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bbad9379 | 1 | /* |
a57eb940 | 2 | * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition |
bbad9379 | 3 | * Internal non-public definitions that provide either classic |
a57eb940 | 4 | * or preemptible semantics. |
bbad9379 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 | * | |
a57eb940 | 20 | * Copyright (c) 2010 Linaro |
bbad9379 PM |
21 | * |
22 | * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com> | |
23 | */ | |
24 | ||
b2c0710c PM |
25 | #include <linux/kthread.h> |
26 | ||
24278d14 PM |
27 | /* Global control variables for rcupdate callback mechanism. */ |
28 | struct rcu_ctrlblk { | |
29 | struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */ | |
30 | struct rcu_head **donetail; /* ->next pointer of last "done" CB. */ | |
31 | struct rcu_head **curtail; /* ->next pointer of last CB. */ | |
32 | }; | |
33 | ||
34 | /* Definition for rcupdate control block. */ | |
35 | static struct rcu_ctrlblk rcu_sched_ctrlblk = { | |
36 | .donetail = &rcu_sched_ctrlblk.rcucblist, | |
37 | .curtail = &rcu_sched_ctrlblk.rcucblist, | |
38 | }; | |
39 | ||
40 | static struct rcu_ctrlblk rcu_bh_ctrlblk = { | |
41 | .donetail = &rcu_bh_ctrlblk.rcucblist, | |
42 | .curtail = &rcu_bh_ctrlblk.rcucblist, | |
43 | }; | |
44 | ||
45 | #ifdef CONFIG_DEBUG_LOCK_ALLOC | |
46 | int rcu_scheduler_active __read_mostly; | |
47 | EXPORT_SYMBOL_GPL(rcu_scheduler_active); | |
48 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
49 | ||
a57eb940 PM |
50 | #ifdef CONFIG_TINY_PREEMPT_RCU |
51 | ||
52 | #include <linux/delay.h> | |
53 | ||
a57eb940 PM |
54 | /* Global control variables for preemptible RCU. */ |
55 | struct rcu_preempt_ctrlblk { | |
56 | struct rcu_ctrlblk rcb; /* curtail: ->next ptr of last CB for GP. */ | |
57 | struct rcu_head **nexttail; | |
58 | /* Tasks blocked in a preemptible RCU */ | |
59 | /* read-side critical section while an */ | |
60 | /* preemptible-RCU grace period is in */ | |
61 | /* progress must wait for a later grace */ | |
62 | /* period. This pointer points to the */ | |
63 | /* ->next pointer of the last task that */ | |
64 | /* must wait for a later grace period, or */ | |
65 | /* to &->rcb.rcucblist if there is no */ | |
66 | /* such task. */ | |
67 | struct list_head blkd_tasks; | |
68 | /* Tasks blocked in RCU read-side critical */ | |
69 | /* section. Tasks are placed at the head */ | |
70 | /* of this list and age towards the tail. */ | |
71 | struct list_head *gp_tasks; | |
72 | /* Pointer to the first task blocking the */ | |
73 | /* current grace period, or NULL if there */ | |
24278d14 | 74 | /* is no such task. */ |
a57eb940 PM |
75 | struct list_head *exp_tasks; |
76 | /* Pointer to first task blocking the */ | |
77 | /* current expedited grace period, or NULL */ | |
78 | /* if there is no such task. If there */ | |
79 | /* is no current expedited grace period, */ | |
80 | /* then there cannot be any such task. */ | |
24278d14 PM |
81 | #ifdef CONFIG_RCU_BOOST |
82 | struct list_head *boost_tasks; | |
83 | /* Pointer to first task that needs to be */ | |
84 | /* priority-boosted, or NULL if no priority */ | |
85 | /* boosting is needed. If there is no */ | |
86 | /* current or expedited grace period, there */ | |
87 | /* can be no such task. */ | |
88 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
a57eb940 PM |
89 | u8 gpnum; /* Current grace period. */ |
90 | u8 gpcpu; /* Last grace period blocked by the CPU. */ | |
91 | u8 completed; /* Last grace period completed. */ | |
92 | /* If all three are equal, RCU is idle. */ | |
24278d14 PM |
93 | s8 boosted_this_gp; /* Has boosting already happened? */ |
94 | unsigned long boost_time; /* When to start boosting (jiffies) */ | |
a57eb940 PM |
95 | }; |
96 | ||
97 | static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = { | |
98 | .rcb.donetail = &rcu_preempt_ctrlblk.rcb.rcucblist, | |
99 | .rcb.curtail = &rcu_preempt_ctrlblk.rcb.rcucblist, | |
100 | .nexttail = &rcu_preempt_ctrlblk.rcb.rcucblist, | |
101 | .blkd_tasks = LIST_HEAD_INIT(rcu_preempt_ctrlblk.blkd_tasks), | |
102 | }; | |
103 | ||
104 | static int rcu_preempted_readers_exp(void); | |
105 | static void rcu_report_exp_done(void); | |
106 | ||
107 | /* | |
108 | * Return true if the CPU has not yet responded to the current grace period. | |
109 | */ | |
dd7c4d89 | 110 | static int rcu_cpu_blocking_cur_gp(void) |
a57eb940 PM |
111 | { |
112 | return rcu_preempt_ctrlblk.gpcpu != rcu_preempt_ctrlblk.gpnum; | |
113 | } | |
114 | ||
115 | /* | |
116 | * Check for a running RCU reader. Because there is only one CPU, | |
117 | * there can be but one running RCU reader at a time. ;-) | |
118 | */ | |
119 | static int rcu_preempt_running_reader(void) | |
120 | { | |
121 | return current->rcu_read_lock_nesting; | |
122 | } | |
123 | ||
124 | /* | |
125 | * Check for preempted RCU readers blocking any grace period. | |
126 | * If the caller needs a reliable answer, it must disable hard irqs. | |
127 | */ | |
128 | static int rcu_preempt_blocked_readers_any(void) | |
129 | { | |
130 | return !list_empty(&rcu_preempt_ctrlblk.blkd_tasks); | |
131 | } | |
132 | ||
133 | /* | |
134 | * Check for preempted RCU readers blocking the current grace period. | |
135 | * If the caller needs a reliable answer, it must disable hard irqs. | |
136 | */ | |
137 | static int rcu_preempt_blocked_readers_cgp(void) | |
138 | { | |
139 | return rcu_preempt_ctrlblk.gp_tasks != NULL; | |
140 | } | |
141 | ||
142 | /* | |
143 | * Return true if another preemptible-RCU grace period is needed. | |
144 | */ | |
145 | static int rcu_preempt_needs_another_gp(void) | |
146 | { | |
147 | return *rcu_preempt_ctrlblk.rcb.curtail != NULL; | |
148 | } | |
149 | ||
150 | /* | |
151 | * Return true if a preemptible-RCU grace period is in progress. | |
152 | * The caller must disable hardirqs. | |
153 | */ | |
154 | static int rcu_preempt_gp_in_progress(void) | |
155 | { | |
156 | return rcu_preempt_ctrlblk.completed != rcu_preempt_ctrlblk.gpnum; | |
157 | } | |
158 | ||
24278d14 PM |
159 | /* |
160 | * Advance a ->blkd_tasks-list pointer to the next entry, instead | |
161 | * returning NULL if at the end of the list. | |
162 | */ | |
163 | static struct list_head *rcu_next_node_entry(struct task_struct *t) | |
164 | { | |
165 | struct list_head *np; | |
166 | ||
167 | np = t->rcu_node_entry.next; | |
168 | if (np == &rcu_preempt_ctrlblk.blkd_tasks) | |
169 | np = NULL; | |
170 | return np; | |
171 | } | |
172 | ||
173 | #ifdef CONFIG_RCU_BOOST | |
174 | ||
175 | #include "rtmutex_common.h" | |
176 | ||
177 | /* | |
178 | * Carry out RCU priority boosting on the task indicated by ->boost_tasks, | |
179 | * and advance ->boost_tasks to the next task in the ->blkd_tasks list. | |
180 | */ | |
181 | static int rcu_boost(void) | |
182 | { | |
183 | unsigned long flags; | |
184 | struct rt_mutex mtx; | |
185 | struct list_head *np; | |
186 | struct task_struct *t; | |
187 | ||
188 | if (rcu_preempt_ctrlblk.boost_tasks == NULL) | |
189 | return 0; /* Nothing to boost. */ | |
190 | raw_local_irq_save(flags); | |
191 | rcu_preempt_ctrlblk.boosted_this_gp++; | |
192 | t = container_of(rcu_preempt_ctrlblk.boost_tasks, struct task_struct, | |
193 | rcu_node_entry); | |
194 | np = rcu_next_node_entry(t); | |
195 | rt_mutex_init_proxy_locked(&mtx, t); | |
196 | t->rcu_boost_mutex = &mtx; | |
197 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BOOSTED; | |
198 | raw_local_irq_restore(flags); | |
199 | rt_mutex_lock(&mtx); | |
200 | rt_mutex_unlock(&mtx); | |
201 | return rcu_preempt_ctrlblk.boost_tasks != NULL; | |
202 | } | |
203 | ||
204 | /* | |
205 | * Check to see if it is now time to start boosting RCU readers blocking | |
206 | * the current grace period, and, if so, tell the rcu_kthread_task to | |
207 | * start boosting them. If there is an expedited boost in progress, | |
208 | * we wait for it to complete. | |
209 | */ | |
210 | static void rcu_initiate_boost(void) | |
211 | { | |
212 | if (rcu_preempt_ctrlblk.gp_tasks != NULL && | |
213 | rcu_preempt_ctrlblk.boost_tasks == NULL && | |
214 | rcu_preempt_ctrlblk.boosted_this_gp == 0 && | |
215 | ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time)) { | |
216 | rcu_preempt_ctrlblk.boost_tasks = rcu_preempt_ctrlblk.gp_tasks; | |
217 | invoke_rcu_kthread(); | |
218 | } | |
219 | } | |
220 | ||
221 | /* | |
222 | * Initiate boosting for an expedited grace period. | |
223 | */ | |
224 | static void rcu_initiate_expedited_boost(void) | |
225 | { | |
226 | unsigned long flags; | |
227 | ||
228 | raw_local_irq_save(flags); | |
229 | if (!list_empty(&rcu_preempt_ctrlblk.blkd_tasks)) { | |
230 | rcu_preempt_ctrlblk.boost_tasks = | |
231 | rcu_preempt_ctrlblk.blkd_tasks.next; | |
232 | rcu_preempt_ctrlblk.boosted_this_gp = -1; | |
233 | invoke_rcu_kthread(); | |
234 | } | |
235 | raw_local_irq_restore(flags); | |
236 | } | |
237 | ||
238 | #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000); | |
239 | ||
240 | /* | |
241 | * Do priority-boost accounting for the start of a new grace period. | |
242 | */ | |
243 | static void rcu_preempt_boost_start_gp(void) | |
244 | { | |
245 | rcu_preempt_ctrlblk.boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; | |
246 | if (rcu_preempt_ctrlblk.boosted_this_gp > 0) | |
247 | rcu_preempt_ctrlblk.boosted_this_gp = 0; | |
248 | } | |
249 | ||
250 | #else /* #ifdef CONFIG_RCU_BOOST */ | |
251 | ||
252 | /* | |
253 | * If there is no RCU priority boosting, we don't boost. | |
254 | */ | |
255 | static int rcu_boost(void) | |
256 | { | |
257 | return 0; | |
258 | } | |
259 | ||
260 | /* | |
261 | * If there is no RCU priority boosting, we don't initiate boosting. | |
262 | */ | |
263 | static void rcu_initiate_boost(void) | |
264 | { | |
265 | } | |
266 | ||
267 | /* | |
268 | * If there is no RCU priority boosting, we don't initiate expedited boosting. | |
269 | */ | |
270 | static void rcu_initiate_expedited_boost(void) | |
271 | { | |
272 | } | |
273 | ||
274 | /* | |
275 | * If there is no RCU priority boosting, nothing to do at grace-period start. | |
276 | */ | |
277 | static void rcu_preempt_boost_start_gp(void) | |
278 | { | |
279 | } | |
280 | ||
281 | #endif /* else #ifdef CONFIG_RCU_BOOST */ | |
282 | ||
a57eb940 PM |
283 | /* |
284 | * Record a preemptible-RCU quiescent state for the specified CPU. Note | |
285 | * that this just means that the task currently running on the CPU is | |
286 | * in a quiescent state. There might be any number of tasks blocked | |
287 | * while in an RCU read-side critical section. | |
288 | * | |
289 | * Unlike the other rcu_*_qs() functions, callers to this function | |
290 | * must disable irqs in order to protect the assignment to | |
291 | * ->rcu_read_unlock_special. | |
292 | * | |
293 | * Because this is a single-CPU implementation, the only way a grace | |
294 | * period can end is if the CPU is in a quiescent state. The reason is | |
295 | * that a blocked preemptible-RCU reader can exit its critical section | |
296 | * only if the CPU is running it at the time. Therefore, when the | |
297 | * last task blocking the current grace period exits its RCU read-side | |
298 | * critical section, neither the CPU nor blocked tasks will be stopping | |
299 | * the current grace period. (In contrast, SMP implementations | |
300 | * might have CPUs running in RCU read-side critical sections that | |
301 | * block later grace periods -- but this is not possible given only | |
302 | * one CPU.) | |
303 | */ | |
304 | static void rcu_preempt_cpu_qs(void) | |
305 | { | |
306 | /* Record both CPU and task as having responded to current GP. */ | |
307 | rcu_preempt_ctrlblk.gpcpu = rcu_preempt_ctrlblk.gpnum; | |
308 | current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; | |
309 | ||
24278d14 | 310 | /* If there is no GP then there is nothing more to do. */ |
a57eb940 PM |
311 | if (!rcu_preempt_gp_in_progress() || rcu_preempt_blocked_readers_cgp()) |
312 | return; | |
24278d14 PM |
313 | /* If there are blocked readers, go check up on boosting. */ |
314 | if (rcu_preempt_blocked_readers_cgp()) { | |
315 | rcu_initiate_boost(); | |
316 | return; | |
317 | } | |
a57eb940 PM |
318 | |
319 | /* Advance callbacks. */ | |
320 | rcu_preempt_ctrlblk.completed = rcu_preempt_ctrlblk.gpnum; | |
321 | rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.rcb.curtail; | |
322 | rcu_preempt_ctrlblk.rcb.curtail = rcu_preempt_ctrlblk.nexttail; | |
323 | ||
324 | /* If there are no blocked readers, next GP is done instantly. */ | |
325 | if (!rcu_preempt_blocked_readers_any()) | |
326 | rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.nexttail; | |
327 | ||
b2c0710c | 328 | /* If there are done callbacks, cause them to be invoked. */ |
a57eb940 | 329 | if (*rcu_preempt_ctrlblk.rcb.donetail != NULL) |
24278d14 | 330 | invoke_rcu_kthread(); |
a57eb940 PM |
331 | } |
332 | ||
333 | /* | |
334 | * Start a new RCU grace period if warranted. Hard irqs must be disabled. | |
335 | */ | |
336 | static void rcu_preempt_start_gp(void) | |
337 | { | |
338 | if (!rcu_preempt_gp_in_progress() && rcu_preempt_needs_another_gp()) { | |
339 | ||
340 | /* Official start of GP. */ | |
341 | rcu_preempt_ctrlblk.gpnum++; | |
342 | ||
343 | /* Any blocked RCU readers block new GP. */ | |
344 | if (rcu_preempt_blocked_readers_any()) | |
345 | rcu_preempt_ctrlblk.gp_tasks = | |
346 | rcu_preempt_ctrlblk.blkd_tasks.next; | |
347 | ||
24278d14 PM |
348 | /* Set up for RCU priority boosting. */ |
349 | rcu_preempt_boost_start_gp(); | |
350 | ||
a57eb940 PM |
351 | /* If there is no running reader, CPU is done with GP. */ |
352 | if (!rcu_preempt_running_reader()) | |
353 | rcu_preempt_cpu_qs(); | |
354 | } | |
355 | } | |
356 | ||
357 | /* | |
358 | * We have entered the scheduler, and the current task might soon be | |
359 | * context-switched away from. If this task is in an RCU read-side | |
360 | * critical section, we will no longer be able to rely on the CPU to | |
361 | * record that fact, so we enqueue the task on the blkd_tasks list. | |
362 | * If the task started after the current grace period began, as recorded | |
363 | * by ->gpcpu, we enqueue at the beginning of the list. Otherwise | |
364 | * before the element referenced by ->gp_tasks (or at the tail if | |
365 | * ->gp_tasks is NULL) and point ->gp_tasks at the newly added element. | |
366 | * The task will dequeue itself when it exits the outermost enclosing | |
367 | * RCU read-side critical section. Therefore, the current grace period | |
368 | * cannot be permitted to complete until the ->gp_tasks pointer becomes | |
369 | * NULL. | |
370 | * | |
371 | * Caller must disable preemption. | |
372 | */ | |
373 | void rcu_preempt_note_context_switch(void) | |
374 | { | |
375 | struct task_struct *t = current; | |
376 | unsigned long flags; | |
377 | ||
378 | local_irq_save(flags); /* must exclude scheduler_tick(). */ | |
379 | if (rcu_preempt_running_reader() && | |
380 | (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { | |
381 | ||
382 | /* Possibly blocking in an RCU read-side critical section. */ | |
383 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; | |
384 | ||
385 | /* | |
386 | * If this CPU has already checked in, then this task | |
387 | * will hold up the next grace period rather than the | |
388 | * current grace period. Queue the task accordingly. | |
389 | * If the task is queued for the current grace period | |
390 | * (i.e., this CPU has not yet passed through a quiescent | |
391 | * state for the current grace period), then as long | |
392 | * as that task remains queued, the current grace period | |
393 | * cannot end. | |
394 | */ | |
395 | list_add(&t->rcu_node_entry, &rcu_preempt_ctrlblk.blkd_tasks); | |
dd7c4d89 | 396 | if (rcu_cpu_blocking_cur_gp()) |
a57eb940 PM |
397 | rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry; |
398 | } | |
399 | ||
400 | /* | |
401 | * Either we were not in an RCU read-side critical section to | |
402 | * begin with, or we have now recorded that critical section | |
403 | * globally. Either way, we can now note a quiescent state | |
404 | * for this CPU. Again, if we were in an RCU read-side critical | |
405 | * section, and if that critical section was blocking the current | |
406 | * grace period, then the fact that the task has been enqueued | |
407 | * means that current grace period continues to be blocked. | |
408 | */ | |
409 | rcu_preempt_cpu_qs(); | |
410 | local_irq_restore(flags); | |
411 | } | |
412 | ||
413 | /* | |
414 | * Tiny-preemptible RCU implementation for rcu_read_lock(). | |
415 | * Just increment ->rcu_read_lock_nesting, shared state will be updated | |
416 | * if we block. | |
417 | */ | |
418 | void __rcu_read_lock(void) | |
419 | { | |
420 | current->rcu_read_lock_nesting++; | |
421 | barrier(); /* needed if we ever invoke rcu_read_lock in rcutiny.c */ | |
422 | } | |
423 | EXPORT_SYMBOL_GPL(__rcu_read_lock); | |
424 | ||
425 | /* | |
426 | * Handle special cases during rcu_read_unlock(), such as needing to | |
427 | * notify RCU core processing or task having blocked during the RCU | |
428 | * read-side critical section. | |
429 | */ | |
430 | static void rcu_read_unlock_special(struct task_struct *t) | |
431 | { | |
432 | int empty; | |
433 | int empty_exp; | |
434 | unsigned long flags; | |
435 | struct list_head *np; | |
436 | int special; | |
437 | ||
438 | /* | |
439 | * NMI handlers cannot block and cannot safely manipulate state. | |
440 | * They therefore cannot possibly be special, so just leave. | |
441 | */ | |
442 | if (in_nmi()) | |
443 | return; | |
444 | ||
445 | local_irq_save(flags); | |
446 | ||
447 | /* | |
448 | * If RCU core is waiting for this CPU to exit critical section, | |
449 | * let it know that we have done so. | |
450 | */ | |
451 | special = t->rcu_read_unlock_special; | |
452 | if (special & RCU_READ_UNLOCK_NEED_QS) | |
453 | rcu_preempt_cpu_qs(); | |
454 | ||
455 | /* Hardware IRQ handlers cannot block. */ | |
456 | if (in_irq()) { | |
457 | local_irq_restore(flags); | |
458 | return; | |
459 | } | |
460 | ||
461 | /* Clean up if blocked during RCU read-side critical section. */ | |
462 | if (special & RCU_READ_UNLOCK_BLOCKED) { | |
463 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; | |
464 | ||
465 | /* | |
466 | * Remove this task from the ->blkd_tasks list and adjust | |
467 | * any pointers that might have been referencing it. | |
468 | */ | |
469 | empty = !rcu_preempt_blocked_readers_cgp(); | |
470 | empty_exp = rcu_preempt_ctrlblk.exp_tasks == NULL; | |
24278d14 | 471 | np = rcu_next_node_entry(t); |
a57eb940 PM |
472 | list_del(&t->rcu_node_entry); |
473 | if (&t->rcu_node_entry == rcu_preempt_ctrlblk.gp_tasks) | |
474 | rcu_preempt_ctrlblk.gp_tasks = np; | |
475 | if (&t->rcu_node_entry == rcu_preempt_ctrlblk.exp_tasks) | |
476 | rcu_preempt_ctrlblk.exp_tasks = np; | |
24278d14 PM |
477 | #ifdef CONFIG_RCU_BOOST |
478 | if (&t->rcu_node_entry == rcu_preempt_ctrlblk.boost_tasks) | |
479 | rcu_preempt_ctrlblk.boost_tasks = np; | |
480 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
a57eb940 PM |
481 | INIT_LIST_HEAD(&t->rcu_node_entry); |
482 | ||
483 | /* | |
484 | * If this was the last task on the current list, and if | |
485 | * we aren't waiting on the CPU, report the quiescent state | |
486 | * and start a new grace period if needed. | |
487 | */ | |
488 | if (!empty && !rcu_preempt_blocked_readers_cgp()) { | |
489 | rcu_preempt_cpu_qs(); | |
490 | rcu_preempt_start_gp(); | |
491 | } | |
492 | ||
493 | /* | |
494 | * If this was the last task on the expedited lists, | |
495 | * then we need wake up the waiting task. | |
496 | */ | |
497 | if (!empty_exp && rcu_preempt_ctrlblk.exp_tasks == NULL) | |
498 | rcu_report_exp_done(); | |
499 | } | |
24278d14 PM |
500 | #ifdef CONFIG_RCU_BOOST |
501 | /* Unboost self if was boosted. */ | |
502 | if (special & RCU_READ_UNLOCK_BOOSTED) { | |
503 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BOOSTED; | |
504 | rt_mutex_unlock(t->rcu_boost_mutex); | |
505 | t->rcu_boost_mutex = NULL; | |
506 | } | |
507 | #endif /* #ifdef CONFIG_RCU_BOOST */ | |
a57eb940 PM |
508 | local_irq_restore(flags); |
509 | } | |
510 | ||
511 | /* | |
512 | * Tiny-preemptible RCU implementation for rcu_read_unlock(). | |
513 | * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost | |
514 | * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then | |
515 | * invoke rcu_read_unlock_special() to clean up after a context switch | |
516 | * in an RCU read-side critical section and other special cases. | |
517 | */ | |
518 | void __rcu_read_unlock(void) | |
519 | { | |
520 | struct task_struct *t = current; | |
521 | ||
522 | barrier(); /* needed if we ever invoke rcu_read_unlock in rcutiny.c */ | |
523 | --t->rcu_read_lock_nesting; | |
524 | barrier(); /* decrement before load of ->rcu_read_unlock_special */ | |
525 | if (t->rcu_read_lock_nesting == 0 && | |
526 | unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) | |
527 | rcu_read_unlock_special(t); | |
528 | #ifdef CONFIG_PROVE_LOCKING | |
529 | WARN_ON_ONCE(t->rcu_read_lock_nesting < 0); | |
530 | #endif /* #ifdef CONFIG_PROVE_LOCKING */ | |
531 | } | |
532 | EXPORT_SYMBOL_GPL(__rcu_read_unlock); | |
533 | ||
534 | /* | |
535 | * Check for a quiescent state from the current CPU. When a task blocks, | |
536 | * the task is recorded in the rcu_preempt_ctrlblk structure, which is | |
537 | * checked elsewhere. This is called from the scheduling-clock interrupt. | |
538 | * | |
539 | * Caller must disable hard irqs. | |
540 | */ | |
541 | static void rcu_preempt_check_callbacks(void) | |
542 | { | |
543 | struct task_struct *t = current; | |
544 | ||
dd7c4d89 PM |
545 | if (rcu_preempt_gp_in_progress() && |
546 | (!rcu_preempt_running_reader() || | |
547 | !rcu_cpu_blocking_cur_gp())) | |
a57eb940 PM |
548 | rcu_preempt_cpu_qs(); |
549 | if (&rcu_preempt_ctrlblk.rcb.rcucblist != | |
550 | rcu_preempt_ctrlblk.rcb.donetail) | |
24278d14 | 551 | invoke_rcu_kthread(); |
dd7c4d89 PM |
552 | if (rcu_preempt_gp_in_progress() && |
553 | rcu_cpu_blocking_cur_gp() && | |
554 | rcu_preempt_running_reader()) | |
a57eb940 PM |
555 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; |
556 | } | |
557 | ||
558 | /* | |
559 | * TINY_PREEMPT_RCU has an extra callback-list tail pointer to | |
b2c0710c | 560 | * update, so this is invoked from rcu_process_callbacks() to |
a57eb940 PM |
561 | * handle that case. Of course, it is invoked for all flavors of |
562 | * RCU, but RCU callbacks can appear only on one of the lists, and | |
563 | * neither ->nexttail nor ->donetail can possibly be NULL, so there | |
564 | * is no need for an explicit check. | |
565 | */ | |
566 | static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp) | |
567 | { | |
568 | if (rcu_preempt_ctrlblk.nexttail == rcp->donetail) | |
569 | rcu_preempt_ctrlblk.nexttail = &rcp->rcucblist; | |
570 | } | |
571 | ||
572 | /* | |
573 | * Process callbacks for preemptible RCU. | |
574 | */ | |
575 | static void rcu_preempt_process_callbacks(void) | |
576 | { | |
b2c0710c | 577 | rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb); |
a57eb940 PM |
578 | } |
579 | ||
580 | /* | |
581 | * Queue a preemptible -RCU callback for invocation after a grace period. | |
582 | */ | |
583 | void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) | |
584 | { | |
585 | unsigned long flags; | |
586 | ||
587 | debug_rcu_head_queue(head); | |
588 | head->func = func; | |
589 | head->next = NULL; | |
590 | ||
591 | local_irq_save(flags); | |
592 | *rcu_preempt_ctrlblk.nexttail = head; | |
593 | rcu_preempt_ctrlblk.nexttail = &head->next; | |
594 | rcu_preempt_start_gp(); /* checks to see if GP needed. */ | |
595 | local_irq_restore(flags); | |
596 | } | |
597 | EXPORT_SYMBOL_GPL(call_rcu); | |
598 | ||
599 | void rcu_barrier(void) | |
600 | { | |
601 | struct rcu_synchronize rcu; | |
602 | ||
603 | init_rcu_head_on_stack(&rcu.head); | |
604 | init_completion(&rcu.completion); | |
605 | /* Will wake me after RCU finished. */ | |
606 | call_rcu(&rcu.head, wakeme_after_rcu); | |
607 | /* Wait for it. */ | |
608 | wait_for_completion(&rcu.completion); | |
609 | destroy_rcu_head_on_stack(&rcu.head); | |
610 | } | |
611 | EXPORT_SYMBOL_GPL(rcu_barrier); | |
612 | ||
613 | /* | |
614 | * synchronize_rcu - wait until a grace period has elapsed. | |
615 | * | |
616 | * Control will return to the caller some time after a full grace | |
617 | * period has elapsed, in other words after all currently executing RCU | |
618 | * read-side critical sections have completed. RCU read-side critical | |
619 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), | |
620 | * and may be nested. | |
621 | */ | |
622 | void synchronize_rcu(void) | |
623 | { | |
624 | #ifdef CONFIG_DEBUG_LOCK_ALLOC | |
625 | if (!rcu_scheduler_active) | |
626 | return; | |
627 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
628 | ||
629 | WARN_ON_ONCE(rcu_preempt_running_reader()); | |
630 | if (!rcu_preempt_blocked_readers_any()) | |
631 | return; | |
632 | ||
633 | /* Once we get past the fastpath checks, same code as rcu_barrier(). */ | |
634 | rcu_barrier(); | |
635 | } | |
636 | EXPORT_SYMBOL_GPL(synchronize_rcu); | |
637 | ||
638 | static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); | |
639 | static unsigned long sync_rcu_preempt_exp_count; | |
640 | static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); | |
641 | ||
642 | /* | |
643 | * Return non-zero if there are any tasks in RCU read-side critical | |
644 | * sections blocking the current preemptible-RCU expedited grace period. | |
645 | * If there is no preemptible-RCU expedited grace period currently in | |
646 | * progress, returns zero unconditionally. | |
647 | */ | |
648 | static int rcu_preempted_readers_exp(void) | |
649 | { | |
650 | return rcu_preempt_ctrlblk.exp_tasks != NULL; | |
651 | } | |
652 | ||
653 | /* | |
654 | * Report the exit from RCU read-side critical section for the last task | |
655 | * that queued itself during or before the current expedited preemptible-RCU | |
656 | * grace period. | |
657 | */ | |
658 | static void rcu_report_exp_done(void) | |
659 | { | |
660 | wake_up(&sync_rcu_preempt_exp_wq); | |
661 | } | |
662 | ||
663 | /* | |
664 | * Wait for an rcu-preempt grace period, but expedite it. The basic idea | |
665 | * is to rely in the fact that there is but one CPU, and that it is | |
666 | * illegal for a task to invoke synchronize_rcu_expedited() while in a | |
667 | * preemptible-RCU read-side critical section. Therefore, any such | |
668 | * critical sections must correspond to blocked tasks, which must therefore | |
669 | * be on the ->blkd_tasks list. So just record the current head of the | |
670 | * list in the ->exp_tasks pointer, and wait for all tasks including and | |
671 | * after the task pointed to by ->exp_tasks to drain. | |
672 | */ | |
673 | void synchronize_rcu_expedited(void) | |
674 | { | |
675 | unsigned long flags; | |
676 | struct rcu_preempt_ctrlblk *rpcp = &rcu_preempt_ctrlblk; | |
677 | unsigned long snap; | |
678 | ||
679 | barrier(); /* ensure prior action seen before grace period. */ | |
680 | ||
681 | WARN_ON_ONCE(rcu_preempt_running_reader()); | |
682 | ||
683 | /* | |
684 | * Acquire lock so that there is only one preemptible RCU grace | |
685 | * period in flight. Of course, if someone does the expedited | |
686 | * grace period for us while we are acquiring the lock, just leave. | |
687 | */ | |
688 | snap = sync_rcu_preempt_exp_count + 1; | |
689 | mutex_lock(&sync_rcu_preempt_exp_mutex); | |
690 | if (ULONG_CMP_LT(snap, sync_rcu_preempt_exp_count)) | |
691 | goto unlock_mb_ret; /* Others did our work for us. */ | |
692 | ||
693 | local_irq_save(flags); | |
694 | ||
695 | /* | |
696 | * All RCU readers have to already be on blkd_tasks because | |
697 | * we cannot legally be executing in an RCU read-side critical | |
698 | * section. | |
699 | */ | |
700 | ||
701 | /* Snapshot current head of ->blkd_tasks list. */ | |
702 | rpcp->exp_tasks = rpcp->blkd_tasks.next; | |
703 | if (rpcp->exp_tasks == &rpcp->blkd_tasks) | |
704 | rpcp->exp_tasks = NULL; | |
705 | local_irq_restore(flags); | |
706 | ||
707 | /* Wait for tail of ->blkd_tasks list to drain. */ | |
708 | if (rcu_preempted_readers_exp()) | |
24278d14 | 709 | rcu_initiate_expedited_boost(); |
a57eb940 PM |
710 | wait_event(sync_rcu_preempt_exp_wq, |
711 | !rcu_preempted_readers_exp()); | |
712 | ||
713 | /* Clean up and exit. */ | |
714 | barrier(); /* ensure expedited GP seen before counter increment. */ | |
715 | sync_rcu_preempt_exp_count++; | |
716 | unlock_mb_ret: | |
717 | mutex_unlock(&sync_rcu_preempt_exp_mutex); | |
718 | barrier(); /* ensure subsequent action seen after grace period. */ | |
719 | } | |
720 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); | |
721 | ||
722 | /* | |
723 | * Does preemptible RCU need the CPU to stay out of dynticks mode? | |
724 | */ | |
725 | int rcu_preempt_needs_cpu(void) | |
726 | { | |
727 | if (!rcu_preempt_running_reader()) | |
728 | rcu_preempt_cpu_qs(); | |
729 | return rcu_preempt_ctrlblk.rcb.rcucblist != NULL; | |
730 | } | |
731 | ||
732 | /* | |
733 | * Check for a task exiting while in a preemptible -RCU read-side | |
734 | * critical section, clean up if so. No need to issue warnings, | |
735 | * as debug_check_no_locks_held() already does this if lockdep | |
736 | * is enabled. | |
737 | */ | |
738 | void exit_rcu(void) | |
739 | { | |
740 | struct task_struct *t = current; | |
741 | ||
742 | if (t->rcu_read_lock_nesting == 0) | |
743 | return; | |
744 | t->rcu_read_lock_nesting = 1; | |
745 | rcu_read_unlock(); | |
746 | } | |
747 | ||
748 | #else /* #ifdef CONFIG_TINY_PREEMPT_RCU */ | |
749 | ||
24278d14 PM |
750 | /* |
751 | * Because preemptible RCU does not exist, it is never necessary to | |
752 | * boost preempted RCU readers. | |
753 | */ | |
754 | static int rcu_boost(void) | |
755 | { | |
756 | return 0; | |
757 | } | |
758 | ||
a57eb940 PM |
759 | /* |
760 | * Because preemptible RCU does not exist, it never has any callbacks | |
761 | * to check. | |
762 | */ | |
763 | static void rcu_preempt_check_callbacks(void) | |
764 | { | |
765 | } | |
766 | ||
767 | /* | |
768 | * Because preemptible RCU does not exist, it never has any callbacks | |
769 | * to remove. | |
770 | */ | |
771 | static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp) | |
772 | { | |
773 | } | |
774 | ||
775 | /* | |
776 | * Because preemptible RCU does not exist, it never has any callbacks | |
777 | * to process. | |
778 | */ | |
779 | static void rcu_preempt_process_callbacks(void) | |
780 | { | |
781 | } | |
782 | ||
783 | #endif /* #else #ifdef CONFIG_TINY_PREEMPT_RCU */ | |
784 | ||
bbad9379 | 785 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
bbad9379 PM |
786 | #include <linux/kernel_stat.h> |
787 | ||
788 | /* | |
789 | * During boot, we forgive RCU lockdep issues. After this function is | |
790 | * invoked, we start taking RCU lockdep issues seriously. | |
791 | */ | |
b2c0710c | 792 | void __init rcu_scheduler_starting(void) |
bbad9379 PM |
793 | { |
794 | WARN_ON(nr_context_switches() > 0); | |
795 | rcu_scheduler_active = 1; | |
796 | } | |
797 | ||
798 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
24278d14 PM |
799 | |
800 | #ifdef CONFIG_RCU_BOOST | |
801 | #define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO | |
802 | #else /* #ifdef CONFIG_RCU_BOOST */ | |
803 | #define RCU_BOOST_PRIO 1 | |
804 | #endif /* #else #ifdef CONFIG_RCU_BOOST */ |