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Source at commit be977234bfb4a6dca8a39e7c52165e4cd536ad71 created 12 years 9 months ago. By Lars-Peter Clausen, jz4740: Fix compile error | |
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1 | /* |
2 | * Read-Copy Update mechanism for mutual exclusion (tree-based version) |
3 | * Internal non-public definitions that provide either classic |
4 | * or preemptable 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 | /* |
31 | * Check the RCU kernel configuration parameters and print informative |
32 | * messages about anything out of the ordinary. If you like #ifdef, you |
33 | * will love this function. |
34 | */ |
35 | static void __init rcu_bootup_announce_oddness(void) |
36 | { |
37 | #ifdef CONFIG_RCU_TRACE |
38 | printk(KERN_INFO "\tRCU debugfs-based tracing is enabled.\n"); |
39 | #endif |
40 | #if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32) |
41 | printk(KERN_INFO "\tCONFIG_RCU_FANOUT set to non-default value of %d\n", |
42 | CONFIG_RCU_FANOUT); |
43 | #endif |
44 | #ifdef CONFIG_RCU_FANOUT_EXACT |
45 | printk(KERN_INFO "\tHierarchical RCU autobalancing is disabled.\n"); |
46 | #endif |
47 | #ifdef CONFIG_RCU_FAST_NO_HZ |
48 | printk(KERN_INFO |
49 | "\tRCU dyntick-idle grace-period acceleration is enabled.\n"); |
50 | #endif |
51 | #ifdef CONFIG_PROVE_RCU |
52 | printk(KERN_INFO "\tRCU lockdep checking is enabled.\n"); |
53 | #endif |
54 | #ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE |
55 | printk(KERN_INFO "\tRCU torture testing starts during boot.\n"); |
56 | #endif |
57 | #ifndef CONFIG_RCU_CPU_STALL_DETECTOR |
58 | printk(KERN_INFO |
59 | "\tRCU-based detection of stalled CPUs is disabled.\n"); |
60 | #endif |
61 | #if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE) |
62 | printk(KERN_INFO "\tVerbose stalled-CPUs detection is disabled.\n"); |
63 | #endif |
64 | #if NUM_RCU_LVL_4 != 0 |
65 | printk(KERN_INFO "\tExperimental four-level hierarchy is enabled.\n"); |
66 | #endif |
67 | } |
68 | |
69 | #ifdef CONFIG_TREE_PREEMPT_RCU |
70 | |
71 | struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state); |
72 | DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data); |
73 | |
74 | static int rcu_preempted_readers_exp(struct rcu_node *rnp); |
75 | |
76 | /* |
77 | * Tell them what RCU they are running. |
78 | */ |
79 | static void __init rcu_bootup_announce(void) |
80 | { |
81 | printk(KERN_INFO "Preemptable hierarchical RCU implementation.\n"); |
82 | rcu_bootup_announce_oddness(); |
83 | } |
84 | |
85 | /* |
86 | * Return the number of RCU-preempt batches processed thus far |
87 | * for debug and statistics. |
88 | */ |
89 | long rcu_batches_completed_preempt(void) |
90 | { |
91 | return rcu_preempt_state.completed; |
92 | } |
93 | EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt); |
94 | |
95 | /* |
96 | * Return the number of RCU batches processed thus far for debug & stats. |
97 | */ |
98 | long rcu_batches_completed(void) |
99 | { |
100 | return rcu_batches_completed_preempt(); |
101 | } |
102 | EXPORT_SYMBOL_GPL(rcu_batches_completed); |
103 | |
104 | /* |
105 | * Force a quiescent state for preemptible RCU. |
106 | */ |
107 | void rcu_force_quiescent_state(void) |
108 | { |
109 | force_quiescent_state(&rcu_preempt_state, 0); |
110 | } |
111 | EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); |
112 | |
113 | /* |
114 | * Record a preemptable-RCU quiescent state for the specified CPU. Note |
115 | * that this just means that the task currently running on the CPU is |
116 | * not in a quiescent state. There might be any number of tasks blocked |
117 | * while in an RCU read-side critical section. |
118 | * |
119 | * Unlike the other rcu_*_qs() functions, callers to this function |
120 | * must disable irqs in order to protect the assignment to |
121 | * ->rcu_read_unlock_special. |
122 | */ |
123 | static void rcu_preempt_qs(int cpu) |
124 | { |
125 | struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu); |
126 | |
127 | rdp->passed_quiesc_completed = rdp->gpnum - 1; |
128 | barrier(); |
129 | rdp->passed_quiesc = 1; |
130 | current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; |
131 | } |
132 | |
133 | /* |
134 | * We have entered the scheduler, and the current task might soon be |
135 | * context-switched away from. If this task is in an RCU read-side |
136 | * critical section, we will no longer be able to rely on the CPU to |
137 | * record that fact, so we enqueue the task on the appropriate entry |
138 | * of the blocked_tasks[] array. The task will dequeue itself when |
139 | * it exits the outermost enclosing RCU read-side critical section. |
140 | * Therefore, the current grace period cannot be permitted to complete |
141 | * until the blocked_tasks[] entry indexed by the low-order bit of |
142 | * rnp->gpnum empties. |
143 | * |
144 | * Caller must disable preemption. |
145 | */ |
146 | static void rcu_preempt_note_context_switch(int cpu) |
147 | { |
148 | struct task_struct *t = current; |
149 | unsigned long flags; |
150 | int phase; |
151 | struct rcu_data *rdp; |
152 | struct rcu_node *rnp; |
153 | |
154 | if (t->rcu_read_lock_nesting && |
155 | (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { |
156 | |
157 | /* Possibly blocking in an RCU read-side critical section. */ |
158 | rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu); |
159 | rnp = rdp->mynode; |
160 | raw_spin_lock_irqsave(&rnp->lock, flags); |
161 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; |
162 | t->rcu_blocked_node = rnp; |
163 | |
164 | /* |
165 | * If this CPU has already checked in, then this task |
166 | * will hold up the next grace period rather than the |
