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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/module.h> |
27 | #include <linux/debugfs.h> |
28 | #include <linux/seq_file.h> |
29 | |
30 | /* Global control variables for rcupdate callback mechanism. */ |
31 | struct rcu_ctrlblk { |
32 | struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */ |
33 | struct rcu_head **donetail; /* ->next pointer of last "done" CB. */ |
34 | struct rcu_head **curtail; /* ->next pointer of last CB. */ |
35 | RCU_TRACE(long qlen); /* Number of pending CBs. */ |
36 | RCU_TRACE(char *name); /* Name of RCU type. */ |
37 | }; |
38 | |
39 | /* Definition for rcupdate control block. */ |
40 | static struct rcu_ctrlblk rcu_sched_ctrlblk = { |
41 | .donetail = &rcu_sched_ctrlblk.rcucblist, |
42 | .curtail = &rcu_sched_ctrlblk.rcucblist, |
43 | RCU_TRACE(.name = "rcu_sched") |
44 | }; |
45 | |
46 | static struct rcu_ctrlblk rcu_bh_ctrlblk = { |
47 | .donetail = &rcu_bh_ctrlblk.rcucblist, |
48 | .curtail = &rcu_bh_ctrlblk.rcucblist, |
49 | RCU_TRACE(.name = "rcu_bh") |
50 | }; |
51 | |
52 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
53 | int rcu_scheduler_active __read_mostly; |
54 | EXPORT_SYMBOL_GPL(rcu_scheduler_active); |
55 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
56 | |
57 | #ifdef CONFIG_TINY_PREEMPT_RCU |
58 | |
59 | #include <linux/delay.h> |
60 | |
61 | /* Global control variables for preemptible RCU. */ |
62 | struct rcu_preempt_ctrlblk { |
63 | struct rcu_ctrlblk rcb; /* curtail: ->next ptr of last CB for GP. */ |
64 | struct rcu_head **nexttail; |
65 | /* Tasks blocked in a preemptible RCU */ |
66 | /* read-side critical section while an */ |
67 | /* preemptible-RCU grace period is in */ |
68 | /* progress must wait for a later grace */ |
69 | /* period. This pointer points to the */ |
70 | /* ->next pointer of the last task that */ |
71 | /* must wait for a later grace period, or */ |
72 | /* to &->rcb.rcucblist if there is no */ |
73 | /* such task. */ |
74 | struct list_head blkd_tasks; |
75 | /* Tasks blocked in RCU read-side critical */ |
76 | /* section. Tasks are placed at the head */ |
77 | /* of this list and age towards the tail. */ |
78 | struct list_head *gp_tasks; |
79 | /* Pointer to the first task blocking the */ |
80 | /* current grace period, or NULL if there */ |
81 | /* is no such task. */ |
82 | struct list_head *exp_tasks; |
83 | /* Pointer to first task blocking the */ |
84 | /* current expedited grace period, or NULL */ |
85 | /* if there is no such task. If there */ |
86 | /* is no current expedited grace period, */ |
87 | /* then there cannot be any such task. */ |
88 | #ifdef CONFIG_RCU_BOOST |
89 | struct list_head *boost_tasks; |
90 | /* Pointer to first task that needs to be */ |
91 | /* priority-boosted, or NULL if no priority */ |
92 | /* boosting is needed. If there is no */ |
93 | /* current or expedited grace period, there */ |
94 | /* can be no such task. */ |
95 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
96 | u8 gpnum; /* Current grace period. */ |
97 | u8 gpcpu; /* Last grace period blocked by the CPU. */ |
98 | u8 completed; /* Last grace period completed. */ |
99 | /* If all three are equal, RCU is idle. */ |
100 | #ifdef CONFIG_RCU_BOOST |
101 | unsigned long boost_time; /* When to start boosting (jiffies) */ |
102 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
103 | #ifdef CONFIG_RCU_TRACE |
104 | unsigned long n_grace_periods; |
105 | #ifdef CONFIG_RCU_BOOST |
106 | unsigned long n_tasks_boosted; |
107 | /* Total number of tasks boosted. */ |
108 | unsigned long n_exp_boosts; |
109 | /* Number of tasks boosted for expedited GP. */ |
110 | unsigned long n_normal_boosts; |
111 | /* Number of tasks boosted for normal GP. */ |
112 | unsigned long n_balk_blkd_tasks; |
113 | /* Refused to boost: no blocked tasks. */ |
114 | unsigned long n_balk_exp_gp_tasks; |
115 | /* Refused to boost: nothing blocking GP. */ |
116 | unsigned long n_balk_boost_tasks; |
117 | /* Refused to boost: already boosting. */ |
118 | unsigned long n_balk_notyet; |
119 | /* Refused to boost: not yet time. */ |
120 | unsigned long n_balk_nos; |
121 | /* Refused to boost: not sure why, though. */ |
122 | /* This can happen due to race conditions. */ |
123 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
124 | #endif /* #ifdef CONFIG_RCU_TRACE */ |
125 | }; |
126 | |
127 | static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = { |
128 | .rcb.donetail = &rcu_preempt_ctrlblk.rcb.rcucblist, |
129 | .rcb.curtail = &rcu_preempt_ctrlblk.rcb.rcucblist, |
130 | .nexttail = &rcu_preempt_ctrlblk.rcb.rcucblist, |
131 | .blkd_tasks = LIST_HEAD_INIT(rcu_preempt_ctrlblk.blkd_tasks), |
132 | RCU_TRACE(.rcb.name = "rcu_preempt") |
133 | }; |
134 | |
135 | static int rcu_preempted_readers_exp(void); |
136 | static void rcu_report_exp_done(void); |
137 | |
138 | /* |
139 | * Return true if the CPU has not yet responded to the current grace period. |
140 | */ |
141 | static int rcu_cpu_blocking_cur_gp(void) |
142 | { |
143 | return rcu_preempt_ctrlblk.gpcpu != rcu_preempt_ctrlblk.gpnum; |
144 | } |
145 | |
146 | /* |
147 | * Check for a running RCU reader. Because there is only one CPU, |
148 | * there can be but one running RCU reader at a time. ;-) |
149 | */ |
150 | static int rcu_preempt_running_reader(void) |
151 | { |
152 | return current->rcu_read_lock_nesting; |
153 | } |
154 | |
155 | /* |
156 | * Check for preempted RCU readers blocking any grace period. |
157 | * If the caller needs a reliable answer, it must disable hard irqs. |
158 | */ |
159 | static int rcu_preempt_blocked_readers_any(void) |
160 | { |
161 | return !list_empty(&rcu_preempt_ctrlblk.blkd_tasks); |
162 | } |
163 | |
164 | /* |
165 | * Check for preempted RCU readers blocking the current grace period. |
166 | * If the caller needs a reliable answer, it must disable hard irqs. |
167 | */ |
168 | static int rcu_preempt_blocked_readers_cgp(void) |
169 | { |
170 | return rcu_preempt_ctrlblk.gp_tasks != NULL; |
171 | } |
172 | |
173 | /* |
174 | * Return true if another preemptible-RCU grace period is needed. |
175 | */ |
176 | static int rcu_preempt_needs_another_gp(void) |
177 | { |
178 | return *rcu_preempt_ctrlblk.rcb.curtail != NULL; |
179 | } |
180 | |
181 | /* |
182 | * Return true if a preemptible-RCU grace period is in progress. |
183 | * The caller must disable hardirqs. |
184 | */ |
185 | static int rcu_preempt_gp_in_progress(void) |
186 | { |
187 | return rcu_preempt_ctrlblk.completed != rcu_preempt_ctrlblk.gpnum; |
188 | } |
189 | |
190 | /* |
191 | * Advance a ->blkd_tasks-list pointer to the next entry, instead |
192 | * returning NULL if at the end of the list. |
193 | */ |
194 | static struct list_head *rcu_next_node_entry(struct task_struct *t) |
195 | { |
196 | struct list_head *np; |
197 | |
198 | np = t->rcu_node_entry.next; |
199 | if (np == &rcu_preempt_ctrlblk.blkd_tasks) |
200 | np = NULL; |
201 | return np; |
202 | } |
203 | |
204 | #ifdef CONFIG_RCU_TRACE |
205 | |
206 | #ifdef CONFIG_RCU_BOOST |
207 | static void rcu_initiate_boost_trace(void); |
208 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
209 | |
210 | /* |
211 | * Dump additional statistice for TINY_PREEMPT_RCU. |
212 | */ |
213 | static void show_tiny_preempt_stats(struct seq_file *m) |
214 | { |
215 | seq_printf(m, "rcu_preempt: qlen=%ld gp=%lu g%u/p%u/c%u tasks=%c%c%c\n", |
216 | rcu_preempt_ctrlblk.rcb.qlen, |
217 | rcu_preempt_ctrlblk.n_grace_periods, |
218 | rcu_preempt_ctrlblk.gpnum, |
219 | rcu_preempt_ctrlblk.gpcpu, |
220 | rcu_preempt_ctrlblk.completed, |
221 | "T."[list_empty(&rcu_preempt_ctrlblk.blkd_tasks)], |
222 | "N."[!rcu_preempt_ctrlblk.gp_tasks], |
223 | "E."[!rcu_preempt_ctrlblk.exp_tasks]); |
224 | #ifdef CONFIG_RCU_BOOST |
225 | seq_printf(m, "%sttb=%c ntb=%lu neb=%lu nnb=%lu j=%04x bt=%04x\n", |
226 | " ", |
227 | "B."[!rcu_preempt_ctrlblk.boost_tasks], |
228 | rcu_preempt_ctrlblk.n_tasks_boosted, |
229 | rcu_preempt_ctrlblk.n_exp_boosts, |
230 | rcu_preempt_ctrlblk.n_normal_boosts, |
231 | (int)(jiffies & 0xffff), |
232 | (int)(rcu_preempt_ctrlblk.boost_time & 0xffff)); |
233 | seq_printf(m, "%s: nt=%lu egt=%lu bt=%lu ny=%lu nos=%lu\n", |
234 | " balk", |
235 | rcu_preempt_ctrlblk.n_balk_blkd_tasks, |
236 | rcu_preempt_ctrlblk.n_balk_exp_gp_tasks, |
237 | rcu_preempt_ctrlblk.n_balk_boost_tasks, |
238 | rcu_preempt_ctrlblk.n_balk_notyet, |
239 | rcu_preempt_ctrlblk.n_balk_nos); |
240 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
241 | } |
242 | |
243 | #endif /* #ifdef CONFIG_RCU_TRACE */ |
244 | |
245 | #ifdef CONFIG_RCU_BOOST |
246 | |
247 | #include "rtmutex_common.h" |
248 | |
249 | #define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO |
250 | |
251 | /* Controls for rcu_kthread() kthread. */ |
252 | static struct task_struct *rcu_kthread_task; |
253 | static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq); |
254 | static unsigned long have_rcu_kthread_work; |
255 | |
256 | /* |
257 | * Carry out RCU priority boosting on the task indicated by ->boost_tasks, |
258 | * and advance ->boost_tasks to the next task in the ->blkd_tasks list. |
259 | */ |
260 | static int rcu_boost(void) |
261 | { |
262 | unsigned long flags; |
263 | struct rt_mutex mtx; |
264 | struct task_struct *t; |
265 | struct list_head *tb; |
266 | |
267 | if (rcu_preempt_ctrlblk.boost_tasks == NULL && |
268 | rcu_preempt_ctrlblk.exp_tasks == NULL) |
269 | return 0; /* Nothing to boost. */ |
270 | |
271 | raw_local_irq_save(flags); |
272 | |
273 | /* |
274 | * Recheck with irqs disabled: all tasks in need of boosting |
275 | * might exit their RCU read-side critical sections on their own |
276 | * if we are preempted just before disabling irqs. |
277 | */ |
278 | if (rcu_preempt_ctrlblk.boost_tasks == NULL && |
279 | rcu_preempt_ctrlblk.exp_tasks == NULL) { |
280 | raw_local_irq_restore(flags); |
281 | return 0; |
282 | } |
283 | |
284 | /* |
285 | * Preferentially boost tasks blocking expedited grace periods. |
286 | * This cannot starve the normal grace periods because a second |
287 | * expedited grace period must boost all blocked tasks, including |
288 | * those blocking the pre-existing normal grace period. |
289 | */ |
290 | if (rcu_preempt_ctrlblk.exp_tasks != NULL) { |
291 | tb = rcu_preempt_ctrlblk.exp_tasks; |
292 | RCU_TRACE(rcu_preempt_ctrlblk.n_exp_boosts++); |
293 | } else { |
294 | tb = rcu_preempt_ctrlblk.boost_tasks; |
295 | RCU_TRACE(rcu_preempt_ctrlblk.n_normal_boosts++); |
296 | } |
297 | RCU_TRACE(rcu_preempt_ctrlblk.n_tasks_boosted++); |
298 | |
299 | /* |
300 | * We boost task t by manufacturing an rt_mutex that appears to |
301 | * be held by task t. We leave a pointer to that rt_mutex where |
302 | * task t can find it, and task t will release the mutex when it |
303 | * exits its outermost RCU read-side critical section. Then |
304 | * simply acquiring this artificial rt_mutex will boost task |
305 | * t's priority. (Thanks to tglx for suggesting this approach!) |
306 | */ |
307 | t = container_of(tb, struct task_struct, rcu_node_entry); |
308 | rt_mutex_init_proxy_locked(&mtx, t); |
309 | t->rcu_boost_mutex = &mtx; |
310 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BOOSTED; |
311 | raw_local_irq_restore(flags); |
312 | rt_mutex_lock(&mtx); |
313 | rt_mutex_unlock(&mtx); /* Keep lockdep happy. */ |
314 | |
315 | return ACCESS_ONCE(rcu_preempt_ctrlblk.boost_tasks) != NULL || |
316 | ACCESS_ONCE(rcu_preempt_ctrlblk.exp_tasks) != NULL; |
317 | } |
318 | |
319 | /* |
320 | * Check to see if it is now time to start boosting RCU readers blocking |
321 | * the current grace period, and, if so, tell the rcu_kthread_task to |
322 | * start boosting them. If there is an expedited boost in progress, |
323 | * we wait for it to complete. |
324 | * |
325 | * If there are no blocked readers blocking the current grace period, |
326 | * return 0 to let the caller know, otherwise return 1. Note that this |
327 | * return value is independent of whether or not boosting was done. |
328 | */ |
329 | static int rcu_initiate_boost(void) |
330 | { |
331 | if (!rcu_preempt_blocked_readers_cgp() && |
332 | rcu_preempt_ctrlblk.exp_tasks == NULL) { |
333 | RCU_TRACE(rcu_preempt_ctrlblk.n_balk_exp_gp_tasks++); |
334 | return 0; |
335 | } |
336 | if (rcu_preempt_ctrlblk.exp_tasks != NULL || |
337 | (rcu_preempt_ctrlblk.gp_tasks != NULL && |
338 | rcu_preempt_ctrlblk.boost_tasks == NULL && |
339 | ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time))) { |
340 | if (rcu_preempt_ctrlblk.exp_tasks == NULL) |
341 | rcu_preempt_ctrlblk.boost_tasks = |
342 | rcu_preempt_ctrlblk.gp_tasks; |
343 | invoke_rcu_callbacks(); |
344 | } else |
345 | RCU_TRACE(rcu_initiate_boost_trace()); |
346 | return 1; |
347 | } |
348 | |
349 | #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) |
350 | |
351 | /* |
352 | * Do priority-boost accounting for the start of a new grace period. |
353 | */ |
354 | static void rcu_preempt_boost_start_gp(void) |
355 | { |
356 | rcu_preempt_ctrlblk.boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; |
357 | } |
358 | |
359 | #else /* #ifdef CONFIG_RCU_BOOST */ |
360 | |
361 | /* |
362 | * If there is no RCU priority boosting, we don't initiate boosting, |
363 | * but we do indicate whether there are blocked readers blocking the |
364 | * current grace period. |
365 | */ |
366 | static int rcu_initiate_boost(void) |
367 | { |
368 | return rcu_preempt_blocked_readers_cgp(); |
369 | } |
370 | |
371 | /* |
372 | * If there is no RCU priority boosting, nothing to do at grace-period start. |
373 | */ |
374 | static void rcu_preempt_boost_start_gp(void) |
375 | { |
376 | } |
377 | |
378 | #endif /* else #ifdef CONFIG_RCU_BOOST */ |
379 | |
380 | /* |
381 | * Record a preemptible-RCU quiescent state for the specified CPU. Note |
382 | * that this just means that the task currently running on the CPU is |
383 | * in a quiescent state. There might be any number of tasks blocked |
384 | * while in an RCU read-side critical section. |
385 | * |
386 | * Unlike the other rcu_*_qs() functions, callers to this function |
387 | * must disable irqs in order to protect the assignment to |
388 | * ->rcu_read_unlock_special. |
389 | * |
390 | * Because this is a single-CPU implementation, the only way a grace |
391 | * period can end is if the CPU is in a quiescent state. The reason is |
392 | * that a blocked preemptible-RCU reader can exit its critical section |
393 | * only if the CPU is running it at the time. Therefore, when the |
394 | * last task blocking the current grace period exits its RCU read-side |
395 | * critical section, neither the CPU nor blocked tasks will be stopping |
396 | * the current grace period. (In contrast, SMP implementations |
397 | * might have CPUs running in RCU read-side critical sections that |
398 | * block later grace periods -- but this is not possible given only |
399 | * one CPU.) |
400 | */ |
401 | static void rcu_preempt_cpu_qs(void) |
402 | { |
403 | /* Record both CPU and task as having responded to current GP. */ |
404 | rcu_preempt_ctrlblk.gpcpu = rcu_preempt_ctrlblk.gpnum; |
405 | current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; |
406 | |
407 | /* If there is no GP then there is nothing more to do. */ |
408 | if (!rcu_preempt_gp_in_progress()) |
409 | return; |
410 | /* |
411 | * Check up on boosting. If there are readers blocking the |
412 | * current grace period, leave. |
413 | */ |
414 | if (rcu_initiate_boost()) |
415 | return; |
416 | |
417 | /* Advance callbacks. */ |
418 | rcu_preempt_ctrlblk.completed = rcu_preempt_ctrlblk.gpnum; |
419 | rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.rcb.curtail; |
420 | rcu_preempt_ctrlblk.rcb.curtail = rcu_preempt_ctrlblk.nexttail; |
421 | |
422 | /* If there are no blocked readers, next GP is done instantly. */ |
423 | if (!rcu_preempt_blocked_readers_any()) |
424 | rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.nexttail; |
425 | |
426 | /* If there are done callbacks, cause them to be invoked. */ |
427 | if (*rcu_preempt_ctrlblk.rcb.donetail != NULL) |
428 | invoke_rcu_callbacks(); |
429 | } |
430 | |
431 | /* |
432 | * Start a new RCU grace period if warranted. Hard irqs must be disabled. |
433 | */ |
434 | static void rcu_preempt_start_gp(void) |
435 | { |
436 | if (!rcu_preempt_gp_in_progress() && rcu_preempt_needs_another_gp()) { |
437 | |
438 | /* Official start of GP. */ |
439 | rcu_preempt_ctrlblk.gpnum++; |
440 | RCU_TRACE(rcu_preempt_ctrlblk.n_grace_periods++); |
441 | |
442 | /* Any blocked RCU readers block new GP. */ |
443 | if (rcu_preempt_blocked_readers_any()) |
444 | rcu_preempt_ctrlblk.gp_tasks = |
445 | rcu_preempt_ctrlblk.blkd_tasks.next; |
446 | |
447 | /* Set up for RCU priority boosting. */ |
448 | rcu_preempt_boost_start_gp(); |
449 | |
450 | /* If there is no running reader, CPU is done with GP. */ |
451 | if (!rcu_preempt_running_reader()) |
452 | rcu_preempt_cpu_qs(); |
453 | } |
454 | } |
455 | |
456 | /* |
457 | * We have entered the scheduler, and the current task might soon be |
458 | * context-switched away from. If this task is in an RCU read-side |
459 | * critical section, we will no longer be able to rely on the CPU to |
460 | * record that fact, so we enqueue the task on the blkd_tasks list. |
461 | * If the task started after the current grace period began, as recorded |
462 | * by ->gpcpu, we enqueue at the beginning of the list. Otherwise |
463 | * before the element referenced by ->gp_tasks (or at the tail if |
464 | * ->gp_tasks is NULL) and point ->gp_tasks at the newly added element. |
465 | * The task will dequeue itself when it exits the outermost enclosing |
466 | * RCU read-side critical section. Therefore, the current grace period |
467 | * cannot be permitted to complete until the ->gp_tasks pointer becomes |
468 | * NULL. |
469 | * |
470 | * Caller must disable preemption. |
471 | */ |
472 | void rcu_preempt_note_context_switch(void) |
473 | { |
474 | struct task_struct *t = current; |
475 | unsigned long flags; |
476 | |
477 | local_irq_save(flags); /* must exclude scheduler_tick(). */ |
478 | if (rcu_preempt_running_reader() && |
479 | (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { |
480 | |
481 | /* Possibly blocking in an RCU read-side critical section. */ |
482 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; |
483 | |
484 | /* |
485 | * If this CPU has already checked in, then this task |
486 | * will hold up the next grace period rather than the |
487 | * current grace period. Queue the task accordingly. |
488 | * If the task is queued for the current grace period |
489 | * (i.e., this CPU has not yet passed through a quiescent |
490 | * state for the current grace period), then as long |
491 | * as that task remains queued, the current grace period |
492 | * cannot end. |
493 | */ |
494 | list_add(&t->rcu_node_entry, &rcu_preempt_ctrlblk.blkd_tasks); |
495 | if (rcu_cpu_blocking_cur_gp()) |
496 | rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry; |
497 | } |
498 | |
499 | /* |
500 | * Either we were not in an RCU read-side critical section to |
501 | * begin with, or we have now recorded that critical section |
502 | * globally. Either way, we can now note a quiescent state |
503 | * for this CPU. Again, if we were in an RCU read-side critical |
504 | * section, and if that critical section was blocking the current |
505 | * grace period, then the fact that the task has been enqueued |
506 | * means that current grace period continues to be blocked. |
507 | */ |
508 | rcu_preempt_cpu_qs(); |
509 | local_irq_restore(flags); |
510 | } |
511 | |
512 | /* |
513 | * Tiny-preemptible RCU implementation for rcu_read_lock(). |
514 | * Just increment ->rcu_read_lock_nesting, shared state will be updated |
515 | * if we block. |
516 | */ |
517 | void __rcu_read_lock(void) |
518 | { |
519 | current->rcu_read_lock_nesting++; |
520 | barrier(); /* needed if we ever invoke rcu_read_lock in rcutiny.c */ |
521 | } |
522 | EXPORT_SYMBOL_GPL(__rcu_read_lock); |
523 | |
524 | /* |
525 | * Handle special cases during rcu_read_unlock(), such as needing to |
526 | * notify RCU core processing or task having blocked during the RCU |
527 | * read-side critical section. |
528 | */ |
529 | static void rcu_read_unlock_special(struct task_struct *t) |
530 | { |
531 | int empty; |
532 | int empty_exp; |
533 | unsigned long flags; |
534 | struct list_head *np; |
535 | int special; |
536 | |
537 | /* |
538 | * NMI handlers cannot block and cannot safely manipulate state. |
539 | * They therefore cannot possibly be special, so just leave. |
540 | */ |
541 | if (in_nmi()) |
542 | return; |
543 | |
544 | local_irq_save(flags); |
545 | |
546 | /* |
547 | * If RCU core is waiting for this CPU to exit critical section, |
548 | * let it know that we have done so. |
549 | */ |
550 | special = t->rcu_read_unlock_special; |
551 | if (special & RCU_READ_UNLOCK_NEED_QS) |
552 | rcu_preempt_cpu_qs(); |
553 | |
554 | /* Hardware IRQ handlers cannot block. */ |
555 | if (in_irq()) { |
556 | local_irq_restore(flags); |
557 | return; |
558 | } |
559 | |
560 | /* Clean up if blocked during RCU read-side critical section. */ |
561 | if (special & RCU_READ_UNLOCK_BLOCKED) { |
562 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; |
563 | |
564 | /* |
565 | * Remove this task from the ->blkd_tasks list and adjust |
566 | * any pointers that might have been referencing it. |
567 | */ |
568 | empty = !rcu_preempt_blocked_readers_cgp(); |
569 | empty_exp = rcu_preempt_ctrlblk.exp_tasks == NULL; |
570 | np = rcu_next_node_entry(t); |
571 | list_del_init(&t->rcu_node_entry); |
572 | if (&t->rcu_node_entry == rcu_preempt_ctrlblk.gp_tasks) |
573 | rcu_preempt_ctrlblk.gp_tasks = np; |
574 | if (&t->rcu_node_entry == rcu_preempt_ctrlblk.exp_tasks) |
575 | rcu_preempt_ctrlblk.exp_tasks = np; |
576 | #ifdef CONFIG_RCU_BOOST |
577 | if (&t->rcu_node_entry == rcu_preempt_ctrlblk.boost_tasks) |
578 | rcu_preempt_ctrlblk.boost_tasks = np; |
579 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
580 | |
581 | /* |
582 | * If this was the last task on the current list, and if |
583 | * we aren't waiting on the CPU, report the quiescent state |
584 | * and start a new grace period if needed. |
585 | */ |
586 | if (!empty && !rcu_preempt_blocked_readers_cgp()) { |
587 | rcu_preempt_cpu_qs(); |
588 | rcu_preempt_start_gp(); |
589 | } |
590 | |
591 | /* |
592 | * If this was the last task on the expedited lists, |
593 | * then we need wake up the waiting task. |
594 | */ |
595 | if (!empty_exp && rcu_preempt_ctrlblk.exp_tasks == NULL) |
596 | rcu_report_exp_done(); |
597 | } |
598 | #ifdef CONFIG_RCU_BOOST |
599 | /* Unboost self if was boosted. */ |
600 | if (special & RCU_READ_UNLOCK_BOOSTED) { |
601 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BOOSTED; |
602 | rt_mutex_unlock(t->rcu_boost_mutex); |
603 | t->rcu_boost_mutex = NULL; |
604 | } |
605 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
606 | local_irq_restore(flags); |
607 | } |
608 | |
609 | /* |
610 | * Tiny-preemptible RCU implementation for rcu_read_unlock(). |
611 | * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost |
612 | * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then |
613 | * invoke rcu_read_unlock_special() to clean up after a context switch |
614 | * in an RCU read-side critical section and other special cases. |
615 | */ |
616 | void __rcu_read_unlock(void) |
617 | { |
618 | struct task_struct *t = current; |
619 | |
620 | barrier(); /* needed if we ever invoke rcu_read_unlock in rcutiny.c */ |
621 | --t->rcu_read_lock_nesting; |
622 | barrier(); /* decrement before load of ->rcu_read_unlock_special */ |
623 | if (t->rcu_read_lock_nesting == 0 && |
624 | unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) |
625 | rcu_read_unlock_special(t); |
626 | #ifdef CONFIG_PROVE_LOCKING |
627 | WARN_ON_ONCE(t->rcu_read_lock_nesting < 0); |
628 | #endif /* #ifdef CONFIG_PROVE_LOCKING */ |
629 | } |
630 | EXPORT_SYMBOL_GPL(__rcu_read_unlock); |
631 | |
632 | /* |
633 | * Check for a quiescent state from the current CPU. When a task blocks, |
634 | * the task is recorded in the rcu_preempt_ctrlblk structure, which is |
635 | * checked elsewhere. This is called from the scheduling-clock interrupt. |
636 | * |
637 | * Caller must disable hard irqs. |
638 | */ |
639 | static void rcu_preempt_check_callbacks(void) |
640 | { |
641 | struct task_struct *t = current; |
642 | |
643 | if (rcu_preempt_gp_in_progress() && |
644 | (!rcu_preempt_running_reader() || |
645 | !rcu_cpu_blocking_cur_gp())) |
646 | rcu_preempt_cpu_qs(); |
647 | if (&rcu_preempt_ctrlblk.rcb.rcucblist != |
648 | rcu_preempt_ctrlblk.rcb.donetail) |
649 | invoke_rcu_callbacks(); |
650 | if (rcu_preempt_gp_in_progress() && |
651 | rcu_cpu_blocking_cur_gp() && |
652 | rcu_preempt_running_reader()) |
653 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; |
654 | } |
655 | |
656 | /* |
657 | * TINY_PREEMPT_RCU has an extra callback-list tail pointer to |
658 | * update, so this is invoked from rcu_process_callbacks() to |
659 | * handle that case. Of course, it is invoked for all flavors of |
660 | * RCU, but RCU callbacks can appear only on one of the lists, and |
661 | * neither ->nexttail nor ->donetail can possibly be NULL, so there |
662 | * is no need for an explicit check. |
663 | */ |
664 | static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp) |
665 | { |
666 | if (rcu_preempt_ctrlblk.nexttail == rcp->donetail) |
667 | rcu_preempt_ctrlblk.nexttail = &rcp->rcucblist; |
668 | } |
669 | |
670 | /* |
671 | * Process callbacks for preemptible RCU. |
672 | */ |
673 | static void rcu_preempt_process_callbacks(void) |
674 | { |
675 | __rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb); |
676 | } |
677 | |
678 | /* |
679 | * Queue a preemptible -RCU callback for invocation after a grace period. |
680 | */ |
681 | void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) |
682 | { |
683 | unsigned long flags; |
684 | |
685 | debug_rcu_head_queue(head); |
686 | head->func = func; |
687 | head->next = NULL; |
688 | |
689 | local_irq_save(flags); |
690 | *rcu_preempt_ctrlblk.nexttail = head; |
691 | rcu_preempt_ctrlblk.nexttail = &head->next; |
692 | RCU_TRACE(rcu_preempt_ctrlblk.rcb.qlen++); |
693 | rcu_preempt_start_gp(); /* checks to see if GP needed. */ |
694 | local_irq_restore(flags); |
695 | } |
696 | EXPORT_SYMBOL_GPL(call_rcu); |
697 | |
698 | /* |
699 | * synchronize_rcu - wait until a grace period has elapsed. |
700 | * |
701 | * Control will return to the caller some time after a full grace |
702 | * period has elapsed, in other words after all currently executing RCU |
703 | * read-side critical sections have completed. RCU read-side critical |
704 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), |
705 | * and may be nested. |
706 | */ |
707 | void synchronize_rcu(void) |
708 | { |
709 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
710 | if (!rcu_scheduler_active) |
711 | return; |
712 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
713 | |
714 | WARN_ON_ONCE(rcu_preempt_running_reader()); |
715 | if (!rcu_preempt_blocked_readers_any()) |
716 | return; |
717 | |
718 | /* Once we get past the fastpath checks, same code as rcu_barrier(). */ |
719 | rcu_barrier(); |
720 | } |
721 | EXPORT_SYMBOL_GPL(synchronize_rcu); |
722 | |
723 | static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); |
724 | static unsigned long sync_rcu_preempt_exp_count; |
725 | static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); |
726 | |
727 | /* |
728 | * Return non-zero if there are any tasks in RCU read-side critical |
729 | * sections blocking the current preemptible-RCU expedited grace period. |
730 | * If there is no preemptible-RCU expedited grace period currently in |
731 | * progress, returns zero unconditionally. |
732 | */ |
733 | static int rcu_preempted_readers_exp(void) |
734 | { |
735 | return rcu_preempt_ctrlblk.exp_tasks != NULL; |
736 | } |
737 | |
738 | /* |
739 | * Report the exit from RCU read-side critical section for the last task |
740 | * that queued itself during or before the current expedited preemptible-RCU |
741 | * grace period. |
742 | */ |
743 | static void rcu_report_exp_done(void) |
744 | { |
745 | wake_up(&sync_rcu_preempt_exp_wq); |
746 | } |
747 | |
748 | /* |
749 | * Wait for an rcu-preempt grace period, but expedite it. The basic idea |
750 | * is to rely in the fact that there is but one CPU, and that it is |
751 | * illegal for a task to invoke synchronize_rcu_expedited() while in a |
752 | * preemptible-RCU read-side critical section. Therefore, any such |
753 | * critical sections must correspond to blocked tasks, which must therefore |
754 | * be on the ->blkd_tasks list. So just record the current head of the |
755 | * list in the ->exp_tasks pointer, and wait for all tasks including and |
756 | * after the task pointed to by ->exp_tasks to drain. |
757 | */ |
758 | void synchronize_rcu_expedited(void) |
759 | { |
760 | unsigned long flags; |
761 | struct rcu_preempt_ctrlblk *rpcp = &rcu_preempt_ctrlblk; |
762 | unsigned long snap; |
763 | |
764 | barrier(); /* ensure prior action seen before grace period. */ |
765 | |
766 | WARN_ON_ONCE(rcu_preempt_running_reader()); |
767 | |
768 | /* |
769 | * Acquire lock so that there is only one preemptible RCU grace |
770 | * period in flight. Of course, if someone does the expedited |
771 | * grace period for us while we are acquiring the lock, just leave. |
772 | */ |
773 | snap = sync_rcu_preempt_exp_count + 1; |
774 | mutex_lock(&sync_rcu_preempt_exp_mutex); |
775 | if (ULONG_CMP_LT(snap, sync_rcu_preempt_exp_count)) |
776 | goto unlock_mb_ret; /* Others did our work for us. */ |
777 | |
778 | local_irq_save(flags); |
779 | |
780 | /* |
781 | * All RCU readers have to already be on blkd_tasks because |
782 | * we cannot legally be executing in an RCU read-side critical |
783 | * section. |
784 | */ |
785 | |
786 | /* Snapshot current head of ->blkd_tasks list. */ |
787 | rpcp->exp_tasks = rpcp->blkd_tasks.next; |
788 | if (rpcp->exp_tasks == &rpcp->blkd_tasks) |
789 | rpcp->exp_tasks = NULL; |
790 | |
791 | /* Wait for tail of ->blkd_tasks list to drain. */ |
792 | if (!rcu_preempted_readers_exp()) |
793 | local_irq_restore(flags); |
794 | else { |
795 | rcu_initiate_boost(); |
796 | local_irq_restore(flags); |
797 | wait_event(sync_rcu_preempt_exp_wq, |
798 | !rcu_preempted_readers_exp()); |
799 | } |
800 | |
801 | /* Clean up and exit. */ |
802 | barrier(); /* ensure expedited GP seen before counter increment. */ |
803 | sync_rcu_preempt_exp_count++; |
804 | unlock_mb_ret: |
805 | mutex_unlock(&sync_rcu_preempt_exp_mutex); |
806 | barrier(); /* ensure subsequent action seen after grace period. */ |
807 | } |
808 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); |
809 | |
810 | /* |
811 | * Does preemptible RCU need the CPU to stay out of dynticks mode? |
812 | */ |
813 | int rcu_preempt_needs_cpu(void) |
814 | { |
815 | if (!rcu_preempt_running_reader()) |
816 | rcu_preempt_cpu_qs(); |
817 | return rcu_preempt_ctrlblk.rcb.rcucblist != NULL; |
818 | } |
819 | |
820 | /* |
821 | * Check for a task exiting while in a preemptible -RCU read-side |
822 | * critical section, clean up if so. No need to issue warnings, |
823 | * as debug_check_no_locks_held() already does this if lockdep |
824 | * is enabled. |
825 | */ |
826 | void exit_rcu(void) |
827 | { |
828 | struct task_struct *t = current; |
829 | |
830 | if (t->rcu_read_lock_nesting == 0) |
831 | return; |
832 | t->rcu_read_lock_nesting = 1; |
833 | __rcu_read_unlock(); |
834 | } |
835 | |
836 | #else /* #ifdef CONFIG_TINY_PREEMPT_RCU */ |
837 | |
838 | #ifdef CONFIG_RCU_TRACE |
839 | |
840 | /* |
841 | * Because preemptible RCU does not exist, it is not necessary to |
842 | * dump out its statistics. |
843 | */ |
844 | static void show_tiny_preempt_stats(struct seq_file *m) |
845 | { |
846 | } |
847 | |
848 | #endif /* #ifdef CONFIG_RCU_TRACE */ |
849 | |
850 | /* |
851 | * Because preemptible RCU does not exist, it never has any callbacks |
852 | * to check. |
853 | */ |
854 | static void rcu_preempt_check_callbacks(void) |
855 | { |
856 | } |
857 | |
858 | /* |
859 | * Because preemptible RCU does not exist, it never has any callbacks |
860 | * to remove. |
861 | */ |
862 | static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp) |
863 | { |
864 | } |
865 | |
866 | /* |
867 | * Because preemptible RCU does not exist, it never has any callbacks |
868 | * to process. |
869 | */ |
870 | static void rcu_preempt_process_callbacks(void) |
871 | { |
872 | } |
873 | |
874 | #endif /* #else #ifdef CONFIG_TINY_PREEMPT_RCU */ |
875 | |
876 | #ifdef CONFIG_RCU_BOOST |
877 | |
878 | /* |
879 | * Wake up rcu_kthread() to process callbacks now eligible for invocation |
880 | * or to boost readers. |
881 | */ |
882 | static void invoke_rcu_callbacks(void) |
883 | { |
884 | have_rcu_kthread_work = 1; |
885 | wake_up(&rcu_kthread_wq); |
886 | } |
887 | |
888 | #ifdef CONFIG_RCU_TRACE |
889 | |
890 | /* |
891 | * Is the current CPU running the RCU-callbacks kthread? |
892 | * Caller must have preemption disabled. |
893 | */ |
894 | static bool rcu_is_callbacks_kthread(void) |
895 | { |
896 | return rcu_kthread_task == current; |
897 | } |
898 | |
899 | #endif /* #ifdef CONFIG_RCU_TRACE */ |
900 | |
901 | /* |
902 | * This kthread invokes RCU callbacks whose grace periods have |
903 | * elapsed. It is awakened as needed, and takes the place of the |
904 | * RCU_SOFTIRQ that is used for this purpose when boosting is disabled. |
905 | * This is a kthread, but it is never stopped, at least not until |
906 | * the system goes down. |
907 | */ |
908 | static int rcu_kthread(void *arg) |
909 | { |
910 | unsigned long work; |
911 | unsigned long morework; |
912 | unsigned long flags; |
913 | |
914 | for (;;) { |
915 | wait_event_interruptible(rcu_kthread_wq, |
916 | have_rcu_kthread_work != 0); |
917 | morework = rcu_boost(); |
918 | local_irq_save(flags); |
919 | work = have_rcu_kthread_work; |
920 | have_rcu_kthread_work = morework; |
921 | local_irq_restore(flags); |
922 | if (work) |
923 | rcu_process_callbacks(NULL); |
924 | schedule_timeout_interruptible(1); /* Leave CPU for others. */ |
925 | } |
926 | |
927 | return 0; /* Not reached, but needed to shut gcc up. */ |
928 | } |
929 | |
930 | /* |
931 | * Spawn the kthread that invokes RCU callbacks. |
932 | */ |
933 | static int __init rcu_spawn_kthreads(void) |
934 | { |
935 | struct sched_param sp; |
936 | |
937 | rcu_kthread_task = kthread_run(rcu_kthread, NULL, "rcu_kthread"); |
938 | sp.sched_priority = RCU_BOOST_PRIO; |
939 | sched_setscheduler_nocheck(rcu_kthread_task, SCHED_FIFO, &sp); |
940 | return 0; |
941 | } |
942 | early_initcall(rcu_spawn_kthreads); |
943 | |
944 | #else /* #ifdef CONFIG_RCU_BOOST */ |
945 | |
946 | /* |
947 | * Start up softirq processing of callbacks. |
948 | */ |
949 | void invoke_rcu_callbacks(void) |
950 | { |
951 | raise_softirq(RCU_SOFTIRQ); |
952 | } |
953 | |
954 | #ifdef CONFIG_RCU_TRACE |
955 | |
956 | /* |
957 | * There is no callback kthread, so this thread is never it. |
958 | */ |
959 | static bool rcu_is_callbacks_kthread(void) |
960 | { |
961 | return false; |
962 | } |
963 | |
964 | #endif /* #ifdef CONFIG_RCU_TRACE */ |
965 | |
966 | void rcu_init(void) |
967 | { |
968 | open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); |
969 | } |
970 | |
971 | #endif /* #else #ifdef CONFIG_RCU_BOOST */ |
972 | |
973 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
974 | #include <linux/kernel_stat.h> |
975 | |
976 | /* |
977 | * During boot, we forgive RCU lockdep issues. After this function is |
978 | * invoked, we start taking RCU lockdep issues seriously. |
979 | */ |
980 | void __init rcu_scheduler_starting(void) |
981 | { |
982 | WARN_ON(nr_context_switches() > 0); |
983 | rcu_scheduler_active = 1; |
984 | } |
985 | |
986 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
987 | |
988 | #ifdef CONFIG_RCU_TRACE |
989 | |
990 | #ifdef CONFIG_RCU_BOOST |
991 | |
992 | static void rcu_initiate_boost_trace(void) |
993 | { |
994 | if (list_empty(&rcu_preempt_ctrlblk.blkd_tasks)) |
995 | rcu_preempt_ctrlblk.n_balk_blkd_tasks++; |
996 | else if (rcu_preempt_ctrlblk.gp_tasks == NULL && |
997 | rcu_preempt_ctrlblk.exp_tasks == NULL) |
998 | rcu_preempt_ctrlblk.n_balk_exp_gp_tasks++; |
999 | else if (rcu_preempt_ctrlblk.boost_tasks != NULL) |
1000 | rcu_preempt_ctrlblk.n_balk_boost_tasks++; |
1001 | else if (!ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time)) |
1002 | rcu_preempt_ctrlblk.n_balk_notyet++; |
1003 | else |
1004 | rcu_preempt_ctrlblk.n_balk_nos++; |
1005 | } |
1006 | |
1007 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
1008 | |
1009 | static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n) |
1010 | { |
1011 | unsigned long flags; |
1012 | |
1013 | raw_local_irq_save(flags); |
1014 | rcp->qlen -= n; |
1015 | raw_local_irq_restore(flags); |
1016 | } |
1017 | |
1018 | /* |
1019 | * Dump statistics for TINY_RCU, such as they are. |
1020 | */ |
1021 | static int show_tiny_stats(struct seq_file *m, void *unused) |
1022 | { |
1023 | show_tiny_preempt_stats(m); |
1024 | seq_printf(m, "rcu_sched: qlen: %ld\n", rcu_sched_ctrlblk.qlen); |
1025 | seq_printf(m, "rcu_bh: qlen: %ld\n", rcu_bh_ctrlblk.qlen); |
1026 | return 0; |
1027 | } |
1028 | |
1029 | static int show_tiny_stats_open(struct inode *inode, struct file *file) |
1030 | { |
1031 | return single_open(file, show_tiny_stats, NULL); |
1032 | } |
1033 | |
1034 | static const struct file_operations show_tiny_stats_fops = { |
1035 | .owner = THIS_MODULE, |
1036 | .open = show_tiny_stats_open, |
1037 | .read = seq_read, |
1038 | .llseek = seq_lseek, |
1039 | .release = single_release, |
1040 | }; |
1041 | |
1042 | static struct dentry *rcudir; |
1043 | |
1044 | static int __init rcutiny_trace_init(void) |
1045 | { |
1046 | struct dentry *retval; |
1047 | |
1048 | rcudir = debugfs_create_dir("rcu", NULL); |
1049 | if (!rcudir) |
1050 | goto free_out; |
1051 | retval = debugfs_create_file("rcudata", 0444, rcudir, |
1052 | NULL, &show_tiny_stats_fops); |
1053 | if (!retval) |
1054 | goto free_out; |
1055 | return 0; |
1056 | free_out: |
1057 | debugfs_remove_recursive(rcudir); |
1058 | return 1; |
1059 | } |
1060 | |
1061 | static void __exit rcutiny_trace_cleanup(void) |
1062 | { |
1063 | debugfs_remove_recursive(rcudir); |
1064 | } |
1065 | |
1066 | module_init(rcutiny_trace_init); |
1067 | module_exit(rcutiny_trace_cleanup); |
1068 | |
1069 | MODULE_AUTHOR("Paul E. McKenney"); |
1070 | MODULE_DESCRIPTION("Read-Copy Update tracing for tiny implementation"); |
1071 | MODULE_LICENSE("GPL"); |
1072 | |
1073 | #endif /* #ifdef CONFIG_RCU_TRACE */ |
1074 |
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