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f41d911f PM |
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 | ||
28 | #ifdef CONFIG_TREE_PREEMPT_RCU | |
29 | ||
30 | struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state); | |
31 | DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data); | |
32 | ||
33 | /* | |
34 | * Tell them what RCU they are running. | |
35 | */ | |
36 | static inline void rcu_bootup_announce(void) | |
37 | { | |
38 | printk(KERN_INFO | |
39 | "Experimental preemptable hierarchical RCU implementation.\n"); | |
40 | } | |
41 | ||
42 | /* | |
43 | * Return the number of RCU-preempt batches processed thus far | |
44 | * for debug and statistics. | |
45 | */ | |
46 | long rcu_batches_completed_preempt(void) | |
47 | { | |
48 | return rcu_preempt_state.completed; | |
49 | } | |
50 | EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt); | |
51 | ||
52 | /* | |
53 | * Return the number of RCU batches processed thus far for debug & stats. | |
54 | */ | |
55 | long rcu_batches_completed(void) | |
56 | { | |
57 | return rcu_batches_completed_preempt(); | |
58 | } | |
59 | EXPORT_SYMBOL_GPL(rcu_batches_completed); | |
60 | ||
61 | /* | |
62 | * Record a preemptable-RCU quiescent state for the specified CPU. Note | |
63 | * that this just means that the task currently running on the CPU is | |
64 | * not in a quiescent state. There might be any number of tasks blocked | |
65 | * while in an RCU read-side critical section. | |
66 | */ | |
c3422bea | 67 | static void rcu_preempt_qs(int cpu) |
f41d911f PM |
68 | { |
69 | struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu); | |
f41d911f | 70 | rdp->passed_quiesc_completed = rdp->completed; |
c3422bea PM |
71 | barrier(); |
72 | rdp->passed_quiesc = 1; | |
f41d911f PM |
73 | } |
74 | ||
75 | /* | |
c3422bea PM |
76 | * We have entered the scheduler, and the current task might soon be |
77 | * context-switched away from. If this task is in an RCU read-side | |
78 | * critical section, we will no longer be able to rely on the CPU to | |
79 | * record that fact, so we enqueue the task on the appropriate entry | |
80 | * of the blocked_tasks[] array. The task will dequeue itself when | |
81 | * it exits the outermost enclosing RCU read-side critical section. | |
82 | * Therefore, the current grace period cannot be permitted to complete | |
83 | * until the blocked_tasks[] entry indexed by the low-order bit of | |
84 | * rnp->gpnum empties. | |
85 | * | |
86 | * Caller must disable preemption. | |
f41d911f | 87 | */ |
c3422bea | 88 | static void rcu_preempt_note_context_switch(int cpu) |
f41d911f PM |
89 | { |
90 | struct task_struct *t = current; | |
c3422bea | 91 | unsigned long flags; |
f41d911f PM |
92 | int phase; |
93 | struct rcu_data *rdp; | |
94 | struct rcu_node *rnp; | |
95 | ||
96 | if (t->rcu_read_lock_nesting && | |
97 | (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { | |
98 | ||
99 | /* Possibly blocking in an RCU read-side critical section. */ | |
100 | rdp = rcu_preempt_state.rda[cpu]; | |
101 | rnp = rdp->mynode; | |
c3422bea | 102 | spin_lock_irqsave(&rnp->lock, flags); |
f41d911f | 103 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; |
86848966 | 104 | t->rcu_blocked_node = rnp; |
f41d911f PM |
105 | |
106 | /* | |
107 | * If this CPU has already checked in, then this task | |
108 | * will hold up the next grace period rather than the | |
109 | * current grace period. Queue the task accordingly. | |
110 | * If the task is queued for the current grace period | |
111 | * (i.e., this CPU has not yet passed through a quiescent | |
112 | * state for the current grace period), then as long | |
113 | * as that task remains queued, the current grace period | |
114 | * cannot end. | |
b0e165c0 PM |
115 | * |
116 | * But first, note that the current CPU must still be | |
117 | * on line! | |
f41d911f | 118 | */ |
b0e165c0 | 119 | WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0); |
f41d911f PM |
120 | phase = !(rnp->qsmask & rdp->grpmask) ^ (rnp->gpnum & 0x1); |
121 | list_add(&t->rcu_node_entry, &rnp->blocked_tasks[phase]); | |
122 | smp_mb(); /* Ensure later ctxt swtch seen after above. */ | |
c3422bea | 123 | spin_unlock_irqrestore(&rnp->lock, flags); |
f41d911f PM |
124 | } |
125 | ||
126 | /* | |
127 | * Either we were not in an RCU read-side critical section to | |
128 | * begin with, or we have now recorded that critical section | |
129 | * globally. Either way, we can now note a quiescent state | |
130 | * for this CPU. Again, if we were in an RCU read-side critical | |
131 | * section, and if that critical section was blocking the current | |
132 | * grace period, then the fact that the task has been enqueued | |
133 | * means that we continue to block the current grace period. | |
134 | */ | |
c3422bea PM |
135 | rcu_preempt_qs(cpu); |
136 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; | |
f41d911f PM |
137 | } |
138 | ||
139 | /* | |
140 | * Tree-preemptable RCU implementation for rcu_read_lock(). | |
141 | * Just increment ->rcu_read_lock_nesting, shared state will be updated | |
142 | * if we block. | |
143 | */ | |
144 | void __rcu_read_lock(void) | |
145 | { | |
146 | ACCESS_ONCE(current->rcu_read_lock_nesting)++; | |
147 | barrier(); /* needed if we ever invoke rcu_read_lock in rcutree.c */ | |
148 | } | |
149 | EXPORT_SYMBOL_GPL(__rcu_read_lock); | |
150 | ||
151 | static void rcu_read_unlock_special(struct task_struct *t) | |
152 | { | |
153 | int empty; | |
154 | unsigned long flags; | |
155 | unsigned long mask; | |
156 | struct rcu_node *rnp; | |
157 | int special; | |
158 | ||
159 | /* NMI handlers cannot block and cannot safely manipulate state. */ | |
160 | if (in_nmi()) | |
161 | return; | |
162 | ||
163 | local_irq_save(flags); | |
164 | ||
165 | /* | |
166 | * If RCU core is waiting for this CPU to exit critical section, | |
167 | * let it know that we have done so. | |
168 | */ | |
169 | special = t->rcu_read_unlock_special; | |
170 | if (special & RCU_READ_UNLOCK_NEED_QS) { | |
171 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; | |
c3422bea | 172 | rcu_preempt_qs(smp_processor_id()); |
f41d911f PM |
173 | } |
174 | ||
175 | /* Hardware IRQ handlers cannot block. */ | |
176 | if (in_irq()) { | |
177 | local_irq_restore(flags); | |
178 | return; | |
179 | } | |
180 | ||
181 | /* Clean up if blocked during RCU read-side critical section. */ | |
182 | if (special & RCU_READ_UNLOCK_BLOCKED) { | |
183 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; | |
184 | ||
dd5d19ba PM |
185 | /* |
186 | * Remove this task from the list it blocked on. The | |
187 | * task can migrate while we acquire the lock, but at | |
188 | * most one time. So at most two passes through loop. | |
189 | */ | |
190 | for (;;) { | |
86848966 | 191 | rnp = t->rcu_blocked_node; |
dd5d19ba | 192 | spin_lock(&rnp->lock); |
86848966 | 193 | if (rnp == t->rcu_blocked_node) |
dd5d19ba PM |
194 | break; |
195 | spin_unlock(&rnp->lock); | |
196 | } | |
f41d911f PM |
197 | empty = list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]); |
198 | list_del_init(&t->rcu_node_entry); | |
dd5d19ba | 199 | t->rcu_blocked_node = NULL; |
f41d911f PM |
200 | |
201 | /* | |
202 | * If this was the last task on the current list, and if | |
203 | * we aren't waiting on any CPUs, report the quiescent state. | |
204 | * Note that both cpu_quiet_msk_finish() and cpu_quiet_msk() | |
205 | * drop rnp->lock and restore irq. | |
206 | */ | |
207 | if (!empty && rnp->qsmask == 0 && | |
208 | list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1])) { | |
c3422bea | 209 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; |
f41d911f PM |
210 | if (rnp->parent == NULL) { |
211 | /* Only one rcu_node in the tree. */ | |
212 | cpu_quiet_msk_finish(&rcu_preempt_state, flags); | |
213 | return; | |
214 | } | |
215 | /* Report up the rest of the hierarchy. */ | |
216 | mask = rnp->grpmask; | |
217 | spin_unlock_irqrestore(&rnp->lock, flags); | |
218 | rnp = rnp->parent; | |
219 | spin_lock_irqsave(&rnp->lock, flags); | |
220 | cpu_quiet_msk(mask, &rcu_preempt_state, rnp, flags); | |
221 | return; | |
222 | } | |
223 | spin_unlock(&rnp->lock); | |
224 | } | |
225 | local_irq_restore(flags); | |
226 | } | |
227 | ||
228 | /* | |
229 | * Tree-preemptable RCU implementation for rcu_read_unlock(). | |
230 | * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost | |
231 | * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then | |
232 | * invoke rcu_read_unlock_special() to clean up after a context switch | |
233 | * in an RCU read-side critical section and other special cases. | |
234 | */ | |
235 | void __rcu_read_unlock(void) | |
236 | { | |
237 | struct task_struct *t = current; | |
238 | ||
239 | barrier(); /* needed if we ever invoke rcu_read_unlock in rcutree.c */ | |
240 | if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 && | |
241 | unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) | |
242 | rcu_read_unlock_special(t); | |
243 | } | |
244 | EXPORT_SYMBOL_GPL(__rcu_read_unlock); | |
245 | ||
246 | #ifdef CONFIG_RCU_CPU_STALL_DETECTOR | |
247 | ||
248 | /* | |
249 | * Scan the current list of tasks blocked within RCU read-side critical | |
250 | * sections, printing out the tid of each. | |
251 | */ | |
252 | static void rcu_print_task_stall(struct rcu_node *rnp) | |
253 | { | |
254 | unsigned long flags; | |
255 | struct list_head *lp; | |
256 | int phase = rnp->gpnum & 0x1; | |
257 | struct task_struct *t; | |
258 | ||
259 | if (!list_empty(&rnp->blocked_tasks[phase])) { | |
260 | spin_lock_irqsave(&rnp->lock, flags); | |
261 | phase = rnp->gpnum & 0x1; /* re-read under lock. */ | |
262 | lp = &rnp->blocked_tasks[phase]; | |
263 | list_for_each_entry(t, lp, rcu_node_entry) | |
264 | printk(" P%d", t->pid); | |
265 | spin_unlock_irqrestore(&rnp->lock, flags); | |
266 | } | |
267 | } | |
268 | ||
269 | #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ | |
270 | ||
b0e165c0 PM |
271 | /* |
272 | * Check that the list of blocked tasks for the newly completed grace | |
273 | * period is in fact empty. It is a serious bug to complete a grace | |
274 | * period that still has RCU readers blocked! This function must be | |
275 | * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock | |
276 | * must be held by the caller. | |
277 | */ | |
278 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) | |
279 | { | |
280 | WARN_ON_ONCE(!list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1])); | |
281 | } | |
282 | ||
f41d911f PM |
283 | /* |
284 | * Check for preempted RCU readers for the specified rcu_node structure. | |
285 | * If the caller needs a reliable answer, it must hold the rcu_node's | |
286 | * >lock. | |
287 | */ | |
288 | static int rcu_preempted_readers(struct rcu_node *rnp) | |
289 | { | |
290 | return !list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]); | |
291 | } | |
292 | ||
33f76148 PM |
293 | #ifdef CONFIG_HOTPLUG_CPU |
294 | ||
dd5d19ba PM |
295 | /* |
296 | * Handle tasklist migration for case in which all CPUs covered by the | |
297 | * specified rcu_node have gone offline. Move them up to the root | |
298 | * rcu_node. The reason for not just moving them to the immediate | |
299 | * parent is to remove the need for rcu_read_unlock_special() to | |
300 | * make more than two attempts to acquire the target rcu_node's lock. | |
301 | * | |
302 | * The caller must hold rnp->lock with irqs disabled. | |
303 | */ | |
304 | static void rcu_preempt_offline_tasks(struct rcu_state *rsp, | |
305 | struct rcu_node *rnp) | |
306 | { | |
307 | int i; | |
308 | struct list_head *lp; | |
309 | struct list_head *lp_root; | |
310 | struct rcu_node *rnp_root = rcu_get_root(rsp); | |
311 | struct task_struct *tp; | |
312 | ||
86848966 PM |
313 | if (rnp == rnp_root) { |
314 | WARN_ONCE(1, "Last CPU thought to be offlined?"); | |
dd5d19ba | 315 | return; /* Shouldn't happen: at least one CPU online. */ |
86848966 | 316 | } |
dd5d19ba PM |
317 | |
318 | /* | |
319 | * Move tasks up to root rcu_node. Rely on the fact that the | |
320 | * root rcu_node can be at most one ahead of the rest of the | |
321 | * rcu_nodes in terms of gp_num value. This fact allows us to | |
322 | * move the blocked_tasks[] array directly, element by element. | |
323 | */ | |
324 | for (i = 0; i < 2; i++) { | |
325 | lp = &rnp->blocked_tasks[i]; | |
326 | lp_root = &rnp_root->blocked_tasks[i]; | |
327 | while (!list_empty(lp)) { | |
328 | tp = list_entry(lp->next, typeof(*tp), rcu_node_entry); | |
329 | spin_lock(&rnp_root->lock); /* irqs already disabled */ | |
330 | list_del(&tp->rcu_node_entry); | |
331 | tp->rcu_blocked_node = rnp_root; | |
332 | list_add(&tp->rcu_node_entry, lp_root); | |
333 | spin_unlock(&rnp_root->lock); /* irqs remain disabled */ | |
334 | } | |
335 | } | |
336 | } | |
337 | ||
33f76148 PM |
338 | /* |
339 | * Do CPU-offline processing for preemptable RCU. | |
340 | */ | |
341 | static void rcu_preempt_offline_cpu(int cpu) | |
342 | { | |
343 | __rcu_offline_cpu(cpu, &rcu_preempt_state); | |
344 | } | |
345 | ||
346 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
347 | ||
f41d911f PM |
348 | /* |
349 | * Check for a quiescent state from the current CPU. When a task blocks, | |
350 | * the task is recorded in the corresponding CPU's rcu_node structure, | |
351 | * which is checked elsewhere. | |
352 | * | |
353 | * Caller must disable hard irqs. | |
354 | */ | |
355 | static void rcu_preempt_check_callbacks(int cpu) | |
356 | { | |
357 | struct task_struct *t = current; | |
358 | ||
359 | if (t->rcu_read_lock_nesting == 0) { | |
c3422bea PM |
360 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; |
361 | rcu_preempt_qs(cpu); | |
f41d911f PM |
362 | return; |
363 | } | |
364 | if (per_cpu(rcu_preempt_data, cpu).qs_pending) { | |
c3422bea | 365 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; |
f41d911f PM |
366 | } |
367 | } | |
368 | ||
369 | /* | |
370 | * Process callbacks for preemptable RCU. | |
371 | */ | |
372 | static void rcu_preempt_process_callbacks(void) | |
373 | { | |
374 | __rcu_process_callbacks(&rcu_preempt_state, | |
375 | &__get_cpu_var(rcu_preempt_data)); | |
376 | } | |
377 | ||
378 | /* | |
379 | * Queue a preemptable-RCU callback for invocation after a grace period. | |
380 | */ | |
381 | void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) | |
382 | { | |
383 | __call_rcu(head, func, &rcu_preempt_state); | |
384 | } | |
385 | EXPORT_SYMBOL_GPL(call_rcu); | |
386 | ||
387 | /* | |
388 | * Check to see if there is any immediate preemptable-RCU-related work | |
389 | * to be done. | |
390 | */ | |
391 | static int rcu_preempt_pending(int cpu) | |
392 | { | |
393 | return __rcu_pending(&rcu_preempt_state, | |
394 | &per_cpu(rcu_preempt_data, cpu)); | |
395 | } | |
396 | ||
397 | /* | |
398 | * Does preemptable RCU need the CPU to stay out of dynticks mode? | |
399 | */ | |
400 | static int rcu_preempt_needs_cpu(int cpu) | |
401 | { | |
402 | return !!per_cpu(rcu_preempt_data, cpu).nxtlist; | |
403 | } | |
404 | ||
405 | /* | |
406 | * Initialize preemptable RCU's per-CPU data. | |
407 | */ | |
408 | static void __cpuinit rcu_preempt_init_percpu_data(int cpu) | |
409 | { | |
410 | rcu_init_percpu_data(cpu, &rcu_preempt_state, 1); | |
411 | } | |
412 | ||
413 | /* | |
414 | * Check for a task exiting while in a preemptable-RCU read-side | |
415 | * critical section, clean up if so. No need to issue warnings, | |
416 | * as debug_check_no_locks_held() already does this if lockdep | |
417 | * is enabled. | |
418 | */ | |
419 | void exit_rcu(void) | |
420 | { | |
421 | struct task_struct *t = current; | |
422 | ||
423 | if (t->rcu_read_lock_nesting == 0) | |
424 | return; | |
425 | t->rcu_read_lock_nesting = 1; | |
426 | rcu_read_unlock(); | |
427 | } | |
428 | ||
429 | #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ | |
430 | ||
431 | /* | |
432 | * Tell them what RCU they are running. | |
433 | */ | |
434 | static inline void rcu_bootup_announce(void) | |
435 | { | |
436 | printk(KERN_INFO "Hierarchical RCU implementation.\n"); | |
437 | } | |
438 | ||
439 | /* | |
440 | * Return the number of RCU batches processed thus far for debug & stats. | |
441 | */ | |
442 | long rcu_batches_completed(void) | |
443 | { | |
444 | return rcu_batches_completed_sched(); | |
445 | } | |
446 | EXPORT_SYMBOL_GPL(rcu_batches_completed); | |
447 | ||
448 | /* | |
449 | * Because preemptable RCU does not exist, we never have to check for | |
450 | * CPUs being in quiescent states. | |
451 | */ | |
c3422bea | 452 | static void rcu_preempt_note_context_switch(int cpu) |
f41d911f PM |
453 | { |
454 | } | |
455 | ||
456 | #ifdef CONFIG_RCU_CPU_STALL_DETECTOR | |
457 | ||
458 | /* | |
459 | * Because preemptable RCU does not exist, we never have to check for | |
460 | * tasks blocked within RCU read-side critical sections. | |
461 | */ | |
462 | static void rcu_print_task_stall(struct rcu_node *rnp) | |
463 | { | |
464 | } | |
465 | ||
466 | #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ | |
467 | ||
b0e165c0 PM |
468 | /* |
469 | * Because there is no preemptable RCU, there can be no readers blocked, | |
470 | * so there is no need to check for blocked tasks. | |
471 | */ | |
472 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) | |
473 | { | |
474 | } | |
475 | ||
f41d911f PM |
476 | /* |
477 | * Because preemptable RCU does not exist, there are never any preempted | |
478 | * RCU readers. | |
479 | */ | |
480 | static int rcu_preempted_readers(struct rcu_node *rnp) | |
481 | { | |
482 | return 0; | |
483 | } | |
484 | ||
33f76148 PM |
485 | #ifdef CONFIG_HOTPLUG_CPU |
486 | ||
dd5d19ba PM |
487 | /* |
488 | * Because preemptable RCU does not exist, it never needs to migrate | |
489 | * tasks that were blocked within RCU read-side critical sections. | |
490 | */ | |
491 | static void rcu_preempt_offline_tasks(struct rcu_state *rsp, | |
492 | struct rcu_node *rnp) | |
493 | { | |
494 | } | |
495 | ||
33f76148 PM |
496 | /* |
497 | * Because preemptable RCU does not exist, it never needs CPU-offline | |
498 | * processing. | |
499 | */ | |
500 | static void rcu_preempt_offline_cpu(int cpu) | |
501 | { | |
502 | } | |
503 | ||
504 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
505 | ||
f41d911f PM |
506 | /* |
507 | * Because preemptable RCU does not exist, it never has any callbacks | |
508 | * to check. | |
509 | */ | |
510 | void rcu_preempt_check_callbacks(int cpu) | |
511 | { | |
512 | } | |
513 | ||
514 | /* | |
515 | * Because preemptable RCU does not exist, it never has any callbacks | |
516 | * to process. | |
517 | */ | |
518 | void rcu_preempt_process_callbacks(void) | |
519 | { | |
520 | } | |
521 | ||
522 | /* | |
523 | * In classic RCU, call_rcu() is just call_rcu_sched(). | |
524 | */ | |
525 | void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) | |
526 | { | |
527 | call_rcu_sched(head, func); | |
528 | } | |
529 | EXPORT_SYMBOL_GPL(call_rcu); | |
530 | ||
531 | /* | |
532 | * Because preemptable RCU does not exist, it never has any work to do. | |
533 | */ | |
534 | static int rcu_preempt_pending(int cpu) | |
535 | { | |
536 | return 0; | |
537 | } | |
538 | ||
539 | /* | |
540 | * Because preemptable RCU does not exist, it never needs any CPU. | |
541 | */ | |
542 | static int rcu_preempt_needs_cpu(int cpu) | |
543 | { | |
544 | return 0; | |
545 | } | |
546 | ||
547 | /* | |
548 | * Because preemptable RCU does not exist, there is no per-CPU | |
549 | * data to initialize. | |
550 | */ | |
551 | static void __cpuinit rcu_preempt_init_percpu_data(int cpu) | |
552 | { | |
553 | } | |
554 | ||
555 | #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ |