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1 | /* |
2 | * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition. |
3 | * |
4 | * This program is free software; you can redistribute it and/or modify |
5 | * it under the terms of the GNU General Public License as published by |
6 | * the Free Software Foundation; either version 2 of the License, or |
7 | * (at your option) any later version. |
8 | * |
9 | * This program is distributed in the hope that it will be useful, |
10 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
11 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
12 | * GNU General Public License for more details. |
13 | * |
14 | * You should have received a copy of the GNU General Public License |
15 | * along with this program; if not, write to the Free Software |
16 | * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
17 | * |
18 | * Copyright IBM Corporation, 2008 |
19 | * |
20 | * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com> |
21 | * |
22 | * For detailed explanation of Read-Copy Update mechanism see - |
23 | * Documentation/RCU |
24 | */ |
25 | #include <linux/completion.h> |
26 | #include <linux/interrupt.h> |
27 | #include <linux/notifier.h> |
28 | #include <linux/rcupdate.h> |
29 | #include <linux/kernel.h> |
30 | #include <linux/export.h> |
31 | #include <linux/mutex.h> |
32 | #include <linux/sched.h> |
33 | #include <linux/types.h> |
34 | #include <linux/init.h> |
35 | #include <linux/time.h> |
36 | #include <linux/cpu.h> |
37 | #include <linux/prefetch.h> |
38 | |
39 | #ifdef CONFIG_RCU_TRACE |
40 | #include <trace/events/rcu.h> |
41 | #endif /* #else #ifdef CONFIG_RCU_TRACE */ |
42 | |
43 | #include "rcu.h" |
44 | |
45 | /* Forward declarations for rcutiny_plugin.h. */ |
46 | struct rcu_ctrlblk; |
47 | static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp); |
48 | static void rcu_process_callbacks(struct softirq_action *unused); |
49 | static void __call_rcu(struct rcu_head *head, |
50 | void (*func)(struct rcu_head *rcu), |
51 | struct rcu_ctrlblk *rcp); |
52 | |
53 | static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; |
54 | |
55 | #include "rcutiny_plugin.h" |
56 | |
57 | /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */ |
58 | static void rcu_idle_enter_common(long long newval) |
59 | { |
60 | if (newval) { |
61 | RCU_TRACE(trace_rcu_dyntick("--=", |
62 | rcu_dynticks_nesting, newval)); |
63 | rcu_dynticks_nesting = newval; |
64 | return; |
65 | } |
66 | RCU_TRACE(trace_rcu_dyntick("Start", rcu_dynticks_nesting, newval)); |
67 | if (!is_idle_task(current)) { |
68 | struct task_struct *idle = idle_task(smp_processor_id()); |
69 | |
70 | RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task", |
71 | rcu_dynticks_nesting, newval)); |
72 | ftrace_dump(DUMP_ALL); |
73 | WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s", |
74 | current->pid, current->comm, |
75 | idle->pid, idle->comm); /* must be idle task! */ |
76 | } |
77 | rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */ |
78 | barrier(); |
79 | rcu_dynticks_nesting = newval; |
80 | } |
81 | |
82 | /* |
83 | * Enter idle, which is an extended quiescent state if we have fully |
84 | * entered that mode (i.e., if the new value of dynticks_nesting is zero). |
85 | */ |
86 | void rcu_idle_enter(void) |
87 | { |
88 | unsigned long flags; |
89 | long long newval; |
90 | |
91 | local_irq_save(flags); |
92 | WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0); |
93 | if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == |
94 | DYNTICK_TASK_NEST_VALUE) |
95 | newval = 0; |
96 | else |
97 | newval = rcu_dynticks_nesting - DYNTICK_TASK_NEST_VALUE; |
98 | rcu_idle_enter_common(newval); |
99 | local_irq_restore(flags); |
100 | } |
101 | EXPORT_SYMBOL_GPL(rcu_idle_enter); |
102 | |
103 | /* |
104 | * Exit an interrupt handler towards idle. |
105 | */ |
106 | void rcu_irq_exit(void) |
107 | { |
108 | unsigned long flags; |
109 | long long newval; |
110 | |
111 | local_irq_save(flags); |
112 | newval = rcu_dynticks_nesting - 1; |
113 | WARN_ON_ONCE(newval < 0); |
114 | rcu_idle_enter_common(newval); |
115 | local_irq_restore(flags); |
116 | } |
117 | EXPORT_SYMBOL_GPL(rcu_irq_exit); |
118 | |
119 | /* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */ |
120 | static void rcu_idle_exit_common(long long oldval) |
121 | { |
122 | if (oldval) { |
123 | RCU_TRACE(trace_rcu_dyntick("++=", |
124 | oldval, rcu_dynticks_nesting)); |
125 | return; |
126 | } |
127 | RCU_TRACE(trace_rcu_dyntick("End", oldval, rcu_dynticks_nesting)); |
128 | if (!is_idle_task(current)) { |
129 | struct task_struct *idle = idle_task(smp_processor_id()); |
130 | |
131 | RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task", |
132 | oldval, rcu_dynticks_nesting)); |
133 | ftrace_dump(DUMP_ALL); |
134 | WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s", |
135 | current->pid, current->comm, |
136 | idle->pid, idle->comm); /* must be idle task! */ |
137 | } |
138 | } |
139 | |
140 | /* |
141 | * Exit idle, so that we are no longer in an extended quiescent state. |
142 | */ |
143 | void rcu_idle_exit(void) |
144 | { |
145 | unsigned long flags; |
146 | long long oldval; |
147 | |
148 | local_irq_save(flags); |
149 | oldval = rcu_dynticks_nesting; |
150 | WARN_ON_ONCE(rcu_dynticks_nesting < 0); |
151 | if (rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) |
152 | rcu_dynticks_nesting += DYNTICK_TASK_NEST_VALUE; |
153 | else |
154 | rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; |
155 | rcu_idle_exit_common(oldval); |
156 | local_irq_restore(flags); |
157 | } |
158 | EXPORT_SYMBOL_GPL(rcu_idle_exit); |
159 | |
160 | /* |
161 | * Enter an interrupt handler, moving away from idle. |
162 | */ |
163 | void rcu_irq_enter(void) |
164 | { |
165 | unsigned long flags; |
166 | long long oldval; |
167 | |
168 | local_irq_save(flags); |
169 | oldval = rcu_dynticks_nesting; |
170 | rcu_dynticks_nesting++; |
171 | WARN_ON_ONCE(rcu_dynticks_nesting == 0); |
172 | rcu_idle_exit_common(oldval); |
173 | local_irq_restore(flags); |
174 | } |
175 | EXPORT_SYMBOL_GPL(rcu_irq_enter); |
176 | |
177 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
178 | |
179 | /* |
180 | * Test whether RCU thinks that the current CPU is idle. |
181 | */ |
182 | int rcu_is_cpu_idle(void) |
183 | { |
184 | return !rcu_dynticks_nesting; |
185 | } |
186 | EXPORT_SYMBOL(rcu_is_cpu_idle); |
187 | |
188 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
189 | |
190 | /* |
191 | * Test whether the current CPU was interrupted from idle. Nested |
192 | * interrupts don't count, we must be running at the first interrupt |
193 | * level. |
194 | */ |
195 | static int rcu_is_cpu_rrupt_from_idle(void) |
196 | { |
197 | return rcu_dynticks_nesting <= 1; |
198 | } |
199 | |
200 | /* |
201 | * Helper function for rcu_sched_qs() and rcu_bh_qs(). |
202 | * Also irqs are disabled to avoid confusion due to interrupt handlers |
203 | * invoking call_rcu(). |
204 | */ |
205 | static int rcu_qsctr_help(struct rcu_ctrlblk *rcp) |
206 | { |
207 | RCU_TRACE(reset_cpu_stall_ticks(rcp)); |
208 | if (rcp->rcucblist != NULL && |
209 | rcp->donetail != rcp->curtail) { |
210 | rcp->donetail = rcp->curtail; |
211 | return 1; |
212 | } |
213 | |
214 | return 0; |
215 | } |
216 | |
217 | /* |
218 | * Record an rcu quiescent state. And an rcu_bh quiescent state while we |
219 | * are at it, given that any rcu quiescent state is also an rcu_bh |
220 | * quiescent state. Use "+" instead of "||" to defeat short circuiting. |
221 | */ |
222 | void rcu_sched_qs(int cpu) |
223 | { |
224 | unsigned long flags; |
225 | |
226 | local_irq_save(flags); |
227 | if (rcu_qsctr_help(&rcu_sched_ctrlblk) + |
228 | rcu_qsctr_help(&rcu_bh_ctrlblk)) |
229 | raise_softirq(RCU_SOFTIRQ); |
230 | local_irq_restore(flags); |
231 | } |
232 | |
233 | /* |
234 | * Record an rcu_bh quiescent state. |
235 | */ |
236 | void rcu_bh_qs(int cpu) |
237 | { |
238 | unsigned long flags; |
239 | |
240 | local_irq_save(flags); |
241 | if (rcu_qsctr_help(&rcu_bh_ctrlblk)) |
242 | raise_softirq(RCU_SOFTIRQ); |
243 | local_irq_restore(flags); |
244 | } |
245 | |
246 | /* |
247 | * Check to see if the scheduling-clock interrupt came from an extended |
248 | * quiescent state, and, if so, tell RCU about it. This function must |
249 | * be called from hardirq context. It is normally called from the |
250 | * scheduling-clock interrupt. |
251 | */ |
252 | void rcu_check_callbacks(int cpu, int user) |
253 | { |
254 | RCU_TRACE(check_cpu_stalls()); |
255 | if (user || rcu_is_cpu_rrupt_from_idle()) |
256 | rcu_sched_qs(cpu); |
257 | else if (!in_softirq()) |
258 | rcu_bh_qs(cpu); |
259 | } |
260 | |
261 | /* |
262 | * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure |
263 | * whose grace period has elapsed. |
264 | */ |
265 | static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp) |
266 | { |
267 | const char *rn = NULL; |
268 | struct rcu_head *next, *list; |
269 | unsigned long flags; |
270 | RCU_TRACE(int cb_count = 0); |
271 | |
272 | /* If no RCU callbacks ready to invoke, just return. */ |
273 | if (&rcp->rcucblist == rcp->donetail) { |
274 | RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1)); |
275 | RCU_TRACE(trace_rcu_batch_end(rcp->name, 0, |
276 | ACCESS_ONCE(rcp->rcucblist), |
277 | need_resched(), |
278 | is_idle_task(current), |
279 | false)); |
280 | return; |
281 | } |
282 | |
283 | /* Move the ready-to-invoke callbacks to a local list. */ |
284 | local_irq_save(flags); |
285 | RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1)); |
286 | list = rcp->rcucblist; |
287 | rcp->rcucblist = *rcp->donetail; |
288 | *rcp->donetail = NULL; |
289 | if (rcp->curtail == rcp->donetail) |
290 | rcp->curtail = &rcp->rcucblist; |
291 | rcp->donetail = &rcp->rcucblist; |
292 | local_irq_restore(flags); |
293 | |
294 | /* Invoke the callbacks on the local list. */ |
295 | RCU_TRACE(rn = rcp->name); |
296 | while (list) { |
297 | next = list->next; |
298 | prefetch(next); |
299 | debug_rcu_head_unqueue(list); |
300 | local_bh_disable(); |
301 | __rcu_reclaim(rn, list); |
302 | local_bh_enable(); |
303 | list = next; |
304 | RCU_TRACE(cb_count++); |
305 | } |
306 | RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count)); |
307 | RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count, 0, need_resched(), |
308 | is_idle_task(current), |
309 | false)); |
310 | } |
311 | |
312 | static void rcu_process_callbacks(struct softirq_action *unused) |
313 | { |
314 | __rcu_process_callbacks(&rcu_sched_ctrlblk); |
315 | __rcu_process_callbacks(&rcu_bh_ctrlblk); |
316 | } |
317 | |
318 | /* |
319 | * Wait for a grace period to elapse. But it is illegal to invoke |
320 | * synchronize_sched() from within an RCU read-side critical section. |
321 | * Therefore, any legal call to synchronize_sched() is a quiescent |
322 | * state, and so on a UP system, synchronize_sched() need do nothing. |
323 | * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the |
324 | * benefits of doing might_sleep() to reduce latency.) |
325 | * |
326 | * Cool, huh? (Due to Josh Triplett.) |
327 | * |
328 | * But we want to make this a static inline later. The cond_resched() |
329 | * currently makes this problematic. |
330 | */ |
331 | void synchronize_sched(void) |
332 | { |
333 | rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) && |
334 | !lock_is_held(&rcu_lock_map) && |
335 | !lock_is_held(&rcu_sched_lock_map), |
336 | "Illegal synchronize_sched() in RCU read-side critical section"); |
337 | cond_resched(); |
338 | } |
339 | EXPORT_SYMBOL_GPL(synchronize_sched); |
340 | |
341 | /* |
342 | * Helper function for call_rcu() and call_rcu_bh(). |
343 | */ |
344 | static void __call_rcu(struct rcu_head *head, |
345 | void (*func)(struct rcu_head *rcu), |
346 | struct rcu_ctrlblk *rcp) |
347 | { |
348 | unsigned long flags; |
349 | |
350 | debug_rcu_head_queue(head); |
351 | head->func = func; |
352 | head->next = NULL; |
353 | |
354 | local_irq_save(flags); |
355 | *rcp->curtail = head; |
356 | rcp->curtail = &head->next; |
357 | RCU_TRACE(rcp->qlen++); |
358 | local_irq_restore(flags); |
359 | } |
360 | |
361 | /* |
362 | * Post an RCU callback to be invoked after the end of an RCU-sched grace |
363 | * period. But since we have but one CPU, that would be after any |
364 | * quiescent state. |
365 | */ |
366 | void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) |
367 | { |
368 | __call_rcu(head, func, &rcu_sched_ctrlblk); |
369 | } |
370 | EXPORT_SYMBOL_GPL(call_rcu_sched); |
371 | |
372 | /* |
373 | * Post an RCU bottom-half callback to be invoked after any subsequent |
374 | * quiescent state. |
375 | */ |
376 | void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) |
377 | { |
378 | __call_rcu(head, func, &rcu_bh_ctrlblk); |
379 | } |
380 | EXPORT_SYMBOL_GPL(call_rcu_bh); |
381 | |
382 | void rcu_init(void) |
383 | { |
384 | open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); |
385 | } |
386 |
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