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