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1 | /* |
2 | * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition |
3 | * Internal non-public definitions that provide either classic |
4 | * or preemptible semantics. |
5 | * |
6 | * This program is free software; you can redistribute it and/or modify |
7 | * it under the terms of the GNU General Public License as published by |
8 | * the Free Software Foundation; either version 2 of the License, or |
9 | * (at your option) any later version. |
10 | * |
11 | * This program is distributed in the hope that it will be useful, |
12 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
13 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
14 | * GNU General Public License for more details. |
15 | * |
16 | * You should have received a copy of the GNU General Public License |
17 | * along with this program; if not, write to the Free Software |
18 | * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
19 | * |
20 | * Copyright (c) 2010 Linaro |
21 | * |
22 | * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com> |
23 | */ |
24 | |
25 | #include <linux/kthread.h> |
26 | #include <linux/debugfs.h> |
27 | #include <linux/seq_file.h> |
28 | |
29 | #ifdef CONFIG_RCU_TRACE |
30 | #define RCU_TRACE(stmt) stmt |
31 | #else /* #ifdef CONFIG_RCU_TRACE */ |
32 | #define RCU_TRACE(stmt) |
33 | #endif /* #else #ifdef CONFIG_RCU_TRACE */ |
34 | |
35 | /* Global control variables for rcupdate callback mechanism. */ |
36 | struct rcu_ctrlblk { |
37 | struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */ |
38 | struct rcu_head **donetail; /* ->next pointer of last "done" CB. */ |
39 | struct rcu_head **curtail; /* ->next pointer of last CB. */ |
40 | RCU_TRACE(long qlen); /* Number of pending CBs. */ |
41 | }; |
42 | |
43 | /* Definition for rcupdate control block. */ |
44 | static struct rcu_ctrlblk rcu_sched_ctrlblk = { |
45 | .donetail = &rcu_sched_ctrlblk.rcucblist, |
46 | .curtail = &rcu_sched_ctrlblk.rcucblist, |
47 | }; |
48 | |
49 | static struct rcu_ctrlblk rcu_bh_ctrlblk = { |
50 | .donetail = &rcu_bh_ctrlblk.rcucblist, |
51 | .curtail = &rcu_bh_ctrlblk.rcucblist, |
52 | }; |
53 | |
54 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
55 | int rcu_scheduler_active __read_mostly; |
56 | EXPORT_SYMBOL_GPL(rcu_scheduler_active); |
57 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
58 | |
59 | #ifdef CONFIG_TINY_PREEMPT_RCU |
60 | |
61 | #include <linux/delay.h> |
62 | |
63 | /* Global control variables for preemptible RCU. */ |
64 | struct rcu_preempt_ctrlblk { |
65 | struct rcu_ctrlblk rcb; /* curtail: ->next ptr of last CB for GP. */ |
66 | struct rcu_head **nexttail; |
67 | /* Tasks blocked in a preemptible RCU */ |
68 | /* read-side critical section while an */ |
69 | /* preemptible-RCU grace period is in */ |
70 | /* progress must wait for a later grace */ |
71 | /* period. This pointer points to the */ |
72 | /* ->next pointer of the last task that */ |
73 | /* must wait for a later grace period, or */ |
74 | /* to &->rcb.rcucblist if there is no */ |
75 | /* such task. */ |
76 | struct list_head blkd_tasks; |
77 | /* Tasks blocked in RCU read-side critical */ |
78 | /* section. Tasks are placed at the head */ |
79 | /* of this list and age towards the tail. */ |
80 | struct list_head *gp_tasks; |
81 | /* Pointer to the first task blocking the */ |
82 | /* current grace period, or NULL if there */ |
83 | /* is no such task. */ |
84 | struct list_head *exp_tasks; |
85 | /* Pointer to first task blocking the */ |
86 | /* current expedited grace period, or NULL */ |
87 | /* if there is no such task. If there */ |
88 | /* is no current expedited grace period, */ |
89 | /* then there cannot be any such task. */ |
90 | #ifdef CONFIG_RCU_BOOST |
91 | struct list_head *boost_tasks; |
92 | /* Pointer to first task that needs to be */ |
93 | /* priority-boosted, or NULL if no priority */ |
94 | /* boosting is needed. If there is no */ |
95 | /* current or expedited grace period, there */ |
96 | /* can be no such task. */ |
97 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
98 | u8 gpnum; /* Current grace period. */ |
99 | u8 gpcpu; /* Last grace period blocked by the CPU. */ |
100 | u8 completed; /* Last grace period completed. */ |
101 | /* If all three are equal, RCU is idle. */ |
102 | #ifdef CONFIG_RCU_BOOST |
103 | unsigned long boost_time; /* When to start boosting (jiffies) */ |
104 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
105 | #ifdef CONFIG_RCU_TRACE |
106 | unsigned long n_grace_periods; |
107 | #ifdef CONFIG_RCU_BOOST |
108 | unsigned long n_tasks_boosted; |
109 | /* Total number of tasks boosted. */ |
110 | unsigned long n_exp_boosts; |
111 | /* Number of tasks boosted for expedited GP. */ |
112 | unsigned long n_normal_boosts; |
113 | /* Number of tasks boosted for normal GP. */ |
114 | unsigned long n_balk_blkd_tasks; |
115 | /* Refused to boost: no blocked tasks. */ |
116 | unsigned long n_balk_exp_gp_tasks; |
117 | /* Refused to boost: nothing blocking GP. */ |
118 | unsigned long n_balk_boost_tasks; |
119 | /* Refused to boost: already boosting. */ |
120 | unsigned long n_balk_notyet; |
121 | /* Refused to boost: not yet time. */ |
122 | unsigned long n_balk_nos; |
123 | /* Refused to boost: not sure why, though. */ |
124 | /* This can happen due to race conditions. */ |
125 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
126 | #endif /* #ifdef CONFIG_RCU_TRACE */ |
127 | }; |
128 | |
129 | static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = { |
130 | .rcb.donetail = &rcu_preempt_ctrlblk.rcb.rcucblist, |
131 | .rcb.curtail = &rcu_preempt_ctrlblk.rcb.rcucblist, |
132 | .nexttail = &rcu_preempt_ctrlblk.rcb.rcucblist, |
133 | .blkd_tasks = LIST_HEAD_INIT(rcu_preempt_ctrlblk.blkd_tasks), |
134 | }; |
135 | |
136 | static int rcu_preempted_readers_exp(void); |
137 | static void rcu_report_exp_done(void); |
138 | |
139 | /* |
140 | * Return true if the CPU has not yet responded to the current grace period. |
141 | */ |
142 | static int rcu_cpu_blocking_cur_gp(void) |
143 | { |
144 | return rcu_preempt_ctrlblk.gpcpu != rcu_preempt_ctrlblk.gpnum; |
145 | } |
146 | |
147 | /* |
148 | * Check for a running RCU reader. Because there is only one CPU, |
149 | * there can be but one running RCU reader at a time. ;-) |
150 | */ |
151 | static int rcu_preempt_running_reader(void) |
152 | { |
153 | return current->rcu_read_lock_nesting; |
154 | } |
155 | |
156 | /* |
157 | * Check for preempted RCU readers blocking any grace period. |
158 | * If the caller needs a reliable answer, it must disable hard irqs. |
159 | */ |
160 | static int rcu_preempt_blocked_readers_any(void) |
161 | { |
162 | return !list_empty(&rcu_preempt_ctrlblk.blkd_tasks); |
163 | } |
164 | |
165 | /* |
166 | * Check for preempted RCU readers blocking the current grace period. |
167 | * If the caller needs a reliable answer, it must disable hard irqs. |
168 | */ |
169 | static int rcu_preempt_blocked_readers_cgp(void) |
170 | { |
171 | return rcu_preempt_ctrlblk.gp_tasks != NULL; |
172 | } |
173 | |
174 | /* |
175 | * Return true if another preemptible-RCU grace period is needed. |
176 | */ |
177 | static int rcu_preempt_needs_another_gp(void) |
178 | { |
179 | return *rcu_preempt_ctrlblk.rcb.curtail != NULL; |
180 | } |
181 | |
182 | /* |
183 | * Return true if a preemptible-RCU grace period is in progress. |
184 | * The caller must disable hardirqs. |
185 | */ |
186 | static int rcu_preempt_gp_in_progress(void) |
187 | { |
188 | return rcu_preempt_ctrlblk.completed != rcu_preempt_ctrlblk.gpnum; |
189 | } |
190 | |
191 | /* |
192 | * Advance a ->blkd_tasks-list pointer to the next entry, instead |
193 | * returning NULL if at the end of the list. |
194 | */ |
195 | static struct list_head *rcu_next_node_entry(struct task_struct *t) |
196 | { |
197 | struct list_head *np; |
198 | |
199 | np = t->rcu_node_entry.next; |
200 | if (np == &rcu_preempt_ctrlblk.blkd_tasks) |
201 | np = NULL; |
202 | return np; |
203 | } |
204 | |
205 | #ifdef CONFIG_RCU_TRACE |
206 | |
207 | #ifdef CONFIG_RCU_BOOST |
208 | static void rcu_initiate_boost_trace(void); |
209 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
210 | |
211 | /* |
212 | * Dump additional statistice for TINY_PREEMPT_RCU. |
213 | */ |
214 | static void show_tiny_preempt_stats(struct seq_file *m) |
215 | { |
216 | seq_printf(m, "rcu_preempt: qlen=%ld gp=%lu g%u/p%u/c%u tasks=%c%c%c\n", |
217 | rcu_preempt_ctrlblk.rcb.qlen, |
218 | rcu_preempt_ctrlblk.n_grace_periods, |
219 | rcu_preempt_ctrlblk.gpnum, |
220 | rcu_preempt_ctrlblk.gpcpu, |
221 | rcu_preempt_ctrlblk.completed, |
222 | "T."[list_empty(&rcu_preempt_ctrlblk.blkd_tasks)], |
223 | "N."[!rcu_preempt_ctrlblk.gp_tasks], |
224 | "E."[!rcu_preempt_ctrlblk.exp_tasks]); |
225 | #ifdef CONFIG_RCU_BOOST |
226 | seq_printf(m, "%sttb=%c ntb=%lu neb=%lu nnb=%lu j=%04x bt=%04x\n", |
227 | " ", |
228 | "B."[!rcu_preempt_ctrlblk.boost_tasks], |
229 | rcu_preempt_ctrlblk.n_tasks_boosted, |
230 | rcu_preempt_ctrlblk.n_exp_boosts, |
231 | rcu_preempt_ctrlblk.n_normal_boosts, |
232 | (int)(jiffies & 0xffff), |
233 | (int)(rcu_preempt_ctrlblk.boost_time & 0xffff)); |
234 | seq_printf(m, "%s: nt=%lu egt=%lu bt=%lu ny=%lu nos=%lu\n", |
235 | " balk", |
236 | rcu_preempt_ctrlblk.n_balk_blkd_tasks, |
237 | rcu_preempt_ctrlblk.n_balk_exp_gp_tasks, |
238 | rcu_preempt_ctrlblk.n_balk_boost_tasks, |
239 | rcu_preempt_ctrlblk.n_balk_notyet, |
240 | rcu_preempt_ctrlblk.n_balk_nos); |
241 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
242 | } |
243 | |
244 | #endif /* #ifdef CONFIG_RCU_TRACE */ |
245 | |
246 | #ifdef CONFIG_RCU_BOOST |
247 | |
248 | #include "rtmutex_common.h" |
249 | |
250 | /* |
251 | * Carry out RCU priority boosting on the task indicated by ->boost_tasks, |
252 | * and advance ->boost_tasks to the next task in the ->blkd_tasks list. |
253 | */ |
254 | static int rcu_boost(void) |
255 | { |
256 | unsigned long flags; |
257 | struct rt_mutex mtx; |
258 | struct task_struct *t; |
259 | struct list_head *tb; |
260 | |
261 | if (rcu_preempt_ctrlblk.boost_tasks == NULL && |
262 | rcu_preempt_ctrlblk.exp_tasks == NULL) |
263 | return 0; /* Nothing to boost. */ |
264 | |
265 | raw_local_irq_save(flags); |
266 | |
267 | /* |
268 | * Recheck with irqs disabled: all tasks in need of boosting |
269 | * might exit their RCU read-side critical sections on their own |
270 | * if we are preempted just before disabling irqs. |
271 | */ |
272 | if (rcu_preempt_ctrlblk.boost_tasks == NULL && |
273 | rcu_preempt_ctrlblk.exp_tasks == NULL) { |
274 | raw_local_irq_restore(flags); |
275 | return 0; |
276 | } |
277 | |
278 | /* |
279 | * Preferentially boost tasks blocking expedited grace periods. |
280 | * This cannot starve the normal grace periods because a second |
281 | * expedited grace period must boost all blocked tasks, including |
282 | * those blocking the pre-existing normal grace period. |
283 | */ |
284 | if (rcu_preempt_ctrlblk.exp_tasks != NULL) { |
285 | tb = rcu_preempt_ctrlblk.exp_tasks; |
286 | RCU_TRACE(rcu_preempt_ctrlblk.n_exp_boosts++); |
287 | } else { |
288 | tb = rcu_preempt_ctrlblk.boost_tasks; |
289 | RCU_TRACE(rcu_preempt_ctrlblk.n_normal_boosts++); |
290 | } |
291 | RCU_TRACE(rcu_preempt_ctrlblk.n_tasks_boosted++); |
292 | |
293 | /* |
294 | * We boost task t by manufacturing an rt_mutex that appears to |
295 | * be held by task t. We leave a pointer to that rt_mutex where |
296 | * task t can find it, and task t will release the mutex when it |
297 | * exits its outermost RCU read-side critical section. Then |
298 | * simply acquiring this artificial rt_mutex will boost task |
299 | * t's priority. (Thanks to tglx for suggesting this approach!) |
300 | */ |
301 | t = container_of(tb, struct task_struct, rcu_node_entry); |
302 | rt_mutex_init_proxy_locked(&mtx, t); |
303 | t->rcu_boost_mutex = &mtx; |
304 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BOOSTED; |
305 | raw_local_irq_restore(flags); |
306 | rt_mutex_lock(&mtx); |
307 | rt_mutex_unlock(&mtx); /* Keep lockdep happy. */ |
308 | |
309 | return rcu_preempt_ctrlblk.boost_tasks != NULL || |
310 | rcu_preempt_ctrlblk.exp_tasks != NULL; |
311 | } |
312 | |
313 | /* |
314 | * Check to see if it is now time to start boosting RCU readers blocking |
315 | * the current grace period, and, if so, tell the rcu_kthread_task to |
316 | * start boosting them. If there is an expedited boost in progress, |
317 | * we wait for it to complete. |
318 | * |
319 | * If there are no blocked readers blocking the current grace period, |
320 | * return 0 to let the caller know, otherwise return 1. Note that this |
321 | * return value is independent of whether or not boosting was done. |
322 | */ |
323 | static int rcu_initiate_boost(void) |
324 | { |
325 | if (!rcu_preempt_blocked_readers_cgp() && |
326 | rcu_preempt_ctrlblk.exp_tasks == NULL) { |
327 | RCU_TRACE(rcu_preempt_ctrlblk.n_balk_exp_gp_tasks++); |
328 | return 0; |
329 | } |
330 | if (rcu_preempt_ctrlblk.exp_tasks != NULL || |
331 | (rcu_preempt_ctrlblk.gp_tasks != NULL && |
332 | rcu_preempt_ctrlblk.boost_tasks == NULL && |
333 | ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time))) { |
334 | if (rcu_preempt_ctrlblk.exp_tasks == NULL) |
335 | rcu_preempt_ctrlblk.boost_tasks = |
336 | rcu_preempt_ctrlblk.gp_tasks; |
337 | invoke_rcu_kthread(); |
338 | } else |
339 | RCU_TRACE(rcu_initiate_boost_trace()); |
340 | return 1; |
341 | } |
342 | |
343 | #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) |
344 | |
345 | /* |
346 | * Do priority-boost accounting for the start of a new grace period. |
347 | */ |
348 | static void rcu_preempt_boost_start_gp(void) |
349 | { |
350 | rcu_preempt_ctrlblk.boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; |
351 | } |
352 | |
353 | #else /* #ifdef CONFIG_RCU_BOOST */ |
354 | |
355 | /* |
356 | * If there is no RCU priority boosting, we don't boost. |
357 | */ |
358 | static int rcu_boost(void) |
359 | { |
360 | return 0; |
361 | } |
362 | |
363 | /* |
364 | * If there is no RCU priority boosting, we don't initiate boosting, |
365 | * but we do indicate whether there are blocked readers blocking the |
366 | * current grace period. |
367 | */ |
368 | static int rcu_initiate_boost(void) |
369 | { |
370 | return rcu_preempt_blocked_readers_cgp(); |
371 | } |
372 | |
373 | /* |
374 | * If there is no RCU priority boosting, nothing to do at grace-period start. |
375 | */ |
376 | static void rcu_preempt_boost_start_gp(void) |
377 | { |
378 | } |
379 | |
380 | #endif /* else #ifdef CONFIG_RCU_BOOST */ |
381 | |
382 | /* |
383 | * Record a preemptible-RCU quiescent state for the specified CPU. Note |
384 | * that this just means that the task currently running on the CPU is |
385 | * in a quiescent state. There might be any number of tasks blocked |
386 | * while in an RCU read-side critical section. |
387 | * |
388 | * Unlike the other rcu_*_qs() functions, callers to this function |
389 | * must disable irqs in order to protect the assignment to |
390 | * ->rcu_read_unlock_special. |
391 | * |
392 | * Because this is a single-CPU implementation, the only way a grace |
393 | * period can end is if the CPU is in a quiescent state. The reason is |
394 | * that a blocked preemptible-RCU reader can exit its critical section |
395 | * only if the CPU is running it at the time. Therefore, when the |
396 | * last task blocking the current grace period exits its RCU read-side |
397 | * critical section, neither the CPU nor blocked tasks will be stopping |
398 | * the current grace period. (In contrast, SMP implementations |
399 | * might have CPUs running in RCU read-side critical sections that |
400 | * block later grace periods -- but this is not possible given only |
401 | * one CPU.) |
402 | */ |
403 | static void rcu_preempt_cpu_qs(void) |
404 | { |
405 | /* Record both CPU and task as having responded to current GP. */ |
406 | rcu_preempt_ctrlblk.gpcpu = rcu_preempt_ctrlblk.gpnum; |
407 | current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; |
408 | |
409 | /* If there is no GP then there is nothing more to do. */ |
410 | if (!rcu_preempt_gp_in_progress()) |
411 | return; |
412 | /* |
413 | * Check up on boosting. If there are readers blocking the |
414 | * current grace period, leave. |
415 | */ |
416 | if (rcu_initiate_boost()) |
417 | return; |
418 | |
419 | /* Advance callbacks. */ |
420 | rcu_preempt_ctrlblk.completed = rcu_preempt_ctrlblk.gpnum; |
421 | rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.rcb.curtail; |
422 | rcu_preempt_ctrlblk.rcb.curtail = rcu_preempt_ctrlblk.nexttail; |
423 | |
424 | /* If there are no blocked readers, next GP is done instantly. */ |
425 | if (!rcu_preempt_blocked_readers_any()) |
426 | rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.nexttail; |
427 | |
428 | /* If there are done callbacks, cause them to be invoked. */ |
429 | if (*rcu_preempt_ctrlblk.rcb.donetail != NULL) |
430 | invoke_rcu_kthread(); |
431 | } |
432 | |
433 | /* |
434 | * Start a new RCU grace period if warranted. Hard irqs must be disabled. |
435 | */ |
436 | static void rcu_preempt_start_gp(void) |
437 | { |
438 | if (!rcu_preempt_gp_in_progress() && rcu_preempt_needs_another_gp()) { |
439 | |
440 | /* Official start of GP. */ |
441 | rcu_preempt_ctrlblk.gpnum++; |
442 | RCU_TRACE(rcu_preempt_ctrlblk.n_grace_periods++); |
443 | |
444 | /* Any blocked RCU readers block new GP. */ |
445 | if (rcu_preempt_blocked_readers_any()) |
446 | rcu_preempt_ctrlblk.gp_tasks = |
447 | rcu_preempt_ctrlblk.blkd_tasks.next; |
448 | |
449 | /* Set up for RCU priority boosting. */ |
450 | rcu_preempt_boost_start_gp(); |
451 | |
452 | /* If there is no running reader, CPU is done with GP. */ |
453 | if (!rcu_preempt_running_reader()) |
454 | rcu_preempt_cpu_qs(); |
455 | } |
456 | } |
457 | |
458 | /* |
459 | * We have entered the scheduler, and the current task might soon be |
460 | * context-switched away from. If this task is in an RCU read-side |
461 | * critical section, we will no longer be able to rely on the CPU to |
462 | * record that fact, so we enqueue the task on the blkd_tasks list. |
463 | * If the task started after the current grace period began, as recorded |
464 | * by ->gpcpu, we enqueue at the beginning of the list. Otherwise |
465 | * before the element referenced by ->gp_tasks (or at the tail if |
466 | * ->gp_tasks is NULL) and point ->gp_tasks at the newly added element. |
467 | * The task will dequeue itself when it exits the outermost enclosing |
468 | * RCU read-side critical section. Therefore, the current grace period |
469 | * cannot be permitted to complete until the ->gp_tasks pointer becomes |
470 | * NULL. |
471 | * |
472 | * Caller must disable preemption. |
473 | */ |
474 | void rcu_preempt_note_context_switch(void) |
475 | { |
476 | struct task_struct *t = current; |
477 | unsigned long flags; |
478 | |
479 | local_irq_save(flags); /* must exclude scheduler_tick(). */ |
480 | if (rcu_preempt_running_reader() && |
481 | (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { |
482 | |
483 | /* Possibly blocking in an RCU read-side critical section. */ |
484 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; |
485 | |
486 | /* |
487 | * If this CPU has already checked in, then this task |
488 | * will hold up the next grace period rather than the |
489 | * current grace period. Queue the task accordingly. |
490 | * If the task is queued for the current grace period |
491 | * (i.e., this CPU has not yet passed through a quiescent |
492 | * state for the current grace period), then as long |
493 | * as that task remains queued, the current grace period |
494 | * cannot end. |
495 | */ |
496 | list_add(&t->rcu_node_entry, &rcu_preempt_ctrlblk.blkd_tasks); |
497 | if (rcu_cpu_blocking_cur_gp()) |
498 | rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry; |
499 | } |
500 | |
501 | /* |
502 | * Either we were not in an RCU read-side critical section to |
503 | * begin with, or we have now recorded that critical section |
504 | * globally. Either way, we can now note a quiescent state |
505 | * for this CPU. Again, if we were in an RCU read-side critical |
506 | * section, and if that critical section was blocking the current |
507 | * grace period, then the fact that the task has been enqueued |
508 | * means that current grace period continues to be blocked. |
509 | */ |
510 | rcu_preempt_cpu_qs(); |
511 | local_irq_restore(flags); |
512 | } |
513 | |
514 | /* |
515 | * Tiny-preemptible RCU implementation for rcu_read_lock(). |
516 | * Just increment ->rcu_read_lock_nesting, shared state will be updated |
517 | * if we block. |
518 | */ |
519 | void __rcu_read_lock(void) |
520 | { |
521 | current->rcu_read_lock_nesting++; |
522 | barrier(); /* needed if we ever invoke rcu_read_lock in rcutiny.c */ |
523 | } |
524 | EXPORT_SYMBOL_GPL(__rcu_read_lock); |
525 | |
526 | /* |
527 | * Handle special cases during rcu_read_unlock(), such as needing to |
528 | * notify RCU core processing or task having blocked during the RCU |
529 | * read-side critical section. |
530 | */ |
531 | static void rcu_read_unlock_special(struct task_struct *t) |
532 | { |
533 | int empty; |
534 | int empty_exp; |
535 | unsigned long flags; |
536 | struct list_head *np; |
537 | int special; |
538 | |
539 | /* |
540 | * NMI handlers cannot block and cannot safely manipulate state. |
541 | * They therefore cannot possibly be special, so just leave. |
542 | */ |
543 | if (in_nmi()) |
544 | return; |
545 | |
546 | local_irq_save(flags); |
547 | |
548 | /* |
549 | * If RCU core is waiting for this CPU to exit critical section, |
550 | * let it know that we have done so. |
551 | */ |
552 | special = t->rcu_read_unlock_special; |
553 | if (special & RCU_READ_UNLOCK_NEED_QS) |
554 | rcu_preempt_cpu_qs(); |
555 | |
556 | /* Hardware IRQ handlers cannot block. */ |
557 | if (in_irq()) { |
558 | local_irq_restore(flags); |
559 | return; |
560 | } |
561 | |
562 | /* Clean up if blocked during RCU read-side critical section. */ |
563 | if (special & RCU_READ_UNLOCK_BLOCKED) { |
564 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; |
565 | |
566 | /* |
567 | * Remove this task from the ->blkd_tasks list and adjust |
568 | * any pointers that might have been referencing it. |
569 | */ |
570 | empty = !rcu_preempt_blocked_readers_cgp(); |
571 | empty_exp = rcu_preempt_ctrlblk.exp_tasks == NULL; |
572 | np = rcu_next_node_entry(t); |
573 | list_del_init(&t->rcu_node_entry); |
574 | if (&t->rcu_node_entry == rcu_preempt_ctrlblk.gp_tasks) |
575 | rcu_preempt_ctrlblk.gp_tasks = np; |
576 | if (&t->rcu_node_entry == rcu_preempt_ctrlblk.exp_tasks) |
577 | rcu_preempt_ctrlblk.exp_tasks = np; |
578 | #ifdef CONFIG_RCU_BOOST |
579 | if (&t->rcu_node_entry == rcu_preempt_ctrlblk.boost_tasks) |
580 | rcu_preempt_ctrlblk.boost_tasks = np; |
581 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
582 | |
583 | /* |
584 | * If this was the last task on the current list, and if |
585 | * we aren't waiting on the CPU, report the quiescent state |
586 | * and start a new grace period if needed. |
587 | */ |
588 | if (!empty && !rcu_preempt_blocked_readers_cgp()) { |
589 | rcu_preempt_cpu_qs(); |
590 | rcu_preempt_start_gp(); |
591 | } |
592 | |
593 | /* |
594 | * If this was the last task on the expedited lists, |
595 | * then we need wake up the waiting task. |
596 | */ |
597 | if (!empty_exp && rcu_preempt_ctrlblk.exp_tasks == NULL) |
598 | rcu_report_exp_done(); |
599 | } |
600 | #ifdef CONFIG_RCU_BOOST |
601 | /* Unboost self if was boosted. */ |
