1 /*
2 * Read-Copy Update mechanism for mutual exclusion
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, 2001
19 *
20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
21 * Manfred Spraul <manfred@colorfullife.com>
22 *
23 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
24 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
25 * Papers:
26 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
27 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
28 *
29 * For detailed explanation of Read-Copy Update mechanism see -
30 * http://lse.sourceforge.net/locking/rcupdate.html
31 *
32 */
33 #include <linux/types.h>
34 #include <linux/kernel.h>
35 #include <linux/init.h>
36 #include <linux/spinlock.h>
37 #include <linux/smp.h>
38 #include <linux/interrupt.h>
39 #include <linux/sched.h>
40 #include <linux/atomic.h>
41 #include <linux/bitops.h>
42 #include <linux/percpu.h>
43 #include <linux/notifier.h>
44 #include <linux/cpu.h>
45 #include <linux/mutex.h>
46 #include <linux/export.h>
47 #include <linux/hardirq.h>
48
49 #define CREATE_TRACE_POINTS
50 #include <trace/events/rcu.h>
51
52 #include "rcu.h"
53
54 #ifdef CONFIG_DEBUG_LOCK_ALLOC
55 static struct lock_class_key rcu_lock_key;
56 struct lockdep_map rcu_lock_map =
57 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
58 EXPORT_SYMBOL_GPL(rcu_lock_map);
59
60 static struct lock_class_key rcu_bh_lock_key;
61 struct lockdep_map rcu_bh_lock_map =
62 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
63 EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
64
65 static struct lock_class_key rcu_sched_lock_key;
66 struct lockdep_map rcu_sched_lock_map =
67 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
68 EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
69 #endif
70
71 #ifdef CONFIG_DEBUG_LOCK_ALLOC
72
debug_lockdep_rcu_enabled(void)73 int debug_lockdep_rcu_enabled(void)
74 {
75 return rcu_scheduler_active && debug_locks &&
76 current->lockdep_recursion == 0;
77 }
78 EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
79
80 /**
81 * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
82 *
83 * Check for bottom half being disabled, which covers both the
84 * CONFIG_PROVE_RCU and not cases. Note that if someone uses
85 * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
86 * will show the situation. This is useful for debug checks in functions
87 * that require that they be called within an RCU read-side critical
88 * section.
89 *
90 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
91 *
92 * Note that rcu_read_lock() is disallowed if the CPU is either idle or
93 * offline from an RCU perspective, so check for those as well.
94 */
rcu_read_lock_bh_held(void)95 int rcu_read_lock_bh_held(void)
96 {
97 if (!debug_lockdep_rcu_enabled())
98 return 1;
99 if (rcu_is_cpu_idle())
100 return 0;
101 if (!rcu_lockdep_current_cpu_online())
102 return 0;
103 return in_softirq() || irqs_disabled();
104 }
105 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
106
107 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
108
109 struct rcu_synchronize {
110 struct rcu_head head;
111 struct completion completion;
112 };
113
114 /*
115 * Awaken the corresponding synchronize_rcu() instance now that a
116 * grace period has elapsed.
117 */
wakeme_after_rcu(struct rcu_head * head)118 static void wakeme_after_rcu(struct rcu_head *head)
119 {
120 struct rcu_synchronize *rcu;
121
122 rcu = container_of(head, struct rcu_synchronize, head);
123 complete(&rcu->completion);
124 }
125
wait_rcu_gp(call_rcu_func_t crf)126 void wait_rcu_gp(call_rcu_func_t crf)
127 {
128 struct rcu_synchronize rcu;
129
130 init_rcu_head_on_stack(&rcu.head);
131 init_completion(&rcu.completion);
132 /* Will wake me after RCU finished. */
133 crf(&rcu.head, wakeme_after_rcu);
134 /* Wait for it. */
135 wait_for_completion(&rcu.completion);
136 destroy_rcu_head_on_stack(&rcu.head);
137 }
138 EXPORT_SYMBOL_GPL(wait_rcu_gp);
139
140 #ifdef CONFIG_PROVE_RCU
141 /*
142 * wrapper function to avoid #include problems.
143 */
rcu_my_thread_group_empty(void)144 int rcu_my_thread_group_empty(void)
145 {
146 return thread_group_empty(current);
147 }
148 EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
149 #endif /* #ifdef CONFIG_PROVE_RCU */
150
151 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
debug_init_rcu_head(struct rcu_head * head)152 static inline void debug_init_rcu_head(struct rcu_head *head)
153 {
154 debug_object_init(head, &rcuhead_debug_descr);
155 }
156
debug_rcu_head_free(struct rcu_head * head)157 static inline void debug_rcu_head_free(struct rcu_head *head)
158 {
159 debug_object_free(head, &rcuhead_debug_descr);
160 }
161
162 /*
163 * fixup_init is called when:
164 * - an active object is initialized
165 */
rcuhead_fixup_init(void * addr,enum debug_obj_state state)166 static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
167 {
168 struct rcu_head *head = addr;
169
170 switch (state) {
171 case ODEBUG_STATE_ACTIVE:
172 /*
173 * Ensure that queued callbacks are all executed.
174 * If we detect that we are nested in a RCU read-side critical
175 * section, we should simply fail, otherwise we would deadlock.
176 * In !PREEMPT configurations, there is no way to tell if we are
177 * in a RCU read-side critical section or not, so we never
178 * attempt any fixup and just print a warning.
179 */
180 #ifndef CONFIG_PREEMPT
181 WARN_ON_ONCE(1);
182 return 0;
183 #endif
184 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
185 irqs_disabled()) {
186 WARN_ON_ONCE(1);
187 return 0;
188 }
189 rcu_barrier();
190 rcu_barrier_sched();
191 rcu_barrier_bh();
192 debug_object_init(head, &rcuhead_debug_descr);
193 return 1;
194 default:
195 return 0;
196 }
197 }
198
199 /*
200 * fixup_activate is called when:
201 * - an active object is activated
202 * - an unknown object is activated (might be a statically initialized object)
203 * Activation is performed internally by call_rcu().
204 */
rcuhead_fixup_activate(void * addr,enum debug_obj_state state)205 static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
206 {
207 struct rcu_head *head = addr;
208
209 switch (state) {
210
211 case ODEBUG_STATE_NOTAVAILABLE:
212 /*
213 * This is not really a fixup. We just make sure that it is
214 * tracked in the object tracker.
215 */
216 debug_object_init(head, &rcuhead_debug_descr);
217 debug_object_activate(head, &rcuhead_debug_descr);
218 return 0;
219
220 case ODEBUG_STATE_ACTIVE:
221 /*
222 * Ensure that queued callbacks are all executed.
223 * If we detect that we are nested in a RCU read-side critical
224 * section, we should simply fail, otherwise we would deadlock.
225 * In !PREEMPT configurations, there is no way to tell if we are
226 * in a RCU read-side critical section or not, so we never
227 * attempt any fixup and just print a warning.
228 */
229 #ifndef CONFIG_PREEMPT
230 WARN_ON_ONCE(1);
231 return 0;
232 #endif
233 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
234 irqs_disabled()) {
235 WARN_ON_ONCE(1);
236 return 0;
237 }
238 rcu_barrier();
239 rcu_barrier_sched();
240 rcu_barrier_bh();
241 debug_object_activate(head, &rcuhead_debug_descr);
242 return 1;
243 default:
244 return 0;
245 }
246 }
247
248 /*
249 * fixup_free is called when:
250 * - an active object is freed
251 */
rcuhead_fixup_free(void * addr,enum debug_obj_state state)252 static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
253 {
254 struct rcu_head *head = addr;
255
256 switch (state) {
257 case ODEBUG_STATE_ACTIVE:
258 /*
259 * Ensure that queued callbacks are all executed.
260 * If we detect that we are nested in a RCU read-side critical
261 * section, we should simply fail, otherwise we would deadlock.
262 * In !PREEMPT configurations, there is no way to tell if we are
263 * in a RCU read-side critical section or not, so we never
264 * attempt any fixup and just print a warning.
265 */
266 #ifndef CONFIG_PREEMPT
267 WARN_ON_ONCE(1);
268 return 0;
269 #endif
270 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
271 irqs_disabled()) {
272 WARN_ON_ONCE(1);
273 return 0;
274 }
275 rcu_barrier();
276 rcu_barrier_sched();
277 rcu_barrier_bh();
278 debug_object_free(head, &rcuhead_debug_descr);
279 return 1;
280 default:
281 return 0;
282 }
283 }
284
285 /**
286 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
287 * @head: pointer to rcu_head structure to be initialized
288 *
289 * This function informs debugobjects of a new rcu_head structure that
290 * has been allocated as an auto variable on the stack. This function
291 * is not required for rcu_head structures that are statically defined or
292 * that are dynamically allocated on the heap. This function has no
293 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
294 */
init_rcu_head_on_stack(struct rcu_head * head)295 void init_rcu_head_on_stack(struct rcu_head *head)
296 {
297 debug_object_init_on_stack(head, &rcuhead_debug_descr);
298 }
299 EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
300
301 /**
302 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
303 * @head: pointer to rcu_head structure to be initialized
304 *
305 * This function informs debugobjects that an on-stack rcu_head structure
306 * is about to go out of scope. As with init_rcu_head_on_stack(), this
307 * function is not required for rcu_head structures that are statically
308 * defined or that are dynamically allocated on the heap. Also as with
309 * init_rcu_head_on_stack(), this function has no effect for
310 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
311 */
destroy_rcu_head_on_stack(struct rcu_head * head)312 void destroy_rcu_head_on_stack(struct rcu_head *head)
313 {
314 debug_object_free(head, &rcuhead_debug_descr);
315 }
316 EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
317
318 struct debug_obj_descr rcuhead_debug_descr = {
319 .name = "rcu_head",
320 .fixup_init = rcuhead_fixup_init,
321 .fixup_activate = rcuhead_fixup_activate,
322 .fixup_free = rcuhead_fixup_free,
323 };
324 EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
325 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
326
327 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
do_trace_rcu_torture_read(char * rcutorturename,struct rcu_head * rhp)328 void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp)
329 {
330 trace_rcu_torture_read(rcutorturename, rhp);
331 }
332 EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
333 #else
334 #define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
335 #endif
336