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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 | |
6cc68793 | 4 | * or preemptible semantics. |
f41d911f PM |
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 | ||
d9a3da06 | 27 | #include <linux/delay.h> |
7b27d547 | 28 | #include <linux/stop_machine.h> |
f41d911f | 29 | |
26845c28 PM |
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 | |
81a294c4 | 57 | #if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE) |
26845c28 PM |
58 | printk(KERN_INFO "\tVerbose stalled-CPUs detection is disabled.\n"); |
59 | #endif | |
60 | #if NUM_RCU_LVL_4 != 0 | |
61 | printk(KERN_INFO "\tExperimental four-level hierarchy is enabled.\n"); | |
62 | #endif | |
63 | } | |
64 | ||
f41d911f PM |
65 | #ifdef CONFIG_TREE_PREEMPT_RCU |
66 | ||
67 | struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state); | |
68 | DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data); | |
27f4d280 | 69 | static struct rcu_state *rcu_state = &rcu_preempt_state; |
f41d911f | 70 | |
10f39bb1 | 71 | static void rcu_read_unlock_special(struct task_struct *t); |
d9a3da06 PM |
72 | static int rcu_preempted_readers_exp(struct rcu_node *rnp); |
73 | ||
f41d911f PM |
74 | /* |
75 | * Tell them what RCU they are running. | |
76 | */ | |
0e0fc1c2 | 77 | static void __init rcu_bootup_announce(void) |
f41d911f | 78 | { |
6cc68793 | 79 | printk(KERN_INFO "Preemptible hierarchical RCU implementation.\n"); |
26845c28 | 80 | rcu_bootup_announce_oddness(); |
f41d911f PM |
81 | } |
82 | ||
83 | /* | |
84 | * Return the number of RCU-preempt batches processed thus far | |
85 | * for debug and statistics. | |
86 | */ | |
87 | long rcu_batches_completed_preempt(void) | |
88 | { | |
89 | return rcu_preempt_state.completed; | |
90 | } | |
91 | EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt); | |
92 | ||
93 | /* | |
94 | * Return the number of RCU batches processed thus far for debug & stats. | |
95 | */ | |
96 | long rcu_batches_completed(void) | |
97 | { | |
98 | return rcu_batches_completed_preempt(); | |
99 | } | |
100 | EXPORT_SYMBOL_GPL(rcu_batches_completed); | |
101 | ||
bf66f18e PM |
102 | /* |
103 | * Force a quiescent state for preemptible RCU. | |
104 | */ | |
105 | void rcu_force_quiescent_state(void) | |
106 | { | |
107 | force_quiescent_state(&rcu_preempt_state, 0); | |
108 | } | |
109 | EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); | |
110 | ||
f41d911f | 111 | /* |
6cc68793 | 112 | * Record a preemptible-RCU quiescent state for the specified CPU. Note |
f41d911f PM |
113 | * that this just means that the task currently running on the CPU is |
114 | * not in a quiescent state. There might be any number of tasks blocked | |
115 | * while in an RCU read-side critical section. | |
25502a6c PM |
116 | * |
117 | * Unlike the other rcu_*_qs() functions, callers to this function | |
118 | * must disable irqs in order to protect the assignment to | |
119 | * ->rcu_read_unlock_special. | |
f41d911f | 120 | */ |
c3422bea | 121 | static void rcu_preempt_qs(int cpu) |
f41d911f PM |
122 | { |
123 | struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu); | |
25502a6c | 124 | |
c64ac3ce | 125 | rdp->passed_quiesc_completed = rdp->gpnum - 1; |
c3422bea PM |
126 | barrier(); |
127 | rdp->passed_quiesc = 1; | |
25502a6c | 128 | current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; |
f41d911f PM |
129 | } |
130 | ||
131 | /* | |
c3422bea PM |
132 | * We have entered the scheduler, and the current task might soon be |
133 | * context-switched away from. If this task is in an RCU read-side | |
134 | * critical section, we will no longer be able to rely on the CPU to | |
12f5f524 PM |
135 | * record that fact, so we enqueue the task on the blkd_tasks list. |
136 | * The task will dequeue itself when it exits the outermost enclosing | |
137 | * RCU read-side critical section. Therefore, the current grace period | |
138 | * cannot be permitted to complete until the blkd_tasks list entries | |
139 | * predating the current grace period drain, in other words, until | |
140 | * rnp->gp_tasks becomes NULL. | |
c3422bea PM |
141 | * |
142 | * Caller must disable preemption. | |
f41d911f | 143 | */ |
c3422bea | 144 | static void rcu_preempt_note_context_switch(int cpu) |
f41d911f PM |
145 | { |
146 | struct task_struct *t = current; | |
c3422bea | 147 | unsigned long flags; |
f41d911f PM |
148 | struct rcu_data *rdp; |
149 | struct rcu_node *rnp; | |
150 | ||
10f39bb1 | 151 | if (t->rcu_read_lock_nesting > 0 && |
f41d911f PM |
152 | (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { |
153 | ||
154 | /* Possibly blocking in an RCU read-side critical section. */ | |
394f99a9 | 155 | rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu); |
f41d911f | 156 | rnp = rdp->mynode; |
1304afb2 | 157 | raw_spin_lock_irqsave(&rnp->lock, flags); |
f41d911f | 158 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; |
86848966 | 159 | t->rcu_blocked_node = rnp; |
f41d911f PM |
160 | |
161 | /* | |
162 | * If this CPU has already checked in, then this task | |
163 | * will hold up the next grace period rather than the | |
164 | * current grace period. Queue the task accordingly. | |
165 | * If the task is queued for the current grace period | |
166 | * (i.e., this CPU has not yet passed through a quiescent | |
167 | * state for the current grace period), then as long | |
168 | * as that task remains queued, the current grace period | |
12f5f524 PM |
169 | * cannot end. Note that there is some uncertainty as |
170 | * to exactly when the current grace period started. | |
171 | * We take a conservative approach, which can result | |
172 | * in unnecessarily waiting on tasks that started very | |
173 | * slightly after the current grace period began. C'est | |
174 | * la vie!!! | |
b0e165c0 PM |
175 | * |
176 | * But first, note that the current CPU must still be | |
177 | * on line! | |
f41d911f | 178 | */ |
b0e165c0 | 179 | WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0); |
e7d8842e | 180 | WARN_ON_ONCE(!list_empty(&t->rcu_node_entry)); |
12f5f524 PM |
181 | if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) { |
182 | list_add(&t->rcu_node_entry, rnp->gp_tasks->prev); | |
183 | rnp->gp_tasks = &t->rcu_node_entry; | |
27f4d280 PM |
184 | #ifdef CONFIG_RCU_BOOST |
185 | if (rnp->boost_tasks != NULL) | |
186 | rnp->boost_tasks = rnp->gp_tasks; | |
187 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
12f5f524 PM |
188 | } else { |
189 | list_add(&t->rcu_node_entry, &rnp->blkd_tasks); | |
190 | if (rnp->qsmask & rdp->grpmask) | |
191 | rnp->gp_tasks = &t->rcu_node_entry; | |
192 | } | |
1304afb2 | 193 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
10f39bb1 PM |
194 | } else if (t->rcu_read_lock_nesting < 0 && |
195 | t->rcu_read_unlock_special) { | |
196 | ||
197 | /* | |
198 | * Complete exit from RCU read-side critical section on | |
199 | * behalf of preempted instance of __rcu_read_unlock(). | |
200 | */ | |
201 | rcu_read_unlock_special(t); | |
f41d911f PM |
202 | } |
203 | ||
204 | /* | |
205 | * Either we were not in an RCU read-side critical section to | |
206 | * begin with, or we have now recorded that critical section | |
207 | * globally. Either way, we can now note a quiescent state | |
208 | * for this CPU. Again, if we were in an RCU read-side critical | |
209 | * section, and if that critical section was blocking the current | |
210 | * grace period, then the fact that the task has been enqueued | |
211 | * means that we continue to block the current grace period. | |
212 | */ | |
e7d8842e | 213 | local_irq_save(flags); |
25502a6c | 214 | rcu_preempt_qs(cpu); |
e7d8842e | 215 | local_irq_restore(flags); |
f41d911f PM |
216 | } |
217 | ||
218 | /* | |
6cc68793 | 219 | * Tree-preemptible RCU implementation for rcu_read_lock(). |
f41d911f PM |
220 | * Just increment ->rcu_read_lock_nesting, shared state will be updated |
221 | * if we block. | |
222 | */ | |
223 | void __rcu_read_lock(void) | |
224 | { | |
80dcf60e | 225 | current->rcu_read_lock_nesting++; |
f41d911f PM |
226 | barrier(); /* needed if we ever invoke rcu_read_lock in rcutree.c */ |
227 | } | |
228 | EXPORT_SYMBOL_GPL(__rcu_read_lock); | |
229 | ||
fc2219d4 PM |
230 | /* |
231 | * Check for preempted RCU readers blocking the current grace period | |
232 | * for the specified rcu_node structure. If the caller needs a reliable | |
233 | * answer, it must hold the rcu_node's ->lock. | |
234 | */ | |
27f4d280 | 235 | static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
fc2219d4 | 236 | { |
12f5f524 | 237 | return rnp->gp_tasks != NULL; |
fc2219d4 PM |
238 | } |
239 | ||
b668c9cf PM |
240 | /* |
241 | * Record a quiescent state for all tasks that were previously queued | |
242 | * on the specified rcu_node structure and that were blocking the current | |
243 | * RCU grace period. The caller must hold the specified rnp->lock with | |
244 | * irqs disabled, and this lock is released upon return, but irqs remain | |
245 | * disabled. | |
246 | */ | |
d3f6bad3 | 247 | static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) |
b668c9cf PM |
248 | __releases(rnp->lock) |
249 | { | |
250 | unsigned long mask; | |
251 | struct rcu_node *rnp_p; | |
252 | ||
27f4d280 | 253 | if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) { |
1304afb2 | 254 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
b668c9cf PM |
255 | return; /* Still need more quiescent states! */ |
256 | } | |
257 | ||
258 | rnp_p = rnp->parent; | |
259 | if (rnp_p == NULL) { | |
260 | /* | |
261 | * Either there is only one rcu_node in the tree, | |
262 | * or tasks were kicked up to root rcu_node due to | |
263 | * CPUs going offline. | |
264 | */ | |
d3f6bad3 | 265 | rcu_report_qs_rsp(&rcu_preempt_state, flags); |
b668c9cf PM |
266 | return; |
267 | } | |
268 | ||
269 | /* Report up the rest of the hierarchy. */ | |
270 | mask = rnp->grpmask; | |
1304afb2 PM |
271 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
272 | raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */ | |
d3f6bad3 | 273 | rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags); |
b668c9cf PM |
274 | } |
275 | ||
12f5f524 PM |
276 | /* |
277 | * Advance a ->blkd_tasks-list pointer to the next entry, instead | |
278 | * returning NULL if at the end of the list. | |
279 | */ | |
280 | static struct list_head *rcu_next_node_entry(struct task_struct *t, | |
281 | struct rcu_node *rnp) | |
282 | { | |
283 | struct list_head *np; | |
284 | ||
285 | np = t->rcu_node_entry.next; | |
286 | if (np == &rnp->blkd_tasks) | |
287 | np = NULL; | |
288 | return np; | |
289 | } | |
290 | ||
b668c9cf PM |
291 | /* |
292 | * Handle special cases during rcu_read_unlock(), such as needing to | |
293 | * notify RCU core processing or task having blocked during the RCU | |
294 | * read-side critical section. | |
295 | */ | |
be0e1e21 | 296 | static noinline void rcu_read_unlock_special(struct task_struct *t) |
f41d911f PM |
297 | { |
298 | int empty; | |
d9a3da06 | 299 | int empty_exp; |
f41d911f | 300 | unsigned long flags; |
12f5f524 | 301 | struct list_head *np; |
f41d911f PM |
302 | struct rcu_node *rnp; |
303 | int special; | |
304 | ||
305 | /* NMI handlers cannot block and cannot safely manipulate state. */ | |
306 | if (in_nmi()) | |
307 | return; | |
308 | ||
309 | local_irq_save(flags); | |
310 | ||
311 | /* | |
312 | * If RCU core is waiting for this CPU to exit critical section, | |
313 | * let it know that we have done so. | |
314 | */ | |
315 | special = t->rcu_read_unlock_special; | |
316 | if (special & RCU_READ_UNLOCK_NEED_QS) { | |
c3422bea | 317 | rcu_preempt_qs(smp_processor_id()); |
f41d911f PM |
318 | } |
319 | ||
320 | /* Hardware IRQ handlers cannot block. */ | |
ec433f0c | 321 | if (in_irq() || in_serving_softirq()) { |
f41d911f PM |
322 | local_irq_restore(flags); |
323 | return; | |
324 | } | |
325 | ||
326 | /* Clean up if blocked during RCU read-side critical section. */ | |
327 | if (special & RCU_READ_UNLOCK_BLOCKED) { | |
328 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; | |
329 | ||
dd5d19ba PM |
330 | /* |
331 | * Remove this task from the list it blocked on. The | |
332 | * task can migrate while we acquire the lock, but at | |
333 | * most one time. So at most two passes through loop. | |
334 | */ | |
335 | for (;;) { | |
86848966 | 336 | rnp = t->rcu_blocked_node; |
1304afb2 | 337 | raw_spin_lock(&rnp->lock); /* irqs already disabled. */ |
86848966 | 338 | if (rnp == t->rcu_blocked_node) |
dd5d19ba | 339 | break; |
1304afb2 | 340 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
dd5d19ba | 341 | } |
27f4d280 | 342 | empty = !rcu_preempt_blocked_readers_cgp(rnp); |
d9a3da06 PM |
343 | empty_exp = !rcu_preempted_readers_exp(rnp); |
344 | smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */ | |
12f5f524 | 345 | np = rcu_next_node_entry(t, rnp); |
f41d911f | 346 | list_del_init(&t->rcu_node_entry); |
12f5f524 PM |
347 | if (&t->rcu_node_entry == rnp->gp_tasks) |
348 | rnp->gp_tasks = np; | |
349 | if (&t->rcu_node_entry == rnp->exp_tasks) | |
350 | rnp->exp_tasks = np; | |
27f4d280 PM |
351 | #ifdef CONFIG_RCU_BOOST |
352 | if (&t->rcu_node_entry == rnp->boost_tasks) | |
353 | rnp->boost_tasks = np; | |
7765be2f PM |
354 | /* Snapshot and clear ->rcu_boosted with rcu_node lock held. */ |
355 | if (t->rcu_boosted) { | |
356 | special |= RCU_READ_UNLOCK_BOOSTED; | |
357 | t->rcu_boosted = 0; | |
358 | } | |
27f4d280 | 359 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
dd5d19ba | 360 | t->rcu_blocked_node = NULL; |
f41d911f PM |
361 | |
362 | /* | |
363 | * If this was the last task on the current list, and if | |
364 | * we aren't waiting on any CPUs, report the quiescent state. | |
d3f6bad3 | 365 | * Note that rcu_report_unblock_qs_rnp() releases rnp->lock. |
f41d911f | 366 | */ |
b668c9cf | 367 | if (empty) |
1304afb2 | 368 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
b668c9cf | 369 | else |
d3f6bad3 | 370 | rcu_report_unblock_qs_rnp(rnp, flags); |
d9a3da06 | 371 | |
27f4d280 PM |
372 | #ifdef CONFIG_RCU_BOOST |
373 | /* Unboost if we were boosted. */ | |
374 | if (special & RCU_READ_UNLOCK_BOOSTED) { | |
27f4d280 PM |
375 | rt_mutex_unlock(t->rcu_boost_mutex); |
376 | t->rcu_boost_mutex = NULL; | |
377 | } | |
378 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
379 | ||
d9a3da06 PM |
380 | /* |
381 | * If this was the last task on the expedited lists, | |
382 | * then we need to report up the rcu_node hierarchy. | |
383 | */ | |
384 | if (!empty_exp && !rcu_preempted_readers_exp(rnp)) | |
385 | rcu_report_exp_rnp(&rcu_preempt_state, rnp); | |
b668c9cf PM |
386 | } else { |
387 | local_irq_restore(flags); | |
f41d911f | 388 | } |
f41d911f PM |
389 | } |
390 | ||
391 | /* | |
6cc68793 | 392 | * Tree-preemptible RCU implementation for rcu_read_unlock(). |
f41d911f PM |
393 | * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost |
394 | * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then | |
395 | * invoke rcu_read_unlock_special() to clean up after a context switch | |
396 | * in an RCU read-side critical section and other special cases. | |
397 | */ | |
398 | void __rcu_read_unlock(void) | |
399 | { | |
400 | struct task_struct *t = current; | |
401 | ||
402 | barrier(); /* needed if we ever invoke rcu_read_unlock in rcutree.c */ | |
10f39bb1 PM |
403 | if (t->rcu_read_lock_nesting != 1) |
404 | --t->rcu_read_lock_nesting; | |
405 | else { | |
406 | t->rcu_read_lock_nesting = INT_MIN; | |
407 | barrier(); /* assign before ->rcu_read_unlock_special load */ | |
be0e1e21 PM |
408 | if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) |
409 | rcu_read_unlock_special(t); | |
10f39bb1 PM |
410 | barrier(); /* ->rcu_read_unlock_special load before assign */ |
411 | t->rcu_read_lock_nesting = 0; | |
be0e1e21 | 412 | } |
cba8244a | 413 | #ifdef CONFIG_PROVE_LOCKING |
10f39bb1 PM |
414 | { |
415 | int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting); | |
416 | ||
417 | WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2); | |
418 | } | |
cba8244a | 419 | #endif /* #ifdef CONFIG_PROVE_LOCKING */ |
f41d911f PM |
420 | } |
421 | EXPORT_SYMBOL_GPL(__rcu_read_unlock); | |
422 | ||
1ed509a2 PM |
423 | #ifdef CONFIG_RCU_CPU_STALL_VERBOSE |
424 | ||
425 | /* | |
426 | * Dump detailed information for all tasks blocking the current RCU | |
427 | * grace period on the specified rcu_node structure. | |
428 | */ | |
429 | static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) | |
430 | { | |
431 | unsigned long flags; | |
1ed509a2 PM |
432 | struct task_struct *t; |
433 | ||
27f4d280 | 434 | if (!rcu_preempt_blocked_readers_cgp(rnp)) |
12f5f524 PM |
435 | return; |
436 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
437 | t = list_entry(rnp->gp_tasks, | |
438 | struct task_struct, rcu_node_entry); | |
439 | list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) | |
440 | sched_show_task(t); | |
441 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
1ed509a2 PM |
442 | } |
443 | ||
444 | /* | |
445 | * Dump detailed information for all tasks blocking the current RCU | |
446 | * grace period. | |
447 | */ | |
448 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
449 | { | |
450 | struct rcu_node *rnp = rcu_get_root(rsp); | |
451 | ||
452 | rcu_print_detail_task_stall_rnp(rnp); | |
453 | rcu_for_each_leaf_node(rsp, rnp) | |
454 | rcu_print_detail_task_stall_rnp(rnp); | |
455 | } | |
456 | ||
457 | #else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ | |
458 | ||
459 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
460 | { | |
461 | } | |
462 | ||
463 | #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ | |
464 | ||
f41d911f PM |
465 | /* |
466 | * Scan the current list of tasks blocked within RCU read-side critical | |
467 | * sections, printing out the tid of each. | |
468 | */ | |
469 | static void rcu_print_task_stall(struct rcu_node *rnp) | |
470 | { | |
f41d911f PM |
471 | struct task_struct *t; |
472 | ||
27f4d280 | 473 | if (!rcu_preempt_blocked_readers_cgp(rnp)) |
12f5f524 PM |
474 | return; |
475 | t = list_entry(rnp->gp_tasks, | |
476 | struct task_struct, rcu_node_entry); | |
477 | list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) | |
478 | printk(" P%d", t->pid); | |
f41d911f PM |
479 | } |
480 | ||
53d84e00 PM |
481 | /* |
482 | * Suppress preemptible RCU's CPU stall warnings by pushing the | |
483 | * time of the next stall-warning message comfortably far into the | |
484 | * future. | |
485 | */ | |
486 | static void rcu_preempt_stall_reset(void) | |
487 | { | |
488 | rcu_preempt_state.jiffies_stall = jiffies + ULONG_MAX / 2; | |
489 | } | |
490 | ||
b0e165c0 PM |
491 | /* |
492 | * Check that the list of blocked tasks for the newly completed grace | |
493 | * period is in fact empty. It is a serious bug to complete a grace | |
494 | * period that still has RCU readers blocked! This function must be | |
495 | * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock | |
496 | * must be held by the caller. | |
12f5f524 PM |
497 | * |
498 | * Also, if there are blocked tasks on the list, they automatically | |
499 | * block the newly created grace period, so set up ->gp_tasks accordingly. | |
b0e165c0 PM |
500 | */ |
501 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) | |
502 | { | |
27f4d280 | 503 | WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)); |
12f5f524 PM |
504 | if (!list_empty(&rnp->blkd_tasks)) |
505 | rnp->gp_tasks = rnp->blkd_tasks.next; | |
28ecd580 | 506 | WARN_ON_ONCE(rnp->qsmask); |
b0e165c0 PM |
507 | } |
508 | ||
33f76148 PM |
509 | #ifdef CONFIG_HOTPLUG_CPU |
510 | ||
dd5d19ba PM |
511 | /* |
512 | * Handle tasklist migration for case in which all CPUs covered by the | |
513 | * specified rcu_node have gone offline. Move them up to the root | |
514 | * rcu_node. The reason for not just moving them to the immediate | |
515 | * parent is to remove the need for rcu_read_unlock_special() to | |
516 | * make more than two attempts to acquire the target rcu_node's lock. | |
b668c9cf PM |
517 | * Returns true if there were tasks blocking the current RCU grace |
518 | * period. | |
dd5d19ba | 519 | * |
237c80c5 PM |
520 | * Returns 1 if there was previously a task blocking the current grace |
521 | * period on the specified rcu_node structure. | |
522 | * | |
dd5d19ba PM |
523 | * The caller must hold rnp->lock with irqs disabled. |
524 | */ | |
237c80c5 PM |
525 | static int rcu_preempt_offline_tasks(struct rcu_state *rsp, |
526 | struct rcu_node *rnp, | |
527 | struct rcu_data *rdp) | |
dd5d19ba | 528 | { |
dd5d19ba PM |
529 | struct list_head *lp; |
530 | struct list_head *lp_root; | |
d9a3da06 | 531 | int retval = 0; |
dd5d19ba | 532 | struct rcu_node *rnp_root = rcu_get_root(rsp); |
12f5f524 | 533 | struct task_struct *t; |
dd5d19ba | 534 | |
86848966 PM |
535 | if (rnp == rnp_root) { |
536 | WARN_ONCE(1, "Last CPU thought to be offlined?"); | |
237c80c5 | 537 | return 0; /* Shouldn't happen: at least one CPU online. */ |
86848966 | 538 | } |
12f5f524 PM |
539 | |
540 | /* If we are on an internal node, complain bitterly. */ | |
541 | WARN_ON_ONCE(rnp != rdp->mynode); | |
dd5d19ba PM |
542 | |
543 | /* | |
12f5f524 PM |
544 | * Move tasks up to root rcu_node. Don't try to get fancy for |
545 | * this corner-case operation -- just put this node's tasks | |
546 | * at the head of the root node's list, and update the root node's | |
547 | * ->gp_tasks and ->exp_tasks pointers to those of this node's, | |
548 | * if non-NULL. This might result in waiting for more tasks than | |
549 | * absolutely necessary, but this is a good performance/complexity | |
550 | * tradeoff. | |
dd5d19ba | 551 | */ |
27f4d280 | 552 | if (rcu_preempt_blocked_readers_cgp(rnp)) |
d9a3da06 PM |
553 | retval |= RCU_OFL_TASKS_NORM_GP; |
554 | if (rcu_preempted_readers_exp(rnp)) | |
555 | retval |= RCU_OFL_TASKS_EXP_GP; | |
12f5f524 PM |
556 | lp = &rnp->blkd_tasks; |
557 | lp_root = &rnp_root->blkd_tasks; | |
558 | while (!list_empty(lp)) { | |
559 | t = list_entry(lp->next, typeof(*t), rcu_node_entry); | |
560 | raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ | |
561 | list_del(&t->rcu_node_entry); | |
562 | t->rcu_blocked_node = rnp_root; | |
563 | list_add(&t->rcu_node_entry, lp_root); | |
564 | if (&t->rcu_node_entry == rnp->gp_tasks) | |
565 | rnp_root->gp_tasks = rnp->gp_tasks; | |
566 | if (&t->rcu_node_entry == rnp->exp_tasks) | |
567 | rnp_root->exp_tasks = rnp->exp_tasks; | |
27f4d280 PM |
568 | #ifdef CONFIG_RCU_BOOST |
569 | if (&t->rcu_node_entry == rnp->boost_tasks) | |
570 | rnp_root->boost_tasks = rnp->boost_tasks; | |
571 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
12f5f524 | 572 | raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ |
dd5d19ba | 573 | } |
27f4d280 PM |
574 | |
575 | #ifdef CONFIG_RCU_BOOST | |
576 | /* In case root is being boosted and leaf is not. */ | |
577 | raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ | |
578 | if (rnp_root->boost_tasks != NULL && | |
579 | rnp_root->boost_tasks != rnp_root->gp_tasks) | |
580 | rnp_root->boost_tasks = rnp_root->gp_tasks; | |
581 | raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ | |
582 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
583 | ||
12f5f524 PM |
584 | rnp->gp_tasks = NULL; |
585 | rnp->exp_tasks = NULL; | |
237c80c5 | 586 | return retval; |
dd5d19ba PM |
587 | } |
588 | ||
33f76148 | 589 | /* |
6cc68793 | 590 | * Do CPU-offline processing for preemptible RCU. |
33f76148 PM |
591 | */ |
592 | static void rcu_preempt_offline_cpu(int cpu) | |
593 | { | |
594 | __rcu_offline_cpu(cpu, &rcu_preempt_state); | |
595 | } | |
596 | ||
597 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
598 | ||
f41d911f PM |
599 | /* |
600 | * Check for a quiescent state from the current CPU. When a task blocks, | |
601 | * the task is recorded in the corresponding CPU's rcu_node structure, | |
602 | * which is checked elsewhere. | |
603 | * | |
604 | * Caller must disable hard irqs. | |
605 | */ | |
606 | static void rcu_preempt_check_callbacks(int cpu) | |
607 | { | |
608 | struct task_struct *t = current; | |
609 | ||
610 | if (t->rcu_read_lock_nesting == 0) { | |
c3422bea | 611 | rcu_preempt_qs(cpu); |
f41d911f PM |
612 | return; |
613 | } | |
10f39bb1 PM |
614 | if (t->rcu_read_lock_nesting > 0 && |
615 | per_cpu(rcu_preempt_data, cpu).qs_pending) | |
c3422bea | 616 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; |
f41d911f PM |
617 | } |
618 | ||
619 | /* | |
6cc68793 | 620 | * Process callbacks for preemptible RCU. |
f41d911f PM |
621 | */ |
622 | static void rcu_preempt_process_callbacks(void) | |
623 | { | |
624 | __rcu_process_callbacks(&rcu_preempt_state, | |
625 | &__get_cpu_var(rcu_preempt_data)); | |
626 | } | |
627 | ||
a46e0899 PM |
628 | #ifdef CONFIG_RCU_BOOST |
629 | ||
09223371 SL |
630 | static void rcu_preempt_do_callbacks(void) |
631 | { | |
632 | rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data)); | |
633 | } | |
634 | ||
a46e0899 PM |
635 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
636 | ||
f41d911f | 637 | /* |
6cc68793 | 638 | * Queue a preemptible-RCU callback for invocation after a grace period. |
f41d911f PM |
639 | */ |
640 | void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) | |
641 | { | |
642 | __call_rcu(head, func, &rcu_preempt_state); | |
643 | } | |
644 | EXPORT_SYMBOL_GPL(call_rcu); | |
645 | ||
6ebb237b PM |
646 | /** |
647 | * synchronize_rcu - wait until a grace period has elapsed. | |
648 | * | |
649 | * Control will return to the caller some time after a full grace | |
650 | * period has elapsed, in other words after all currently executing RCU | |
77d8485a PM |
651 | * read-side critical sections have completed. Note, however, that |
652 | * upon return from synchronize_rcu(), the caller might well be executing | |
653 | * concurrently with new RCU read-side critical sections that began while | |
654 | * synchronize_rcu() was waiting. RCU read-side critical sections are | |
655 | * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. | |
6ebb237b PM |
656 | */ |
657 | void synchronize_rcu(void) | |
658 | { | |
659 | struct rcu_synchronize rcu; | |
660 | ||
661 | if (!rcu_scheduler_active) | |
662 | return; | |
663 | ||
72d5a9f7 | 664 | init_rcu_head_on_stack(&rcu.head); |
6ebb237b PM |
665 | init_completion(&rcu.completion); |
666 | /* Will wake me after RCU finished. */ | |
667 | call_rcu(&rcu.head, wakeme_after_rcu); | |
668 | /* Wait for it. */ | |
669 | wait_for_completion(&rcu.completion); | |
72d5a9f7 | 670 | destroy_rcu_head_on_stack(&rcu.head); |
6ebb237b PM |
671 | } |
672 | EXPORT_SYMBOL_GPL(synchronize_rcu); | |
673 | ||
d9a3da06 PM |
674 | static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); |
675 | static long sync_rcu_preempt_exp_count; | |
676 | static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); | |
677 | ||
678 | /* | |
679 | * Return non-zero if there are any tasks in RCU read-side critical | |
680 | * sections blocking the current preemptible-RCU expedited grace period. | |
681 | * If there is no preemptible-RCU expedited grace period currently in | |
682 | * progress, returns zero unconditionally. | |
683 | */ | |
684 | static int rcu_preempted_readers_exp(struct rcu_node *rnp) | |
685 | { | |
12f5f524 | 686 | return rnp->exp_tasks != NULL; |
d9a3da06 PM |
687 | } |
688 | ||
689 | /* | |
690 | * return non-zero if there is no RCU expedited grace period in progress | |
691 | * for the specified rcu_node structure, in other words, if all CPUs and | |
692 | * tasks covered by the specified rcu_node structure have done their bit | |
693 | * for the current expedited grace period. Works only for preemptible | |
694 | * RCU -- other RCU implementation use other means. | |
695 | * | |
696 | * Caller must hold sync_rcu_preempt_exp_mutex. | |
697 | */ | |
698 | static int sync_rcu_preempt_exp_done(struct rcu_node *rnp) | |
699 | { | |
700 | return !rcu_preempted_readers_exp(rnp) && | |
701 | ACCESS_ONCE(rnp->expmask) == 0; | |
702 | } | |
703 | ||
704 | /* | |
705 | * Report the exit from RCU read-side critical section for the last task | |
706 | * that queued itself during or before the current expedited preemptible-RCU | |
707 | * grace period. This event is reported either to the rcu_node structure on | |
708 | * which the task was queued or to one of that rcu_node structure's ancestors, | |
709 | * recursively up the tree. (Calm down, calm down, we do the recursion | |
710 | * iteratively!) | |
711 | * | |
712 | * Caller must hold sync_rcu_preempt_exp_mutex. | |
713 | */ | |
714 | static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp) | |
715 | { | |
716 | unsigned long flags; | |
717 | unsigned long mask; | |
718 | ||
1304afb2 | 719 | raw_spin_lock_irqsave(&rnp->lock, flags); |
d9a3da06 | 720 | for (;;) { |
131906b0 PM |
721 | if (!sync_rcu_preempt_exp_done(rnp)) { |
722 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
d9a3da06 | 723 | break; |
131906b0 | 724 | } |
d9a3da06 | 725 | if (rnp->parent == NULL) { |
131906b0 | 726 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
d9a3da06 PM |
727 | wake_up(&sync_rcu_preempt_exp_wq); |
728 | break; | |
729 | } | |
730 | mask = rnp->grpmask; | |
1304afb2 | 731 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ |
d9a3da06 | 732 | rnp = rnp->parent; |
1304afb2 | 733 | raw_spin_lock(&rnp->lock); /* irqs already disabled */ |
d9a3da06 PM |
734 | rnp->expmask &= ~mask; |
735 | } | |
d9a3da06 PM |
736 | } |
737 | ||
738 | /* | |
739 | * Snapshot the tasks blocking the newly started preemptible-RCU expedited | |
740 | * grace period for the specified rcu_node structure. If there are no such | |
741 | * tasks, report it up the rcu_node hierarchy. | |
742 | * | |
743 | * Caller must hold sync_rcu_preempt_exp_mutex and rsp->onofflock. | |
744 | */ | |
745 | static void | |
746 | sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp) | |
747 | { | |
1217ed1b | 748 | unsigned long flags; |
12f5f524 | 749 | int must_wait = 0; |
d9a3da06 | 750 | |
1217ed1b PM |
751 | raw_spin_lock_irqsave(&rnp->lock, flags); |
752 | if (list_empty(&rnp->blkd_tasks)) | |
753 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
754 | else { | |
12f5f524 | 755 | rnp->exp_tasks = rnp->blkd_tasks.next; |
1217ed1b | 756 | rcu_initiate_boost(rnp, flags); /* releases rnp->lock */ |
12f5f524 PM |
757 | must_wait = 1; |
758 | } | |
d9a3da06 PM |
759 | if (!must_wait) |
760 | rcu_report_exp_rnp(rsp, rnp); | |
761 | } | |
762 | ||
019129d5 | 763 | /* |
d9a3da06 PM |
764 | * Wait for an rcu-preempt grace period, but expedite it. The basic idea |
765 | * is to invoke synchronize_sched_expedited() to push all the tasks to | |
12f5f524 | 766 | * the ->blkd_tasks lists and wait for this list to drain. |
019129d5 PM |
767 | */ |
768 | void synchronize_rcu_expedited(void) | |
769 | { | |
d9a3da06 PM |
770 | unsigned long flags; |
771 | struct rcu_node *rnp; | |
772 | struct rcu_state *rsp = &rcu_preempt_state; | |
773 | long snap; | |
774 | int trycount = 0; | |
775 | ||
776 | smp_mb(); /* Caller's modifications seen first by other CPUs. */ | |
777 | snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1; | |
778 | smp_mb(); /* Above access cannot bleed into critical section. */ | |
779 | ||
780 | /* | |
781 | * Acquire lock, falling back to synchronize_rcu() if too many | |
782 | * lock-acquisition failures. Of course, if someone does the | |
783 | * expedited grace period for us, just leave. | |
784 | */ | |
785 | while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) { | |
786 | if (trycount++ < 10) | |
787 | udelay(trycount * num_online_cpus()); | |
788 | else { | |
789 | synchronize_rcu(); | |
790 | return; | |
791 | } | |
792 | if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0) | |
793 | goto mb_ret; /* Others did our work for us. */ | |
794 | } | |
795 | if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0) | |
796 | goto unlock_mb_ret; /* Others did our work for us. */ | |
797 | ||
12f5f524 | 798 | /* force all RCU readers onto ->blkd_tasks lists. */ |
d9a3da06 PM |
799 | synchronize_sched_expedited(); |
800 | ||
1304afb2 | 801 | raw_spin_lock_irqsave(&rsp->onofflock, flags); |
d9a3da06 PM |
802 | |
803 | /* Initialize ->expmask for all non-leaf rcu_node structures. */ | |
804 | rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) { | |
1304afb2 | 805 | raw_spin_lock(&rnp->lock); /* irqs already disabled. */ |
d9a3da06 | 806 | rnp->expmask = rnp->qsmaskinit; |
1304afb2 | 807 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
d9a3da06 PM |
808 | } |
809 | ||
12f5f524 | 810 | /* Snapshot current state of ->blkd_tasks lists. */ |
d9a3da06 PM |
811 | rcu_for_each_leaf_node(rsp, rnp) |
812 | sync_rcu_preempt_exp_init(rsp, rnp); | |
813 | if (NUM_RCU_NODES > 1) | |
814 | sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp)); | |
815 | ||
1304afb2 | 816 | raw_spin_unlock_irqrestore(&rsp->onofflock, flags); |
d9a3da06 | 817 | |
12f5f524 | 818 | /* Wait for snapshotted ->blkd_tasks lists to drain. */ |
d9a3da06 PM |
819 | rnp = rcu_get_root(rsp); |
820 | wait_event(sync_rcu_preempt_exp_wq, | |
821 | sync_rcu_preempt_exp_done(rnp)); | |
822 | ||
823 | /* Clean up and exit. */ | |
824 | smp_mb(); /* ensure expedited GP seen before counter increment. */ | |
825 | ACCESS_ONCE(sync_rcu_preempt_exp_count)++; | |
826 | unlock_mb_ret: | |
827 | mutex_unlock(&sync_rcu_preempt_exp_mutex); | |
828 | mb_ret: | |
829 | smp_mb(); /* ensure subsequent action seen after grace period. */ | |
019129d5 PM |
830 | } |
831 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); | |
832 | ||
f41d911f | 833 | /* |
6cc68793 | 834 | * Check to see if there is any immediate preemptible-RCU-related work |
f41d911f PM |
835 | * to be done. |
836 | */ | |
837 | static int rcu_preempt_pending(int cpu) | |
838 | { | |
839 | return __rcu_pending(&rcu_preempt_state, | |
840 | &per_cpu(rcu_preempt_data, cpu)); | |
841 | } | |
842 | ||
843 | /* | |
6cc68793 | 844 | * Does preemptible RCU need the CPU to stay out of dynticks mode? |
f41d911f PM |
845 | */ |
846 | static int rcu_preempt_needs_cpu(int cpu) | |
847 | { | |
848 | return !!per_cpu(rcu_preempt_data, cpu).nxtlist; | |
849 | } | |
850 | ||
e74f4c45 PM |
851 | /** |
852 | * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. | |
853 | */ | |
854 | void rcu_barrier(void) | |
855 | { | |
856 | _rcu_barrier(&rcu_preempt_state, call_rcu); | |
857 | } | |
858 | EXPORT_SYMBOL_GPL(rcu_barrier); | |
859 | ||
f41d911f | 860 | /* |
6cc68793 | 861 | * Initialize preemptible RCU's per-CPU data. |
f41d911f PM |
862 | */ |
863 | static void __cpuinit rcu_preempt_init_percpu_data(int cpu) | |
864 | { | |
865 | rcu_init_percpu_data(cpu, &rcu_preempt_state, 1); | |
866 | } | |
867 | ||
e74f4c45 | 868 | /* |
6cc68793 | 869 | * Move preemptible RCU's callbacks from dying CPU to other online CPU. |
e74f4c45 | 870 | */ |
29494be7 | 871 | static void rcu_preempt_send_cbs_to_online(void) |
e74f4c45 | 872 | { |
29494be7 | 873 | rcu_send_cbs_to_online(&rcu_preempt_state); |
e74f4c45 PM |
874 | } |
875 | ||
1eba8f84 | 876 | /* |
6cc68793 | 877 | * Initialize preemptible RCU's state structures. |
1eba8f84 PM |
878 | */ |
879 | static void __init __rcu_init_preempt(void) | |
880 | { | |
394f99a9 | 881 | rcu_init_one(&rcu_preempt_state, &rcu_preempt_data); |
1eba8f84 PM |
882 | } |
883 | ||
f41d911f | 884 | /* |
6cc68793 | 885 | * Check for a task exiting while in a preemptible-RCU read-side |
f41d911f PM |
886 | * critical section, clean up if so. No need to issue warnings, |
887 | * as debug_check_no_locks_held() already does this if lockdep | |
888 | * is enabled. | |
889 | */ | |
890 | void exit_rcu(void) | |
891 | { | |
892 | struct task_struct *t = current; | |
893 | ||
894 | if (t->rcu_read_lock_nesting == 0) | |
895 | return; | |
896 | t->rcu_read_lock_nesting = 1; | |
13491a0e | 897 | __rcu_read_unlock(); |
f41d911f PM |
898 | } |
899 | ||
900 | #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ | |
901 | ||
27f4d280 PM |
902 | static struct rcu_state *rcu_state = &rcu_sched_state; |
903 | ||
f41d911f PM |
904 | /* |
905 | * Tell them what RCU they are running. | |
906 | */ | |
0e0fc1c2 | 907 | static void __init rcu_bootup_announce(void) |
f41d911f PM |
908 | { |
909 | printk(KERN_INFO "Hierarchical RCU implementation.\n"); | |
26845c28 | 910 | rcu_bootup_announce_oddness(); |
f41d911f PM |
911 | } |
912 | ||
913 | /* | |
914 | * Return the number of RCU batches processed thus far for debug & stats. | |
915 | */ | |
916 | long rcu_batches_completed(void) | |
917 | { | |
918 | return rcu_batches_completed_sched(); | |
919 | } | |
920 | EXPORT_SYMBOL_GPL(rcu_batches_completed); | |
921 | ||
bf66f18e PM |
922 | /* |
923 | * Force a quiescent state for RCU, which, because there is no preemptible | |
924 | * RCU, becomes the same as rcu-sched. | |
925 | */ | |
926 | void rcu_force_quiescent_state(void) | |
927 | { | |
928 | rcu_sched_force_quiescent_state(); | |
929 | } | |
930 | EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); | |
931 | ||
f41d911f | 932 | /* |
6cc68793 | 933 | * Because preemptible RCU does not exist, we never have to check for |
f41d911f PM |
934 | * CPUs being in quiescent states. |
935 | */ | |
c3422bea | 936 | static void rcu_preempt_note_context_switch(int cpu) |
f41d911f PM |
937 | { |
938 | } | |
939 | ||
fc2219d4 | 940 | /* |
6cc68793 | 941 | * Because preemptible RCU does not exist, there are never any preempted |
fc2219d4 PM |
942 | * RCU readers. |
943 | */ | |
27f4d280 | 944 | static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
fc2219d4 PM |
945 | { |
946 | return 0; | |
947 | } | |
948 | ||
b668c9cf PM |
949 | #ifdef CONFIG_HOTPLUG_CPU |
950 | ||
951 | /* Because preemptible RCU does not exist, no quieting of tasks. */ | |
d3f6bad3 | 952 | static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) |
b668c9cf | 953 | { |
1304afb2 | 954 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
b668c9cf PM |
955 | } |
956 | ||
957 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
958 | ||
1ed509a2 | 959 | /* |
6cc68793 | 960 | * Because preemptible RCU does not exist, we never have to check for |
1ed509a2 PM |
961 | * tasks blocked within RCU read-side critical sections. |
962 | */ | |
963 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
964 | { | |
965 | } | |
966 | ||
f41d911f | 967 | /* |
6cc68793 | 968 | * Because preemptible RCU does not exist, we never have to check for |
f41d911f PM |
969 | * tasks blocked within RCU read-side critical sections. |
970 | */ | |
971 | static void rcu_print_task_stall(struct rcu_node *rnp) | |
972 | { | |
973 | } | |
974 | ||
53d84e00 PM |
975 | /* |
976 | * Because preemptible RCU does not exist, there is no need to suppress | |
977 | * its CPU stall warnings. | |
978 | */ | |
979 | static void rcu_preempt_stall_reset(void) | |
980 | { | |
981 | } | |
982 | ||
b0e165c0 | 983 | /* |
6cc68793 | 984 | * Because there is no preemptible RCU, there can be no readers blocked, |
49e29126 PM |
985 | * so there is no need to check for blocked tasks. So check only for |
986 | * bogus qsmask values. | |
b0e165c0 PM |
987 | */ |
988 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) | |
989 | { | |
49e29126 | 990 | WARN_ON_ONCE(rnp->qsmask); |
b0e165c0 PM |
991 | } |
992 | ||
33f76148 PM |
993 | #ifdef CONFIG_HOTPLUG_CPU |
994 | ||
dd5d19ba | 995 | /* |
6cc68793 | 996 | * Because preemptible RCU does not exist, it never needs to migrate |
237c80c5 PM |
997 | * tasks that were blocked within RCU read-side critical sections, and |
998 | * such non-existent tasks cannot possibly have been blocking the current | |
999 | * grace period. | |
dd5d19ba | 1000 | */ |
237c80c5 PM |
1001 | static int rcu_preempt_offline_tasks(struct rcu_state *rsp, |
1002 | struct rcu_node *rnp, | |
1003 | struct rcu_data *rdp) | |
dd5d19ba | 1004 | { |
237c80c5 | 1005 | return 0; |
dd5d19ba PM |
1006 | } |
1007 | ||
33f76148 | 1008 | /* |
6cc68793 | 1009 | * Because preemptible RCU does not exist, it never needs CPU-offline |
33f76148 PM |
1010 | * processing. |
1011 | */ | |
1012 | static void rcu_preempt_offline_cpu(int cpu) | |
1013 | { | |
1014 | } | |
1015 | ||
1016 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
1017 | ||
f41d911f | 1018 | /* |
6cc68793 | 1019 | * Because preemptible RCU does not exist, it never has any callbacks |
f41d911f PM |
1020 | * to check. |
1021 | */ | |
1eba8f84 | 1022 | static void rcu_preempt_check_callbacks(int cpu) |
f41d911f PM |
1023 | { |
1024 | } | |
1025 | ||
1026 | /* | |
6cc68793 | 1027 | * Because preemptible RCU does not exist, it never has any callbacks |
f41d911f PM |
1028 | * to process. |
1029 | */ | |
1eba8f84 | 1030 | static void rcu_preempt_process_callbacks(void) |
f41d911f PM |
1031 | { |
1032 | } | |
1033 | ||
019129d5 PM |
1034 | /* |
1035 | * Wait for an rcu-preempt grace period, but make it happen quickly. | |
6cc68793 | 1036 | * But because preemptible RCU does not exist, map to rcu-sched. |
019129d5 PM |
1037 | */ |
1038 | void synchronize_rcu_expedited(void) | |
1039 | { | |
1040 | synchronize_sched_expedited(); | |
1041 | } | |
1042 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); | |
1043 | ||
d9a3da06 PM |
1044 | #ifdef CONFIG_HOTPLUG_CPU |
1045 | ||
1046 | /* | |
6cc68793 | 1047 | * Because preemptible RCU does not exist, there is never any need to |
d9a3da06 PM |
1048 | * report on tasks preempted in RCU read-side critical sections during |
1049 | * expedited RCU grace periods. | |
1050 | */ | |
1051 | static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp) | |
1052 | { | |
1053 | return; | |
1054 | } | |
1055 | ||
1056 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
1057 | ||
f41d911f | 1058 | /* |
6cc68793 | 1059 | * Because preemptible RCU does not exist, it never has any work to do. |
f41d911f PM |
1060 | */ |
1061 | static int rcu_preempt_pending(int cpu) | |
1062 | { | |
1063 | return 0; | |
1064 | } | |
1065 | ||
1066 | /* | |
6cc68793 | 1067 | * Because preemptible RCU does not exist, it never needs any CPU. |
f41d911f PM |
1068 | */ |
1069 | static int rcu_preempt_needs_cpu(int cpu) | |
1070 | { | |
1071 | return 0; | |
1072 | } | |
1073 | ||
e74f4c45 | 1074 | /* |
6cc68793 | 1075 | * Because preemptible RCU does not exist, rcu_barrier() is just |
e74f4c45 PM |
1076 | * another name for rcu_barrier_sched(). |
1077 | */ | |
1078 | void rcu_barrier(void) | |
1079 | { | |
1080 | rcu_barrier_sched(); | |
1081 | } | |
1082 | EXPORT_SYMBOL_GPL(rcu_barrier); | |
1083 | ||
f41d911f | 1084 | /* |
6cc68793 | 1085 | * Because preemptible RCU does not exist, there is no per-CPU |
f41d911f PM |
1086 | * data to initialize. |
1087 | */ | |
1088 | static void __cpuinit rcu_preempt_init_percpu_data(int cpu) | |
1089 | { | |
1090 | } | |
1091 | ||
e74f4c45 | 1092 | /* |
6cc68793 | 1093 | * Because there is no preemptible RCU, there are no callbacks to move. |
e74f4c45 | 1094 | */ |
29494be7 | 1095 | static void rcu_preempt_send_cbs_to_online(void) |
e74f4c45 PM |
1096 | { |
1097 | } | |
1098 | ||
1eba8f84 | 1099 | /* |
6cc68793 | 1100 | * Because preemptible RCU does not exist, it need not be initialized. |
1eba8f84 PM |
1101 | */ |
1102 | static void __init __rcu_init_preempt(void) | |
1103 | { | |
1104 | } | |
1105 | ||
f41d911f | 1106 | #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ |
8bd93a2c | 1107 | |
27f4d280 PM |
1108 | #ifdef CONFIG_RCU_BOOST |
1109 | ||
1110 | #include "rtmutex_common.h" | |
1111 | ||
0ea1f2eb PM |
1112 | #ifdef CONFIG_RCU_TRACE |
1113 | ||
1114 | static void rcu_initiate_boost_trace(struct rcu_node *rnp) | |
1115 | { | |
1116 | if (list_empty(&rnp->blkd_tasks)) | |
1117 | rnp->n_balk_blkd_tasks++; | |
1118 | else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL) | |
1119 | rnp->n_balk_exp_gp_tasks++; | |
1120 | else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL) | |
1121 | rnp->n_balk_boost_tasks++; | |
1122 | else if (rnp->gp_tasks != NULL && rnp->qsmask != 0) | |
1123 | rnp->n_balk_notblocked++; | |
1124 | else if (rnp->gp_tasks != NULL && | |
a9f4793d | 1125 | ULONG_CMP_LT(jiffies, rnp->boost_time)) |
0ea1f2eb PM |
1126 | rnp->n_balk_notyet++; |
1127 | else | |
1128 | rnp->n_balk_nos++; | |
1129 | } | |
1130 | ||
1131 | #else /* #ifdef CONFIG_RCU_TRACE */ | |
1132 | ||
1133 | static void rcu_initiate_boost_trace(struct rcu_node *rnp) | |
1134 | { | |
1135 | } | |
1136 | ||
1137 | #endif /* #else #ifdef CONFIG_RCU_TRACE */ | |
1138 | ||
27f4d280 PM |
1139 | /* |
1140 | * Carry out RCU priority boosting on the task indicated by ->exp_tasks | |
1141 | * or ->boost_tasks, advancing the pointer to the next task in the | |
1142 | * ->blkd_tasks list. | |
1143 | * | |
1144 | * Note that irqs must be enabled: boosting the task can block. | |
1145 | * Returns 1 if there are more tasks needing to be boosted. | |
1146 | */ | |
1147 | static int rcu_boost(struct rcu_node *rnp) | |
1148 | { | |
1149 | unsigned long flags; | |
1150 | struct rt_mutex mtx; | |
1151 | struct task_struct *t; | |
1152 | struct list_head *tb; | |
1153 | ||
1154 | if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) | |
1155 | return 0; /* Nothing left to boost. */ | |
1156 | ||
1157 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
1158 | ||
1159 | /* | |
1160 | * Recheck under the lock: all tasks in need of boosting | |
1161 | * might exit their RCU read-side critical sections on their own. | |
1162 | */ | |
1163 | if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) { | |
1164 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
1165 | return 0; | |
1166 | } | |
1167 | ||
1168 | /* | |
1169 | * Preferentially boost tasks blocking expedited grace periods. | |
1170 | * This cannot starve the normal grace periods because a second | |
1171 | * expedited grace period must boost all blocked tasks, including | |
1172 | * those blocking the pre-existing normal grace period. | |
1173 | */ | |
0ea1f2eb | 1174 | if (rnp->exp_tasks != NULL) { |
27f4d280 | 1175 | tb = rnp->exp_tasks; |
0ea1f2eb PM |
1176 | rnp->n_exp_boosts++; |
1177 | } else { | |
27f4d280 | 1178 | tb = rnp->boost_tasks; |
0ea1f2eb PM |
1179 | rnp->n_normal_boosts++; |
1180 | } | |
1181 | rnp->n_tasks_boosted++; | |
27f4d280 PM |
1182 | |
1183 | /* | |
1184 | * We boost task t by manufacturing an rt_mutex that appears to | |
1185 | * be held by task t. We leave a pointer to that rt_mutex where | |
1186 | * task t can find it, and task t will release the mutex when it | |
1187 | * exits its outermost RCU read-side critical section. Then | |
1188 | * simply acquiring this artificial rt_mutex will boost task | |
1189 | * t's priority. (Thanks to tglx for suggesting this approach!) | |
1190 | * | |
1191 | * Note that task t must acquire rnp->lock to remove itself from | |
1192 | * the ->blkd_tasks list, which it will do from exit() if from | |
1193 | * nowhere else. We therefore are guaranteed that task t will | |
1194 | * stay around at least until we drop rnp->lock. Note that | |
1195 | * rnp->lock also resolves races between our priority boosting | |
1196 | * and task t's exiting its outermost RCU read-side critical | |
1197 | * section. | |
1198 | */ | |
1199 | t = container_of(tb, struct task_struct, rcu_node_entry); | |
1200 | rt_mutex_init_proxy_locked(&mtx, t); | |
1201 | t->rcu_boost_mutex = &mtx; | |
7765be2f | 1202 | t->rcu_boosted = 1; |
27f4d280 PM |
1203 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
1204 | rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */ | |
1205 | rt_mutex_unlock(&mtx); /* Keep lockdep happy. */ | |
1206 | ||
1207 | return rnp->exp_tasks != NULL || rnp->boost_tasks != NULL; | |
1208 | } | |
1209 | ||
1210 | /* | |
1211 | * Timer handler to initiate waking up of boost kthreads that | |
1212 | * have yielded the CPU due to excessive numbers of tasks to | |
1213 | * boost. We wake up the per-rcu_node kthread, which in turn | |
1214 | * will wake up the booster kthread. | |
1215 | */ | |
1216 | static void rcu_boost_kthread_timer(unsigned long arg) | |
1217 | { | |
1217ed1b | 1218 | invoke_rcu_node_kthread((struct rcu_node *)arg); |
27f4d280 PM |
1219 | } |
1220 | ||
1221 | /* | |
1222 | * Priority-boosting kthread. One per leaf rcu_node and one for the | |
1223 | * root rcu_node. | |
1224 | */ | |
1225 | static int rcu_boost_kthread(void *arg) | |
1226 | { | |
1227 | struct rcu_node *rnp = (struct rcu_node *)arg; | |
1228 | int spincnt = 0; | |
1229 | int more2boost; | |
1230 | ||
1231 | for (;;) { | |
d71df90e | 1232 | rnp->boost_kthread_status = RCU_KTHREAD_WAITING; |
08bca60a | 1233 | rcu_wait(rnp->boost_tasks || rnp->exp_tasks); |
d71df90e | 1234 | rnp->boost_kthread_status = RCU_KTHREAD_RUNNING; |
27f4d280 PM |
1235 | more2boost = rcu_boost(rnp); |
1236 | if (more2boost) | |
1237 | spincnt++; | |
1238 | else | |
1239 | spincnt = 0; | |
1240 | if (spincnt > 10) { | |
1241 | rcu_yield(rcu_boost_kthread_timer, (unsigned long)rnp); | |
1242 | spincnt = 0; | |
1243 | } | |
1244 | } | |
1217ed1b | 1245 | /* NOTREACHED */ |
27f4d280 PM |
1246 | return 0; |
1247 | } | |
1248 | ||
1249 | /* | |
1250 | * Check to see if it is time to start boosting RCU readers that are | |
1251 | * blocking the current grace period, and, if so, tell the per-rcu_node | |
1252 | * kthread to start boosting them. If there is an expedited grace | |
1253 | * period in progress, it is always time to boost. | |
1254 | * | |
1217ed1b PM |
1255 | * The caller must hold rnp->lock, which this function releases, |
1256 | * but irqs remain disabled. The ->boost_kthread_task is immortal, | |
1257 | * so we don't need to worry about it going away. | |
27f4d280 | 1258 | */ |
1217ed1b | 1259 | static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
27f4d280 PM |
1260 | { |
1261 | struct task_struct *t; | |
1262 | ||
0ea1f2eb PM |
1263 | if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) { |
1264 | rnp->n_balk_exp_gp_tasks++; | |
1217ed1b | 1265 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 | 1266 | return; |
0ea1f2eb | 1267 | } |
27f4d280 PM |
1268 | if (rnp->exp_tasks != NULL || |
1269 | (rnp->gp_tasks != NULL && | |
1270 | rnp->boost_tasks == NULL && | |
1271 | rnp->qsmask == 0 && | |
1272 | ULONG_CMP_GE(jiffies, rnp->boost_time))) { | |
1273 | if (rnp->exp_tasks == NULL) | |
1274 | rnp->boost_tasks = rnp->gp_tasks; | |
1217ed1b | 1275 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 PM |
1276 | t = rnp->boost_kthread_task; |
1277 | if (t != NULL) | |
1278 | wake_up_process(t); | |
1217ed1b | 1279 | } else { |
0ea1f2eb | 1280 | rcu_initiate_boost_trace(rnp); |
1217ed1b PM |
1281 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
1282 | } | |
27f4d280 PM |
1283 | } |
1284 | ||
a46e0899 PM |
1285 | /* |
1286 | * Wake up the per-CPU kthread to invoke RCU callbacks. | |
1287 | */ | |
1288 | static void invoke_rcu_callbacks_kthread(void) | |
1289 | { | |
1290 | unsigned long flags; | |
1291 | ||
1292 | local_irq_save(flags); | |
1293 | __this_cpu_write(rcu_cpu_has_work, 1); | |
1294 | if (__this_cpu_read(rcu_cpu_kthread_task) == NULL) { | |
1295 | local_irq_restore(flags); | |
1296 | return; | |
1297 | } | |
1298 | wake_up_process(__this_cpu_read(rcu_cpu_kthread_task)); | |
1299 | local_irq_restore(flags); | |
1300 | } | |
1301 | ||
0f962a5e PM |
1302 | /* |
1303 | * Set the affinity of the boost kthread. The CPU-hotplug locks are | |
1304 | * held, so no one should be messing with the existence of the boost | |
1305 | * kthread. | |
1306 | */ | |
27f4d280 PM |
1307 | static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, |
1308 | cpumask_var_t cm) | |
1309 | { | |
27f4d280 PM |
1310 | struct task_struct *t; |
1311 | ||
27f4d280 PM |
1312 | t = rnp->boost_kthread_task; |
1313 | if (t != NULL) | |
1314 | set_cpus_allowed_ptr(rnp->boost_kthread_task, cm); | |
27f4d280 PM |
1315 | } |
1316 | ||
1317 | #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) | |
1318 | ||
1319 | /* | |
1320 | * Do priority-boost accounting for the start of a new grace period. | |
1321 | */ | |
1322 | static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) | |
1323 | { | |
1324 | rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; | |
1325 | } | |
1326 | ||
27f4d280 PM |
1327 | /* |
1328 | * Create an RCU-boost kthread for the specified node if one does not | |
1329 | * already exist. We only create this kthread for preemptible RCU. | |
1330 | * Returns zero if all is well, a negated errno otherwise. | |
1331 | */ | |
1332 | static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp, | |
1333 | struct rcu_node *rnp, | |
1334 | int rnp_index) | |
1335 | { | |
1336 | unsigned long flags; | |
1337 | struct sched_param sp; | |
1338 | struct task_struct *t; | |
1339 | ||
1340 | if (&rcu_preempt_state != rsp) | |
1341 | return 0; | |
a46e0899 | 1342 | rsp->boost = 1; |
27f4d280 PM |
1343 | if (rnp->boost_kthread_task != NULL) |
1344 | return 0; | |
1345 | t = kthread_create(rcu_boost_kthread, (void *)rnp, | |
1346 | "rcub%d", rnp_index); | |
1347 | if (IS_ERR(t)) | |
1348 | return PTR_ERR(t); | |
1349 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
1350 | rnp->boost_kthread_task = t; | |
1351 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
27f4d280 PM |
1352 | sp.sched_priority = RCU_KTHREAD_PRIO; |
1353 | sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); | |
9a432736 | 1354 | wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ |
27f4d280 PM |
1355 | return 0; |
1356 | } | |
1357 | ||
f8b7fc6b PM |
1358 | #ifdef CONFIG_HOTPLUG_CPU |
1359 | ||
1360 | /* | |
1361 | * Stop the RCU's per-CPU kthread when its CPU goes offline,. | |
1362 | */ | |
1363 | static void rcu_stop_cpu_kthread(int cpu) | |
1364 | { | |
1365 | struct task_struct *t; | |
1366 | ||
1367 | /* Stop the CPU's kthread. */ | |
1368 | t = per_cpu(rcu_cpu_kthread_task, cpu); | |
1369 | if (t != NULL) { | |
1370 | per_cpu(rcu_cpu_kthread_task, cpu) = NULL; | |
1371 | kthread_stop(t); | |
1372 | } | |
1373 | } | |
1374 | ||
1375 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
1376 | ||
1377 | static void rcu_kthread_do_work(void) | |
1378 | { | |
1379 | rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data)); | |
1380 | rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data)); | |
1381 | rcu_preempt_do_callbacks(); | |
1382 | } | |
1383 | ||
1384 | /* | |
1385 | * Wake up the specified per-rcu_node-structure kthread. | |
1386 | * Because the per-rcu_node kthreads are immortal, we don't need | |
1387 | * to do anything to keep them alive. | |
1388 | */ | |
1389 | static void invoke_rcu_node_kthread(struct rcu_node *rnp) | |
1390 | { | |
1391 | struct task_struct *t; | |
1392 | ||
1393 | t = rnp->node_kthread_task; | |
1394 | if (t != NULL) | |
1395 | wake_up_process(t); | |
1396 | } | |
1397 | ||
1398 | /* | |
1399 | * Set the specified CPU's kthread to run RT or not, as specified by | |
1400 | * the to_rt argument. The CPU-hotplug locks are held, so the task | |
1401 | * is not going away. | |
1402 | */ | |
1403 | static void rcu_cpu_kthread_setrt(int cpu, int to_rt) | |
1404 | { | |
1405 | int policy; | |
1406 | struct sched_param sp; | |
1407 | struct task_struct *t; | |
1408 | ||
1409 | t = per_cpu(rcu_cpu_kthread_task, cpu); | |
1410 | if (t == NULL) | |
1411 | return; | |
1412 | if (to_rt) { | |
1413 | policy = SCHED_FIFO; | |
1414 | sp.sched_priority = RCU_KTHREAD_PRIO; | |
1415 | } else { | |
1416 | policy = SCHED_NORMAL; | |
1417 | sp.sched_priority = 0; | |
1418 | } | |
1419 | sched_setscheduler_nocheck(t, policy, &sp); | |
1420 | } | |
1421 | ||
1422 | /* | |
1423 | * Timer handler to initiate the waking up of per-CPU kthreads that | |
1424 | * have yielded the CPU due to excess numbers of RCU callbacks. | |
1425 | * We wake up the per-rcu_node kthread, which in turn will wake up | |
1426 | * the booster kthread. | |
1427 | */ | |
1428 | static void rcu_cpu_kthread_timer(unsigned long arg) | |
1429 | { | |
1430 | struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, arg); | |
1431 | struct rcu_node *rnp = rdp->mynode; | |
1432 | ||
1433 | atomic_or(rdp->grpmask, &rnp->wakemask); | |
1434 | invoke_rcu_node_kthread(rnp); | |
1435 | } | |
1436 | ||
1437 | /* | |
1438 | * Drop to non-real-time priority and yield, but only after posting a | |
1439 | * timer that will cause us to regain our real-time priority if we | |
1440 | * remain preempted. Either way, we restore our real-time priority | |
1441 | * before returning. | |
1442 | */ | |
1443 | static void rcu_yield(void (*f)(unsigned long), unsigned long arg) | |
1444 | { | |
1445 | struct sched_param sp; | |
1446 | struct timer_list yield_timer; | |
1447 | ||
1448 | setup_timer_on_stack(&yield_timer, f, arg); | |
1449 | mod_timer(&yield_timer, jiffies + 2); | |
1450 | sp.sched_priority = 0; | |
1451 | sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp); | |
1452 | set_user_nice(current, 19); | |
1453 | schedule(); | |
1454 | sp.sched_priority = RCU_KTHREAD_PRIO; | |
1455 | sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); | |
1456 | del_timer(&yield_timer); | |
1457 | } | |
1458 | ||
1459 | /* | |
1460 | * Handle cases where the rcu_cpu_kthread() ends up on the wrong CPU. | |
1461 | * This can happen while the corresponding CPU is either coming online | |
1462 | * or going offline. We cannot wait until the CPU is fully online | |
1463 | * before starting the kthread, because the various notifier functions | |
1464 | * can wait for RCU grace periods. So we park rcu_cpu_kthread() until | |
1465 | * the corresponding CPU is online. | |
1466 | * | |
1467 | * Return 1 if the kthread needs to stop, 0 otherwise. | |
1468 | * | |
1469 | * Caller must disable bh. This function can momentarily enable it. | |
1470 | */ | |
1471 | static int rcu_cpu_kthread_should_stop(int cpu) | |
1472 | { | |
1473 | while (cpu_is_offline(cpu) || | |
1474 | !cpumask_equal(¤t->cpus_allowed, cpumask_of(cpu)) || | |
1475 | smp_processor_id() != cpu) { | |
1476 | if (kthread_should_stop()) | |
1477 | return 1; | |
1478 | per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; | |
1479 | per_cpu(rcu_cpu_kthread_cpu, cpu) = raw_smp_processor_id(); | |
1480 | local_bh_enable(); | |
1481 | schedule_timeout_uninterruptible(1); | |
1482 | if (!cpumask_equal(¤t->cpus_allowed, cpumask_of(cpu))) | |
1483 | set_cpus_allowed_ptr(current, cpumask_of(cpu)); | |
1484 | local_bh_disable(); | |
1485 | } | |
1486 | per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu; | |
1487 | return 0; | |
1488 | } | |
1489 | ||
1490 | /* | |
1491 | * Per-CPU kernel thread that invokes RCU callbacks. This replaces the | |
1492 | * earlier RCU softirq. | |
1493 | */ | |
1494 | static int rcu_cpu_kthread(void *arg) | |
1495 | { | |
1496 | int cpu = (int)(long)arg; | |
1497 | unsigned long flags; | |
1498 | int spincnt = 0; | |
1499 | unsigned int *statusp = &per_cpu(rcu_cpu_kthread_status, cpu); | |
1500 | char work; | |
1501 | char *workp = &per_cpu(rcu_cpu_has_work, cpu); | |
1502 | ||
1503 | for (;;) { | |
1504 | *statusp = RCU_KTHREAD_WAITING; | |
1505 | rcu_wait(*workp != 0 || kthread_should_stop()); | |
1506 | local_bh_disable(); | |
1507 | if (rcu_cpu_kthread_should_stop(cpu)) { | |
1508 | local_bh_enable(); | |
1509 | break; | |
1510 | } | |
1511 | *statusp = RCU_KTHREAD_RUNNING; | |
1512 | per_cpu(rcu_cpu_kthread_loops, cpu)++; | |
1513 | local_irq_save(flags); | |
1514 | work = *workp; | |
1515 | *workp = 0; | |
1516 | local_irq_restore(flags); | |
1517 | if (work) | |
1518 | rcu_kthread_do_work(); | |
1519 | local_bh_enable(); | |
1520 | if (*workp != 0) | |
1521 | spincnt++; | |
1522 | else | |
1523 | spincnt = 0; | |
1524 | if (spincnt > 10) { | |
1525 | *statusp = RCU_KTHREAD_YIELDING; | |
1526 | rcu_yield(rcu_cpu_kthread_timer, (unsigned long)cpu); | |
1527 | spincnt = 0; | |
1528 | } | |
1529 | } | |
1530 | *statusp = RCU_KTHREAD_STOPPED; | |
1531 | return 0; | |
1532 | } | |
1533 | ||
1534 | /* | |
1535 | * Spawn a per-CPU kthread, setting up affinity and priority. | |
1536 | * Because the CPU hotplug lock is held, no other CPU will be attempting | |
1537 | * to manipulate rcu_cpu_kthread_task. There might be another CPU | |
1538 | * attempting to access it during boot, but the locking in kthread_bind() | |
1539 | * will enforce sufficient ordering. | |
1540 | * | |
1541 | * Please note that we cannot simply refuse to wake up the per-CPU | |
1542 | * kthread because kthreads are created in TASK_UNINTERRUPTIBLE state, | |
1543 | * which can result in softlockup complaints if the task ends up being | |
1544 | * idle for more than a couple of minutes. | |
1545 | * | |
1546 | * However, please note also that we cannot bind the per-CPU kthread to its | |
1547 | * CPU until that CPU is fully online. We also cannot wait until the | |
1548 | * CPU is fully online before we create its per-CPU kthread, as this would | |
1549 | * deadlock the system when CPU notifiers tried waiting for grace | |
1550 | * periods. So we bind the per-CPU kthread to its CPU only if the CPU | |
1551 | * is online. If its CPU is not yet fully online, then the code in | |
1552 | * rcu_cpu_kthread() will wait until it is fully online, and then do | |
1553 | * the binding. | |
1554 | */ | |
1555 | static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu) | |
1556 | { | |
1557 | struct sched_param sp; | |
1558 | struct task_struct *t; | |
1559 | ||
b0d30417 | 1560 | if (!rcu_scheduler_fully_active || |
f8b7fc6b PM |
1561 | per_cpu(rcu_cpu_kthread_task, cpu) != NULL) |
1562 | return 0; | |
1563 | t = kthread_create(rcu_cpu_kthread, (void *)(long)cpu, "rcuc%d", cpu); | |
1564 | if (IS_ERR(t)) | |
1565 | return PTR_ERR(t); | |
1566 | if (cpu_online(cpu)) | |
1567 | kthread_bind(t, cpu); | |
1568 | per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu; | |
1569 | WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL); | |
1570 | sp.sched_priority = RCU_KTHREAD_PRIO; | |
1571 | sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); | |
1572 | per_cpu(rcu_cpu_kthread_task, cpu) = t; | |
1573 | wake_up_process(t); /* Get to TASK_INTERRUPTIBLE quickly. */ | |
1574 | return 0; | |
1575 | } | |
1576 | ||
1577 | /* | |
1578 | * Per-rcu_node kthread, which is in charge of waking up the per-CPU | |
1579 | * kthreads when needed. We ignore requests to wake up kthreads | |
1580 | * for offline CPUs, which is OK because force_quiescent_state() | |
1581 | * takes care of this case. | |
1582 | */ | |
1583 | static int rcu_node_kthread(void *arg) | |
1584 | { | |
1585 | int cpu; | |
1586 | unsigned long flags; | |
1587 | unsigned long mask; | |
1588 | struct rcu_node *rnp = (struct rcu_node *)arg; | |
1589 | struct sched_param sp; | |
1590 | struct task_struct *t; | |
1591 | ||
1592 | for (;;) { | |
1593 | rnp->node_kthread_status = RCU_KTHREAD_WAITING; | |
1594 | rcu_wait(atomic_read(&rnp->wakemask) != 0); | |
1595 | rnp->node_kthread_status = RCU_KTHREAD_RUNNING; | |
1596 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
1597 | mask = atomic_xchg(&rnp->wakemask, 0); | |
1598 | rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */ | |
1599 | for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) { | |
1600 | if ((mask & 0x1) == 0) | |
1601 | continue; | |
1602 | preempt_disable(); | |
1603 | t = per_cpu(rcu_cpu_kthread_task, cpu); | |
1604 | if (!cpu_online(cpu) || t == NULL) { | |
1605 | preempt_enable(); | |
1606 | continue; | |
1607 | } | |
1608 | per_cpu(rcu_cpu_has_work, cpu) = 1; | |
1609 | sp.sched_priority = RCU_KTHREAD_PRIO; | |
1610 | sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); | |
1611 | preempt_enable(); | |
1612 | } | |
1613 | } | |
1614 | /* NOTREACHED */ | |
1615 | rnp->node_kthread_status = RCU_KTHREAD_STOPPED; | |
1616 | return 0; | |
1617 | } | |
1618 | ||
1619 | /* | |
1620 | * Set the per-rcu_node kthread's affinity to cover all CPUs that are | |
1621 | * served by the rcu_node in question. The CPU hotplug lock is still | |
1622 | * held, so the value of rnp->qsmaskinit will be stable. | |
1623 | * | |
1624 | * We don't include outgoingcpu in the affinity set, use -1 if there is | |
1625 | * no outgoing CPU. If there are no CPUs left in the affinity set, | |
1626 | * this function allows the kthread to execute on any CPU. | |
1627 | */ | |
1628 | static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) | |
1629 | { | |
1630 | cpumask_var_t cm; | |
1631 | int cpu; | |
1632 | unsigned long mask = rnp->qsmaskinit; | |
1633 | ||
1634 | if (rnp->node_kthread_task == NULL) | |
1635 | return; | |
1636 | if (!alloc_cpumask_var(&cm, GFP_KERNEL)) | |
1637 | return; | |
1638 | cpumask_clear(cm); | |
1639 | for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) | |
1640 | if ((mask & 0x1) && cpu != outgoingcpu) | |
1641 | cpumask_set_cpu(cpu, cm); | |
1642 | if (cpumask_weight(cm) == 0) { | |
1643 | cpumask_setall(cm); | |
1644 | for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) | |
1645 | cpumask_clear_cpu(cpu, cm); | |
1646 | WARN_ON_ONCE(cpumask_weight(cm) == 0); | |
1647 | } | |
1648 | set_cpus_allowed_ptr(rnp->node_kthread_task, cm); | |
1649 | rcu_boost_kthread_setaffinity(rnp, cm); | |
1650 | free_cpumask_var(cm); | |
1651 | } | |
1652 | ||
1653 | /* | |
1654 | * Spawn a per-rcu_node kthread, setting priority and affinity. | |
1655 | * Called during boot before online/offline can happen, or, if | |
1656 | * during runtime, with the main CPU-hotplug locks held. So only | |
1657 | * one of these can be executing at a time. | |
1658 | */ | |
1659 | static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp, | |
1660 | struct rcu_node *rnp) | |
1661 | { | |
1662 | unsigned long flags; | |
1663 | int rnp_index = rnp - &rsp->node[0]; | |
1664 | struct sched_param sp; | |
1665 | struct task_struct *t; | |
1666 | ||
b0d30417 | 1667 | if (!rcu_scheduler_fully_active || |
f8b7fc6b PM |
1668 | rnp->qsmaskinit == 0) |
1669 | return 0; | |
1670 | if (rnp->node_kthread_task == NULL) { | |
1671 | t = kthread_create(rcu_node_kthread, (void *)rnp, | |
1672 | "rcun%d", rnp_index); | |
1673 | if (IS_ERR(t)) | |
1674 | return PTR_ERR(t); | |
1675 | raw_spin_lock_irqsave(&rnp->lock, flags); | |
1676 | rnp->node_kthread_task = t; | |
1677 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
1678 | sp.sched_priority = 99; | |
1679 | sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); | |
1680 | wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ | |
1681 | } | |
1682 | return rcu_spawn_one_boost_kthread(rsp, rnp, rnp_index); | |
1683 | } | |
1684 | ||
1685 | /* | |
1686 | * Spawn all kthreads -- called as soon as the scheduler is running. | |
1687 | */ | |
1688 | static int __init rcu_spawn_kthreads(void) | |
1689 | { | |
1690 | int cpu; | |
1691 | struct rcu_node *rnp; | |
1692 | ||
b0d30417 | 1693 | rcu_scheduler_fully_active = 1; |
f8b7fc6b PM |
1694 | for_each_possible_cpu(cpu) { |
1695 | per_cpu(rcu_cpu_has_work, cpu) = 0; | |
1696 | if (cpu_online(cpu)) | |
1697 | (void)rcu_spawn_one_cpu_kthread(cpu); | |
1698 | } | |
1699 | rnp = rcu_get_root(rcu_state); | |
1700 | (void)rcu_spawn_one_node_kthread(rcu_state, rnp); | |
1701 | if (NUM_RCU_NODES > 1) { | |
1702 | rcu_for_each_leaf_node(rcu_state, rnp) | |
1703 | (void)rcu_spawn_one_node_kthread(rcu_state, rnp); | |
1704 | } | |
1705 | return 0; | |
1706 | } | |
1707 | early_initcall(rcu_spawn_kthreads); | |
1708 | ||
1709 | static void __cpuinit rcu_prepare_kthreads(int cpu) | |
1710 | { | |
1711 | struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu); | |
1712 | struct rcu_node *rnp = rdp->mynode; | |
1713 | ||
1714 | /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */ | |
b0d30417 | 1715 | if (rcu_scheduler_fully_active) { |
f8b7fc6b PM |
1716 | (void)rcu_spawn_one_cpu_kthread(cpu); |
1717 | if (rnp->node_kthread_task == NULL) | |
1718 | (void)rcu_spawn_one_node_kthread(rcu_state, rnp); | |
1719 | } | |
1720 | } | |
1721 | ||
27f4d280 PM |
1722 | #else /* #ifdef CONFIG_RCU_BOOST */ |
1723 | ||
1217ed1b | 1724 | static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
27f4d280 | 1725 | { |
1217ed1b | 1726 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 PM |
1727 | } |
1728 | ||
a46e0899 | 1729 | static void invoke_rcu_callbacks_kthread(void) |
27f4d280 | 1730 | { |
a46e0899 | 1731 | WARN_ON_ONCE(1); |
27f4d280 PM |
1732 | } |
1733 | ||
1734 | static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) | |
1735 | { | |
1736 | } | |
1737 | ||
f8b7fc6b PM |
1738 | #ifdef CONFIG_HOTPLUG_CPU |
1739 | ||
1740 | static void rcu_stop_cpu_kthread(int cpu) | |
1741 | { | |
1742 | } | |
1743 | ||
1744 | #endif /* #ifdef CONFIG_HOTPLUG_CPU */ | |
1745 | ||
1746 | static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) | |
1747 | { | |
1748 | } | |
1749 | ||
1750 | static void rcu_cpu_kthread_setrt(int cpu, int to_rt) | |
1751 | { | |
1752 | } | |
1753 | ||
b0d30417 PM |
1754 | static int __init rcu_scheduler_really_started(void) |
1755 | { | |
1756 | rcu_scheduler_fully_active = 1; | |
1757 | return 0; | |
1758 | } | |
1759 | early_initcall(rcu_scheduler_really_started); | |
1760 | ||
f8b7fc6b PM |
1761 | static void __cpuinit rcu_prepare_kthreads(int cpu) |
1762 | { | |
1763 | } | |
1764 | ||
27f4d280 PM |
1765 | #endif /* #else #ifdef CONFIG_RCU_BOOST */ |
1766 | ||
7b27d547 LJ |
1767 | #ifndef CONFIG_SMP |
1768 | ||
1769 | void synchronize_sched_expedited(void) | |
1770 | { | |
1771 | cond_resched(); | |
1772 | } | |
1773 | EXPORT_SYMBOL_GPL(synchronize_sched_expedited); | |
1774 | ||
1775 | #else /* #ifndef CONFIG_SMP */ | |
1776 | ||
e27fc964 TH |
1777 | static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0); |
1778 | static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0); | |
7b27d547 LJ |
1779 | |
1780 | static int synchronize_sched_expedited_cpu_stop(void *data) | |
1781 | { | |
1782 | /* | |
1783 | * There must be a full memory barrier on each affected CPU | |
1784 | * between the time that try_stop_cpus() is called and the | |
1785 | * time that it returns. | |
1786 | * | |
1787 | * In the current initial implementation of cpu_stop, the | |
1788 | * above condition is already met when the control reaches | |
1789 | * this point and the following smp_mb() is not strictly | |
1790 | * necessary. Do smp_mb() anyway for documentation and | |
1791 | * robustness against future implementation changes. | |
1792 | */ | |
1793 | smp_mb(); /* See above comment block. */ | |
1794 | return 0; | |
1795 | } | |
1796 | ||
1797 | /* | |
1798 | * Wait for an rcu-sched grace period to elapse, but use "big hammer" | |
1799 | * approach to force grace period to end quickly. This consumes | |
1800 | * significant time on all CPUs, and is thus not recommended for | |
1801 | * any sort of common-case code. | |
1802 | * | |
1803 | * Note that it is illegal to call this function while holding any | |
1804 | * lock that is acquired by a CPU-hotplug notifier. Failing to | |
1805 | * observe this restriction will result in deadlock. | |
db3a8920 | 1806 | * |
e27fc964 TH |
1807 | * This implementation can be thought of as an application of ticket |
1808 | * locking to RCU, with sync_sched_expedited_started and | |
1809 | * sync_sched_expedited_done taking on the roles of the halves | |
1810 | * of the ticket-lock word. Each task atomically increments | |
1811 | * sync_sched_expedited_started upon entry, snapshotting the old value, | |
1812 | * then attempts to stop all the CPUs. If this succeeds, then each | |
1813 | * CPU will have executed a context switch, resulting in an RCU-sched | |
1814 | * grace period. We are then done, so we use atomic_cmpxchg() to | |
1815 | * update sync_sched_expedited_done to match our snapshot -- but | |
1816 | * only if someone else has not already advanced past our snapshot. | |
1817 | * | |
1818 | * On the other hand, if try_stop_cpus() fails, we check the value | |
1819 | * of sync_sched_expedited_done. If it has advanced past our | |
1820 | * initial snapshot, then someone else must have forced a grace period | |
1821 | * some time after we took our snapshot. In this case, our work is | |
1822 | * done for us, and we can simply return. Otherwise, we try again, | |
1823 | * but keep our initial snapshot for purposes of checking for someone | |
1824 | * doing our work for us. | |
1825 | * | |
1826 | * If we fail too many times in a row, we fall back to synchronize_sched(). | |
7b27d547 LJ |
1827 | */ |
1828 | void synchronize_sched_expedited(void) | |
1829 | { | |
e27fc964 | 1830 | int firstsnap, s, snap, trycount = 0; |
7b27d547 | 1831 | |
e27fc964 TH |
1832 | /* Note that atomic_inc_return() implies full memory barrier. */ |
1833 | firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started); | |
7b27d547 | 1834 | get_online_cpus(); |
e27fc964 TH |
1835 | |
1836 | /* | |
1837 | * Each pass through the following loop attempts to force a | |
1838 | * context switch on each CPU. | |
1839 | */ | |
7b27d547 LJ |
1840 | while (try_stop_cpus(cpu_online_mask, |
1841 | synchronize_sched_expedited_cpu_stop, | |
1842 | NULL) == -EAGAIN) { | |
1843 | put_online_cpus(); | |
e27fc964 TH |
1844 | |
1845 | /* No joy, try again later. Or just synchronize_sched(). */ | |
7b27d547 LJ |
1846 | if (trycount++ < 10) |
1847 | udelay(trycount * num_online_cpus()); | |
1848 | else { | |
1849 | synchronize_sched(); | |
1850 | return; | |
1851 | } | |
e27fc964 TH |
1852 | |
1853 | /* Check to see if someone else did our work for us. */ | |
1854 | s = atomic_read(&sync_sched_expedited_done); | |
1855 | if (UINT_CMP_GE((unsigned)s, (unsigned)firstsnap)) { | |
7b27d547 LJ |
1856 | smp_mb(); /* ensure test happens before caller kfree */ |
1857 | return; | |
1858 | } | |
e27fc964 TH |
1859 | |
1860 | /* | |
1861 | * Refetching sync_sched_expedited_started allows later | |
1862 | * callers to piggyback on our grace period. We subtract | |
1863 | * 1 to get the same token that the last incrementer got. | |
1864 | * We retry after they started, so our grace period works | |
1865 | * for them, and they started after our first try, so their | |
1866 | * grace period works for us. | |
1867 | */ | |
7b27d547 | 1868 | get_online_cpus(); |
e27fc964 TH |
1869 | snap = atomic_read(&sync_sched_expedited_started) - 1; |
1870 | smp_mb(); /* ensure read is before try_stop_cpus(). */ | |
7b27d547 | 1871 | } |
e27fc964 TH |
1872 | |
1873 | /* | |
1874 | * Everyone up to our most recent fetch is covered by our grace | |
1875 | * period. Update the counter, but only if our work is still | |
1876 | * relevant -- which it won't be if someone who started later | |
1877 | * than we did beat us to the punch. | |
1878 | */ | |
1879 | do { | |
1880 | s = atomic_read(&sync_sched_expedited_done); | |
1881 | if (UINT_CMP_GE((unsigned)s, (unsigned)snap)) { | |
1882 | smp_mb(); /* ensure test happens before caller kfree */ | |
1883 | break; | |
1884 | } | |
1885 | } while (atomic_cmpxchg(&sync_sched_expedited_done, s, snap) != s); | |
1886 | ||
7b27d547 LJ |
1887 | put_online_cpus(); |
1888 | } | |
1889 | EXPORT_SYMBOL_GPL(synchronize_sched_expedited); | |
1890 | ||
1891 | #endif /* #else #ifndef CONFIG_SMP */ | |
1892 | ||
8bd93a2c PM |
1893 | #if !defined(CONFIG_RCU_FAST_NO_HZ) |
1894 | ||
1895 | /* | |
1896 | * Check to see if any future RCU-related work will need to be done | |
1897 | * by the current CPU, even if none need be done immediately, returning | |
1898 | * 1 if so. This function is part of the RCU implementation; it is -not- | |
1899 | * an exported member of the RCU API. | |
1900 | * | |
1901 | * Because we have preemptible RCU, just check whether this CPU needs | |
1902 | * any flavor of RCU. Do not chew up lots of CPU cycles with preemption | |
1903 | * disabled in a most-likely vain attempt to cause RCU not to need this CPU. | |
1904 | */ | |
1905 | int rcu_needs_cpu(int cpu) | |
1906 | { | |
1907 | return rcu_needs_cpu_quick_check(cpu); | |
1908 | } | |
1909 | ||
a47cd880 PM |
1910 | /* |
1911 | * Check to see if we need to continue a callback-flush operations to | |
1912 | * allow the last CPU to enter dyntick-idle mode. But fast dyntick-idle | |
1913 | * entry is not configured, so we never do need to. | |
1914 | */ | |
1915 | static void rcu_needs_cpu_flush(void) | |
1916 | { | |
1917 | } | |
1918 | ||
8bd93a2c PM |
1919 | #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
1920 | ||
1921 | #define RCU_NEEDS_CPU_FLUSHES 5 | |
a47cd880 | 1922 | static DEFINE_PER_CPU(int, rcu_dyntick_drain); |
71da8132 | 1923 | static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff); |
8bd93a2c PM |
1924 | |
1925 | /* | |
1926 | * Check to see if any future RCU-related work will need to be done | |
1927 | * by the current CPU, even if none need be done immediately, returning | |
1928 | * 1 if so. This function is part of the RCU implementation; it is -not- | |
1929 | * an exported member of the RCU API. | |
1930 | * | |
1931 | * Because we are not supporting preemptible RCU, attempt to accelerate | |
1932 | * any current grace periods so that RCU no longer needs this CPU, but | |
1933 | * only if all other CPUs are already in dynticks-idle mode. This will | |
1934 | * allow the CPU cores to be powered down immediately, as opposed to after | |
1935 | * waiting many milliseconds for grace periods to elapse. | |
a47cd880 PM |
1936 | * |
1937 | * Because it is not legal to invoke rcu_process_callbacks() with irqs | |
1938 | * disabled, we do one pass of force_quiescent_state(), then do a | |
a46e0899 | 1939 | * invoke_rcu_core() to cause rcu_process_callbacks() to be invoked |
27f4d280 | 1940 | * later. The per-cpu rcu_dyntick_drain variable controls the sequencing. |
8bd93a2c PM |
1941 | */ |
1942 | int rcu_needs_cpu(int cpu) | |
1943 | { | |
a47cd880 | 1944 | int c = 0; |
77e38ed3 | 1945 | int snap; |
8bd93a2c PM |
1946 | int thatcpu; |
1947 | ||
622ea685 PM |
1948 | /* Check for being in the holdoff period. */ |
1949 | if (per_cpu(rcu_dyntick_holdoff, cpu) == jiffies) | |
1950 | return rcu_needs_cpu_quick_check(cpu); | |
1951 | ||
8bd93a2c | 1952 | /* Don't bother unless we are the last non-dyntick-idle CPU. */ |
77e38ed3 PM |
1953 | for_each_online_cpu(thatcpu) { |
1954 | if (thatcpu == cpu) | |
1955 | continue; | |
23b5c8fa PM |
1956 | snap = atomic_add_return(0, &per_cpu(rcu_dynticks, |
1957 | thatcpu).dynticks); | |
77e38ed3 | 1958 | smp_mb(); /* Order sampling of snap with end of grace period. */ |
23b5c8fa | 1959 | if ((snap & 0x1) != 0) { |
a47cd880 | 1960 | per_cpu(rcu_dyntick_drain, cpu) = 0; |
71da8132 | 1961 | per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1; |
8bd93a2c | 1962 | return rcu_needs_cpu_quick_check(cpu); |
8bd93a2c | 1963 | } |
77e38ed3 | 1964 | } |
a47cd880 PM |
1965 | |
1966 | /* Check and update the rcu_dyntick_drain sequencing. */ | |
1967 | if (per_cpu(rcu_dyntick_drain, cpu) <= 0) { | |
1968 | /* First time through, initialize the counter. */ | |
1969 | per_cpu(rcu_dyntick_drain, cpu) = RCU_NEEDS_CPU_FLUSHES; | |
1970 | } else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) { | |
1971 | /* We have hit the limit, so time to give up. */ | |
71da8132 | 1972 | per_cpu(rcu_dyntick_holdoff, cpu) = jiffies; |
a47cd880 PM |
1973 | return rcu_needs_cpu_quick_check(cpu); |
1974 | } | |
1975 | ||
1976 | /* Do one step pushing remaining RCU callbacks through. */ | |
1977 | if (per_cpu(rcu_sched_data, cpu).nxtlist) { | |
1978 | rcu_sched_qs(cpu); | |
1979 | force_quiescent_state(&rcu_sched_state, 0); | |
1980 | c = c || per_cpu(rcu_sched_data, cpu).nxtlist; | |
1981 | } | |
1982 | if (per_cpu(rcu_bh_data, cpu).nxtlist) { | |
1983 | rcu_bh_qs(cpu); | |
1984 | force_quiescent_state(&rcu_bh_state, 0); | |
1985 | c = c || per_cpu(rcu_bh_data, cpu).nxtlist; | |
8bd93a2c PM |
1986 | } |
1987 | ||
1988 | /* If RCU callbacks are still pending, RCU still needs this CPU. */ | |
622ea685 | 1989 | if (c) |
a46e0899 | 1990 | invoke_rcu_core(); |
8bd93a2c PM |
1991 | return c; |
1992 | } | |
1993 | ||
a47cd880 PM |
1994 | /* |
1995 | * Check to see if we need to continue a callback-flush operations to | |
1996 | * allow the last CPU to enter dyntick-idle mode. | |
1997 | */ | |
1998 | static void rcu_needs_cpu_flush(void) | |
1999 | { | |
2000 | int cpu = smp_processor_id(); | |
71da8132 | 2001 | unsigned long flags; |
a47cd880 PM |
2002 | |
2003 | if (per_cpu(rcu_dyntick_drain, cpu) <= 0) | |
2004 | return; | |
71da8132 | 2005 | local_irq_save(flags); |
a47cd880 | 2006 | (void)rcu_needs_cpu(cpu); |
71da8132 | 2007 | local_irq_restore(flags); |
a47cd880 PM |
2008 | } |
2009 | ||
8bd93a2c | 2010 | #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |