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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 <asm/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/module.h>
47 #include <linux/hardirq.h>
48
49 #ifdef CONFIG_DEBUG_LOCK_ALLOC
50 static struct lock_class_key rcu_lock_key;
51 struct lockdep_map rcu_lock_map =
52 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
53 EXPORT_SYMBOL_GPL(rcu_lock_map);
54
55 static struct lock_class_key rcu_bh_lock_key;
56 struct lockdep_map rcu_bh_lock_map =
57 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
58 EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
59
60 static struct lock_class_key rcu_sched_lock_key;
61 struct lockdep_map rcu_sched_lock_map =
62 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
63 EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
64 #endif
65
66 #ifdef CONFIG_DEBUG_LOCK_ALLOC
67
68 int debug_lockdep_rcu_enabled(void)
69 {
70 return rcu_scheduler_active && debug_locks &&
71 current->lockdep_recursion == 0;
72 }
73 EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
74
75 /**
76 * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
77 *
78 * Check for bottom half being disabled, which covers both the
79 * CONFIG_PROVE_RCU and not cases. Note that if someone uses
80 * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
81 * will show the situation. This is useful for debug checks in functions
82 * that require that they be called within an RCU read-side critical
83 * section.
84 *
85 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
86 */
87 int rcu_read_lock_bh_held(void)
88 {
89 if (!debug_lockdep_rcu_enabled())
90 return 1;
91 return in_softirq() || irqs_disabled();
92 }
93 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
94
95 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
96
97 /*
98 * Awaken the corresponding synchronize_rcu() instance now that a
99 * grace period has elapsed.
100 */
101 void wakeme_after_rcu(struct rcu_head *head)
102 {
103 struct rcu_synchronize *rcu;
104
105 rcu = container_of(head, struct rcu_synchronize, head);
106 complete(&rcu->completion);
107 }
108
109 #ifdef CONFIG_PROVE_RCU
110 /*
111 * wrapper function to avoid #include problems.
112 */
113 int rcu_my_thread_group_empty(void)
114 {
115 return thread_group_empty(current);
116 }
117 EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
118 #endif /* #ifdef CONFIG_PROVE_RCU */
119
120 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
121 static inline void debug_init_rcu_head(struct rcu_head *head)
122 {
123 debug_object_init(head, &rcuhead_debug_descr);
124 }
125
126 static inline void debug_rcu_head_free(struct rcu_head *head)
127 {
128 debug_object_free(head, &rcuhead_debug_descr);
129 }
130
131 /*
132 * fixup_init is called when:
133 * - an active object is initialized
134 */
135 static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
136 {
137 struct rcu_head *head = addr;
138
139 switch (state) {
140 case ODEBUG_STATE_ACTIVE:
141 /*
142 * Ensure that queued callbacks are all executed.
143 * If we detect that we are nested in a RCU read-side critical
144 * section, we should simply fail, otherwise we would deadlock.
145 */
146 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
147 irqs_disabled()) {
148 WARN_ON(1);
149 return 0;
150 }
151 rcu_barrier();
152 rcu_barrier_sched();
153 rcu_barrier_bh();
154 debug_object_init(head, &rcuhead_debug_descr);
155 return 1;
156 default:
157 return 0;
158 }
159 }
160
161 /*
162 * fixup_activate is called when:
163 * - an active object is activated
164 * - an unknown object is activated (might be a statically initialized object)
165 * Activation is performed internally by call_rcu().
166 */
167 static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
168 {
169 struct rcu_head *head = addr;
170
171 switch (state) {
172
173 case ODEBUG_STATE_NOTAVAILABLE:
174 /*
175 * This is not really a fixup. We just make sure that it is
176 * tracked in the object tracker.
177 */
178 debug_object_init(head, &rcuhead_debug_descr);
179 debug_object_activate(head, &rcuhead_debug_descr);
180 return 0;
181
182 case ODEBUG_STATE_ACTIVE:
183 /*
184 * Ensure that queued callbacks are all executed.
185 * If we detect that we are nested in a RCU read-side critical
186 * section, we should simply fail, otherwise we would deadlock.
187 */
188 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
189 irqs_disabled()) {
190 WARN_ON(1);
191 return 0;
192 }
193 rcu_barrier();
194 rcu_barrier_sched();
195 rcu_barrier_bh();
196 debug_object_activate(head, &rcuhead_debug_descr);
197 return 1;
198 default:
199 return 0;
200 }
201 }
202
203 /*
204 * fixup_free is called when:
205 * - an active object is freed
206 */
207 static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
208 {
209 struct rcu_head *head = addr;
210
211 switch (state) {
212 case ODEBUG_STATE_ACTIVE:
213 /*
214 * Ensure that queued callbacks are all executed.
215 * If we detect that we are nested in a RCU read-side critical
216 * section, we should simply fail, otherwise we would deadlock.
217 */
218 #ifndef CONFIG_PREEMPT
219 WARN_ON(1);
220 return 0;
221 #else
222 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
223 irqs_disabled()) {
224 WARN_ON(1);
225 return 0;
226 }
227 rcu_barrier();
228 rcu_barrier_sched();
229 rcu_barrier_bh();
230 debug_object_free(head, &rcuhead_debug_descr);
231 return 1;
232 #endif
233 default:
234 return 0;
235 }
236 }
237
238 /**
239 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
240 * @head: pointer to rcu_head structure to be initialized
241 *
242 * This function informs debugobjects of a new rcu_head structure that
243 * has been allocated as an auto variable on the stack. This function
244 * is not required for rcu_head structures that are statically defined or
245 * that are dynamically allocated on the heap. This function has no
246 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
247 */
248 void init_rcu_head_on_stack(struct rcu_head *head)
249 {
250 debug_object_init_on_stack(head, &rcuhead_debug_descr);
251 }
252 EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
253
254 /**
255 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
256 * @head: pointer to rcu_head structure to be initialized
257 *
258 * This function informs debugobjects that an on-stack rcu_head structure
259 * is about to go out of scope. As with init_rcu_head_on_stack(), this
260 * function is not required for rcu_head structures that are statically
261 * defined or that are dynamically allocated on the heap. Also as with
262 * init_rcu_head_on_stack(), this function has no effect for
263 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
264 */
265 void destroy_rcu_head_on_stack(struct rcu_head *head)
266 {
267 debug_object_free(head, &rcuhead_debug_descr);
268 }
269 EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
270
271 struct debug_obj_descr rcuhead_debug_descr = {
272 .name = "rcu_head",
273 .fixup_init = rcuhead_fixup_init,
274 .fixup_activate = rcuhead_fixup_activate,
275 .fixup_free = rcuhead_fixup_free,
276 };
277 EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
278 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */