1 /* SPDX-License-Identifier: GPL-2.0+ */
2 /*
3  * Sleepable Read-Copy Update mechanism for mutual exclusion
4  *
5  * Copyright (C) IBM Corporation, 2006
6  * Copyright (C) Fujitsu, 2012
7  *
8  * Author: Paul McKenney <paulmck@linux.ibm.com>
9  *	   Lai Jiangshan <laijs@cn.fujitsu.com>
10  *
11  * For detailed explanation of Read-Copy Update mechanism see -
12  *		Documentation/RCU/ *.txt
13  *
14  */
15 
16 #ifndef _LINUX_SRCU_H
17 #define _LINUX_SRCU_H
18 
19 #include <linux/mutex.h>
20 #include <linux/rcupdate.h>
21 #include <linux/workqueue.h>
22 #include <linux/rcu_segcblist.h>
23 
24 struct srcu_struct;
25 
26 #ifdef CONFIG_DEBUG_LOCK_ALLOC
27 
28 int __init_srcu_struct(struct srcu_struct *ssp, const char *name,
29 		       struct lock_class_key *key);
30 
31 #define init_srcu_struct(ssp) \
32 ({ \
33 	static struct lock_class_key __srcu_key; \
34 	\
35 	__init_srcu_struct((ssp), #ssp, &__srcu_key); \
36 })
37 
38 #define __SRCU_DEP_MAP_INIT(srcu_name)	.dep_map = { .name = #srcu_name },
39 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
40 
41 int init_srcu_struct(struct srcu_struct *ssp);
42 
43 #define __SRCU_DEP_MAP_INIT(srcu_name)
44 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
45 
46 #ifdef CONFIG_TINY_SRCU
47 #include <linux/srcutiny.h>
48 #elif defined(CONFIG_TREE_SRCU)
49 #include <linux/srcutree.h>
50 #elif defined(CONFIG_SRCU)
51 #error "Unknown SRCU implementation specified to kernel configuration"
52 #else
53 /* Dummy definition for things like notifiers.  Actual use gets link error. */
54 struct srcu_struct { };
55 #endif
56 
57 void call_srcu(struct srcu_struct *ssp, struct rcu_head *head,
58 		void (*func)(struct rcu_head *head));
59 void cleanup_srcu_struct(struct srcu_struct *ssp);
60 int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp);
61 void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
62 void synchronize_srcu(struct srcu_struct *ssp);
63 unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp);
64 unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp);
65 bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie);
66 
67 #ifdef CONFIG_SRCU
68 void srcu_init(void);
69 #else /* #ifdef CONFIG_SRCU */
srcu_init(void)70 static inline void srcu_init(void) { }
71 #endif /* #else #ifdef CONFIG_SRCU */
72 
73 #ifdef CONFIG_DEBUG_LOCK_ALLOC
74 
75 /**
76  * srcu_read_lock_held - might we be in SRCU read-side critical section?
77  * @ssp: The srcu_struct structure to check
78  *
79  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
80  * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
81  * this assumes we are in an SRCU read-side critical section unless it can
82  * prove otherwise.
83  *
84  * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
85  * and while lockdep is disabled.
86  *
87  * Note that SRCU is based on its own statemachine and it doesn't
88  * relies on normal RCU, it can be called from the CPU which
89  * is in the idle loop from an RCU point of view or offline.
90  */
srcu_read_lock_held(const struct srcu_struct * ssp)91 static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
92 {
93 	if (!debug_lockdep_rcu_enabled())
94 		return 1;
95 	return lock_is_held(&ssp->dep_map);
96 }
97 
98 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
99 
srcu_read_lock_held(const struct srcu_struct * ssp)100 static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
101 {
102 	return 1;
103 }
104 
105 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
106 
107 /**
108  * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
109  * @p: the pointer to fetch and protect for later dereferencing
110  * @ssp: pointer to the srcu_struct, which is used to check that we
111  *	really are in an SRCU read-side critical section.
112  * @c: condition to check for update-side use
113  *
114  * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
115  * critical section will result in an RCU-lockdep splat, unless @c evaluates
116  * to 1.  The @c argument will normally be a logical expression containing
117  * lockdep_is_held() calls.
118  */
119 #define srcu_dereference_check(p, ssp, c) \
120 	__rcu_dereference_check((p), __UNIQUE_ID(rcu), \
121 				(c) || srcu_read_lock_held(ssp), __rcu)
122 
123 /**
124  * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
125  * @p: the pointer to fetch and protect for later dereferencing
126  * @ssp: pointer to the srcu_struct, which is used to check that we
127  *	really are in an SRCU read-side critical section.
128  *
129  * Makes rcu_dereference_check() do the dirty work.  If PROVE_RCU
130  * is enabled, invoking this outside of an RCU read-side critical
131  * section will result in an RCU-lockdep splat.
132  */
133 #define srcu_dereference(p, ssp) srcu_dereference_check((p), (ssp), 0)
134 
135 /**
136  * srcu_dereference_notrace - no tracing and no lockdep calls from here
137  * @p: the pointer to fetch and protect for later dereferencing
138  * @ssp: pointer to the srcu_struct, which is used to check that we
139  *	really are in an SRCU read-side critical section.
140  */
141 #define srcu_dereference_notrace(p, ssp) srcu_dereference_check((p), (ssp), 1)
142 
143 /**
144  * srcu_read_lock - register a new reader for an SRCU-protected structure.
145  * @ssp: srcu_struct in which to register the new reader.
146  *
147  * Enter an SRCU read-side critical section.  Note that SRCU read-side
148  * critical sections may be nested.  However, it is illegal to
149  * call anything that waits on an SRCU grace period for the same
150  * srcu_struct, whether directly or indirectly.  Please note that
151  * one way to indirectly wait on an SRCU grace period is to acquire
152  * a mutex that is held elsewhere while calling synchronize_srcu() or
153  * synchronize_srcu_expedited().
154  *
155  * Note that srcu_read_lock() and the matching srcu_read_unlock() must
156  * occur in the same context, for example, it is illegal to invoke
157  * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
158  * was invoked in process context.
159  */
srcu_read_lock(struct srcu_struct * ssp)160 static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
161 {
162 	int retval;
163 
164 	retval = __srcu_read_lock(ssp);
165 	rcu_lock_acquire(&(ssp)->dep_map);
166 	return retval;
167 }
168 
169 /* Used by tracing, cannot be traced and cannot invoke lockdep. */
170 static inline notrace int
srcu_read_lock_notrace(struct srcu_struct * ssp)171 srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
172 {
173 	int retval;
174 
175 	retval = __srcu_read_lock(ssp);
176 	return retval;
177 }
178 
179 /**
180  * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
181  * @ssp: srcu_struct in which to unregister the old reader.
182  * @idx: return value from corresponding srcu_read_lock().
183  *
184  * Exit an SRCU read-side critical section.
185  */
srcu_read_unlock(struct srcu_struct * ssp,int idx)186 static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
187 	__releases(ssp)
188 {
189 	WARN_ON_ONCE(idx & ~0x1);
190 	rcu_lock_release(&(ssp)->dep_map);
191 	__srcu_read_unlock(ssp, idx);
192 }
193 
194 /* Used by tracing, cannot be traced and cannot call lockdep. */
195 static inline notrace void
srcu_read_unlock_notrace(struct srcu_struct * ssp,int idx)196 srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp)
197 {
198 	__srcu_read_unlock(ssp, idx);
199 }
200 
201 /**
202  * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
203  *
204  * Converts the preceding srcu_read_unlock into a two-way memory barrier.
205  *
206  * Call this after srcu_read_unlock, to guarantee that all memory operations
207  * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
208  * the preceding srcu_read_unlock.
209  */
smp_mb__after_srcu_read_unlock(void)210 static inline void smp_mb__after_srcu_read_unlock(void)
211 {
212 	/* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
213 }
214 
215 #endif
216