xref: /openbmc/linux/kernel/rcu/tiny.c (revision 6774def6)
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, you can access it online at
16  * http://www.gnu.org/licenses/gpl-2.0.html.
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 #include <linux/ftrace_event.h>
39 
40 #include "rcu.h"
41 
42 /* Forward declarations for tiny_plugin.h. */
43 struct rcu_ctrlblk;
44 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
45 static void rcu_process_callbacks(struct softirq_action *unused);
46 static void __call_rcu(struct rcu_head *head,
47 		       void (*func)(struct rcu_head *rcu),
48 		       struct rcu_ctrlblk *rcp);
49 
50 static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
51 
52 #include "tiny_plugin.h"
53 
54 /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcu/tree.c. */
55 static void rcu_idle_enter_common(long long newval)
56 {
57 	if (newval) {
58 		RCU_TRACE(trace_rcu_dyntick(TPS("--="),
59 					    rcu_dynticks_nesting, newval));
60 		rcu_dynticks_nesting = newval;
61 		return;
62 	}
63 	RCU_TRACE(trace_rcu_dyntick(TPS("Start"),
64 				    rcu_dynticks_nesting, newval));
65 	if (IS_ENABLED(CONFIG_RCU_TRACE) && !is_idle_task(current)) {
66 		struct task_struct *idle __maybe_unused = idle_task(smp_processor_id());
67 
68 		RCU_TRACE(trace_rcu_dyntick(TPS("Entry error: not idle task"),
69 					    rcu_dynticks_nesting, newval));
70 		ftrace_dump(DUMP_ALL);
71 		WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
72 			  current->pid, current->comm,
73 			  idle->pid, idle->comm); /* must be idle task! */
74 	}
75 	rcu_sched_qs(); /* implies rcu_bh_inc() */
76 	barrier();
77 	rcu_dynticks_nesting = newval;
78 }
79 
80 /*
81  * Enter idle, which is an extended quiescent state if we have fully
82  * entered that mode (i.e., if the new value of dynticks_nesting is zero).
83  */
84 void rcu_idle_enter(void)
85 {
86 	unsigned long flags;
87 	long long newval;
88 
89 	local_irq_save(flags);
90 	WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
91 	if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) ==
92 	    DYNTICK_TASK_NEST_VALUE)
93 		newval = 0;
94 	else
95 		newval = rcu_dynticks_nesting - DYNTICK_TASK_NEST_VALUE;
96 	rcu_idle_enter_common(newval);
97 	local_irq_restore(flags);
98 }
99 EXPORT_SYMBOL_GPL(rcu_idle_enter);
100 
101 /*
102  * Exit an interrupt handler towards idle.
103  */
104 void rcu_irq_exit(void)
105 {
106 	unsigned long flags;
107 	long long newval;
108 
109 	local_irq_save(flags);
110 	newval = rcu_dynticks_nesting - 1;
111 	WARN_ON_ONCE(newval < 0);
112 	rcu_idle_enter_common(newval);
113 	local_irq_restore(flags);
114 }
115 EXPORT_SYMBOL_GPL(rcu_irq_exit);
116 
117 /* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcu/tree.c. */
118 static void rcu_idle_exit_common(long long oldval)
119 {
120 	if (oldval) {
121 		RCU_TRACE(trace_rcu_dyntick(TPS("++="),
122 					    oldval, rcu_dynticks_nesting));
123 		return;
124 	}
125 	RCU_TRACE(trace_rcu_dyntick(TPS("End"), oldval, rcu_dynticks_nesting));
126 	if (IS_ENABLED(CONFIG_RCU_TRACE) && !is_idle_task(current)) {
127 		struct task_struct *idle __maybe_unused = idle_task(smp_processor_id());
128 
129 		RCU_TRACE(trace_rcu_dyntick(TPS("Exit error: not idle task"),
130 			  oldval, rcu_dynticks_nesting));
131 		ftrace_dump(DUMP_ALL);
132 		WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
133 			  current->pid, current->comm,
134 			  idle->pid, idle->comm); /* must be idle task! */
135 	}
136 }
137 
138 /*
139  * Exit idle, so that we are no longer in an extended quiescent state.
140  */
141 void rcu_idle_exit(void)
142 {
143 	unsigned long flags;
144 	long long oldval;
145 
146 	local_irq_save(flags);
147 	oldval = rcu_dynticks_nesting;
148 	WARN_ON_ONCE(rcu_dynticks_nesting < 0);
149 	if (rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK)
150 		rcu_dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
151 	else
152 		rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
153 	rcu_idle_exit_common(oldval);
154 	local_irq_restore(flags);
155 }
156 EXPORT_SYMBOL_GPL(rcu_idle_exit);
157 
158 /*
159  * Enter an interrupt handler, moving away from idle.
160  */
161 void rcu_irq_enter(void)
162 {
163 	unsigned long flags;
164 	long long oldval;
165 
166 	local_irq_save(flags);
167 	oldval = rcu_dynticks_nesting;
168 	rcu_dynticks_nesting++;
169 	WARN_ON_ONCE(rcu_dynticks_nesting == 0);
170 	rcu_idle_exit_common(oldval);
171 	local_irq_restore(flags);
172 }
173 EXPORT_SYMBOL_GPL(rcu_irq_enter);
174 
175 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE)
176 
177 /*
178  * Test whether RCU thinks that the current CPU is idle.
179  */
180 bool notrace __rcu_is_watching(void)
181 {
182 	return rcu_dynticks_nesting;
183 }
184 EXPORT_SYMBOL(__rcu_is_watching);
185 
186 #endif /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */
187 
188 /*
189  * Test whether the current CPU was interrupted from idle.  Nested
190  * interrupts don't count, we must be running at the first interrupt
191  * level.
192  */
193 static int rcu_is_cpu_rrupt_from_idle(void)
194 {
195 	return rcu_dynticks_nesting <= 1;
196 }
197 
198 /*
199  * Helper function for rcu_sched_qs() and rcu_bh_qs().
200  * Also irqs are disabled to avoid confusion due to interrupt handlers
201  * invoking call_rcu().
202  */
203 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
204 {
205 	RCU_TRACE(reset_cpu_stall_ticks(rcp));
206 	if (rcp->rcucblist != NULL &&
207 	    rcp->donetail != rcp->curtail) {
208 		rcp->donetail = rcp->curtail;
209 		return 1;
210 	}
211 
212 	return 0;
213 }
214 
215 /*
216  * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
217  * are at it, given that any rcu quiescent state is also an rcu_bh
218  * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
219  */
220 void rcu_sched_qs(void)
221 {
222 	unsigned long flags;
223 
224 	local_irq_save(flags);
225 	if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
226 	    rcu_qsctr_help(&rcu_bh_ctrlblk))
227 		raise_softirq(RCU_SOFTIRQ);
228 	local_irq_restore(flags);
229 }
230 
231 /*
232  * Record an rcu_bh quiescent state.
233  */
234 void rcu_bh_qs(void)
235 {
236 	unsigned long flags;
237 
238 	local_irq_save(flags);
239 	if (rcu_qsctr_help(&rcu_bh_ctrlblk))
240 		raise_softirq(RCU_SOFTIRQ);
241 	local_irq_restore(flags);
242 }
243 
244 /*
245  * Check to see if the scheduling-clock interrupt came from an extended
246  * quiescent state, and, if so, tell RCU about it.  This function must
247  * be called from hardirq context.  It is normally called from the
248  * scheduling-clock interrupt.
249  */
250 void rcu_check_callbacks(int cpu, int user)
251 {
252 	RCU_TRACE(check_cpu_stalls());
253 	if (user || rcu_is_cpu_rrupt_from_idle())
254 		rcu_sched_qs();
255 	else if (!in_softirq())
256 		rcu_bh_qs();
257 	if (user)
258 		rcu_note_voluntary_context_switch(current);
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,
308 				      cb_count, 0, need_resched(),
309 				      is_idle_task(current),
310 				      false));
311 }
312 
313 static void rcu_process_callbacks(struct softirq_action *unused)
314 {
315 	__rcu_process_callbacks(&rcu_sched_ctrlblk);
316 	__rcu_process_callbacks(&rcu_bh_ctrlblk);
317 }
318 
319 /*
320  * Wait for a grace period to elapse.  But it is illegal to invoke
321  * synchronize_sched() from within an RCU read-side critical section.
322  * Therefore, any legal call to synchronize_sched() is a quiescent
323  * state, and so on a UP system, synchronize_sched() need do nothing.
324  * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
325  * benefits of doing might_sleep() to reduce latency.)
326  *
327  * Cool, huh?  (Due to Josh Triplett.)
328  *
329  * But we want to make this a static inline later.  The cond_resched()
330  * currently makes this problematic.
331  */
332 void synchronize_sched(void)
333 {
334 	rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
335 			   !lock_is_held(&rcu_lock_map) &&
336 			   !lock_is_held(&rcu_sched_lock_map),
337 			   "Illegal synchronize_sched() in RCU read-side critical section");
338 	cond_resched();
339 }
340 EXPORT_SYMBOL_GPL(synchronize_sched);
341 
342 /*
343  * Helper function for call_rcu() and call_rcu_bh().
344  */
345 static void __call_rcu(struct rcu_head *head,
346 		       void (*func)(struct rcu_head *rcu),
347 		       struct rcu_ctrlblk *rcp)
348 {
349 	unsigned long flags;
350 
351 	debug_rcu_head_queue(head);
352 	head->func = func;
353 	head->next = NULL;
354 
355 	local_irq_save(flags);
356 	*rcp->curtail = head;
357 	rcp->curtail = &head->next;
358 	RCU_TRACE(rcp->qlen++);
359 	local_irq_restore(flags);
360 }
361 
362 /*
363  * Post an RCU callback to be invoked after the end of an RCU-sched grace
364  * period.  But since we have but one CPU, that would be after any
365  * quiescent state.
366  */
367 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
368 {
369 	__call_rcu(head, func, &rcu_sched_ctrlblk);
370 }
371 EXPORT_SYMBOL_GPL(call_rcu_sched);
372 
373 /*
374  * Post an RCU bottom-half callback to be invoked after any subsequent
375  * quiescent state.
376  */
377 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
378 {
379 	__call_rcu(head, func, &rcu_bh_ctrlblk);
380 }
381 EXPORT_SYMBOL_GPL(call_rcu_bh);
382 
383 void rcu_init(void)
384 {
385 	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
386 }
387