
654 | &__get_cpu_var(rcu_preempt_data)); |
655 | } |
656 | |
657 | #ifdef CONFIG_RCU_BOOST |
658 | |
659 | static void rcu_preempt_do_callbacks(void) |
660 | { |
661 | rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data)); |
662 | } |
663 | |
664 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
665 | |
666 | /* |
667 | * Queue a preemptible-RCU callback for invocation after a grace period. |
668 | */ |
669 | void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) |
670 | { |
671 | __call_rcu(head, func, &rcu_preempt_state); |
672 | } |
673 | EXPORT_SYMBOL_GPL(call_rcu); |
674 | |
675 | /** |
676 | * synchronize_rcu - wait until a grace period has elapsed. |
677 | * |
678 | * Control will return to the caller some time after a full grace |
679 | * period has elapsed, in other words after all currently executing RCU |
680 | * read-side critical sections have completed. Note, however, that |
681 | * upon return from synchronize_rcu(), the caller might well be executing |
682 | * concurrently with new RCU read-side critical sections that began while |
683 | * synchronize_rcu() was waiting. RCU read-side critical sections are |
684 | * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. |
685 | */ |
686 | void synchronize_rcu(void) |
687 | { |
688 | if (!rcu_scheduler_active) |
689 | return; |
690 | wait_rcu_gp(call_rcu); |
691 | } |
692 | EXPORT_SYMBOL_GPL(synchronize_rcu); |
693 | |
694 | static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); |
695 | static long sync_rcu_preempt_exp_count; |
696 | static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); |
697 | |
698 | /* |
699 | * Return non-zero if there are any tasks in RCU read-side critical |
700 | * sections blocking the current preemptible-RCU expedited grace period. |
701 | * If there is no preemptible-RCU expedited grace period currently in |
702 | * progress, returns zero unconditionally. |
703 | */ |
704 | static int rcu_preempted_readers_exp(struct rcu_node *rnp) |
705 | { |
706 | return rnp->exp_tasks != NULL; |
707 | } |
708 | |
709 | /* |
710 | * return non-zero if there is no RCU expedited grace period in progress |
711 | * for the specified rcu_node structure, in other words, if all CPUs and |
712 | * tasks covered by the specified rcu_node structure have done their bit |
713 | * for the current expedited grace period. Works only for preemptible |
714 | * RCU -- other RCU implementation use other means. |
715 | * |
716 | * Caller must hold sync_rcu_preempt_exp_mutex. |
717 | */ |
718 | static int sync_rcu_preempt_exp_done(struct rcu_node *rnp) |
719 | { |
720 | return !rcu_preempted_readers_exp(rnp) && |
721 | ACCESS_ONCE(rnp->expmask) == 0; |
722 | } |
723 | |
724 | /* |
725 | * Report the exit from RCU read-side critical section for the last task |
726 | * that queued itself during or before the current expedited preemptible-RCU |
727 | * grace period. This event is reported either to the rcu_node structure on |
728 | * which the task was queued or to one of that rcu_node structure's ancestors, |
729 | * recursively up the tree. (Calm down, calm down, we do the recursion |
730 | * iteratively!) |
731 | * |
732 | * Caller must hold sync_rcu_preempt_exp_mutex. |
733 | */ |
734 | static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp) |
735 | { |
736 | unsigned long flags; |
737 | unsigned long mask; |
738 | |
739 | raw_spin_lock_irqsave(&rnp->lock, flags); |
740 | for (;;) { |
741 | if (!sync_rcu_preempt_exp_done(rnp)) { |
742 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
743 | break; |
744 | } |
745 | if (rnp->parent == NULL) { |
746 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
747 | wake_up(&sync_rcu_preempt_exp_wq); |
748 | break; |
749 | } |
750 | mask = rnp->grpmask; |
751 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ |
752 | rnp = rnp->parent; |
753 | raw_spin_lock(&rnp->lock); /* irqs already disabled */ |
754 | rnp->expmask &= ~mask; |
755 | } |
756 | } |
757 | |
758 | /* |
759 | * Snapshot the tasks blocking the newly started preemptible-RCU expedited |
760 | * grace period for the specified rcu_node structure. If there are no such |
761 | * tasks, report it up the rcu_node hierarchy. |
762 | * |
763 | * Caller must hold sync_rcu_preempt_exp_mutex and rsp->onofflock. |
764 | */ |
765 | static void |
766 | sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp) |
767 | { |
768 | unsigned long flags; |
769 | int must_wait = 0; |
770 | |
771 | raw_spin_lock_irqsave(&rnp->lock, flags); |
772 | if (list_empty(&rnp->blkd_tasks)) |
773 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
774 | else { |
775 | rnp->exp_tasks = rnp->blkd_tasks.next; |
776 | rcu_initiate_boost(rnp, flags); /* releases rnp->lock */ |
777 | must_wait = 1; |
778 | } |
779 | if (!must_wait) |
780 | rcu_report_exp_rnp(rsp, rnp); |
781 | } |
782 | |
783 | /* |
784 | * Wait for an rcu-preempt grace period, but expedite it. The basic idea |
785 | * is to invoke synchronize_sched_expedited() to push all the tasks to |
786 | * the ->blkd_tasks lists and wait for this list to drain. |
787 | */ |
788 | void synchronize_rcu_expedited(void) |
789 | { |
790 | unsigned long flags; |
791 | struct rcu_node *rnp; |
792 | struct rcu_state *rsp = &rcu_preempt_state; |
793 | long snap; |
794 | int trycount = 0; |
795 | |
796 | smp_mb(); /* Caller's modifications seen first by other CPUs. */ |
797 | snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1; |
798 | smp_mb(); /* Above access cannot bleed into critical section. */ |
799 | |
800 | /* |
801 | * Acquire lock, falling back to synchronize_rcu() if too many |
802 | * lock-acquisition failures. Of course, if someone does the |
803 | * expedited grace period for us, just leave. |
804 | */ |
805 | while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) { |
806 | if (trycount++ < 10) |
807 | udelay(trycount * num_online_cpus()); |
808 | else { |
809 | synchronize_rcu(); |
810 | return; |
811 | } |
812 | if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0) |
813 | goto mb_ret; /* Others did our work for us. */ |
814 | } |
815 | if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0) |
816 | goto unlock_mb_ret; /* Others did our work for us. */ |
817 | |
818 | /* force all RCU readers onto ->blkd_tasks lists. */ |
819 | synchronize_sched_expedited(); |
820 | |
821 | raw_spin_lock_irqsave(&rsp->onofflock, flags); |
822 | |
823 | /* Initialize ->expmask for all non-leaf rcu_node structures. */ |
824 | rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) { |
825 | raw_spin_lock(&rnp->lock); /* irqs already disabled. */ |
826 | rnp->expmask = rnp->qsmaskinit; |
827 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
828 | } |
829 | |
830 | /* Snapshot current state of ->blkd_tasks lists. */ |
831 | rcu_for_each_leaf_node(rsp, rnp) |
832 | sync_rcu_preempt_exp_init(rsp, rnp); |
833 | if (NUM_RCU_NODES > 1) |
834 | sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp)); |
835 | |
836 | raw_spin_unlock_irqrestore(&rsp->onofflock, flags); |
837 | |
838 | /* Wait for snapshotted ->blkd_tasks lists to drain. */ |
839 | rnp = rcu_get_root(rsp); |
840 | wait_event(sync_rcu_preempt_exp_wq, |
841 | sync_rcu_preempt_exp_done(rnp)); |
842 | |
843 | /* Clean up and exit. */ |
844 | smp_mb(); /* ensure expedited GP seen before counter increment. */ |
845 | ACCESS_ONCE(sync_rcu_preempt_exp_count)++; |
846 | unlock_mb_ret: |
847 | mutex_unlock(&sync_rcu_preempt_exp_mutex); |
848 | mb_ret: |
849 | smp_mb(); /* ensure subsequent action seen after grace period. */ |
850 | } |
851 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); |
852 | |
853 | /* |
854 | * Check to see if there is any immediate preemptible-RCU-related work |
855 | * to be done. |
856 | */ |
857 | static int rcu_preempt_pending(int cpu) |
858 | { |
859 | return __rcu_pending(&rcu_preempt_state, |
860 | &per_cpu(rcu_preempt_data, cpu)); |
861 | } |
862 | |
863 | /* |
864 | * Does preemptible RCU need the CPU to stay out of dynticks mode? |
865 | */ |
866 | static int rcu_preempt_needs_cpu(int cpu) |
867 | { |
868 | return !!per_cpu(rcu_preempt_data, cpu).nxtlist; |
869 | } |
870 | |
871 | /** |
872 | * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. |
873 | */ |
874 | void rcu_barrier(void) |
875 | { |
876 | _rcu_barrier(&rcu_preempt_state, call_rcu); |
877 | } |
878 | EXPORT_SYMBOL_GPL(rcu_barrier); |
879 | |
880 | /* |
881 | * Initialize preemptible RCU's per-CPU data. |
882 | */ |
883 | static void __cpuinit rcu_preempt_init_percpu_data(int cpu) |
884 | { |
885 | rcu_init_percpu_data(cpu, &rcu_preempt_state, 1); |
886 | } |
887 | |
888 | /* |
889 | * Move preemptible RCU's callbacks from dying CPU to other online CPU. |
890 | */ |
891 | static void rcu_preempt_send_cbs_to_online(void) |
892 | { |
893 | rcu_send_cbs_to_online(&rcu_preempt_state); |
894 | } |
895 | |
896 | /* |
897 | * Initialize preemptible RCU's state structures. |
898 | */ |
899 | static void __init __rcu_init_preempt(void) |
900 | { |
901 | rcu_init_one(&rcu_preempt_state, &rcu_preempt_data); |
902 | } |
903 | |
904 | /* |
905 | * Check for a task exiting while in a preemptible-RCU read-side |
906 | * critical section, clean up if so. No need to issue warnings, |
907 | * as debug_check_no_locks_held() already does this if lockdep |
908 | * is enabled. |
909 | */ |
910 | void exit_rcu(void) |
911 | { |
912 | struct task_struct *t = current; |
913 | |
914 | if (t->rcu_read_lock_nesting == 0) |
915 | return; |
916 | t->rcu_read_lock_nesting = 1; |
917 | __rcu_read_unlock(); |
918 | } |
919 | |
920 | #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ |
921 | |
922 | static struct rcu_state *rcu_state = &rcu_sched_state; |
923 | |
924 | /* |
925 | * Tell them what RCU they are running. |
926 | */ |
927 | static void __init rcu_bootup_announce(void) |
928 | { |
929 | printk(KERN_INFO "Hierarchical RCU implementation.\n"); |
930 | rcu_bootup_announce_oddness(); |
931 | } |
932 | |
933 | /* |
934 | * Return the number of RCU batches processed thus far for debug & stats. |
935 | */ |
936 | long rcu_batches_completed(void) |
937 | { |
938 | return rcu_batches_completed_sched(); |
939 | } |
940 | EXPORT_SYMBOL_GPL(rcu_batches_completed); |
941 | |
942 | /* |
943 | * Force a quiescent state for RCU, which, because there is no preemptible |
944 | * RCU, becomes the same as rcu-sched. |
945 | */ |
946 | void rcu_force_quiescent_state(void) |
947 | { |
948 | rcu_sched_force_quiescent_state(); |
949 | } |
950 | EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); |
951 | |
952 | /* |
953 | * Because preemptible RCU does not exist, we never have to check for |
954 | * CPUs being in quiescent states. |
955 | */ |
956 | static void rcu_preempt_note_context_switch(int cpu) |
957 | { |
958 | } |
959 | |
960 | /* |
961 | * Because preemptible RCU does not exist, there are never any preempted |
962 | * RCU readers. |
963 | */ |
964 | static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
965 | { |
966 | return 0; |
967 | } |
968 | |
969 | #ifdef CONFIG_HOTPLUG_CPU |
970 | |
971 | /* Because preemptible RCU does not exist, no quieting of tasks. */ |
972 | static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) |
973 | { |
974 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
975 | } |
976 | |
977 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
978 | |
979 | /* |
980 | * Because preemptible RCU does not exist, we never have to check for |
981 | * tasks blocked within RCU read-side critical sections. |
982 | */ |
983 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) |
984 | { |
985 | } |
986 | |
987 | /* |
988 | * Because preemptible RCU does not exist, we never have to check for |
989 | * tasks blocked within RCU read-side critical sections. |
990 | */ |
991 | static int rcu_print_task_stall(struct rcu_node *rnp) |
992 | { |
993 | return 0; |
994 | } |
995 | |
996 | /* |
997 | * Because preemptible RCU does not exist, there is no need to suppress |
998 | * its CPU stall warnings. |
999 | */ |
1000 | static void rcu_preempt_stall_reset(void) |
1001 | { |
1002 | } |
1003 | |
1004 | /* |
1005 | * Because there is no preemptible RCU, there can be no readers blocked, |
1006 | * so there is no need to check for blocked tasks. So check only for |
1007 | * bogus qsmask values. |
1008 | */ |
1009 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) |
1010 | { |
1011 | WARN_ON_ONCE(rnp->qsmask); |
1012 | } |
1013 | |
1014 | #ifdef CONFIG_HOTPLUG_CPU |
1015 | |
1016 | /* |
1017 | * Because preemptible RCU does not exist, it never needs to migrate |
1018 | * tasks that were blocked within RCU read-side critical sections, and |
1019 | * such non-existent tasks cannot possibly have been blocking the current |
1020 | * grace period. |
1021 | */ |
1022 | static int rcu_preempt_offline_tasks(struct rcu_state *rsp, |
1023 | struct rcu_node *rnp, |
1024 | struct rcu_data *rdp) |
1025 | { |
1026 | return 0; |
1027 | } |
1028 | |
1029 | /* |
1030 | * Because preemptible RCU does not exist, it never needs CPU-offline |
1031 | * processing. |
1032 | */ |
1033 | static void rcu_preempt_offline_cpu(int cpu) |
1034 | { |
1035 | } |
1036 | |
1037 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
1038 | |
1039 | /* |
1040 | * Because preemptible RCU does not exist, it never has any callbacks |
1041 | * to check. |
1042 | */ |
1043 | static void rcu_preempt_check_callbacks(int cpu) |
1044 | { |
1045 | } |
1046 | |
1047 | /* |
1048 | * Because preemptible RCU does not exist, it never has any callbacks |
1049 | * to process. |
1050 | */ |
1051 | static void rcu_preempt_process_callbacks(void) |
1052 | { |
1053 | } |
1054 | |
1055 | /* |
1056 | * Wait for an rcu-preempt grace period, but make it happen quickly. |
1057 | * But because preemptible RCU does not exist, map to rcu-sched. |
1058 | */ |
1059 | void synchronize_rcu_expedited(void) |
1060 | { |
1061 | synchronize_sched_expedited(); |
1062 | } |
1063 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); |
1064 | |
1065 | #ifdef CONFIG_HOTPLUG_CPU |
1066 | |
1067 | /* |
1068 | * Because preemptible RCU does not exist, there is never any need to |
1069 | * report on tasks preempted in RCU read-side critical sections during |
1070 | * expedited RCU grace periods. |
1071 | */ |
1072 | static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp) |
1073 | { |
1074 | return; |
1075 | } |
1076 | |
1077 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
1078 | |
1079 | /* |
1080 | * Because preemptible RCU does not exist, it never has any work to do. |
1081 | */ |
1082 | static int rcu_preempt_pending(int cpu) |
1083 | { |
1084 | return 0; |
1085 | } |
1086 | |
1087 | /* |
1088 | * Because preemptible RCU does not exist, it never needs any CPU. |
1089 | */ |
1090 | static int rcu_preempt_needs_cpu(int cpu) |
1091 | { |
1092 | return 0; |
1093 | } |
1094 | |
1095 | /* |
1096 | * Because preemptible RCU does not exist, rcu_barrier() is just |
1097 | * another name for rcu_barrier_sched(). |
1098 | */ |
1099 | void rcu_barrier(void) |
1100 | { |
1101 | rcu_barrier_sched(); |
1102 | } |
1103 | EXPORT_SYMBOL_GPL(rcu_barrier); |
1104 | |
1105 | /* |
1106 | * Because preemptible RCU does not exist, there is no per-CPU |
1107 | * data to initialize. |
1108 | */ |
1109 | static void __cpuinit rcu_preempt_init_percpu_data(int cpu) |
1110 | { |
1111 | } |
1112 | |
1113 | /* |
1114 | * Because there is no preemptible RCU, there are no callbacks to move. |
1115 | */ |
1116 | static void rcu_preempt_send_cbs_to_online(void) |
1117 | { |
1118 | } |
1119 | |
1120 | /* |
1121 | * Because preemptible RCU does not exist, it need not be initialized. |
1122 | */ |
1123 | static void __init __rcu_init_preempt(void) |
1124 | { |
1125 | } |
1126 | |
1127 | #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ |
1128 | |
1129 | #ifdef CONFIG_RCU_BOOST |
1130 | |
1131 | #include "rtmutex_common.h" |
1132 | |
1133 | #ifdef CONFIG_RCU_TRACE |
1134 | |
1135 | static void rcu_initiate_boost_trace(struct rcu_node *rnp) |
1136 | { |
1137 | if (list_empty(&rnp->blkd_tasks)) |
1138 | rnp->n_balk_blkd_tasks++; |
1139 | else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL) |
1140 | rnp->n_balk_exp_gp_tasks++; |
1141 | else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL) |
1142 | rnp->n_balk_boost_tasks++; |
1143 | else if (rnp->gp_tasks != NULL && rnp->qsmask != 0) |
1144 | rnp->n_balk_notblocked++; |
1145 | else if (rnp->gp_tasks != NULL && |
1146 | ULONG_CMP_LT(jiffies, rnp->boost_time)) |
1147 | rnp->n_balk_notyet++; |
1148 | else |
1149 | rnp->n_balk_nos++; |
1150 | } |
1151 | |
1152 | #else /* #ifdef CONFIG_RCU_TRACE */ |
1153 | |
1154 | static void rcu_initiate_boost_trace(struct rcu_node *rnp) |
1155 | { |
1156 | } |
1157 | |
1158 | #endif /* #else #ifdef CONFIG_RCU_TRACE */ |
1159 | |
1160 | static struct lock_class_key rcu_boost_class; |
1161 | |
1162 | /* |
1163 | * Carry out RCU priority boosting on the task indicated by ->exp_tasks |
1164 | * or ->boost_tasks, advancing the pointer to the next task in the |
1165 | * ->blkd_tasks list. |
1166 | * |
1167 | * Note that irqs must be enabled: boosting the task can block. |
1168 | * Returns 1 if there are more tasks needing to be boosted. |
1169 | */ |
1170 | static int rcu_boost(struct rcu_node *rnp) |
1171 | { |
1172 | unsigned long flags; |
1173 | struct rt_mutex mtx; |
1174 | struct task_struct *t; |
1175 | struct list_head *tb; |
1176 | |
1177 | if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) |
1178 | return 0; /* Nothing left to boost. */ |
1179 | |
1180 | raw_spin_lock_irqsave(&rnp->lock, flags); |
1181 | |
1182 | /* |
1183 | * Recheck under the lock: all tasks in need of boosting |
1184 | * might exit their RCU read-side critical sections on their own. |
1185 | */ |
1186 | if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) { |
1187 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
1188 | return 0; |
1189 | } |
1190 | |
1191 | /* |
1192 | * Preferentially boost tasks blocking expedited grace periods. |
1193 | * This cannot starve the normal grace periods because a second |
1194 | * expedited grace period must boost all blocked tasks, including |
1195 | * those blocking the pre-existing normal grace period. |
1196 | */ |
1197 | if (rnp->exp_tasks != NULL) { |
1198 | tb = rnp->exp_tasks; |
1199 | rnp->n_exp_boosts++; |
1200 | } else { |
1201 | tb = rnp->boost_tasks; |
1202 | rnp->n_normal_boosts++; |
1203 | } |
1204 | rnp->n_tasks_boosted++; |
1205 | |
1206 | /* |
1207 | * We boost task t by manufacturing an rt_mutex that appears to |
1208 | * be held by task t. We leave a pointer to that rt_mutex where |
1209 | * task t can find it, and task t will release the mutex when it |
1210 | * exits its outermost RCU read-side critical section. Then |
1211 | * simply acquiring this artificial rt_mutex will boost task |
1212 | * t's priority. (Thanks to tglx for suggesting this approach!) |
1213 | * |
1214 | * Note that task t must acquire rnp->lock to remove itself from |
1215 | * the ->blkd_tasks list, which it will do from exit() if from |
1216 | * nowhere else. We therefore are guaranteed that task t will |
1217 | * stay around at least until we drop rnp->lock. Note that |
1218 | * rnp->lock also resolves races between our priority boosting |
1219 | * and task t's exiting its outermost RCU read-side critical |
1220 | * section. |
1221 | */ |
1222 | t = container_of(tb, struct task_struct, rcu_node_entry); |
1223 | rt_mutex_init_proxy_locked(&mtx, t); |
1224 | /* Avoid lockdep false positives. This rt_mutex is its own thing. */ |
1225 | lockdep_set_class_and_name(&mtx.wait_lock, &rcu_boost_class, |
1226 | "rcu_boost_mutex"); |
1227 | t->rcu_boost_mutex = &mtx; |
1228 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
1229 | rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */ |
1230 | rt_mutex_unlock(&mtx); /* Keep lockdep happy. */ |
1231 | |
1232 | return rnp->exp_tasks != NULL || rnp->boost_tasks != NULL; |
1233 | } |
1234 | |
1235 | /* |
1236 | * Timer handler to initiate waking up of boost kthreads that |
1237 | * have yielded the CPU due to excessive numbers of tasks to |
1238 | * boost. We wake up the per-rcu_node kthread, which in turn |
1239 | * will wake up the booster kthread. |
1240 | */ |
1241 | static void rcu_boost_kthread_timer(unsigned long arg) |
1242 | { |
1243 | invoke_rcu_node_kthread((struct rcu_node *)arg); |
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("Start boost kthread@init"); |
1257 | for (;;) { |
1258 | rnp->boost_kthread_status = RCU_KTHREAD_WAITING; |
1259 | trace_rcu_utilization("End boost kthread@rcu_wait"); |
1260 | rcu_wait(rnp->boost_tasks || rnp->exp_tasks); |
1261 | trace_rcu_utilization("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 | trace_rcu_utilization("End boost kthread@rcu_yield"); |
1270 | rcu_yield(rcu_boost_kthread_timer, (unsigned long)rnp); |
1271 | trace_rcu_utilization("Start boost kthread@rcu_yield"); |
1272 | spincnt = 0; |
1273 | } |
1274 | } |
1275 | /* NOTREACHED */ |
1276 | trace_rcu_utilization("End boost kthread@notreached"); |
1277 | return 0; |
1278 | } |
1279 | |
1280 | /* |
1281 | * Check to see if it is time to start boosting RCU readers that are |
1282 | * blocking the current grace period, and, if so, tell the per-rcu_node |
1283 | * kthread to start boosting them. If there is an expedited grace |
1284 | * period in progress, it is always time to boost. |
1285 | * |
1286 | * The caller must hold rnp->lock, which this function releases, |
1287 | * but irqs remain disabled. The ->boost_kthread_task is immortal, |
1288 | * so we don't need to worry about it going away. |
1289 | */ |
1290 | static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
1291 | { |
1292 | struct task_struct *t; |
1293 | |
1294 | if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) { |
1295 | rnp->n_balk_exp_gp_tasks++; |
1296 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
1297 | return; |
1298 | } |
1299 | if (rnp->exp_tasks != NULL || |
1300 | (rnp->gp_tasks != NULL && |
1301 | rnp->boost_tasks == NULL && |
1302 | rnp->qsmask == 0 && |
1303 | ULONG_CMP_GE(jiffies, rnp->boost_time))) { |
1304 | if (rnp->exp_tasks == NULL) |
1305 | rnp->boost_tasks = rnp->gp_tasks; |
1306 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
1307 | t = rnp->boost_kthread_task; |
1308 | if (t != NULL) |
1309 | wake_up_process(t); |
1310 | } else { |
1311 | rcu_initiate_boost_trace(rnp); |
1312 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
1313 | } |
1314 | } |
1315 | |
1316 | /* |
1317 | * Wake up the per-CPU kthread to invoke RCU callbacks. |
1318 | */ |
1319 | static void invoke_rcu_callbacks_kthread(void) |
1320 | { |
1321 | unsigned long flags; |
1322 | |
1323 | local_irq_save(flags); |
1324 | __this_cpu_write(rcu_cpu_has_work, 1); |
1325 | if (__this_cpu_read(rcu_cpu_kthread_task) != NULL && |
1326 | current != __this_cpu_read(rcu_cpu_kthread_task)) |
1327 | wake_up_process(__this_cpu_read(rcu_cpu_kthread_task)); |
1328 | local_irq_restore(flags); |
1329 | } |
1330 | |
1331 | /* |
1332 | * Set the affinity of the boost kthread. The CPU-hotplug locks are |
1333 | * held, so no one should be messing with the existence of the boost |
1334 | * kthread. |
1335 | */ |
1336 | static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, |
1337 | cpumask_var_t cm) |
1338 | { |
1339 | struct task_struct *t; |
1340 | |
1341 | t = rnp->boost_kthread_task; |
1342 | if (t != NULL) |
1343 | set_cpus_allowed_ptr(rnp->boost_kthread_task, cm); |
1344 | } |
1345 | |
1346 | #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) |
1347 | |
1348 | /* |
1349 | * Do priority-boost accounting for the start of a new grace period. |
1350 | */ |
1351 | static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) |
1352 | { |
1353 | rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; |
1354 | } |
1355 | |
1356 | /* |
1357 | * Create an RCU-boost kthread for the specified node if one does not |
1358 | * already exist. We only create this kthread for preemptible RCU. |
1359 | * Returns zero if all is well, a negated errno otherwise. |
1360 | */ |
1361 | static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp, |
1362 | struct rcu_node *rnp, |
1363 | int rnp_index) |
1364 | { |
1365 | unsigned long flags; |
1366 | struct sched_param sp; |
1367 | struct task_struct *t; |
1368 | |
1369 | if (&rcu_preempt_state != rsp) |
1370 | return 0; |
1371 | rsp->boost = 1; |
1372 | if (rnp->boost_kthread_task != NULL) |
1373 | return 0; |
1374 | t = kthread_create(rcu_boost_kthread, (void *)rnp, |
1375 | "rcub/%d", rnp_index); |
1376 | if (IS_ERR(t)) |
1377 | return PTR_ERR(t); |
1378 | raw_spin_lock_irqsave(&rnp->lock, flags); |
1379 | rnp->boost_kthread_task = t; |
1380 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
1381 | sp.sched_priority = RCU_BOOST_PRIO; |
1382 | sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); |
1383 | wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ |
1384 | return 0; |
1385 | } |
1386 | |
1387 | #ifdef CONFIG_HOTPLUG_CPU |
1388 | |
1389 | /* |
1390 | * Stop the RCU's per-CPU kthread when its CPU goes offline,. |
1391 | */ |
1392 | static void rcu_stop_cpu_kthread(int cpu) |
1393 | { |
1394 | struct task_struct *t; |
1395 | |
1396 | /* Stop the CPU's kthread. */ |
1397 | t = per_cpu(rcu_cpu_kthread_task, cpu); |
1398 | if (t != NULL) { |
1399 | per_cpu(rcu_cpu_kthread_task, cpu) = NULL; |
1400 | kthread_stop(t); |
1401 | } |
1402 | } |
1403 | |
1404 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
1405 | |
1406 | static void rcu_kthread_do_work(void) |
1407 | { |
1408 | rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data)); |
1409 | rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data)); |
1410 | rcu_preempt_do_callbacks(); |
1411 | } |
1412 | |
1413 | /* |
1414 | * Wake up the specified per-rcu_node-structure kthread. |
1415 | * Because the per-rcu_node kthreads are immortal, we don't need |
1416 | * to do anything to keep them alive. |
1417 | */ |
1418 | static void invoke_rcu_node_kthread(struct rcu_node *rnp) |
1419 | { |
1420 | struct task_struct *t; |
1421 | |
1422 | t = rnp->node_kthread_task; |
1423 | if (t != NULL) |
1424 | wake_up_process(t); |
1425 | } |
1426 | |
1427 | /* |
1428 | * Set the specified CPU's kthread to run RT or not, as specified by |
1429 | * the to_rt argument. The CPU-hotplug locks are held, so the task |
1430 | * is not going away. |
1431 | */ |
1432 | static void rcu_cpu_kthread_setrt(int cpu, int to_rt) |
1433 | { |
1434 | int policy; |
1435 | struct sched_param sp; |
1436 | struct task_struct *t; |
1437 | |
1438 | t = per_cpu(rcu_cpu_kthread_task, cpu); |
1439 | if (t == NULL) |
1440 | return; |
1441 | if (to_rt) { |
1442 | policy = SCHED_FIFO; |
1443 | sp.sched_priority = RCU_KTHREAD_PRIO; |
1444 | } else { |
1445 | policy = SCHED_NORMAL; |
1446 | sp.sched_priority = 0; |
1447 | } |
1448 | sched_setscheduler_nocheck(t, policy, &sp); |
1449 | } |
1450 | |
1451 | /* |
1452 | * Timer handler to initiate the waking up of per-CPU kthreads that |
1453 | * have yielded the CPU due to excess numbers of RCU callbacks. |
1454 | * We wake up the per-rcu_node kthread, which in turn will wake up |
1455 | * the booster kthread. |
1456 | */ |
1457 | static void rcu_cpu_kthread_timer(unsigned long arg) |
1458 | { |
1459 | struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, arg); |
1460 | struct rcu_node *rnp = rdp->mynode; |
1461 | |
1462 | atomic_or(rdp->grpmask, &rnp->wakemask); |
1463 | invoke_rcu_node_kthread(rnp); |
1464 | } |
1465 | |
1466 | /* |
1467 | * Drop to non-real-time priority and yield, but only after posting a |
1468 | * timer that will cause us to regain our real-time priority if we |
1469 | * remain preempted. Either way, we restore our real-time priority |
1470 | * before returning. |
1471 | */ |
1472 | static void rcu_yield(void (*f)(unsigned long), unsigned long arg) |
1473 | { |
1474 | struct sched_param sp; |
1475 | struct timer_list yield_timer; |
1476 | int prio = current->rt_priority; |
1477 | |
1478 | setup_timer_on_stack(&yield_timer, f, arg); |
1479 | mod_timer(&yield_timer, jiffies + 2); |
1480 | sp.sched_priority = 0; |
1481 | sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp); |
1482 | set_user_nice(current, 19); |
1483 | schedule(); |
1484 | set_user_nice(current, 0); |
1485 | sp.sched_priority = prio; |
1486 | sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); |
1487 | del_timer(&yield_timer); |
1488 | } |
1489 | |
1490 | /* |
1491 | * Handle cases where the rcu_cpu_kthread() ends up on the wrong CPU. |
1492 | * This can happen while the corresponding CPU is either coming online |
1493 | * or going offline. We cannot wait until the CPU is fully online |
1494 | * before starting the kthread, because the various notifier functions |
1495 | * can wait for RCU grace periods. So we park rcu_cpu_kthread() until |
1496 | * the corresponding CPU is online. |
1497 | * |
1498 | * Return 1 if the kthread needs to stop, 0 otherwise. |
1499 | * |
1500 | * Caller must disable bh. This function can momentarily enable it. |
1501 | */ |
1502 | static int rcu_cpu_kthread_should_stop(int cpu) |
1503 | { |
1504 | while (cpu_is_offline(cpu) || |
1505 | !cpumask_equal(¤t->cpus_allowed, cpumask_of(cpu)) || |
1506 | smp_processor_id() != cpu) { |
1507 | if (kthread_should_stop()) |
1508 | return 1; |
1509 | per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; |
1510 | per_cpu(rcu_cpu_kthread_cpu, cpu) = raw_smp_processor_id(); |
1511 | local_bh_enable(); |
1512 | schedule_timeout_uninterruptible(1); |
1513 | if (!cpumask_equal(¤t->cpus_allowed, cpumask_of(cpu))) |
1514 | set_cpus_allowed_ptr(current, cpumask_of(cpu)); |
1515 | local_bh_disable(); |
1516 | } |
1517 | per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu; |
1518 | return 0; |
1519 | } |
1520 | |
1521 | /* |
1522 | * Per-CPU kernel thread that invokes RCU callbacks. This replaces the |
1523 | * RCU softirq used in flavors and configurations of RCU that do not |
1524 | * support RCU priority boosting. |
1525 | */ |
1526 | static int rcu_cpu_kthread(void *arg) |
1527 | { |
1528 | int cpu = (int)(long)arg; |
1529 | unsigned long flags; |
1530 | int spincnt = 0; |
1531 | unsigned int *statusp = &per_cpu(rcu_cpu_kthread_status, cpu); |
1532 | char work; |
1533 | char *workp = &per_cpu(rcu_cpu_has_work, cpu); |
1534 | |
1535 | trace_rcu_utilization("Start CPU kthread@init"); |
1536 | for (;;) { |
1537 | *statusp = RCU_KTHREAD_WAITING; |
1538 | trace_rcu_utilization("End CPU kthread@rcu_wait"); |
1539 | rcu_wait(*workp != 0 || kthread_should_stop()); |
1540 | trace_rcu_utilization("Start CPU kthread@rcu_wait"); |
1541 | local_bh_disable(); |
1542 | if (rcu_cpu_kthread_should_stop(cpu)) { |
1543 | local_bh_enable(); |
1544 | break; |
1545 | } |
1546 | *statusp = RCU_KTHREAD_RUNNING; |
1547 | per_cpu(rcu_cpu_kthread_loops, cpu)++; |
1548 | local_irq_save(flags); |
1549 | work = *workp; |
1550 | *workp = 0; |
1551 | local_irq_restore(flags); |
1552 | if (work) |
1553 | rcu_kthread_do_work(); |
1554 | local_bh_enable(); |
1555 | if (*workp != 0) |
1556 | spincnt++; |
1557 | else |
1558 | spincnt = 0; |
1559 | if (spincnt > 10) { |
1560 | *statusp = RCU_KTHREAD_YIELDING; |
1561 | trace_rcu_utilization("End CPU kthread@rcu_yield"); |
1562 | rcu_yield(rcu_cpu_kthread_timer, (unsigned long)cpu); |
1563 | trace_rcu_utilization("Start CPU kthread@rcu_yield"); |
1564 | spincnt = 0; |
1565 | } |
1566 | } |
1567 | *statusp = RCU_KTHREAD_STOPPED; |
1568 | trace_rcu_utilization("End CPU kthread@term"); |
1569 | return 0; |
1570 | } |
1571 | |
1572 | /* |
1573 | * Spawn a per-CPU kthread, setting up affinity and priority. |
1574 | * Because the CPU hotplug lock is held, no other CPU will be attempting |
1575 | * to manipulate rcu_cpu_kthread_task. There might be another CPU |
1576 | * attempting to access it during boot, but the locking in kthread_bind() |
1577 | * will enforce sufficient ordering. |
1578 | * |
1579 | * Please note that we cannot simply refuse to wake up the per-CPU |
1580 | * kthread because kthreads are created in TASK_UNINTERRUPTIBLE state, |
1581 | * which can result in softlockup complaints if the task ends up being |
1582 | * idle for more than a couple of minutes. |
1583 | * |
1584 | * However, please note also that we cannot bind the per-CPU kthread to its |
1585 | * CPU until that CPU is fully online. We also cannot wait until the |
1586 | * CPU is fully online before we create its per-CPU kthread, as this would |
1587 | * deadlock the system when CPU notifiers tried waiting for grace |
1588 | * periods. So we bind the per-CPU kthread to its CPU only if the CPU |
1589 | * is online. If its CPU is not yet fully online, then the code in |
1590 | * rcu_cpu_kthread() will wait until it is fully online, and then do |
1591 | * the binding. |
1592 | */ |
1593 | static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu) |
1594 | { |
1595 | struct sched_param sp; |
1596 | struct task_struct *t; |
1597 | |
1598 | if (!rcu_scheduler_fully_active || |
1599 | per_cpu(rcu_cpu_kthread_task, cpu) != NULL) |
1600 | return 0; |
1601 | t = kthread_create_on_node(rcu_cpu_kthread, |
1602 | (void *)(long)cpu, |
1603 | cpu_to_node(cpu), |
1604 | "rcuc/%d", cpu); |
1605 | if (IS_ERR(t)) |
1606 | return PTR_ERR(t); |
1607 | if (cpu_online(cpu)) |
1608 | kthread_bind(t, cpu); |
1609 | per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu; |
1610 | WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL); |
1611 | sp.sched_priority = RCU_KTHREAD_PRIO; |
1612 | sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); |
1613 | per_cpu(rcu_cpu_kthread_task, cpu) = t; |
1614 | wake_up_process(t); /* Get to TASK_INTERRUPTIBLE quickly. */ |
1615 | return 0; |
1616 | } |
1617 | |
1618 | /* |
1619 | * Per-rcu_node kthread, which is in charge of waking up the per-CPU |
1620 | * kthreads when needed. We ignore requests to wake up kthreads |
1621 | * for offline CPUs, which is OK because force_quiescent_state() |
1622 | * takes care of this case. |
1623 | */ |
1624 | static int rcu_node_kthread(void *arg) |
1625 | { |
1626 | int cpu; |
1627 | unsigned long flags; |
1628 | unsigned long mask; |
1629 | struct rcu_node *rnp = (struct rcu_node *)arg; |
1630 | struct sched_param sp; |
1631 | struct task_struct *t; |
1632 | |
1633 | for (;;) { |
1634 | rnp->node_kthread_status = RCU_KTHREAD_WAITING; |
1635 | rcu_wait(atomic_read(&rnp->wakemask) != 0); |
1636 | rnp->node_kthread_status = RCU_KTHREAD_RUNNING; |
1637 | raw_spin_lock_irqsave(&rnp->lock, flags); |
1638 | mask = atomic_xchg(&rnp->wakemask, 0); |
1639 | rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */ |
1640 | for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) { |
1641 | if ((mask & 0x1) == 0) |
1642 | continue; |
1643 | preempt_disable(); |
1644 | t = per_cpu(rcu_cpu_kthread_task, cpu); |
1645 | if (!cpu_online(cpu) || t == NULL) { |
1646 | preempt_enable(); |
1647 | continue; |
1648 | } |
1649 | per_cpu(rcu_cpu_has_work, cpu) = 1; |
1650 | sp.sched_priority = RCU_KTHREAD_PRIO; |
1651 | sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); |
1652 | preempt_enable(); |
1653 | } |
1654 | } |
1655 | /* NOTREACHED */ |
1656 | rnp->node_kthread_status = RCU_KTHREAD_STOPPED; |
1657 | return 0; |
1658 | } |
1659 | |
1660 | /* |
1661 | * Set the per-rcu_node kthread's affinity to cover all CPUs that are |
1662 | * served by the rcu_node in question. The CPU hotplug lock is still |
1663 | * held, so the value of rnp->qsmaskinit will be stable. |
1664 | * |
1665 | * We don't include outgoingcpu in the affinity set, use -1 if there is |
1666 | * no outgoing CPU. If there are no CPUs left in the affinity set, |
1667 | * this function allows the kthread to execute on any CPU. |
1668 | */ |
1669 | static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) |
1670 | { |
1671 | cpumask_var_t cm; |
1672 | int cpu; |
1673 | unsigned long mask = rnp->qsmaskinit; |
1674 | |
1675 | if (rnp->node_kthread_task == NULL) |
1676 | return; |
1677 | if (!alloc_cpumask_var(&cm, GFP_KERNEL)) |
1678 | return; |
1679 | cpumask_clear(cm); |
1680 | for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) |
1681 | if ((mask & 0x1) && cpu != outgoingcpu) |
1682 | cpumask_set_cpu(cpu, cm); |
1683 | if (cpumask_weight(cm) == 0) { |
1684 | cpumask_setall(cm); |
1685 | for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) |
1686 | cpumask_clear_cpu(cpu, cm); |
1687 | WARN_ON_ONCE(cpumask_weight(cm) == 0); |
1688 | } |
1689 | set_cpus_allowed_ptr(rnp->node_kthread_task, cm); |
1690 | rcu_boost_kthread_setaffinity(rnp, cm); |
1691 | free_cpumask_var(cm); |
1692 | } |
1693 | |
1694 | /* |
1695 | * Spawn a per-rcu_node kthread, setting priority and affinity. |
1696 | * Called during boot before online/offline can happen, or, if |
1697 | * during runtime, with the main CPU-hotplug locks held. So only |
1698 | * one of these can be executing at a time. |
1699 | */ |
1700 | static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp, |
1701 | struct rcu_node *rnp) |
1702 | { |
1703 | unsigned long flags; |
1704 | int rnp_index = rnp - &rsp->node[0]; |
1705 | struct sched_param sp; |
1706 | struct task_struct *t; |
1707 | |
1708 | if (!rcu_scheduler_fully_active || |
1709 | rnp->qsmaskinit == 0) |
1710 | return 0; |
1711 | if (rnp->node_kthread_task == NULL) { |
1712 | t = kthread_create(rcu_node_kthread, (void *)rnp, |
1713 | "rcun/%d", rnp_index); |
1714 | if (IS_ERR(t)) |
1715 | return PTR_ERR(t); |
1716 | raw_spin_lock_irqsave(&rnp->lock, flags); |
1717 | rnp->node_kthread_task = t; |
1718 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
1719 | sp.sched_priority = 99; |
1720 | sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); |
1721 | wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ |
1722 | } |
1723 | return rcu_spawn_one_boost_kthread(rsp, rnp, rnp_index); |
1724 | } |
1725 | |
1726 | /* |
1727 | * Spawn all kthreads -- called as soon as the scheduler is running. |
1728 | */ |
1729 | static int __init rcu_spawn_kthreads(void) |
1730 | { |
1731 | int cpu; |
1732 | struct rcu_node *rnp; |
1733 | |
1734 | rcu_scheduler_fully_active = 1; |
1735 | for_each_possible_cpu(cpu) { |
1736 | per_cpu(rcu_cpu_has_work, cpu) = 0; |
1737 | if (cpu_online(cpu)) |
1738 | (void)rcu_spawn_one_cpu_kthread(cpu); |
1739 | } |
1740 | rnp = rcu_get_root(rcu_state); |
1741 | (void)rcu_spawn_one_node_kthread(rcu_state, rnp); |
1742 | if (NUM_RCU_NODES > 1) { |
1743 | rcu_for_each_leaf_node(rcu_state, rnp) |
1744 | (void)rcu_spawn_one_node_kthread(rcu_state, rnp); |
1745 | } |
1746 | return 0; |
1747 | } |
1748 | early_initcall(rcu_spawn_kthreads); |
1749 | |
1750 | static void __cpuinit rcu_prepare_kthreads(int cpu) |
1751 | { |
1752 | struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu); |
1753 | struct rcu_node *rnp = rdp->mynode; |
1754 | |
1755 | /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */ |
1756 | if (rcu_scheduler_fully_active) { |
1757 | (void)rcu_spawn_one_cpu_kthread(cpu); |
1758 | if (rnp->node_kthread_task == NULL) |
1759 | (void)rcu_spawn_one_node_kthread(rcu_state, rnp); |
1760 | } |
1761 | } |
1762 | |
1763 | #else /* #ifdef CONFIG_RCU_BOOST */ |
1764 | |
1765 | static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
1766 | { |
1767 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
1768 | } |
1769 | |
1770 | static void invoke_rcu_callbacks_kthread(void) |
1771 | { |
1772 | WARN_ON_ONCE(1); |
1773 | } |
1774 | |
1775 | static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) |
1776 | { |
1777 | } |
1778 | |
1779 | #ifdef CONFIG_HOTPLUG_CPU |
1780 | |
1781 | static void rcu_stop_cpu_kthread(int cpu) |
1782 | { |
1783 | } |
1784 | |
1785 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
1786 | |
1787 | static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) |
1788 | { |
1789 | } |
1790 | |
1791 | static void rcu_cpu_kthread_setrt(int cpu, int to_rt) |
1792 | { |
1793 | } |
1794 | |
1795 | static int __init rcu_scheduler_really_started(void) |
1796 | { |
1797 | rcu_scheduler_fully_active = 1; |
1798 | return 0; |
1799 | } |
1800 | early_initcall(rcu_scheduler_really_started); |
1801 | |
1802 | static void __cpuinit rcu_prepare_kthreads(int cpu) |
1803 | { |
1804 | } |
1805 | |
1806 | #endif /* #else #ifdef CONFIG_RCU_BOOST */ |
1807 | |
1808 | #ifndef CONFIG_SMP |
1809 | |
1810 | void synchronize_sched_expedited(void) |
1811 | { |
1812 | cond_resched(); |
1813 | } |
1814 | EXPORT_SYMBOL_GPL(synchronize_sched_expedited); |
1815 | |
1816 | #else /* #ifndef CONFIG_SMP */ |
1817 | |
1818 | static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0); |
1819 | static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0); |
1820 | |
1821 | static int synchronize_sched_expedited_cpu_stop(void *data) |
1822 | { |
1823 | /* |
1824 | * There must be a full memory barrier on each affected CPU |
1825 | * between the time that try_stop_cpus() is called and the |
1826 | * time that it returns. |
1827 | * |
1828 | * In the current initial implementation of cpu_stop, the |
1829 | * above condition is already met when the control reaches |
1830 | * this point and the following smp_mb() is not strictly |
1831 | * necessary. Do smp_mb() anyway for documentation and |
1832 | * robustness against future implementation changes. |
1833 | */ |
1834 | smp_mb(); /* See above comment block. */ |
1835 | return 0; |
1836 | } |
1837 | |
1838 | /* |
1839 | * Wait for an rcu-sched grace period to elapse, but use "big hammer" |
1840 | * approach to force grace period to end quickly. This consumes |
1841 | * significant time on all CPUs, and is thus not recommended for |
1842 | * any sort of common-case code. |
1843 | * |
1844 | * Note that it is illegal to call this function while holding any |
1845 | * lock that is acquired by a CPU-hotplug notifier. Failing to |
1846 | * observe this restriction will result in deadlock. |
1847 | * |
1848 | * This implementation can be thought of as an application of ticket |
1849 | * locking to RCU, with sync_sched_expedited_started and |
1850 | * sync_sched_expedited_done taking on the roles of the halves |
1851 | * of the ticket-lock word. Each task atomically increments |
1852 | * sync_sched_expedited_started upon entry, snapshotting the old value, |
1853 | * then attempts to stop all the CPUs. If this succeeds, then each |
1854 | * CPU will have executed a context switch, resulting in an RCU-sched |
1855 | * grace period. We are then done, so we use atomic_cmpxchg() to |
1856 | * update sync_sched_expedited_done to match our snapshot -- but |
1857 | * only if someone else has not already advanced past our snapshot. |
1858 | * |
1859 | * On the other hand, if try_stop_cpus() fails, we check the value |
1860 | * of sync_sched_expedited_done. If it has advanced past our |
1861 | * initial snapshot, then someone else must have forced a grace period |
1862 | * some time after we took our snapshot. In this case, our work is |
1863 | * done for us, and we can simply return. Otherwise, we try again, |
1864 | * but keep our initial snapshot for purposes of checking for someone |
1865 | * doing our work for us. |
1866 | * |
1867 | * If we fail too many times in a row, we fall back to synchronize_sched(). |
1868 | */ |
1869 | void synchronize_sched_expedited(void) |
1870 | { |
1871 | int firstsnap, s, snap, trycount = 0; |
1872 | |
1873 | /* Note that atomic_inc_return() implies full memory barrier. */ |
1874 | firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started); |
1875 | get_online_cpus(); |
1876 | |
1877 | /* |
1878 | * Each pass through the following loop attempts to force a |
1879 | * context switch on each CPU. |
1880 | */ |
1881 | while (try_stop_cpus(cpu_online_mask, |
1882 | synchronize_sched_expedited_cpu_stop, |
1883 | NULL) == -EAGAIN) { |
1884 | put_online_cpus(); |
1885 | |
1886 | /* No joy, try again later. Or just synchronize_sched(). */ |
1887 | if (trycount++ < 10) |
1888 | udelay(trycount * num_online_cpus()); |
1889 | else { |
1890 | synchronize_sched(); |
1891 | return; |
1892 | } |
1893 | |
1894 | /* Check to see if someone else did our work for us. */ |
1895 | s = atomic_read(&sync_sched_expedited_done); |
1896 | if (UINT_CMP_GE((unsigned)s, (unsigned)firstsnap)) { |
1897 | smp_mb(); /* ensure test happens before caller kfree */ |
1898 | return; |
1899 | } |
1900 | |
1901 | /* |
1902 | * Refetching sync_sched_expedited_started allows later |
1903 | * callers to piggyback on our grace period. We subtract |
1904 | * 1 to get the same token that the last incrementer got. |
1905 | * We retry after they started, so our grace period works |
1906 | * for them, and they started after our first try, so their |
1907 | * grace period works for us. |
1908 | */ |
1909 | get_online_cpus(); |
1910 | snap = atomic_read(&sync_sched_expedited_started) - 1; |
1911 | smp_mb(); /* ensure read is before try_stop_cpus(). */ |
1912 | } |
1913 | |
1914 | /* |
1915 | * Everyone up to our most recent fetch is covered by our grace |
1916 | * period. Update the counter, but only if our work is still |
1917 | * relevant -- which it won't be if someone who started later |
1918 | * than we did beat us to the punch. |
1919 | */ |
1920 | do { |
1921 | s = atomic_read(&sync_sched_expedited_done); |
1922 | if (UINT_CMP_GE((unsigned)s, (unsigned)snap)) { |
1923 | smp_mb(); /* ensure test happens before caller kfree */ |
1924 | break; |
1925 | } |
1926 | } while (atomic_cmpxchg(&sync_sched_expedited_done, s, snap) != s); |
1927 | |
1928 | put_online_cpus(); |
1929 | } |
1930 | EXPORT_SYMBOL_GPL(synchronize_sched_expedited); |
1931 | |
1932 | #endif /* #else #ifndef CONFIG_SMP */ |
1933 | |
1934 | #if !defined(CONFIG_RCU_FAST_NO_HZ) |
1935 | |
1936 | /* |
1937 | * Check to see if any future RCU-related work will need to be done |
1938 | * by the current CPU, even if none need be done immediately, returning |
1939 | * 1 if so. This function is part of the RCU implementation; it is -not- |
1940 | * an exported member of the RCU API. |
1941 | * |
1942 | * Because we have preemptible RCU, just check whether this CPU needs |
1943 | * any flavor of RCU. Do not chew up lots of CPU cycles with preemption |
1944 | * disabled in a most-likely vain attempt to cause RCU not to need this CPU. |
1945 | */ |
1946 | int rcu_needs_cpu(int cpu) |
1947 | { |
1948 | return rcu_needs_cpu_quick_check(cpu); |
1949 | } |
1950 | |
1951 | #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
1952 | |
1953 | #define RCU_NEEDS_CPU_FLUSHES 5 |
1954 | static DEFINE_PER_CPU(int, rcu_dyntick_drain); |
1955 | static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff); |
1956 | |
1957 | /* |
1958 | * Check to see if any future RCU-related work will need to be done |
1959 | * by the current CPU, even if none need be done immediately, returning |
1960 | * 1 if so. This function is part of the RCU implementation; it is -not- |
1961 | * an exported member of the RCU API. |
1962 | * |
1963 | * Because we are not supporting preemptible RCU, attempt to accelerate |
1964 | * any current grace periods so that RCU no longer needs this CPU, but |
1965 | * only if all other CPUs are already in dynticks-idle mode. This will |
1966 | * allow the CPU cores to be powered down immediately, as opposed to after |
1967 | * waiting many milliseconds for grace periods to elapse. |
1968 | * |
1969 | * Because it is not legal to invoke rcu_process_callbacks() with irqs |
1970 | * disabled, we do one pass of force_quiescent_state(), then do a |
1971 | * invoke_rcu_core() to cause rcu_process_callbacks() to be invoked |
1972 | * later. The per-cpu rcu_dyntick_drain variable controls the sequencing. |
1973 | */ |
1974 | int rcu_needs_cpu(int cpu) |
1975 | { |
1976 | int c = 0; |
1977 | int snap; |
1978 | int thatcpu; |
1979 | |
1980 | /* Check for being in the holdoff period. */ |
1981 | if (per_cpu(rcu_dyntick_holdoff, cpu) == jiffies) |
1982 | return rcu_needs_cpu_quick_check(cpu); |
1983 | |
1984 | /* Don't bother unless we are the last non-dyntick-idle CPU. */ |
1985 | for_each_online_cpu(thatcpu) { |
1986 | if (thatcpu == cpu) |
1987 | continue; |
1988 | snap = atomic_add_return(0, &per_cpu(rcu_dynticks, |
1989 | thatcpu).dynticks); |
1990 | smp_mb(); /* Order sampling of snap with end of grace period. */ |
1991 | if ((snap & 0x1) != 0) { |
1992 | per_cpu(rcu_dyntick_drain, cpu) = 0; |
1993 | per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1; |
1994 | return rcu_needs_cpu_quick_check(cpu); |
1995 | } |
1996 | } |
1997 | |
1998 | /* Check and update the rcu_dyntick_drain sequencing. */ |
1999 | if (per_cpu(rcu_dyntick_drain, cpu) <= 0) { |
2000 | /* First time through, initialize the counter. */ |
2001 | per_cpu(rcu_dyntick_drain, cpu) = RCU_NEEDS_CPU_FLUSHES; |
2002 | } else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) { |
2003 | /* We have hit the limit, so time to give up. */ |
2004 | per_cpu(rcu_dyntick_holdoff, cpu) = jiffies; |
2005 | return rcu_needs_cpu_quick_check(cpu); |
2006 | } |
2007 | |
2008 | /* Do one step pushing remaining RCU callbacks through. */ |
2009 | if (per_cpu(rcu_sched_data, cpu).nxtlist) { |
2010 | rcu_sched_qs(cpu); |
2011 | force_quiescent_state(&rcu_sched_state, 0); |
2012 | c = c || per_cpu(rcu_sched_data, cpu).nxtlist; |
2013 | } |
2014 | if (per_cpu(rcu_bh_data, cpu).nxtlist) { |
2015 | rcu_bh_qs(cpu); |
2016 | force_quiescent_state(&rcu_bh_state, 0); |
2017 | c = c || per_cpu(rcu_bh_data, cpu).nxtlist; |
2018 | } |
2019 | |
2020 | /* If RCU callbacks are still pending, RCU still needs this CPU. */ |
2021 | if (c) |
2022 | invoke_rcu_core(); |
2023 | return c; |
2024 | } |
2025 | |
2026 | #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
2027 |
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