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1 /*
2  * Sleepable 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, you can access it online at
16  * http://www.gnu.org/licenses/gpl-2.0.html.
17  *
18  * Copyright (C) IBM Corporation, 2006
19  * Copyright (C) Fujitsu, 2012
20  *
21  * Author: Paul McKenney <paulmck@us.ibm.com>
22  *	   Lai Jiangshan <laijs@cn.fujitsu.com>
23  *
24  * For detailed explanation of Read-Copy Update mechanism see -
25  * 		Documentation/RCU/ *.txt
26  *
27  */
28 
29 #ifndef _LINUX_SRCU_H
30 #define _LINUX_SRCU_H
31 
32 #include <linux/mutex.h>
33 #include <linux/rcupdate.h>
34 #include <linux/workqueue.h>
35 
36 struct srcu_struct_array {
37 	unsigned long c[2];
38 	unsigned long seq[2];
39 };
40 
41 struct rcu_batch {
42 	struct rcu_head *head, **tail;
43 };
44 
45 #define RCU_BATCH_INIT(name) { NULL, &(name.head) }
46 
47 struct srcu_struct {
48 	unsigned completed;
49 	struct srcu_struct_array __percpu *per_cpu_ref;
50 	spinlock_t queue_lock; /* protect ->batch_queue, ->running */
51 	bool running;
52 	/* callbacks just queued */
53 	struct rcu_batch batch_queue;
54 	/* callbacks try to do the first check_zero */
55 	struct rcu_batch batch_check0;
56 	/* callbacks done with the first check_zero and the flip */
57 	struct rcu_batch batch_check1;
58 	struct rcu_batch batch_done;
59 	struct delayed_work work;
60 #ifdef CONFIG_DEBUG_LOCK_ALLOC
61 	struct lockdep_map dep_map;
62 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
63 };
64 
65 #ifdef CONFIG_DEBUG_LOCK_ALLOC
66 
67 int __init_srcu_struct(struct srcu_struct *sp, const char *name,
68 		       struct lock_class_key *key);
69 
70 #define init_srcu_struct(sp) \
71 ({ \
72 	static struct lock_class_key __srcu_key; \
73 	\
74 	__init_srcu_struct((sp), #sp, &__srcu_key); \
75 })
76 
77 #define __SRCU_DEP_MAP_INIT(srcu_name)	.dep_map = { .name = #srcu_name },
78 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
79 
80 int init_srcu_struct(struct srcu_struct *sp);
81 
82 #define __SRCU_DEP_MAP_INIT(srcu_name)
83 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
84 
85 void process_srcu(struct work_struct *work);
86 
87 #define __SRCU_STRUCT_INIT(name)					\
88 	{								\
89 		.completed = -300,					\
90 		.per_cpu_ref = &name##_srcu_array,			\
91 		.queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock),	\
92 		.running = false,					\
93 		.batch_queue = RCU_BATCH_INIT(name.batch_queue),	\
94 		.batch_check0 = RCU_BATCH_INIT(name.batch_check0),	\
95 		.batch_check1 = RCU_BATCH_INIT(name.batch_check1),	\
96 		.batch_done = RCU_BATCH_INIT(name.batch_done),		\
97 		.work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\
98 		__SRCU_DEP_MAP_INIT(name)				\
99 	}
100 
101 /*
102  * define and init a srcu struct at build time.
103  * dont't call init_srcu_struct() nor cleanup_srcu_struct() on it.
104  */
105 #define DEFINE_SRCU(name)						\
106 	static DEFINE_PER_CPU(struct srcu_struct_array, name##_srcu_array);\
107 	struct srcu_struct name = __SRCU_STRUCT_INIT(name);
108 
109 #define DEFINE_STATIC_SRCU(name)					\
110 	static DEFINE_PER_CPU(struct srcu_struct_array, name##_srcu_array);\
111 	static struct srcu_struct name = __SRCU_STRUCT_INIT(name);
112 
113 /**
114  * call_srcu() - Queue a callback for invocation after an SRCU grace period
115  * @sp: srcu_struct in queue the callback
116  * @head: structure to be used for queueing the SRCU callback.
117  * @func: function to be invoked after the SRCU grace period
118  *
119  * The callback function will be invoked some time after a full SRCU
120  * grace period elapses, in other words after all pre-existing SRCU
121  * read-side critical sections have completed.  However, the callback
122  * function might well execute concurrently with other SRCU read-side
123  * critical sections that started after call_srcu() was invoked.  SRCU
124  * read-side critical sections are delimited by srcu_read_lock() and
125  * srcu_read_unlock(), and may be nested.
126  *
127  * The callback will be invoked from process context, but must nevertheless
128  * be fast and must not block.
129  */
130 void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
131 		void (*func)(struct rcu_head *head));
132 
133 void cleanup_srcu_struct(struct srcu_struct *sp);
134 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
135 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
136 void synchronize_srcu(struct srcu_struct *sp);
137 void synchronize_srcu_expedited(struct srcu_struct *sp);
138 long srcu_batches_completed(struct srcu_struct *sp);
139 void srcu_barrier(struct srcu_struct *sp);
140 
141 #ifdef CONFIG_DEBUG_LOCK_ALLOC
142 
143 /**
144  * srcu_read_lock_held - might we be in SRCU read-side critical section?
145  *
146  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
147  * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
148  * this assumes we are in an SRCU read-side critical section unless it can
149  * prove otherwise.
150  *
151  * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
152  * and while lockdep is disabled.
153  *
154  * Note that SRCU is based on its own statemachine and it doesn't
155  * relies on normal RCU, it can be called from the CPU which
156  * is in the idle loop from an RCU point of view or offline.
157  */
srcu_read_lock_held(struct srcu_struct * sp)158 static inline int srcu_read_lock_held(struct srcu_struct *sp)
159 {
160 	if (!debug_lockdep_rcu_enabled())
161 		return 1;
162 	return lock_is_held(&sp->dep_map);
163 }
164 
165 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
166 
srcu_read_lock_held(struct srcu_struct * sp)167 static inline int srcu_read_lock_held(struct srcu_struct *sp)
168 {
169 	return 1;
170 }
171 
172 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
173 
174 /**
175  * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
176  * @p: the pointer to fetch and protect for later dereferencing
177  * @sp: pointer to the srcu_struct, which is used to check that we
178  *	really are in an SRCU read-side critical section.
179  * @c: condition to check for update-side use
180  *
181  * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
182  * critical section will result in an RCU-lockdep splat, unless @c evaluates
183  * to 1.  The @c argument will normally be a logical expression containing
184  * lockdep_is_held() calls.
185  */
186 #define srcu_dereference_check(p, sp, c) \
187 	__rcu_dereference_check((p), srcu_read_lock_held(sp) || (c), __rcu)
188 
189 /**
190  * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
191  * @p: the pointer to fetch and protect for later dereferencing
192  * @sp: pointer to the srcu_struct, which is used to check that we
193  *	really are in an SRCU read-side critical section.
194  *
195  * Makes rcu_dereference_check() do the dirty work.  If PROVE_RCU
196  * is enabled, invoking this outside of an RCU read-side critical
197  * section will result in an RCU-lockdep splat.
198  */
199 #define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
200 
201 /**
202  * srcu_read_lock - register a new reader for an SRCU-protected structure.
203  * @sp: srcu_struct in which to register the new reader.
204  *
205  * Enter an SRCU read-side critical section.  Note that SRCU read-side
206  * critical sections may be nested.  However, it is illegal to
207  * call anything that waits on an SRCU grace period for the same
208  * srcu_struct, whether directly or indirectly.  Please note that
209  * one way to indirectly wait on an SRCU grace period is to acquire
210  * a mutex that is held elsewhere while calling synchronize_srcu() or
211  * synchronize_srcu_expedited().
212  *
213  * Note that srcu_read_lock() and the matching srcu_read_unlock() must
214  * occur in the same context, for example, it is illegal to invoke
215  * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
216  * was invoked in process context.
217  */
srcu_read_lock(struct srcu_struct * sp)218 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
219 {
220 	int retval = __srcu_read_lock(sp);
221 
222 	rcu_lock_acquire(&(sp)->dep_map);
223 	return retval;
224 }
225 
226 /**
227  * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
228  * @sp: srcu_struct in which to unregister the old reader.
229  * @idx: return value from corresponding srcu_read_lock().
230  *
231  * Exit an SRCU read-side critical section.
232  */
srcu_read_unlock(struct srcu_struct * sp,int idx)233 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
234 	__releases(sp)
235 {
236 	rcu_lock_release(&(sp)->dep_map);
237 	__srcu_read_unlock(sp, idx);
238 }
239 
240 /**
241  * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
242  *
243  * Converts the preceding srcu_read_unlock into a two-way memory barrier.
244  *
245  * Call this after srcu_read_unlock, to guarantee that all memory operations
246  * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
247  * the preceding srcu_read_unlock.
248  */
smp_mb__after_srcu_read_unlock(void)249 static inline void smp_mb__after_srcu_read_unlock(void)
250 {
251 	/* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
252 }
253 
254 #endif
255