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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 | s8 boosted_this_gp; /* Has boosting already happened? */ |
104 | unsigned long boost_time; /* When to start boosting (jiffies) */ |
105 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
106 | #ifdef CONFIG_RCU_TRACE |
107 | unsigned long n_grace_periods; |
108 | #ifdef CONFIG_RCU_BOOST |
109 | unsigned long n_tasks_boosted; |
110 | unsigned long n_exp_boosts; |
111 | unsigned long n_normal_boosts; |
112 | unsigned long n_normal_balk_blkd_tasks; |
113 | unsigned long n_normal_balk_gp_tasks; |
114 | unsigned long n_normal_balk_boost_tasks; |
115 | unsigned long n_normal_balk_boosted; |
116 | unsigned long n_normal_balk_notyet; |
117 | unsigned long n_normal_balk_nos; |
118 | unsigned long n_exp_balk_blkd_tasks; |
119 | unsigned long n_exp_balk_nos; |
120 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
121 | #endif /* #ifdef CONFIG_RCU_TRACE */ |
122 | }; |
123 | |
124 | static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = { |
125 | .rcb.donetail = &rcu_preempt_ctrlblk.rcb.rcucblist, |
126 | .rcb.curtail = &rcu_preempt_ctrlblk.rcb.rcucblist, |
127 | .nexttail = &rcu_preempt_ctrlblk.rcb.rcucblist, |
128 | .blkd_tasks = LIST_HEAD_INIT(rcu_preempt_ctrlblk.blkd_tasks), |
129 | }; |
130 | |
131 | static int rcu_preempted_readers_exp(void); |
132 | static void rcu_report_exp_done(void); |
133 | |
134 | /* |
135 | * Return true if the CPU has not yet responded to the current grace period. |
136 | */ |
137 | static int rcu_cpu_blocking_cur_gp(void) |
138 | { |
139 | return rcu_preempt_ctrlblk.gpcpu != rcu_preempt_ctrlblk.gpnum; |
140 | } |
141 | |
142 | /* |
143 | * Check for a running RCU reader. Because there is only one CPU, |
144 | * there can be but one running RCU reader at a time. ;-) |
145 | */ |
146 | static int rcu_preempt_running_reader(void) |
147 | { |
148 | return current->rcu_read_lock_nesting; |
149 | } |
150 | |
151 | /* |
152 | * Check for preempted RCU readers blocking any grace period. |
153 | * If the caller needs a reliable answer, it must disable hard irqs. |
154 | */ |
155 | static int rcu_preempt_blocked_readers_any(void) |
156 | { |
157 | return !list_empty(&rcu_preempt_ctrlblk.blkd_tasks); |
158 | } |
159 | |
160 | /* |
161 | * Check for preempted RCU readers blocking the current grace period. |
162 | * If the caller needs a reliable answer, it must disable hard irqs. |
163 | */ |
164 | static int rcu_preempt_blocked_readers_cgp(void) |
165 | { |
166 | return rcu_preempt_ctrlblk.gp_tasks != NULL; |
167 | } |
168 | |
169 | /* |
170 | * Return true if another preemptible-RCU grace period is needed. |
171 | */ |
172 | static int rcu_preempt_needs_another_gp(void) |
173 | { |
174 | return *rcu_preempt_ctrlblk.rcb.curtail != NULL; |
175 | } |
176 | |
177 | /* |
178 | * Return true if a preemptible-RCU grace period is in progress. |
179 | * The caller must disable hardirqs. |
180 | */ |
181 | static int rcu_preempt_gp_in_progress(void) |
182 | { |
183 | return rcu_preempt_ctrlblk.completed != rcu_preempt_ctrlblk.gpnum; |
184 | } |
185 | |
186 | /* |
187 | * Advance a ->blkd_tasks-list pointer to the next entry, instead |
188 | * returning NULL if at the end of the list. |
189 | */ |
190 | static struct list_head *rcu_next_node_entry(struct task_struct *t) |
191 | { |
192 | struct list_head *np; |
193 | |
194 | np = t->rcu_node_entry.next; |
195 | if (np == &rcu_preempt_ctrlblk.blkd_tasks) |
196 | np = NULL; |
197 | return np; |
198 | } |
199 | |
200 | #ifdef CONFIG_RCU_TRACE |
201 | |
202 | #ifdef CONFIG_RCU_BOOST |
203 | static void rcu_initiate_boost_trace(void); |
204 | static void rcu_initiate_exp_boost_trace(void); |
205 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
206 | |
207 | /* |
208 | * Dump additional statistice for TINY_PREEMPT_RCU. |
209 | */ |
210 | static void show_tiny_preempt_stats(struct seq_file *m) |
211 | { |
212 | seq_printf(m, "rcu_preempt: qlen=%ld gp=%lu g%u/p%u/c%u tasks=%c%c%c\n", |
213 | rcu_preempt_ctrlblk.rcb.qlen, |
214 | rcu_preempt_ctrlblk.n_grace_periods, |
215 | rcu_preempt_ctrlblk.gpnum, |
216 | rcu_preempt_ctrlblk.gpcpu, |
217 | rcu_preempt_ctrlblk.completed, |
218 | "T."[list_empty(&rcu_preempt_ctrlblk.blkd_tasks)], |
219 | "N."[!rcu_preempt_ctrlblk.gp_tasks], |
220 | "E."[!rcu_preempt_ctrlblk.exp_tasks]); |
221 | #ifdef CONFIG_RCU_BOOST |
222 | seq_printf(m, " ttb=%c btg=", |
223 | "B."[!rcu_preempt_ctrlblk.boost_tasks]); |
224 | switch (rcu_preempt_ctrlblk.boosted_this_gp) { |
225 | case -1: |
226 | seq_puts(m, "exp"); |
227 | break; |
228 | case 0: |
229 | seq_puts(m, "no"); |
230 | break; |
231 | case 1: |
232 | seq_puts(m, "begun"); |
233 | break; |
234 | case 2: |
235 | seq_puts(m, "done"); |
236 | break; |
237 | default: |
238 | seq_printf(m, "?%d?", rcu_preempt_ctrlblk.boosted_this_gp); |
239 | } |
240 | seq_printf(m, " ntb=%lu neb=%lu nnb=%lu j=%04x bt=%04x\n", |
241 | rcu_preempt_ctrlblk.n_tasks_boosted, |
242 | rcu_preempt_ctrlblk.n_exp_boosts, |
243 | rcu_preempt_ctrlblk.n_normal_boosts, |
244 | (int)(jiffies & 0xffff), |
245 | (int)(rcu_preempt_ctrlblk.boost_time & 0xffff)); |
246 | seq_printf(m, " %s: nt=%lu gt=%lu bt=%lu b=%lu ny=%lu nos=%lu\n", |
247 | "normal balk", |
248 | rcu_preempt_ctrlblk.n_normal_balk_blkd_tasks, |
249 | rcu_preempt_ctrlblk.n_normal_balk_gp_tasks, |
250 | rcu_preempt_ctrlblk.n_normal_balk_boost_tasks, |
251 | rcu_preempt_ctrlblk.n_normal_balk_boosted, |
252 | rcu_preempt_ctrlblk.n_normal_balk_notyet, |
253 | rcu_preempt_ctrlblk.n_normal_balk_nos); |
254 | seq_printf(m, " exp balk: bt=%lu nos=%lu\n", |
255 | rcu_preempt_ctrlblk.n_exp_balk_blkd_tasks, |
256 | rcu_preempt_ctrlblk.n_exp_balk_nos); |
257 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
258 | } |
259 | |
260 | #endif /* #ifdef CONFIG_RCU_TRACE */ |
261 | |
262 | #ifdef CONFIG_RCU_BOOST |
263 | |
264 | #include "rtmutex_common.h" |
265 | |
266 | /* |
267 | * Carry out RCU priority boosting on the task indicated by ->boost_tasks, |
268 | * and advance ->boost_tasks to the next task in the ->blkd_tasks list. |
269 | */ |
270 | static int rcu_boost(void) |
271 | { |
272 | unsigned long flags; |
273 | struct rt_mutex mtx; |
274 | struct list_head *np; |
275 | struct task_struct *t; |
276 | |
277 | if (rcu_preempt_ctrlblk.boost_tasks == NULL) |
278 | return 0; /* Nothing to boost. */ |
279 | raw_local_irq_save(flags); |
280 | rcu_preempt_ctrlblk.boosted_this_gp++; |
281 | t = container_of(rcu_preempt_ctrlblk.boost_tasks, struct task_struct, |
282 | rcu_node_entry); |
283 | np = rcu_next_node_entry(t); |
284 | rt_mutex_init_proxy_locked(&mtx, t); |
285 | t->rcu_boost_mutex = &mtx; |
286 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BOOSTED; |
287 | raw_local_irq_restore(flags); |
288 | rt_mutex_lock(&mtx); |
289 | RCU_TRACE(rcu_preempt_ctrlblk.n_tasks_boosted++); |
290 | rcu_preempt_ctrlblk.boosted_this_gp++; |
291 | rt_mutex_unlock(&mtx); |
292 | return rcu_preempt_ctrlblk.boost_tasks != NULL; |
293 | } |
294 | |
295 | /* |
296 | * Check to see if it is now time to start boosting RCU readers blocking |
297 | * the current grace period, and, if so, tell the rcu_kthread_task to |
298 | * start boosting them. If there is an expedited boost in progress, |
299 | * we wait for it to complete. |
300 | * |
301 | * If there are no blocked readers blocking the current grace period, |
302 | * return 0 to let the caller know, otherwise return 1. Note that this |
303 | * return value is independent of whether or not boosting was done. |
304 | */ |
305 | static int rcu_initiate_boost(void) |
306 | { |
307 | if (!rcu_preempt_blocked_readers_cgp()) { |
308 | RCU_TRACE(rcu_preempt_ctrlblk.n_normal_balk_blkd_tasks++); |
309 | return 0; |
310 | } |
311 | if (rcu_preempt_ctrlblk.gp_tasks != NULL && |
312 | rcu_preempt_ctrlblk.boost_tasks == NULL && |
313 | rcu_preempt_ctrlblk.boosted_this_gp == 0 && |
314 | ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time)) { |
315 | rcu_preempt_ctrlblk.boost_tasks = rcu_preempt_ctrlblk.gp_tasks; |
316 | invoke_rcu_kthread(); |
317 | RCU_TRACE(rcu_preempt_ctrlblk.n_normal_boosts++); |
318 | } else |
319 | RCU_TRACE(rcu_initiate_boost_trace()); |
320 | return 1; |
321 | } |
322 | |
323 | /* |
324 | * Initiate boosting for an expedited grace period. |
325 | */ |
326 | static void rcu_initiate_expedited_boost(void) |
327 | { |
328 | unsigned long flags; |
329 | |
330 | raw_local_irq_save(flags); |
331 | if (!list_empty(&rcu_preempt_ctrlblk.blkd_tasks)) { |
332 | rcu_preempt_ctrlblk.boost_tasks = |
333 | rcu_preempt_ctrlblk.blkd_tasks.next; |
334 | rcu_preempt_ctrlblk.boosted_this_gp = -1; |
335 | invoke_rcu_kthread(); |
336 | RCU_TRACE(rcu_preempt_ctrlblk.n_exp_boosts++); |
337 | } else |
338 | RCU_TRACE(rcu_initiate_exp_boost_trace()); |
339 | raw_local_irq_restore(flags); |
340 | } |
341 | |
342 | #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000); |
343 | |
344 | /* |
345 | * Do priority-boost accounting for the start of a new grace period. |
346 | */ |
347 | static void rcu_preempt_boost_start_gp(void) |
348 | { |
349 | rcu_preempt_ctrlblk.boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; |
350 | if (rcu_preempt_ctrlblk.boosted_this_gp > 0) |
351 | rcu_preempt_ctrlblk.boosted_this_gp = 0; |
352 | } |
353 | |
354 | #else /* #ifdef CONFIG_RCU_BOOST */ |
355 | |
356 | /* |
357 | * If there is no RCU priority boosting, we don't boost. |
358 | */ |
359 | static int rcu_boost(void) |
360 | { |
361 | return 0; |
362 | } |
363 | |
364 | /* |
365 | * If there is no RCU priority boosting, we don't initiate boosting, |
366 | * but we do indicate whether there are blocked readers blocking the |
367 | * current grace period. |
368 | */ |
369 | static int rcu_initiate_boost(void) |
370 | { |
371 | return rcu_preempt_blocked_readers_cgp(); |
372 | } |
373 | |
374 | /* |
375 | * If there is no RCU priority boosting, we don't initiate expedited boosting. |
376 | */ |
377 | static void rcu_initiate_expedited_boost(void) |
378 | { |
379 | } |
380 | |
381 | /* |
382 | * If there is no RCU priority boosting, nothing to do at grace-period start. |
383 | */ |
384 | static void rcu_preempt_boost_start_gp(void) |
385 | { |
386 | } |
387 | |
388 | #endif /* else #ifdef CONFIG_RCU_BOOST */ |
389 | |
390 | /* |
391 | * Record a preemptible-RCU quiescent state for the specified CPU. Note |
392 | * that this just means that the task currently running on the CPU is |
393 | * in a quiescent state. There might be any number of tasks blocked |
394 | * while in an RCU read-side critical section. |
395 | * |
396 | * Unlike the other rcu_*_qs() functions, callers to this function |
397 | * must disable irqs in order to protect the assignment to |
398 | * ->rcu_read_unlock_special. |
399 | * |
400 | * Because this is a single-CPU implementation, the only way a grace |
401 | * period can end is if the CPU is in a quiescent state. The reason is |
402 | * that a blocked preemptible-RCU reader can exit its critical section |
403 | * only if the CPU is running it at the time. Therefore, when the |
404 | * last task blocking the current grace period exits its RCU read-side |
405 | * critical section, neither the CPU nor blocked tasks will be stopping |
406 | * the current grace period. (In contrast, SMP implementations |
407 | * might have CPUs running in RCU read-side critical sections that |
408 | * block later grace periods -- but this is not possible given only |
409 | * one CPU.) |
410 | */ |
411 | static void rcu_preempt_cpu_qs(void) |
412 | { |
413 | /* Record both CPU and task as having responded to current GP. */ |
414 | rcu_preempt_ctrlblk.gpcpu = rcu_preempt_ctrlblk.gpnum; |
415 | current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; |
416 | |
417 | /* If there is no GP then there is nothing more to do. */ |
418 | if (!rcu_preempt_gp_in_progress()) |
419 | return; |
420 | /* |
421 | * Check up on boosting. If there are no readers blocking the |
422 | * current grace period, leave. |
423 | */ |
424 | if (rcu_initiate_boost()) |
425 | return; |
426 | |
427 | /* Advance callbacks. */ |
428 | rcu_preempt_ctrlblk.completed = rcu_preempt_ctrlblk.gpnum; |
429 | rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.rcb.curtail; |
430 | rcu_preempt_ctrlblk.rcb.curtail = rcu_preempt_ctrlblk.nexttail; |
431 | |
432 | /* If there are no blocked readers, next GP is done instantly. */ |
433 | if (!rcu_preempt_blocked_readers_any()) |
434 | rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.nexttail; |
435 | |
436 | /* If there are done callbacks, cause them to be invoked. */ |
437 | if (*rcu_preempt_ctrlblk.rcb.donetail != NULL) |
438 | invoke_rcu_kthread(); |
439 | } |
440 | |
441 | /* |
442 | * Start a new RCU grace period if warranted. Hard irqs must be disabled. |
443 | */ |
444 | static void rcu_preempt_start_gp(void) |
445 | { |
446 | if (!rcu_preempt_gp_in_progress() && rcu_preempt_needs_another_gp()) { |
447 | |
448 | /* Official start of GP. */ |
449 | rcu_preempt_ctrlblk.gpnum++; |
450 | RCU_TRACE(rcu_preempt_ctrlblk.n_grace_periods++); |
451 | |
452 | /* Any blocked RCU readers block new GP. */ |
453 | if (rcu_preempt_blocked_readers_any()) |
454 | rcu_preempt_ctrlblk.gp_tasks = |
455 | rcu_preempt_ctrlblk.blkd_tasks.next; |
456 | |
457 | /* Set up for RCU priority boosting. */ |
458 | rcu_preempt_boost_start_gp(); |
459 | |
460 | /* If there is no running reader, CPU is done with GP. */ |
461 | if (!rcu_preempt_running_reader()) |
462 | rcu_preempt_cpu_qs(); |
463 | } |
464 | } |
465 | |
466 | /* |
467 | * We have entered the scheduler, and the current task might soon be |
468 | * context-switched away from. If this task is in an RCU read-side |
469 | * critical section, we will no longer be able to rely on the CPU to |
470 | * record that fact, so we enqueue the task on the blkd_tasks list. |
471 | * If the task started after the current grace period began, as recorded |
472 | * by ->gpcpu, we enqueue at the beginning of the list. Otherwise |
473 | * before the element referenced by ->gp_tasks (or at the tail if |
474 | * ->gp_tasks is NULL) and point ->gp_tasks at the newly added element. |
475 | * The task will dequeue itself when it exits the outermost enclosing |
476 | * RCU read-side critical section. Therefore, the current grace period |
477 | * cannot be permitted to complete until the ->gp_tasks pointer becomes |
478 | * NULL. |
479 | * |
480 | * Caller must disable preemption. |
481 | */ |
482 | void rcu_preempt_note_context_switch(void) |
483 | { |
484 | struct task_struct *t = current; |
485 | unsigned long flags; |
486 | |
487 | local_irq_save(flags); /* must exclude scheduler_tick(). */ |
488 | if (rcu_preempt_running_reader() && |
489 | (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { |
490 | |
491 | /* Possibly blocking in an RCU read-side critical section. */ |
492 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; |
493 | |
494 | /* |
495 | * If this CPU has already checked in, then this task |
496 | * will hold up the next grace period rather than the |
497 | * current grace period. Queue the task accordingly. |
498 | * If the task is queued for the current grace period |
499 | * (i.e., this CPU has not yet passed through a quiescent |
500 | * state for the current grace period), then as long |
501 | * as that task remains queued, the current grace period |
502 | * cannot end. |
503 | */ |
504 | list_add(&t->rcu_node_entry, &rcu_preempt_ctrlblk.blkd_tasks); |
505 | if (rcu_cpu_blocking_cur_gp()) |
506 | rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry; |
507 | } |
508 | |
509 | /* |
510 | * Either we were not in an RCU read-side critical section to |
511 | * begin with, or we have now recorded that critical section |
512 | * globally. Either way, we can now note a quiescent state |
513 | * for this CPU. Again, if we were in an RCU read-side critical |
514 | * section, and if that critical section was blocking the current |
515 | * grace period, then the fact that the task has been enqueued |
516 | * means that current grace period continues to be blocked. |
517 | */ |
518 | rcu_preempt_cpu_qs(); |
519 | local_irq_restore(flags); |
520 | } |
521 | |
522 | /* |
523 | * Tiny-preemptible RCU implementation for rcu_read_lock(). |
524 | * Just increment ->rcu_read_lock_nesting, shared state will be updated |
525 | * if we block. |
526 | */ |
527 | void __rcu_read_lock(void) |
528 | { |
529 | current->rcu_read_lock_nesting++; |
530 | barrier(); /* needed if we ever invoke rcu_read_lock in rcutiny.c */ |
531 | } |
532 | EXPORT_SYMBOL_GPL(__rcu_read_lock); |
533 | |
534 | /* |
535 | * Handle special cases during rcu_read_unlock(), such as needing to |
536 | * notify RCU core processing or task having blocked during the RCU |
537 | * read-side critical section. |
538 | */ |
539 | static void rcu_read_unlock_special(struct task_struct *t) |
540 | { |
541 | int empty; |
542 | int empty_exp; |
543 | unsigned long flags; |
544 | struct list_head *np; |
545 | int special; |
546 | |
547 | /* |
548 | * NMI handlers cannot block and cannot safely manipulate state. |
549 | * They therefore cannot possibly be special, so just leave. |
550 | */ |
551 | if (in_nmi()) |
552 | return; |
553 | |
554 | local_irq_save(flags); |
555 | |
556 | /* |
557 | * If RCU core is waiting for this CPU to exit critical section, |
558 | * let it know that we have done so. |
559 | */ |
560 | special = t->rcu_read_unlock_special; |
561 | if (special & RCU_READ_UNLOCK_NEED_QS) |
562 | rcu_preempt_cpu_qs(); |
563 | |
564 | /* Hardware IRQ handlers cannot block. */ |
565 | if (in_irq()) { |
566 | local_irq_restore(flags); |
567 | return; |
568 | } |
569 | |
570 | /* Clean up if blocked during RCU read-side critical section. */ |
571 | if (special & RCU_READ_UNLOCK_BLOCKED) { |
572 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; |
573 | |
574 | /* |
575 | * Remove this task from the ->blkd_tasks list and adjust |
576 | * any pointers that might have been referencing it. |
577 | */ |
578 | empty = !rcu_preempt_blocked_readers_cgp(); |
579 | empty_exp = rcu_preempt_ctrlblk.exp_tasks == NULL; |
580 | np = rcu_next_node_entry(t); |
581 | list_del(&t->rcu_node_entry); |
582 | if (&t->rcu_node_entry == rcu_preempt_ctrlblk.gp_tasks) |
583 | rcu_preempt_ctrlblk.gp_tasks = np; |
584 | if (&t->rcu_node_entry == rcu_preempt_ctrlblk.exp_tasks) |
585 | rcu_preempt_ctrlblk.exp_tasks = np; |
586 | #ifdef CONFIG_RCU_BOOST |
587 | if (&t->rcu_node_entry == rcu_preempt_ctrlblk.boost_tasks) |
588 | rcu_preempt_ctrlblk.boost_tasks = np; |
589 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
590 | INIT_LIST_HEAD(&t->rcu_node_entry); |
591 | |
592 | /* |
593 | * If this was the last task on the current list, and if |
594 | * we aren't waiting on the CPU, report the quiescent state |
595 | * and start a new grace period if needed. |
596 | */ |
597 | if (!empty && !rcu_preempt_blocked_readers_cgp()) { |
598 | rcu_preempt_cpu_qs(); |
599 | rcu_preempt_start_gp(); |
600 | } |
601 | |
602 | /* |
603 | * If this was the last task on the expedited lists, |
604 | * then we need wake up the waiting task. |
605 | */ |
606 | if (!empty_exp && rcu_preempt_ctrlblk.exp_tasks == NULL) |
607 | rcu_report_exp_done(); |
608 | } |
609 | #ifdef CONFIG_RCU_BOOST |
610 | /* Unboost self if was boosted. */ |
611 | if (special & RCU_READ_UNLOCK_BOOSTED) { |
612 | t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BOOSTED; |
613 | rt_mutex_unlock(t->rcu_boost_mutex); |
614 | t->rcu_boost_mutex = NULL; |
615 | } |
616 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
617 | local_irq_restore(flags); |
618 | } |
619 | |
620 | /* |
621 | * Tiny-preemptible RCU implementation for rcu_read_unlock(). |
622 | * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost |
623 | * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then |
624 | * invoke rcu_read_unlock_special() to clean up after a context switch |
625 | * in an RCU read-side critical section and other special cases. |
626 | */ |
627 | void __rcu_read_unlock(void) |
628 | { |
629 | struct task_struct *t = current; |
630 | |
631 | barrier(); /* needed if we ever invoke rcu_read_unlock in rcutiny.c */ |
632 | --t->rcu_read_lock_nesting; |
633 | barrier(); /* decrement before load of ->rcu_read_unlock_special */ |
634 | if (t->rcu_read_lock_nesting == 0 && |
635 | unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) |
636 | rcu_read_unlock_special(t); |
637 | #ifdef CONFIG_PROVE_LOCKING |
638 | WARN_ON_ONCE(t->rcu_read_lock_nesting < 0); |
639 | #endif /* #ifdef CONFIG_PROVE_LOCKING */ |
640 | } |
641 | EXPORT_SYMBOL_GPL(__rcu_read_unlock); |
642 | |
643 | /* |
644 | * Check for a quiescent state from the current CPU. When a task blocks, |
645 | * the task is recorded in the rcu_preempt_ctrlblk structure, which is |
646 | * checked elsewhere. This is called from the scheduling-clock interrupt. |
647 | * |
648 | * Caller must disable hard irqs. |
649 | */ |
650 | static void rcu_preempt_check_callbacks(void) |
651 | { |
652 | struct task_struct *t = current; |
653 | |
654 | if (rcu_preempt_gp_in_progress() && |
655 | (!rcu_preempt_running_reader() || |
656 | !rcu_cpu_blocking_cur_gp())) |
657 | rcu_preempt_cpu_qs(); |
658 | if (&rcu_preempt_ctrlblk.rcb.rcucblist != |
659 | rcu_preempt_ctrlblk.rcb.donetail) |
660 | invoke_rcu_kthread(); |
661 | if (rcu_preempt_gp_in_progress() && |
662 | rcu_cpu_blocking_cur_gp() && |
663 | rcu_preempt_running_reader()) |
664 | t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; |
665 | } |
666 | |
667 | /* |
668 | * TINY_PREEMPT_RCU has an extra callback-list tail pointer to |
669 | * update, so this is invoked from rcu_process_callbacks() to |
670 | * handle that case. Of course, it is invoked for all flavors of |
671 | * RCU, but RCU callbacks can appear only on one of the lists, and |
672 | * neither ->nexttail nor ->donetail can possibly be NULL, so there |
673 | * is no need for an explicit check. |
674 | */ |
675 | static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp) |
676 | { |
677 | if (rcu_preempt_ctrlblk.nexttail == rcp->donetail) |
678 | rcu_preempt_ctrlblk.nexttail = &rcp->rcucblist; |
679 | } |
680 | |
681 | /* |
682 | * Process callbacks for preemptible RCU. |
683 | */ |
684 | static void rcu_preempt_process_callbacks(void) |
685 | { |
686 | rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb); |
687 | } |
688 | |
689 | /* |
690 | * Queue a preemptible -RCU callback for invocation after a grace period. |
691 | */ |
692 | void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) |
693 | { |
694 | unsigned long flags; |
695 | |
696 | debug_rcu_head_queue(head); |
697 | head->func = func; |
698 | head->next = NULL; |
699 | |
700 | local_irq_save(flags); |
701 | *rcu_preempt_ctrlblk.nexttail = head; |
702 | rcu_preempt_ctrlblk.nexttail = &head->next; |
703 | RCU_TRACE(rcu_preempt_ctrlblk.rcb.qlen++); |
704 | rcu_preempt_start_gp(); /* checks to see if GP needed. */ |
705 | local_irq_restore(flags); |
706 | } |
707 | EXPORT_SYMBOL_GPL(call_rcu); |
708 | |
709 | void rcu_barrier(void) |
710 | { |
711 | struct rcu_synchronize rcu; |
712 | |
713 | init_rcu_head_on_stack(&rcu.head); |
714 | init_completion(&rcu.completion); |
715 | /* Will wake me after RCU finished. */ |
716 | call_rcu(&rcu.head, wakeme_after_rcu); |
717 | /* Wait for it. */ |
718 | wait_for_completion(&rcu.completion); |
719 | destroy_rcu_head_on_stack(&rcu.head); |
720 | } |
721 | EXPORT_SYMBOL_GPL(rcu_barrier); |
722 | |
723 | /* |
724 | * synchronize_rcu - wait until a grace period has elapsed. |
725 | * |
726 | * Control will return to the caller some time after a full grace |
727 | * period has elapsed, in other words after all currently executing RCU |
728 | * read-side critical sections have completed. RCU read-side critical |
729 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), |
730 | * and may be nested. |
731 | */ |
732 | void synchronize_rcu(void) |
733 | { |
734 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
735 | if (!rcu_scheduler_active) |
736 | return; |
737 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
738 | |
739 | WARN_ON_ONCE(rcu_preempt_running_reader()); |
740 | if (!rcu_preempt_blocked_readers_any()) |
741 | return; |
742 | |
743 | /* Once we get past the fastpath checks, same code as rcu_barrier(). */ |
744 | rcu_barrier(); |
745 | } |
746 | EXPORT_SYMBOL_GPL(synchronize_rcu); |
747 | |
748 | static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); |
749 | static unsigned long sync_rcu_preempt_exp_count; |
750 | static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); |
751 | |
752 | /* |
753 | * Return non-zero if there are any tasks in RCU read-side critical |
754 | * sections blocking the current preemptible-RCU expedited grace period. |
755 | * If there is no preemptible-RCU expedited grace period currently in |
756 | * progress, returns zero unconditionally. |
757 | */ |
758 | static int rcu_preempted_readers_exp(void) |
759 | { |
760 | return rcu_preempt_ctrlblk.exp_tasks != NULL; |
761 | } |
762 | |
763 | /* |
764 | * Report the exit from RCU read-side critical section for the last task |
765 | * that queued itself during or before the current expedited preemptible-RCU |
766 | * grace period. |
767 | */ |
768 | static void rcu_report_exp_done(void) |
769 | { |
770 | wake_up(&sync_rcu_preempt_exp_wq); |
771 | } |
772 | |
773 | /* |
774 | * Wait for an rcu-preempt grace period, but expedite it. The basic idea |
775 | * is to rely in the fact that there is but one CPU, and that it is |
776 | * illegal for a task to invoke synchronize_rcu_expedited() while in a |
777 | * preemptible-RCU read-side critical section. Therefore, any such |
778 | * critical sections must correspond to blocked tasks, which must therefore |
779 | * be on the ->blkd_tasks list. So just record the current head of the |
780 | * list in the ->exp_tasks pointer, and wait for all tasks including and |
781 | * after the task pointed to by ->exp_tasks to drain. |
782 | */ |
783 | void synchronize_rcu_expedited(void) |
784 | { |
785 | unsigned long flags; |
786 | struct rcu_preempt_ctrlblk *rpcp = &rcu_preempt_ctrlblk; |
787 | unsigned long snap; |
788 | |
789 | barrier(); /* ensure prior action seen before grace period. */ |
790 | |
791 | WARN_ON_ONCE(rcu_preempt_running_reader()); |
792 | |
793 | /* |
794 | * Acquire lock so that there is only one preemptible RCU grace |
795 | * period in flight. Of course, if someone does the expedited |
796 | * grace period for us while we are acquiring the lock, just leave. |
797 | */ |
798 | snap = sync_rcu_preempt_exp_count + 1; |
799 | mutex_lock(&sync_rcu_preempt_exp_mutex); |
800 | if (ULONG_CMP_LT(snap, sync_rcu_preempt_exp_count)) |
801 | goto unlock_mb_ret; /* Others did our work for us. */ |
802 | |
803 | local_irq_save(flags); |
804 | |
805 | /* |
806 | * All RCU readers have to already be on blkd_tasks because |
807 | * we cannot legally be executing in an RCU read-side critical |
808 | * section. |
809 | */ |
810 | |
811 | /* Snapshot current head of ->blkd_tasks list. */ |
812 | rpcp->exp_tasks = rpcp->blkd_tasks.next; |
813 | if (rpcp->exp_tasks == &rpcp->blkd_tasks) |
814 | rpcp->exp_tasks = NULL; |
815 | local_irq_restore(flags); |
816 | |
817 | /* Wait for tail of ->blkd_tasks list to drain. */ |
818 | if (rcu_preempted_readers_exp()) |
819 | rcu_initiate_expedited_boost(); |
820 | wait_event(sync_rcu_preempt_exp_wq, |
821 | !rcu_preempted_readers_exp()); |
822 | |
823 | /* Clean up and exit. */ |
824 | barrier(); /* ensure expedited GP seen before counter increment. */ |
825 | sync_rcu_preempt_exp_count++; |
826 | unlock_mb_ret: |
827 | mutex_unlock(&sync_rcu_preempt_exp_mutex); |
828 | barrier(); /* ensure subsequent action seen after grace period. */ |
829 | } |
830 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); |
831 | |
832 | /* |
833 | * Does preemptible RCU need the CPU to stay out of dynticks mode? |
834 | */ |
835 | int rcu_preempt_needs_cpu(void) |
836 | { |
837 | if (!rcu_preempt_running_reader()) |
838 | rcu_preempt_cpu_qs(); |
839 | return rcu_preempt_ctrlblk.rcb.rcucblist != NULL; |
840 | } |
841 | |
842 | /* |
843 | * Check for a task exiting while in a preemptible -RCU read-side |
844 | * critical section, clean up if so. No need to issue warnings, |
845 | * as debug_check_no_locks_held() already does this if lockdep |
846 | * is enabled. |
847 | */ |
848 | void exit_rcu(void) |
849 | { |
850 | struct task_struct *t = current; |
851 | |
852 | if (t->rcu_read_lock_nesting == 0) |
853 | return; |
854 | t->rcu_read_lock_nesting = 1; |
855 | rcu_read_unlock(); |
856 | } |
857 | |
858 | #else /* #ifdef CONFIG_TINY_PREEMPT_RCU */ |
859 | |
860 | #ifdef CONFIG_RCU_TRACE |
861 | |
862 | /* |
863 | * Because preemptible RCU does not exist, it is not necessary to |
864 | * dump out its statistics. |
865 | */ |
866 | static void show_tiny_preempt_stats(struct seq_file *m) |
867 | { |
868 | } |
869 | |
870 | #endif /* #ifdef CONFIG_RCU_TRACE */ |
871 | |
872 | /* |
873 | * Because preemptible RCU does not exist, it is never necessary to |
874 | * boost preempted RCU readers. |
875 | */ |
876 | static int rcu_boost(void) |
877 | { |
878 | return 0; |
879 | } |
880 | |
881 | /* |
882 | * Because preemptible RCU does not exist, it never has any callbacks |
883 | * to check. |
884 | */ |
885 | static void rcu_preempt_check_callbacks(void) |
886 | { |
887 | } |
888 | |
889 | /* |
890 | * Because preemptible RCU does not exist, it never has any callbacks |
891 | * to remove. |
892 | */ |
893 | static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp) |
894 | { |
895 | } |
896 | |
897 | /* |
898 | * Because preemptible RCU does not exist, it never has any callbacks |
899 | * to process. |
900 | */ |
901 | static void rcu_preempt_process_callbacks(void) |
902 | { |
903 | } |
904 | |
905 | #endif /* #else #ifdef CONFIG_TINY_PREEMPT_RCU */ |
906 | |
907 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
908 | #include <linux/kernel_stat.h> |
909 | |
910 | /* |
911 | * During boot, we forgive RCU lockdep issues. After this function is |
912 | * invoked, we start taking RCU lockdep issues seriously. |
913 | */ |
914 | void __init rcu_scheduler_starting(void) |
915 | { |
916 | WARN_ON(nr_context_switches() > 0); |
917 | rcu_scheduler_active = 1; |
918 | } |
919 | |
920 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
921 | |
922 | #ifdef CONFIG_RCU_BOOST |
923 | #define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO |
924 | #else /* #ifdef CONFIG_RCU_BOOST */ |
925 | #define RCU_BOOST_PRIO 1 |
926 | #endif /* #else #ifdef CONFIG_RCU_BOOST */ |
927 | |
928 | #ifdef CONFIG_RCU_TRACE |
929 | |
930 | #ifdef CONFIG_RCU_BOOST |
931 | |
932 | static void rcu_initiate_boost_trace(void) |
933 | { |
934 | if (rcu_preempt_ctrlblk.gp_tasks == NULL) |
935 | rcu_preempt_ctrlblk.n_normal_balk_gp_tasks++; |
936 | else if (rcu_preempt_ctrlblk.boost_tasks != NULL) |
937 | rcu_preempt_ctrlblk.n_normal_balk_boost_tasks++; |
938 | else if (rcu_preempt_ctrlblk.boosted_this_gp != 0) |
939 | rcu_preempt_ctrlblk.n_normal_balk_boosted++; |
940 | else if (!ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time)) |
941 | rcu_preempt_ctrlblk.n_normal_balk_notyet++; |
942 | else |
943 | rcu_preempt_ctrlblk.n_normal_balk_nos++; |
944 | } |
945 | |
946 | static void rcu_initiate_exp_boost_trace(void) |
947 | { |
948 | if (list_empty(&rcu_preempt_ctrlblk.blkd_tasks)) |
949 | rcu_preempt_ctrlblk.n_exp_balk_blkd_tasks++; |
950 | else |
951 | rcu_preempt_ctrlblk.n_exp_balk_nos++; |
952 | } |
953 | |
954 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
955 | |
956 | static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n) |
957 | { |
958 | unsigned long flags; |
959 | |
960 | raw_local_irq_save(flags); |
961 | rcp->qlen -= n; |
962 | raw_local_irq_restore(flags); |
963 | } |
964 | |
965 | /* |
966 | * Dump statistics for TINY_RCU, such as they are. |
967 | */ |
968 | static int show_tiny_stats(struct seq_file *m, void *unused) |
969 | { |
970 | show_tiny_preempt_stats(m); |
971 | seq_printf(m, "rcu_sched: qlen: %ld\n", rcu_sched_ctrlblk.qlen); |
972 | seq_printf(m, "rcu_bh: qlen: %ld\n", rcu_bh_ctrlblk.qlen); |
973 | return 0; |
974 | } |
975 | |
976 | static int show_tiny_stats_open(struct inode *inode, struct file *file) |
977 | { |
978 | return single_open(file, show_tiny_stats, NULL); |
979 | } |
980 | |
981 | static const struct file_operations show_tiny_stats_fops = { |
982 | .owner = THIS_MODULE, |
983 | .open = show_tiny_stats_open, |
984 | .read = seq_read, |
985 | .llseek = seq_lseek, |
986 | .release = single_release, |
987 | }; |
988 | |
989 | static struct dentry *rcudir; |
990 | |
991 | static int __init rcutiny_trace_init(void) |
992 | { |
993 | struct dentry *retval; |
994 | |
995 | rcudir = debugfs_create_dir("rcu", NULL); |
996 | if (!rcudir) |
997 | goto free_out; |
998 | retval = debugfs_create_file("rcudata", 0444, rcudir, |
999 | NULL, &show_tiny_stats_fops); |
1000 | if (!retval) |
1001 | goto free_out; |
1002 | return 0; |
1003 | free_out: |
1004 | debugfs_remove_recursive(rcudir); |
1005 | return 1; |
1006 | } |
1007 | |
1008 | static void __exit rcutiny_trace_cleanup(void) |
1009 | { |
1010 | debugfs_remove_recursive(rcudir); |
1011 | } |
1012 | |
1013 | module_init(rcutiny_trace_init); |
1014 | module_exit(rcutiny_trace_cleanup); |
1015 | |
1016 | MODULE_AUTHOR("Paul E. McKenney"); |
1017 | MODULE_DESCRIPTION("Read-Copy Update tracing for tiny implementation"); |
1018 | MODULE_LICENSE("GPL"); |
1019 | |
1020 | #endif /* #ifdef CONFIG_RCU_TRACE */ |
1021 |
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