167 | * current grace period. Queue the task accordingly. |
168 | * If the task is queued for the current grace period |
169 | * (i.e., this CPU has not yet passed through a quiescent |
170 | * state for the current grace period), then as long |
171 | * as that task remains queued, the current grace period |
172 | * cannot end. |
173 | * |
174 | * But first, note that the current CPU must still be |
175 | * on line! |
176 | */ |
177 | WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0); |
178 | WARN_ON_ONCE(!list_empty(&t->rcu_node_entry)); |
179 | phase = (rnp->gpnum + !(rnp->qsmask & rdp->grpmask)) & 0x1; |
180 | list_add(&t->rcu_node_entry, &rnp->blocked_tasks[phase]); |
181 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
182 | } |
183 | |
184 | /* |
185 | * Either we were not in an RCU read-side critical section to |
186 | * begin with, or we have now recorded that critical section |
187 | * globally. Either way, we can now note a quiescent state |
188 | * for this CPU. Again, if we were in an RCU read-side critical |
189 | * section, and if that critical section was blocking the current |
190 | * grace period, then the fact that the task has been enqueued |
191 | * means that we continue to block the current grace period. |
192 | */ |
193 | local_irq_save(flags); |
194 | rcu_preempt_qs(cpu); |
195 | local_irq_restore(flags); |
196 | } |
197 | |
198 | /* |
199 | * Tree-preemptable RCU implementation for rcu_read_lock(). |
200 | * Just increment ->rcu_read_lock_nesting, shared state will be updated |
201 | * if we block. |
202 | */ |
203 | void __rcu_read_lock(void) |
204 | { |
205 | current->rcu_read_lock_nesting++; |
206 | barrier(); /* needed if we ever invoke rcu_read_lock in rcutree.c */ |
207 | } |
208 | EXPORT_SYMBOL_GPL(__rcu_read_lock); |
209 | |
210 | /* |
211 | * Check for preempted RCU readers blocking the current grace period |
212 | * for the specified rcu_node structure. If the caller needs a reliable |
213 | * answer, it must hold the rcu_node's ->lock. |
214 | */ |
215 | static int rcu_preempted_readers(struct rcu_node *rnp) |
216 | { |
217 | int phase = rnp->gpnum & 0x1; |
218 | |
219 | return !list_empty(&rnp->blocked_tasks[phase]) || |
220 | !list_empty(&rnp->blocked_tasks[phase + 2]); |
221 | } |
222 | |
223 | /* |
224 | * Record a quiescent state for all tasks that were previously queued |
225 | * on the specified rcu_node structure and that were blocking the current |
226 | * RCU grace period. The caller must hold the specified rnp->lock with |
227 | * irqs disabled, and this lock is released upon return, but irqs remain |
228 | * disabled. |
229 | */ |
230 | static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) |
231 | __releases(rnp->lock) |
232 | { |
233 | unsigned long mask; |
234 | struct rcu_node *rnp_p; |
235 | |
236 | if (rnp->qsmask != 0 || rcu_preempted_readers(rnp)) { |
237 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
238 | return; /* Still need more quiescent states! */ |
239 | } |
240 | |
241 | rnp_p = rnp->parent; |
242 | if (rnp_p == NULL) { |
243 | /* |
244 | * Either there is only one rcu_node in the tree, |
245 | * or tasks were kicked up to root rcu_node due to |
246 | * CPUs going offline. |
247 | */ |
248 | rcu_report_qs_rsp(&rcu_preempt_state, flags); |
249 | return; |
250 | } |
251 | |
252 | /* Report up the rest of the hierarchy. */ |
253 | mask = rnp->grpmask; |
254 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
255 | raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */ |
256 | rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags); |
257 | } |
258 | |
259 | /* |
260 | * Handle special cases during rcu_read_unlock(), such as needing to |
261 | * notify RCU core processing or task having blocked during the RCU |
262 | * read-side critical section. |
263 | */ |
264 | static void rcu_read_unlock_special(struct task_struct *t) |
265 | { |
266 | int empty; |
267 | int empty_exp; |
268 | unsigned long flags; |
269 | struct rcu_node *rnp; |
270 | int special; |
271 | |
272 | /* NMI handlers cannot block and cannot safely manipulate state. */ |
273 | if (in_nmi()) |
274 | return; |
275 | |
276 | local_irq_save(flags); |
277 | |
278 | /* |
279 | * If RCU core is waiting for this CPU to exit critical section, |
280 | * let it know that we have done so. |
281 | */ |
282 | special = t->rcu_read_unlock_special; |
283 | if (special & RCU_READ_UNLOCK_NEED_QS) { |
284 | rcu_preempt_qs(smp_processor_id()); |
285 | } |
286 | |
287 | /* Hardware IRQ handlers cannot block. */ |
288 | if (in_irq()) { |
289 | local_irq_restore(flags); |
290 | return; |
291 | } |
292 | |
293 | /* Clean up if blocked during RCU read-side critical section. */ |
294 | if (special & RCU_READ_UNLOCK_BLOCKED) { |
295 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; |
296 | |
297 | /* |
298 | * Remove this task from the list it blocked on. The |
299 | * task can migrate while we acquire the lock, but at |
300 | * most one time. So at most two passes through loop. |
301 | */ |
302 | for (;;) { |
303 | rnp = t->rcu_blocked_node; |
304 | raw_spin_lock(&rnp->lock); /* irqs already disabled. */ |
305 | if (rnp == t->rcu_blocked_node) |
306 | break; |
307 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
308 | } |
309 | empty = !rcu_preempted_readers(rnp); |
310 | empty_exp = !rcu_preempted_readers_exp(rnp); |
311 | smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */ |
312 | list_del_init(&t->rcu_node_entry); |
313 | t->rcu_blocked_node = NULL; |
314 | |
315 | /* |
316 | * If this was the last task on the current list, and if |
317 | * we aren't waiting on any CPUs, report the quiescent state. |
318 | * Note that rcu_report_unblock_qs_rnp() releases rnp->lock. |
319 | */ |
320 | if (empty) |
321 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
322 | else |
323 | rcu_report_unblock_qs_rnp(rnp, flags); |
324 | |
325 | /* |
326 | * If this was the last task on the expedited lists, |
327 | * then we need to report up the rcu_node hierarchy. |
328 | */ |
329 | if (!empty_exp && !rcu_preempted_readers_exp(rnp)) |
330 | rcu_report_exp_rnp(&rcu_preempt_state, rnp); |
331 | } else { |
332 | local_irq_restore(flags); |
333 | } |
334 | } |
335 | |
336 | /* |
337 | * Tree-preemptable RCU implementation for rcu_read_unlock(). |
338 | * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost |
339 | * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then |
340 | * invoke rcu_read_unlock_special() to clean up after a context switch |
341 | * in an RCU read-side critical section and other special cases. |
342 | */ |
343 | void __rcu_read_unlock(void) |
344 | { |
345 | struct task_struct *t = current; |
346 | |
347 | barrier(); /* needed if we ever invoke rcu_read_unlock in rcutree.c */ |
348 | --t->rcu_read_lock_nesting; |
349 | barrier(); /* decrement before load of ->rcu_read_unlock_special */ |
350 | if (t->rcu_read_lock_nesting == 0 && |
351 | unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) |
352 | rcu_read_unlock_special(t); |
353 | #ifdef CONFIG_PROVE_LOCKING |
354 | WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0); |
355 | #endif /* #ifdef CONFIG_PROVE_LOCKING */ |
356 | } |
357 | EXPORT_SYMBOL_GPL(__rcu_read_unlock); |
358 | |
359 | #ifdef CONFIG_RCU_CPU_STALL_DETECTOR |
360 | |
361 | #ifdef CONFIG_RCU_CPU_STALL_VERBOSE |
362 | |
363 | /* |
364 | * Dump detailed information for all tasks blocking the current RCU |
365 | * grace period on the specified rcu_node structure. |
366 | */ |
367 | static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) |
368 | { |
369 | unsigned long flags; |
370 | struct list_head *lp; |
371 | int phase; |
372 | struct task_struct *t; |
373 | |
374 | if (rcu_preempted_readers(rnp)) { |
375 | raw_spin_lock_irqsave(&rnp->lock, flags); |
376 | phase = rnp->gpnum & 0x1; |
377 | lp = &rnp->blocked_tasks[phase]; |
378 | list_for_each_entry(t, lp, rcu_node_entry) |
379 | sched_show_task(t); |
380 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
381 | } |
382 | } |
383 | |
384 | /* |
385 | * Dump detailed information for all tasks blocking the current RCU |
386 | * grace period. |
387 | */ |
388 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) |
389 | { |
390 | struct rcu_node *rnp = rcu_get_root(rsp); |
391 | |
392 | rcu_print_detail_task_stall_rnp(rnp); |
393 | rcu_for_each_leaf_node(rsp, rnp) |
394 | rcu_print_detail_task_stall_rnp(rnp); |
395 | } |
396 | |
397 | #else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ |
398 | |
399 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) |
400 | { |
401 | } |
402 | |
403 | #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ |
404 | |
405 | /* |
406 | * Scan the current list of tasks blocked within RCU read-side critical |
407 | * sections, printing out the tid of each. |
408 | */ |
409 | static void rcu_print_task_stall(struct rcu_node *rnp) |
410 | { |
411 | struct list_head *lp; |
412 | int phase; |
413 | struct task_struct *t; |
414 | |
415 | if (rcu_preempted_readers(rnp)) { |
416 | phase = rnp->gpnum & 0x1; |
417 | lp = &rnp->blocked_tasks[phase]; |
418 | list_for_each_entry(t, lp, rcu_node_entry) |
419 | printk(" P%d", t->pid); |
420 | } |
421 | } |
422 | |
423 | /* |
424 | * Suppress preemptible RCU's CPU stall warnings by pushing the |
425 | * time of the next stall-warning message comfortably far into the |
426 | * future. |
427 | */ |
428 | static void rcu_preempt_stall_reset(void) |
429 | { |
430 | rcu_preempt_state.jiffies_stall = jiffies + ULONG_MAX / 2; |
431 | } |
432 | |
433 | #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ |
434 | |
435 | /* |
436 | * Check that the list of blocked tasks for the newly completed grace |
437 | * period is in fact empty. It is a serious bug to complete a grace |
438 | * period that still has RCU readers blocked! This function must be |
439 | * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock |
440 | * must be held by the caller. |
441 | */ |
442 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) |
443 | { |
444 | WARN_ON_ONCE(rcu_preempted_readers(rnp)); |
445 | WARN_ON_ONCE(rnp->qsmask); |
446 | } |
447 | |
448 | #ifdef CONFIG_HOTPLUG_CPU |
449 | |
450 | /* |
451 | * Handle tasklist migration for case in which all CPUs covered by the |
452 | * specified rcu_node have gone offline. Move them up to the root |
453 | * rcu_node. The reason for not just moving them to the immediate |
454 | * parent is to remove the need for rcu_read_unlock_special() to |
455 | * make more than two attempts to acquire the target rcu_node's lock. |
456 | * Returns true if there were tasks blocking the current RCU grace |
457 | * period. |
458 | * |
459 | * Returns 1 if there was previously a task blocking the current grace |
460 | * period on the specified rcu_node structure. |
461 | * |
462 | * The caller must hold rnp->lock with irqs disabled. |
463 | */ |
464 | static int rcu_preempt_offline_tasks(struct rcu_state *rsp, |
465 | struct rcu_node *rnp, |
466 | struct rcu_data *rdp) |
467 | { |
468 | int i; |
469 | struct list_head *lp; |
470 | struct list_head *lp_root; |
471 | int retval = 0; |
472 | struct rcu_node *rnp_root = rcu_get_root(rsp); |
473 | struct task_struct *tp; |
474 | |
475 | if (rnp == rnp_root) { |
476 | WARN_ONCE(1, "Last CPU thought to be offlined?"); |
477 | return 0; /* Shouldn't happen: at least one CPU online. */ |
478 | } |
479 | WARN_ON_ONCE(rnp != rdp->mynode && |
480 | (!list_empty(&rnp->blocked_tasks[0]) || |
481 | !list_empty(&rnp->blocked_tasks[1]) || |
482 | !list_empty(&rnp->blocked_tasks[2]) || |
483 | !list_empty(&rnp->blocked_tasks[3]))); |
484 | |
485 | /* |
486 | * Move tasks up to root rcu_node. Rely on the fact that the |
487 | * root rcu_node can be at most one ahead of the rest of the |
488 | * rcu_nodes in terms of gp_num value. This fact allows us to |
489 | * move the blocked_tasks[] array directly, element by element. |
490 | */ |
491 | if (rcu_preempted_readers(rnp)) |
492 | retval |= RCU_OFL_TASKS_NORM_GP; |
493 | if (rcu_preempted_readers_exp(rnp)) |
494 | retval |= RCU_OFL_TASKS_EXP_GP; |
495 | for (i = 0; i < 4; i++) { |
496 | lp = &rnp->blocked_tasks[i]; |
497 | lp_root = &rnp_root->blocked_tasks[i]; |
498 | while (!list_empty(lp)) { |
499 | tp = list_entry(lp->next, typeof(*tp), rcu_node_entry); |
500 | raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ |
501 | list_del(&tp->rcu_node_entry); |
502 | tp->rcu_blocked_node = rnp_root; |
503 | list_add(&tp->rcu_node_entry, lp_root); |
504 | raw_spin_unlock(&rnp_root->lock); /* irqs remain disabled */ |
505 | } |
506 | } |
507 | return retval; |
508 | } |
509 | |
510 | /* |
511 | * Do CPU-offline processing for preemptable RCU. |
512 | */ |
513 | static void rcu_preempt_offline_cpu(int cpu) |
514 | { |
515 | __rcu_offline_cpu(cpu, &rcu_preempt_state); |
516 | } |
517 | |
518 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
519 | |
520 | /* |
521 | * Check for a quiescent state from the current CPU. When a task blocks, |
522 | * the task is recorded in the corresponding CPU's rcu_node structure, |
523 | * which is checked elsewhere. |
524 | * |
525 | * Caller must disable hard irqs. |
526 | */ |
527 | static void rcu_preempt_check_callbacks(int cpu) |
528 | { |
529 | struct task_struct *t = current; |
530 | |
531 | if (t->rcu_read_lock_nesting == 0) { |
532 | rcu_preempt_qs(cpu); |
533 | return; |
534 | } |
535 | if (per_cpu(rcu_preempt_data, cpu).qs_pending) |
536 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; |
537 | } |
538 | |
539 | /* |
540 | * Process callbacks for preemptable RCU. |
541 | */ |
542 | static void rcu_preempt_process_callbacks(void) |
543 | { |
544 | __rcu_process_callbacks(&rcu_preempt_state, |
545 | &__get_cpu_var(rcu_preempt_data)); |
546 | } |
547 | |
548 | /* |
549 | * Queue a preemptable-RCU callback for invocation after a grace period. |
550 | */ |
551 | void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) |
552 | { |
553 | __call_rcu(head, func, &rcu_preempt_state); |
554 | } |
555 | EXPORT_SYMBOL_GPL(call_rcu); |
556 | |
557 | /** |
558 | * synchronize_rcu - wait until a grace period has elapsed. |
559 | * |
560 | * Control will return to the caller some time after a full grace |
561 | * period has elapsed, in other words after all currently executing RCU |
562 | * read-side critical sections have completed. Note, however, that |
563 | * upon return from synchronize_rcu(), the caller might well be executing |
564 | * concurrently with new RCU read-side critical sections that began while |
565 | * synchronize_rcu() was waiting. RCU read-side critical sections are |
566 | * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. |
567 | */ |
568 | void synchronize_rcu(void) |
569 | { |
570 | struct rcu_synchronize rcu; |
571 | |
572 | if (!rcu_scheduler_active) |
573 | return; |
574 | |
575 | init_rcu_head_on_stack(&rcu.head); |
576 | init_completion(&rcu.completion); |
577 | /* Will wake me after RCU finished. */ |
578 | call_rcu(&rcu.head, wakeme_after_rcu); |
579 | /* Wait for it. */ |
580 | wait_for_completion(&rcu.completion); |
581 | destroy_rcu_head_on_stack(&rcu.head); |
582 | } |
583 | EXPORT_SYMBOL_GPL(synchronize_rcu); |
584 | |
585 | static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); |
586 | static long sync_rcu_preempt_exp_count; |
587 | static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); |
588 | |
589 | /* |
590 | * Return non-zero if there are any tasks in RCU read-side critical |
591 | * sections blocking the current preemptible-RCU expedited grace period. |
592 | * If there is no preemptible-RCU expedited grace period currently in |
593 | * progress, returns zero unconditionally. |
594 | */ |
595 | static int rcu_preempted_readers_exp(struct rcu_node *rnp) |
596 | { |
597 | return !list_empty(&rnp->blocked_tasks[2]) || |
598 | !list_empty(&rnp->blocked_tasks[3]); |
599 | } |
600 | |
601 | /* |
602 | * return non-zero if there is no RCU expedited grace period in progress |
603 | * for the specified rcu_node structure, in other words, if all CPUs and |
604 | * tasks covered by the specified rcu_node structure have done their bit |
605 | * for the current expedited grace period. Works only for preemptible |
606 | * RCU -- other RCU implementation use other means. |
607 | * |
608 | * Caller must hold sync_rcu_preempt_exp_mutex. |
609 | */ |
610 | static int sync_rcu_preempt_exp_done(struct rcu_node *rnp) |
611 | { |
612 | return !rcu_preempted_readers_exp(rnp) && |
613 | ACCESS_ONCE(rnp->expmask) == 0; |
614 | } |
615 | |
616 | /* |
617 | * Report the exit from RCU read-side critical section for the last task |
618 | * that queued itself during or before the current expedited preemptible-RCU |
619 | * grace period. This event is reported either to the rcu_node structure on |
620 | * which the task was queued or to one of that rcu_node structure's ancestors, |
621 | * recursively up the tree. (Calm down, calm down, we do the recursion |
622 | * iteratively!) |
623 | * |
624 | * Caller must hold sync_rcu_preempt_exp_mutex. |
625 | */ |
626 | static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp) |
627 | { |
628 | unsigned long flags; |
629 | unsigned long mask; |
630 | |
631 | raw_spin_lock_irqsave(&rnp->lock, flags); |
632 | for (;;) { |
633 | if (!sync_rcu_preempt_exp_done(rnp)) |
634 | break; |
635 | if (rnp->parent == NULL) { |
636 | wake_up(&sync_rcu_preempt_exp_wq); |
637 | break; |
638 | } |
639 | mask = rnp->grpmask; |
640 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ |
641 | rnp = rnp->parent; |
642 | raw_spin_lock(&rnp->lock); /* irqs already disabled */ |
643 | rnp->expmask &= ~mask; |
644 | } |
645 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
646 | } |
647 | |
648 | /* |
649 | * Snapshot the tasks blocking the newly started preemptible-RCU expedited |
650 | * grace period for the specified rcu_node structure. If there are no such |
651 | * tasks, report it up the rcu_node hierarchy. |
652 | * |
653 | * Caller must hold sync_rcu_preempt_exp_mutex and rsp->onofflock. |
654 | */ |
655 | static void |
656 | sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp) |
657 | { |
658 | int must_wait; |
659 | |
660 | raw_spin_lock(&rnp->lock); /* irqs already disabled */ |
661 | list_splice_init(&rnp->blocked_tasks[0], &rnp->blocked_tasks[2]); |
662 | list_splice_init(&rnp->blocked_tasks[1], &rnp->blocked_tasks[3]); |
663 | must_wait = rcu_preempted_readers_exp(rnp); |
664 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ |
665 | if (!must_wait) |
666 | rcu_report_exp_rnp(rsp, rnp); |
667 | } |
668 | |
669 | /* |
670 | * Wait for an rcu-preempt grace period, but expedite it. The basic idea |
671 | * is to invoke synchronize_sched_expedited() to push all the tasks to |
672 | * the ->blocked_tasks[] lists, move all entries from the first set of |
673 | * ->blocked_tasks[] lists to the second set, and finally wait for this |
674 | * second set to drain. |
675 | */ |
676 | void synchronize_rcu_expedited(void) |
677 | { |
678 | unsigned long flags; |
679 | struct rcu_node *rnp; |
680 | struct rcu_state *rsp = &rcu_preempt_state; |
681 | long snap; |
682 | int trycount = 0; |
683 | |
684 | smp_mb(); /* Caller's modifications seen first by other CPUs. */ |
685 | snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1; |
686 | smp_mb(); /* Above access cannot bleed into critical section. */ |
687 | |
688 | /* |
689 | * Acquire lock, falling back to synchronize_rcu() if too many |
690 | * lock-acquisition failures. Of course, if someone does the |
691 | * expedited grace period for us, just leave. |
692 | */ |
693 | while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) { |
694 | if (trycount++ < 10) |
695 | udelay(trycount * num_online_cpus()); |
696 | else { |
697 | synchronize_rcu(); |
698 | return; |
699 | } |
700 | if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0) |
701 | goto mb_ret; /* Others did our work for us. */ |
702 | } |
703 | if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0) |
704 | goto unlock_mb_ret; /* Others did our work for us. */ |
705 | |
706 | /* force all RCU readers onto blocked_tasks[]. */ |
707 | synchronize_sched_expedited(); |
708 | |
709 | raw_spin_lock_irqsave(&rsp->onofflock, flags); |
710 | |
711 | /* Initialize ->expmask for all non-leaf rcu_node structures. */ |
712 | rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) { |
713 | raw_spin_lock(&rnp->lock); /* irqs already disabled. */ |
714 | rnp->expmask = rnp->qsmaskinit; |
715 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
716 | } |
717 | |
718 | /* Snapshot current state of ->blocked_tasks[] lists. */ |
719 | rcu_for_each_leaf_node(rsp, rnp) |
720 | sync_rcu_preempt_exp_init(rsp, rnp); |
721 | if (NUM_RCU_NODES > 1) |
722 | sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp)); |
723 | |
724 | raw_spin_unlock_irqrestore(&rsp->onofflock, flags); |
725 | |
726 | /* Wait for snapshotted ->blocked_tasks[] lists to drain. */ |
727 | rnp = rcu_get_root(rsp); |
728 | wait_event(sync_rcu_preempt_exp_wq, |
729 | sync_rcu_preempt_exp_done(rnp)); |
730 | |
731 | /* Clean up and exit. */ |
732 | smp_mb(); /* ensure expedited GP seen before counter increment. */ |
733 | ACCESS_ONCE(sync_rcu_preempt_exp_count)++; |
734 | unlock_mb_ret: |
735 | mutex_unlock(&sync_rcu_preempt_exp_mutex); |
736 | mb_ret: |
737 | smp_mb(); /* ensure subsequent action seen after grace period. */ |
738 | } |
739 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); |
740 | |
741 | /* |
742 | * Check to see if there is any immediate preemptable-RCU-related work |
743 | * to be done. |
744 | */ |
745 | static int rcu_preempt_pending(int cpu) |
746 | { |
747 | return __rcu_pending(&rcu_preempt_state, |
748 | &per_cpu(rcu_preempt_data, cpu)); |
749 | } |
750 | |
751 | /* |
752 | * Does preemptable RCU need the CPU to stay out of dynticks mode? |
753 | */ |
754 | static int rcu_preempt_needs_cpu(int cpu) |
755 | { |
756 | return !!per_cpu(rcu_preempt_data, cpu).nxtlist; |
757 | } |
758 | |
759 | /** |
760 | * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. |
761 | */ |
762 | void rcu_barrier(void) |
763 | { |
764 | _rcu_barrier(&rcu_preempt_state, call_rcu); |
765 | } |
766 | EXPORT_SYMBOL_GPL(rcu_barrier); |
767 | |
768 | /* |
769 | * Initialize preemptable RCU's per-CPU data. |
770 | */ |
771 | static void __cpuinit rcu_preempt_init_percpu_data(int cpu) |
772 | { |
773 | rcu_init_percpu_data(cpu, &rcu_preempt_state, 1); |
774 | } |
775 | |
776 | /* |
777 | * Move preemptable RCU's callbacks from dying CPU to other online CPU. |
778 | */ |
779 | static void rcu_preempt_send_cbs_to_online(void) |
780 | { |
781 | rcu_send_cbs_to_online(&rcu_preempt_state); |
782 | } |
783 | |
784 | /* |
785 | * Initialize preemptable RCU's state structures. |
786 | */ |
787 | static void __init __rcu_init_preempt(void) |
788 | { |
789 | rcu_init_one(&rcu_preempt_state, &rcu_preempt_data); |
790 | } |
791 | |
792 | /* |
793 | * Check for a task exiting while in a preemptable-RCU read-side |
794 | * critical section, clean up if so. No need to issue warnings, |
795 | * as debug_check_no_locks_held() already does this if lockdep |
796 | * is enabled. |
797 | */ |
798 | void exit_rcu(void) |
799 | { |
800 | struct task_struct *t = current; |
801 | |
802 | if (t->rcu_read_lock_nesting == 0) |
803 | return; |
804 | t->rcu_read_lock_nesting = 1; |
805 | rcu_read_unlock(); |
806 | } |
807 | |
808 | #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ |
809 | |
810 | /* |
811 | * Tell them what RCU they are running. |
812 | */ |
813 | static void __init rcu_bootup_announce(void) |
814 | { |
815 | printk(KERN_INFO "Hierarchical RCU implementation.\n"); |
816 | rcu_bootup_announce_oddness(); |
817 | } |
818 | |
819 | /* |
820 | * Return the number of RCU batches processed thus far for debug & stats. |
821 | */ |
822 | long rcu_batches_completed(void) |
823 | { |
824 | return rcu_batches_completed_sched(); |
825 | } |
826 | EXPORT_SYMBOL_GPL(rcu_batches_completed); |
827 | |
828 | /* |
829 | * Force a quiescent state for RCU, which, because there is no preemptible |
830 | * RCU, becomes the same as rcu-sched. |
831 | */ |
832 | void rcu_force_quiescent_state(void) |
833 | { |
834 | rcu_sched_force_quiescent_state(); |
835 | } |
836 | EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); |
837 | |
838 | /* |
839 | * Because preemptable RCU does not exist, we never have to check for |
840 | * CPUs being in quiescent states. |
841 | */ |
842 | static void rcu_preempt_note_context_switch(int cpu) |
843 | { |
844 | } |
845 | |
846 | /* |
847 | * Because preemptable RCU does not exist, there are never any preempted |
848 | * RCU readers. |
849 | */ |
850 | static int rcu_preempted_readers(struct rcu_node *rnp) |
851 | { |
852 | return 0; |
853 | } |
854 | |
855 | #ifdef CONFIG_HOTPLUG_CPU |
856 | |
857 | /* Because preemptible RCU does not exist, no quieting of tasks. */ |
858 | static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) |
859 | { |
860 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
861 | } |
862 | |
863 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
864 | |
865 | #ifdef CONFIG_RCU_CPU_STALL_DETECTOR |
866 | |
867 | /* |
868 | * Because preemptable RCU does not exist, we never have to check for |
869 | * tasks blocked within RCU read-side critical sections. |
870 | */ |
871 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) |
872 | { |
873 | } |
874 | |
875 | /* |
876 | * Because preemptable RCU does not exist, we never have to check for |
877 | * tasks blocked within RCU read-side critical sections. |
878 | */ |
879 | static void rcu_print_task_stall(struct rcu_node *rnp) |
880 | { |
881 | } |
882 | |
883 | /* |
884 | * Because preemptible RCU does not exist, there is no need to suppress |
885 | * its CPU stall warnings. |
886 | */ |
887 | static void rcu_preempt_stall_reset(void) |
888 | { |
889 | } |
890 | |
891 | #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ |
892 | |
893 | /* |
894 | * Because there is no preemptable RCU, there can be no readers blocked, |
895 | * so there is no need to check for blocked tasks. So check only for |
896 | * bogus qsmask values. |
897 | */ |
898 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) |
899 | { |
900 | WARN_ON_ONCE(rnp->qsmask); |
901 | } |
902 | |
903 | #ifdef CONFIG_HOTPLUG_CPU |
904 | |
905 | /* |
906 | * Because preemptable RCU does not exist, it never needs to migrate |
907 | * tasks that were blocked within RCU read-side critical sections, and |
908 | * such non-existent tasks cannot possibly have been blocking the current |
909 | * grace period. |
910 | */ |
911 | static int rcu_preempt_offline_tasks(struct rcu_state *rsp, |
912 | struct rcu_node *rnp, |
913 | struct rcu_data *rdp) |
914 | { |
915 | return 0; |
916 | } |
917 | |
918 | /* |
919 | * Because preemptable RCU does not exist, it never needs CPU-offline |
920 | * processing. |
921 | */ |
922 | static void rcu_preempt_offline_cpu(int cpu) |
923 | { |
924 | } |
925 | |
926 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
927 | |
928 | /* |
929 | * Because preemptable RCU does not exist, it never has any callbacks |
930 | * to check. |
931 | */ |
932 | static void rcu_preempt_check_callbacks(int cpu) |
933 | { |
934 | } |
935 | |
936 | /* |
937 | * Because preemptable RCU does not exist, it never has any callbacks |
938 | * to process. |
939 | */ |
940 | static void rcu_preempt_process_callbacks(void) |
941 | { |
942 | } |
943 | |
944 | /* |
945 | * Wait for an rcu-preempt grace period, but make it happen quickly. |
946 | * But because preemptable RCU does not exist, map to rcu-sched. |
947 | */ |
948 | void synchronize_rcu_expedited(void) |
949 | { |
950 | synchronize_sched_expedited(); |
951 | } |
952 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); |
953 | |
954 | #ifdef CONFIG_HOTPLUG_CPU |
955 | |
956 | /* |
957 | * Because preemptable RCU does not exist, there is never any need to |
958 | * report on tasks preempted in RCU read-side critical sections during |
959 | * expedited RCU grace periods. |
960 | */ |
961 | static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp) |
962 | { |
963 | return; |
964 | } |
965 | |
966 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ |
967 | |
968 | /* |
969 | * Because preemptable RCU does not exist, it never has any work to do. |
970 | */ |
971 | static int rcu_preempt_pending(int cpu) |
972 | { |
973 | return 0; |
974 | } |
975 | |
976 | /* |
977 | * Because preemptable RCU does not exist, it never needs any CPU. |
978 | */ |
979 | static int rcu_preempt_needs_cpu(int cpu) |
980 | { |
981 | return 0; |
982 | } |
983 | |
984 | /* |
985 | * Because preemptable RCU does not exist, rcu_barrier() is just |
986 | * another name for rcu_barrier_sched(). |
987 | */ |
988 | void rcu_barrier(void) |
989 | { |
990 | rcu_barrier_sched(); |
991 | } |
992 | EXPORT_SYMBOL_GPL(rcu_barrier); |
993 | |
994 | /* |
995 | * Because preemptable RCU does not exist, there is no per-CPU |
996 | * data to initialize. |
997 | */ |
998 | static void __cpuinit rcu_preempt_init_percpu_data(int cpu) |
999 | { |
1000 | } |
1001 | |
1002 | /* |
1003 | * Because there is no preemptable RCU, there are no callbacks to move. |
1004 | */ |
1005 | static void rcu_preempt_send_cbs_to_online(void) |
1006 | { |
1007 | } |
1008 | |
1009 | /* |
1010 | * Because preemptable RCU does not exist, it need not be initialized. |
1011 | */ |
1012 | static void __init __rcu_init_preempt(void) |
1013 | { |
1014 | } |
1015 | |
1016 | #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ |
1017 | |
1018 | #ifndef CONFIG_SMP |
1019 | |
1020 | void synchronize_sched_expedited(void) |
1021 | { |
1022 | cond_resched(); |
1023 | } |
1024 | EXPORT_SYMBOL_GPL(synchronize_sched_expedited); |
1025 | |
1026 | #else /* #ifndef CONFIG_SMP */ |
1027 | |
1028 | static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0); |
1029 | static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0); |
1030 | |
1031 | static int synchronize_sched_expedited_cpu_stop(void *data) |
1032 | { |
1033 | /* |
1034 | * There must be a full memory barrier on each affected CPU |
1035 | * between the time that try_stop_cpus() is called and the |
1036 | * time that it returns. |
1037 | * |
1038 | * In the current initial implementation of cpu_stop, the |
1039 | * above condition is already met when the control reaches |
1040 | * this point and the following smp_mb() is not strictly |
1041 | * necessary. Do smp_mb() anyway for documentation and |
1042 | * robustness against future implementation changes. |
1043 | */ |
1044 | smp_mb(); /* See above comment block. */ |
1045 | return 0; |
1046 | } |
1047 | |
1048 | /* |
1049 | * Wait for an rcu-sched grace period to elapse, but use "big hammer" |
1050 | * approach to force grace period to end quickly. This consumes |
1051 | * significant time on all CPUs, and is thus not recommended for |
1052 | * any sort of common-case code. |
1053 | * |
1054 | * Note that it is illegal to call this function while holding any |
1055 | * lock that is acquired by a CPU-hotplug notifier. Failing to |
1056 | * observe this restriction will result in deadlock. |
1057 | * |
1058 | * This implementation can be thought of as an application of ticket |
1059 | * locking to RCU, with sync_sched_expedited_started and |
1060 | * sync_sched_expedited_done taking on the roles of the halves |
1061 | * of the ticket-lock word. Each task atomically increments |
1062 | * sync_sched_expedited_started upon entry, snapshotting the old value, |
1063 | * then attempts to stop all the CPUs. If this succeeds, then each |
1064 | * CPU will have executed a context switch, resulting in an RCU-sched |
1065 | * grace period. We are then done, so we use atomic_cmpxchg() to |
1066 | * update sync_sched_expedited_done to match our snapshot -- but |
1067 | * only if someone else has not already advanced past our snapshot. |
1068 | * |
1069 | * On the other hand, if try_stop_cpus() fails, we check the value |
1070 | * of sync_sched_expedited_done. If it has advanced past our |
1071 | * initial snapshot, then someone else must have forced a grace period |
1072 | * some time after we took our snapshot. In this case, our work is |
1073 | * done for us, and we can simply return. Otherwise, we try again, |
1074 | * but keep our initial snapshot for purposes of checking for someone |
1075 | * doing our work for us. |
1076 | * |
1077 | * If we fail too many times in a row, we fall back to synchronize_sched(). |
1078 | */ |
1079 | void synchronize_sched_expedited(void) |
1080 | { |
1081 | int firstsnap, s, snap, trycount = 0; |
1082 | |
1083 | /* Note that atomic_inc_return() implies full memory barrier. */ |
1084 | firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started); |
1085 | get_online_cpus(); |
1086 | |
1087 | /* |
1088 | * Each pass through the following loop attempts to force a |
1089 | * context switch on each CPU. |
1090 | */ |
1091 | while (try_stop_cpus(cpu_online_mask, |
1092 | synchronize_sched_expedited_cpu_stop, |
1093 | NULL) == -EAGAIN) { |
1094 | put_online_cpus(); |
1095 | |
1096 | /* No joy, try again later. Or just synchronize_sched(). */ |
1097 | if (trycount++ < 10) |
1098 | udelay(trycount * num_online_cpus()); |
1099 | else { |
1100 | synchronize_sched(); |
1101 | return; |
1102 | } |
1103 | |
1104 | /* Check to see if someone else did our work for us. */ |
1105 | s = atomic_read(&sync_sched_expedited_done); |
1106 | if (UINT_CMP_GE((unsigned)s, (unsigned)firstsnap)) { |
1107 | smp_mb(); /* ensure test happens before caller kfree */ |
1108 | return; |
1109 | } |
1110 | |
1111 | /* |
1112 | * Refetching sync_sched_expedited_started allows later |
1113 | * callers to piggyback on our grace period. We subtract |
1114 | * 1 to get the same token that the last incrementer got. |
1115 | * We retry after they started, so our grace period works |
1116 | * for them, and they started after our first try, so their |
1117 | * grace period works for us. |
1118 | */ |
1119 | get_online_cpus(); |
1120 | snap = atomic_read(&sync_sched_expedited_started) - 1; |
1121 | smp_mb(); /* ensure read is before try_stop_cpus(). */ |
1122 | } |
1123 | |
1124 | /* |
1125 | * Everyone up to our most recent fetch is covered by our grace |
1126 | * period. Update the counter, but only if our work is still |
1127 | * relevant -- which it won't be if someone who started later |
1128 | * than we did beat us to the punch. |
1129 | */ |
1130 | do { |
1131 | s = atomic_read(&sync_sched_expedited_done); |
1132 | if (UINT_CMP_GE((unsigned)s, (unsigned)snap)) { |
1133 | smp_mb(); /* ensure test happens before caller kfree */ |
1134 | break; |
1135 | } |
1136 | } while (atomic_cmpxchg(&sync_sched_expedited_done, s, snap) != s); |
1137 | |
1138 | put_online_cpus(); |
1139 | } |
1140 | EXPORT_SYMBOL_GPL(synchronize_sched_expedited); |
1141 | |
1142 | #endif /* #else #ifndef CONFIG_SMP */ |
1143 | |
1144 | #if !defined(CONFIG_RCU_FAST_NO_HZ) |
1145 | |
1146 | /* |
1147 | * Check to see if any future RCU-related work will need to be done |
1148 | * by the current CPU, even if none need be done immediately, returning |
1149 | * 1 if so. This function is part of the RCU implementation; it is -not- |
1150 | * an exported member of the RCU API. |
1151 | * |
1152 | * Because we have preemptible RCU, just check whether this CPU needs |
1153 | * any flavor of RCU. Do not chew up lots of CPU cycles with preemption |
1154 | * disabled in a most-likely vain attempt to cause RCU not to need this CPU. |
1155 | */ |
1156 | int rcu_needs_cpu(int cpu) |
1157 | { |
1158 | return rcu_needs_cpu_quick_check(cpu); |
1159 | } |
1160 | |
1161 | /* |
1162 | * Check to see if we need to continue a callback-flush operations to |
1163 | * allow the last CPU to enter dyntick-idle mode. But fast dyntick-idle |
1164 | * entry is not configured, so we never do need to. |
1165 | */ |
1166 | static void rcu_needs_cpu_flush(void) |
1167 | { |
1168 | } |
1169 | |
1170 | #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
1171 | |
1172 | #define RCU_NEEDS_CPU_FLUSHES 5 |
1173 | static DEFINE_PER_CPU(int, rcu_dyntick_drain); |
1174 | static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff); |
1175 | |
1176 | /* |
1177 | * Check to see if any future RCU-related work will need to be done |
1178 | * by the current CPU, even if none need be done immediately, returning |
1179 | * 1 if so. This function is part of the RCU implementation; it is -not- |
1180 | * an exported member of the RCU API. |
1181 | * |
1182 | * Because we are not supporting preemptible RCU, attempt to accelerate |
1183 | * any current grace periods so that RCU no longer needs this CPU, but |
1184 | * only if all other CPUs are already in dynticks-idle mode. This will |
1185 | * allow the CPU cores to be powered down immediately, as opposed to after |
1186 | * waiting many milliseconds for grace periods to elapse. |
1187 | * |
1188 | * Because it is not legal to invoke rcu_process_callbacks() with irqs |
1189 | * disabled, we do one pass of force_quiescent_state(), then do a |
1190 | * raise_softirq() to cause rcu_process_callbacks() to be invoked later. |
1191 | * The per-cpu rcu_dyntick_drain variable controls the sequencing. |
1192 | */ |
1193 | int rcu_needs_cpu(int cpu) |
1194 | { |
1195 | int c = 0; |
1196 | int snap; |
1197 | int snap_nmi; |
1198 | int thatcpu; |
1199 | |
1200 | /* Check for being in the holdoff period. */ |
1201 | if (per_cpu(rcu_dyntick_holdoff, cpu) == jiffies) |
1202 | return rcu_needs_cpu_quick_check(cpu); |
1203 | |
1204 | /* Don't bother unless we are the last non-dyntick-idle CPU. */ |
1205 | for_each_online_cpu(thatcpu) { |
1206 | if (thatcpu == cpu) |
1207 | continue; |
1208 | snap = per_cpu(rcu_dynticks, thatcpu).dynticks; |
1209 | snap_nmi = per_cpu(rcu_dynticks, thatcpu).dynticks_nmi; |
1210 | smp_mb(); /* Order sampling of snap with end of grace period. */ |
1211 | if (((snap & 0x1) != 0) || ((snap_nmi & 0x1) != 0)) { |
1212 | per_cpu(rcu_dyntick_drain, cpu) = 0; |
1213 | per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1; |
1214 | return rcu_needs_cpu_quick_check(cpu); |
1215 | } |
1216 | } |
1217 | |
1218 | /* Check and update the rcu_dyntick_drain sequencing. */ |
1219 | if (per_cpu(rcu_dyntick_drain, cpu) <= 0) { |
1220 | /* First time through, initialize the counter. */ |
1221 | per_cpu(rcu_dyntick_drain, cpu) = RCU_NEEDS_CPU_FLUSHES; |
1222 | } else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) { |
1223 | /* We have hit the limit, so time to give up. */ |
1224 | per_cpu(rcu_dyntick_holdoff, cpu) = jiffies; |
1225 | return rcu_needs_cpu_quick_check(cpu); |
1226 | } |
1227 | |
1228 | /* Do one step pushing remaining RCU callbacks through. */ |
1229 | if (per_cpu(rcu_sched_data, cpu).nxtlist) { |
1230 | rcu_sched_qs(cpu); |
1231 | force_quiescent_state(&rcu_sched_state, 0); |
1232 | c = c || per_cpu(rcu_sched_data, cpu).nxtlist; |
1233 | } |
1234 | if (per_cpu(rcu_bh_data, cpu).nxtlist) { |
1235 | rcu_bh_qs(cpu); |
1236 | force_quiescent_state(&rcu_bh_state, 0); |
1237 | c = c || per_cpu(rcu_bh_data, cpu).nxtlist; |
1238 | } |
1239 | |
1240 | /* If RCU callbacks are still pending, RCU still needs this CPU. */ |
1241 | if (c) |
1242 | raise_softirq(RCU_SOFTIRQ); |
1243 | return c; |
1244 | } |
1245 | |
1246 | /* |
1247 | * Check to see if we need to continue a callback-flush operations to |
1248 | * allow the last CPU to enter dyntick-idle mode. |
1249 | */ |
1250 | static void rcu_needs_cpu_flush(void) |
1251 | { |
1252 | int cpu = smp_processor_id(); |
1253 | unsigned long flags; |
1254 | |
1255 | if (per_cpu(rcu_dyntick_drain, cpu) <= 0) |
1256 | return; |
1257 | local_irq_save(flags); |
1258 | (void)rcu_needs_cpu(cpu); |
1259 | local_irq_restore(flags); |
1260 | } |
1261 | |
1262 | #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
1263 |
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