602 | if (special & RCU_READ_UNLOCK_BOOSTED) { |
603 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BOOSTED; |
604 | rt_mutex_unlock(t->rcu_boost_mutex); |
605 | t->rcu_boost_mutex = NULL; |
606 | } |
607 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
608 | local_irq_restore(flags); |
609 | } |
610 | |
611 | /* |
612 | * Tiny-preemptible RCU implementation for rcu_read_unlock(). |
613 | * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost |
614 | * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then |
615 | * invoke rcu_read_unlock_special() to clean up after a context switch |
616 | * in an RCU read-side critical section and other special cases. |
617 | */ |
618 | void __rcu_read_unlock(void) |
619 | { |
620 | struct task_struct *t = current; |
621 | |
622 | barrier(); /* needed if we ever invoke rcu_read_unlock in rcutiny.c */ |
623 | --t->rcu_read_lock_nesting; |
624 | barrier(); /* decrement before load of ->rcu_read_unlock_special */ |
625 | if (t->rcu_read_lock_nesting == 0 && |
626 | unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) |
627 | rcu_read_unlock_special(t); |
628 | #ifdef CONFIG_PROVE_LOCKING |
629 | WARN_ON_ONCE(t->rcu_read_lock_nesting < 0); |
630 | #endif /* #ifdef CONFIG_PROVE_LOCKING */ |
631 | } |
632 | EXPORT_SYMBOL_GPL(__rcu_read_unlock); |
633 | |
634 | /* |
635 | * Check for a quiescent state from the current CPU. When a task blocks, |
636 | * the task is recorded in the rcu_preempt_ctrlblk structure, which is |
637 | * checked elsewhere. This is called from the scheduling-clock interrupt. |
638 | * |
639 | * Caller must disable hard irqs. |
640 | */ |
641 | static void rcu_preempt_check_callbacks(void) |
642 | { |
643 | struct task_struct *t = current; |
644 | |
645 | if (rcu_preempt_gp_in_progress() && |
646 | (!rcu_preempt_running_reader() || |
647 | !rcu_cpu_blocking_cur_gp())) |
648 | rcu_preempt_cpu_qs(); |
649 | if (&rcu_preempt_ctrlblk.rcb.rcucblist != |
650 | rcu_preempt_ctrlblk.rcb.donetail) |
651 | invoke_rcu_kthread(); |
652 | if (rcu_preempt_gp_in_progress() && |
653 | rcu_cpu_blocking_cur_gp() && |
654 | rcu_preempt_running_reader()) |
655 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; |
656 | } |
657 | |
658 | /* |
659 | * TINY_PREEMPT_RCU has an extra callback-list tail pointer to |
660 | * update, so this is invoked from rcu_process_callbacks() to |
661 | * handle that case. Of course, it is invoked for all flavors of |
662 | * RCU, but RCU callbacks can appear only on one of the lists, and |
663 | * neither ->nexttail nor ->donetail can possibly be NULL, so there |
664 | * is no need for an explicit check. |
665 | */ |
666 | static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp) |
667 | { |
668 | if (rcu_preempt_ctrlblk.nexttail == rcp->donetail) |
669 | rcu_preempt_ctrlblk.nexttail = &rcp->rcucblist; |
670 | } |
671 | |
672 | /* |
673 | * Process callbacks for preemptible RCU. |
674 | */ |
675 | static void rcu_preempt_process_callbacks(void) |
676 | { |
677 | rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb); |
678 | } |
679 | |
680 | /* |
681 | * Queue a preemptible -RCU callback for invocation after a grace period. |
682 | */ |
683 | void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) |
684 | { |
685 | unsigned long flags; |
686 | |
687 | debug_rcu_head_queue(head); |
688 | head->func = func; |
689 | head->next = NULL; |
690 | |
691 | local_irq_save(flags); |
692 | *rcu_preempt_ctrlblk.nexttail = head; |
693 | rcu_preempt_ctrlblk.nexttail = &head->next; |
694 | RCU_TRACE(rcu_preempt_ctrlblk.rcb.qlen++); |
695 | rcu_preempt_start_gp(); /* checks to see if GP needed. */ |
696 | local_irq_restore(flags); |
697 | } |
698 | EXPORT_SYMBOL_GPL(call_rcu); |
699 | |
700 | void rcu_barrier(void) |
701 | { |
702 | struct rcu_synchronize rcu; |
703 | |
704 | init_rcu_head_on_stack(&rcu.head); |
705 | init_completion(&rcu.completion); |
706 | /* Will wake me after RCU finished. */ |
707 | call_rcu(&rcu.head, wakeme_after_rcu); |
708 | /* Wait for it. */ |
709 | wait_for_completion(&rcu.completion); |
710 | destroy_rcu_head_on_stack(&rcu.head); |
711 | } |
712 | EXPORT_SYMBOL_GPL(rcu_barrier); |
713 | |
714 | /* |
715 | * synchronize_rcu - wait until a grace period has elapsed. |
716 | * |
717 | * Control will return to the caller some time after a full grace |
718 | * period has elapsed, in other words after all currently executing RCU |
719 | * read-side critical sections have completed. RCU read-side critical |
720 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), |
721 | * and may be nested. |
722 | */ |
723 | void synchronize_rcu(void) |
724 | { |
725 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
726 | if (!rcu_scheduler_active) |
727 | return; |
728 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
729 | |
730 | WARN_ON_ONCE(rcu_preempt_running_reader()); |
731 | if (!rcu_preempt_blocked_readers_any()) |
732 | return; |
733 | |
734 | /* Once we get past the fastpath checks, same code as rcu_barrier(). */ |
735 | rcu_barrier(); |
736 | } |
737 | EXPORT_SYMBOL_GPL(synchronize_rcu); |
738 | |
739 | static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); |
740 | static unsigned long sync_rcu_preempt_exp_count; |
741 | static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); |
742 | |
743 | /* |
744 | * Return non-zero if there are any tasks in RCU read-side critical |
745 | * sections blocking the current preemptible-RCU expedited grace period. |
746 | * If there is no preemptible-RCU expedited grace period currently in |
747 | * progress, returns zero unconditionally. |
748 | */ |
749 | static int rcu_preempted_readers_exp(void) |
750 | { |
751 | return rcu_preempt_ctrlblk.exp_tasks != NULL; |
752 | } |
753 | |
754 | /* |
755 | * Report the exit from RCU read-side critical section for the last task |
756 | * that queued itself during or before the current expedited preemptible-RCU |
757 | * grace period. |
758 | */ |
759 | static void rcu_report_exp_done(void) |
760 | { |
761 | wake_up(&sync_rcu_preempt_exp_wq); |
762 | } |
763 | |
764 | /* |
765 | * Wait for an rcu-preempt grace period, but expedite it. The basic idea |
766 | * is to rely in the fact that there is but one CPU, and that it is |
767 | * illegal for a task to invoke synchronize_rcu_expedited() while in a |
768 | * preemptible-RCU read-side critical section. Therefore, any such |
769 | * critical sections must correspond to blocked tasks, which must therefore |
770 | * be on the ->blkd_tasks list. So just record the current head of the |
771 | * list in the ->exp_tasks pointer, and wait for all tasks including and |
772 | * after the task pointed to by ->exp_tasks to drain. |
773 | */ |
774 | void synchronize_rcu_expedited(void) |
775 | { |
776 | unsigned long flags; |
777 | struct rcu_preempt_ctrlblk *rpcp = &rcu_preempt_ctrlblk; |
778 | unsigned long snap; |
779 | |
780 | barrier(); /* ensure prior action seen before grace period. */ |
781 | |
782 | WARN_ON_ONCE(rcu_preempt_running_reader()); |
783 | |
784 | /* |
785 | * Acquire lock so that there is only one preemptible RCU grace |
786 | * period in flight. Of course, if someone does the expedited |
787 | * grace period for us while we are acquiring the lock, just leave. |
788 | */ |
789 | snap = sync_rcu_preempt_exp_count + 1; |
790 | mutex_lock(&sync_rcu_preempt_exp_mutex); |
791 | if (ULONG_CMP_LT(snap, sync_rcu_preempt_exp_count)) |
792 | goto unlock_mb_ret; /* Others did our work for us. */ |
793 | |
794 | local_irq_save(flags); |
795 | |
796 | /* |
797 | * All RCU readers have to already be on blkd_tasks because |
798 | * we cannot legally be executing in an RCU read-side critical |
799 | * section. |
800 | */ |
801 | |
802 | /* Snapshot current head of ->blkd_tasks list. */ |
803 | rpcp->exp_tasks = rpcp->blkd_tasks.next; |
804 | if (rpcp->exp_tasks == &rpcp->blkd_tasks) |
805 | rpcp->exp_tasks = NULL; |
806 | |
807 | /* Wait for tail of ->blkd_tasks list to drain. */ |
808 | if (!rcu_preempted_readers_exp()) |
809 | local_irq_restore(flags); |
810 | else { |
811 | rcu_initiate_boost(); |
812 | local_irq_restore(flags); |
813 | wait_event(sync_rcu_preempt_exp_wq, |
814 | !rcu_preempted_readers_exp()); |
815 | } |
816 | |
817 | /* Clean up and exit. */ |
818 | barrier(); /* ensure expedited GP seen before counter increment. */ |
819 | sync_rcu_preempt_exp_count++; |
820 | unlock_mb_ret: |
821 | mutex_unlock(&sync_rcu_preempt_exp_mutex); |
822 | barrier(); /* ensure subsequent action seen after grace period. */ |
823 | } |
824 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); |
825 | |
826 | /* |
827 | * Does preemptible RCU need the CPU to stay out of dynticks mode? |
828 | */ |
829 | int rcu_preempt_needs_cpu(void) |
830 | { |
831 | if (!rcu_preempt_running_reader()) |
832 | rcu_preempt_cpu_qs(); |
833 | return rcu_preempt_ctrlblk.rcb.rcucblist != NULL; |
834 | } |
835 | |
836 | /* |
837 | * Check for a task exiting while in a preemptible -RCU read-side |
838 | * critical section, clean up if so. No need to issue warnings, |
839 | * as debug_check_no_locks_held() already does this if lockdep |
840 | * is enabled. |
841 | */ |
842 | void exit_rcu(void) |
843 | { |
844 | struct task_struct *t = current; |
845 | |
846 | if (t->rcu_read_lock_nesting == 0) |
847 | return; |
848 | t->rcu_read_lock_nesting = 1; |
849 | __rcu_read_unlock(); |
850 | } |
851 | |
852 | #else /* #ifdef CONFIG_TINY_PREEMPT_RCU */ |
853 | |
854 | #ifdef CONFIG_RCU_TRACE |
855 | |
856 | /* |
857 | * Because preemptible RCU does not exist, it is not necessary to |
858 | * dump out its statistics. |
859 | */ |
860 | static void show_tiny_preempt_stats(struct seq_file *m) |
861 | { |
862 | } |
863 | |
864 | #endif /* #ifdef CONFIG_RCU_TRACE */ |
865 | |
866 | /* |
867 | * Because preemptible RCU does not exist, it is never necessary to |
868 | * boost preempted RCU readers. |
869 | */ |
870 | static int rcu_boost(void) |
871 | { |
872 | return 0; |
873 | } |
874 | |
875 | /* |
876 | * Because preemptible RCU does not exist, it never has any callbacks |
877 | * to check. |
878 | */ |
879 | static void rcu_preempt_check_callbacks(void) |
880 | { |
881 | } |
882 | |
883 | /* |
884 | * Because preemptible RCU does not exist, it never has any callbacks |
885 | * to remove. |
886 | */ |
887 | static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp) |
888 | { |
889 | } |
890 | |
891 | /* |
892 | * Because preemptible RCU does not exist, it never has any callbacks |
893 | * to process. |
894 | */ |
895 | static void rcu_preempt_process_callbacks(void) |
896 | { |
897 | } |
898 | |
899 | #endif /* #else #ifdef CONFIG_TINY_PREEMPT_RCU */ |
900 | |
901 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
902 | #include <linux/kernel_stat.h> |
903 | |
904 | /* |
905 | * During boot, we forgive RCU lockdep issues. After this function is |
906 | * invoked, we start taking RCU lockdep issues seriously. |
907 | */ |
908 | void __init rcu_scheduler_starting(void) |
909 | { |
910 | WARN_ON(nr_context_switches() > 0); |
911 | rcu_scheduler_active = 1; |
912 | } |
913 | |
914 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
915 | |
916 | #ifdef CONFIG_RCU_BOOST |
917 | #define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO |
918 | #else /* #ifdef CONFIG_RCU_BOOST */ |
919 | #define RCU_BOOST_PRIO 1 |
920 | #endif /* #else #ifdef CONFIG_RCU_BOOST */ |
921 | |
922 | #ifdef CONFIG_RCU_TRACE |
923 | |
924 | #ifdef CONFIG_RCU_BOOST |
925 | |
926 | static void rcu_initiate_boost_trace(void) |
927 | { |
928 | if (list_empty(&rcu_preempt_ctrlblk.blkd_tasks)) |
929 | rcu_preempt_ctrlblk.n_balk_blkd_tasks++; |
930 | else if (rcu_preempt_ctrlblk.gp_tasks == NULL && |
931 | rcu_preempt_ctrlblk.exp_tasks == NULL) |
932 | rcu_preempt_ctrlblk.n_balk_exp_gp_tasks++; |
933 | else if (rcu_preempt_ctrlblk.boost_tasks != NULL) |
934 | rcu_preempt_ctrlblk.n_balk_boost_tasks++; |
935 | else if (!ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time)) |
936 | rcu_preempt_ctrlblk.n_balk_notyet++; |
937 | else |
938 | rcu_preempt_ctrlblk.n_balk_nos++; |
939 | } |
940 | |
941 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
942 | |
943 | static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n) |
944 | { |
945 | unsigned long flags; |
946 | |
947 | raw_local_irq_save(flags); |
948 | rcp->qlen -= n; |
949 | raw_local_irq_restore(flags); |
950 | } |
951 | |
952 | /* |
953 | * Dump statistics for TINY_RCU, such as they are. |
954 | */ |
955 | static int show_tiny_stats(struct seq_file *m, void *unused) |
956 | { |
957 | show_tiny_preempt_stats(m); |
958 | seq_printf(m, "rcu_sched: qlen: %ld\n", rcu_sched_ctrlblk.qlen); |
959 | seq_printf(m, "rcu_bh: qlen: %ld\n", rcu_bh_ctrlblk.qlen); |
960 | return 0; |
961 | } |
962 | |
963 | static int show_tiny_stats_open(struct inode *inode, struct file *file) |
964 | { |
965 | return single_open(file, show_tiny_stats, NULL); |
966 | } |
967 | |
968 | static const struct file_operations show_tiny_stats_fops = { |
969 | .owner = THIS_MODULE, |
970 | .open = show_tiny_stats_open, |
971 | .read = seq_read, |
972 | .llseek = seq_lseek, |
973 | .release = single_release, |
974 | }; |
975 | |
976 | static struct dentry *rcudir; |
977 | |
978 | static int __init rcutiny_trace_init(void) |
979 | { |
980 | struct dentry *retval; |
981 | |
982 | rcudir = debugfs_create_dir("rcu", NULL); |
983 | if (!rcudir) |
984 | goto free_out; |
985 | retval = debugfs_create_file("rcudata", 0444, rcudir, |
986 | NULL, &show_tiny_stats_fops); |
987 | if (!retval) |
988 | goto free_out; |
989 | return 0; |
990 | free_out: |
991 | debugfs_remove_recursive(rcudir); |
992 | return 1; |
993 | } |
994 | |
995 | static void __exit rcutiny_trace_cleanup(void) |
996 | { |
997 | debugfs_remove_recursive(rcudir); |
998 | } |
999 | |
1000 | module_init(rcutiny_trace_init); |
1001 | module_exit(rcutiny_trace_cleanup); |
1002 | |
1003 | MODULE_AUTHOR("Paul E. McKenney"); |
1004 | MODULE_DESCRIPTION("Read-Copy Update tracing for tiny implementation"); |
1005 | MODULE_LICENSE("GPL"); |
1006 | |
1007 | #endif /* #ifdef CONFIG_RCU_TRACE */ |
1008 |
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