1 /* SPDX-License-Identifier: GPL-2.0+ */
3 * Sleepable Read-Copy Update mechanism for mutual exclusion
5 * Copyright (C) IBM Corporation, 2006
6 * Copyright (C) Fujitsu, 2012
8 * Author: Paul McKenney <paulmck@linux.ibm.com>
9 * Lai Jiangshan <laijs@cn.fujitsu.com>
11 * For detailed explanation of Read-Copy Update mechanism see -
12 * Documentation/RCU/ *.txt
19 #include <linux/mutex.h>
20 #include <linux/rcupdate.h>
21 #include <linux/workqueue.h>
22 #include <linux/rcu_segcblist.h>
26 #ifdef CONFIG_DEBUG_LOCK_ALLOC
28 int __init_srcu_struct(struct srcu_struct *ssp, const char *name,
29 struct lock_class_key *key);
31 #define init_srcu_struct(ssp) \
33 static struct lock_class_key __srcu_key; \
35 __init_srcu_struct((ssp), #ssp, &__srcu_key); \
38 #define __SRCU_DEP_MAP_INIT(srcu_name) .dep_map = { .name = #srcu_name },
39 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
41 int init_srcu_struct(struct srcu_struct *ssp);
43 #define __SRCU_DEP_MAP_INIT(srcu_name)
44 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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"
53 /* Dummy definition for things like notifiers. Actual use gets link error. */
54 struct srcu_struct { };
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, bool quiesced);
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);
65 * cleanup_srcu_struct - deconstruct a sleep-RCU structure
66 * @ssp: structure to clean up.
68 * Must invoke this after you are finished using a given srcu_struct that
69 * was initialized via init_srcu_struct(), else you leak memory.
71 static inline void cleanup_srcu_struct(struct srcu_struct *ssp)
73 _cleanup_srcu_struct(ssp, false);
77 * cleanup_srcu_struct_quiesced - deconstruct a quiesced sleep-RCU structure
78 * @ssp: structure to clean up.
80 * Must invoke this after you are finished using a given srcu_struct that
81 * was initialized via init_srcu_struct(), else you leak memory. Also,
82 * all grace-period processing must have completed.
84 * "Completed" means that the last synchronize_srcu() and
85 * synchronize_srcu_expedited() calls must have returned before the call
86 * to cleanup_srcu_struct_quiesced(). It also means that the callback
87 * from the last call_srcu() must have been invoked before the call to
88 * cleanup_srcu_struct_quiesced(), but you can use srcu_barrier() to help
89 * with this last. Violating these rules will get you a WARN_ON() splat
90 * (with high probability, anyway), and will also cause the srcu_struct
93 static inline void cleanup_srcu_struct_quiesced(struct srcu_struct *ssp)
95 _cleanup_srcu_struct(ssp, true);
98 #ifdef CONFIG_DEBUG_LOCK_ALLOC
101 * srcu_read_lock_held - might we be in SRCU read-side critical section?
102 * @ssp: The srcu_struct structure to check
104 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
105 * read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
106 * this assumes we are in an SRCU read-side critical section unless it can
109 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
110 * and while lockdep is disabled.
112 * Note that SRCU is based on its own statemachine and it doesn't
113 * relies on normal RCU, it can be called from the CPU which
114 * is in the idle loop from an RCU point of view or offline.
116 static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
118 if (!debug_lockdep_rcu_enabled())
120 return lock_is_held(&ssp->dep_map);
123 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
125 static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
130 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
133 * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
134 * @p: the pointer to fetch and protect for later dereferencing
135 * @ssp: pointer to the srcu_struct, which is used to check that we
136 * really are in an SRCU read-side critical section.
137 * @c: condition to check for update-side use
139 * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
140 * critical section will result in an RCU-lockdep splat, unless @c evaluates
141 * to 1. The @c argument will normally be a logical expression containing
142 * lockdep_is_held() calls.
144 #define srcu_dereference_check(p, ssp, c) \
145 __rcu_dereference_check((p), (c) || srcu_read_lock_held(ssp), __rcu)
148 * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
149 * @p: the pointer to fetch and protect for later dereferencing
150 * @ssp: pointer to the srcu_struct, which is used to check that we
151 * really are in an SRCU read-side critical section.
153 * Makes rcu_dereference_check() do the dirty work. If PROVE_RCU
154 * is enabled, invoking this outside of an RCU read-side critical
155 * section will result in an RCU-lockdep splat.
157 #define srcu_dereference(p, ssp) srcu_dereference_check((p), (ssp), 0)
160 * srcu_dereference_notrace - no tracing and no lockdep calls from here
161 * @p: the pointer to fetch and protect for later dereferencing
162 * @ssp: pointer to the srcu_struct, which is used to check that we
163 * really are in an SRCU read-side critical section.
165 #define srcu_dereference_notrace(p, ssp) srcu_dereference_check((p), (ssp), 1)
168 * srcu_read_lock - register a new reader for an SRCU-protected structure.
169 * @ssp: srcu_struct in which to register the new reader.
171 * Enter an SRCU read-side critical section. Note that SRCU read-side
172 * critical sections may be nested. However, it is illegal to
173 * call anything that waits on an SRCU grace period for the same
174 * srcu_struct, whether directly or indirectly. Please note that
175 * one way to indirectly wait on an SRCU grace period is to acquire
176 * a mutex that is held elsewhere while calling synchronize_srcu() or
177 * synchronize_srcu_expedited().
179 * Note that srcu_read_lock() and the matching srcu_read_unlock() must
180 * occur in the same context, for example, it is illegal to invoke
181 * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
182 * was invoked in process context.
184 static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
188 retval = __srcu_read_lock(ssp);
189 rcu_lock_acquire(&(ssp)->dep_map);
193 /* Used by tracing, cannot be traced and cannot invoke lockdep. */
194 static inline notrace int
195 srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
199 retval = __srcu_read_lock(ssp);
204 * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
205 * @ssp: srcu_struct in which to unregister the old reader.
206 * @idx: return value from corresponding srcu_read_lock().
208 * Exit an SRCU read-side critical section.
210 static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
213 WARN_ON_ONCE(idx & ~0x1);
214 rcu_lock_release(&(ssp)->dep_map);
215 __srcu_read_unlock(ssp, idx);
218 /* Used by tracing, cannot be traced and cannot call lockdep. */
219 static inline notrace void
220 srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp)
222 __srcu_read_unlock(ssp, idx);
226 * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
228 * Converts the preceding srcu_read_unlock into a two-way memory barrier.
230 * Call this after srcu_read_unlock, to guarantee that all memory operations
231 * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
232 * the preceding srcu_read_unlock.
234 static inline void smp_mb__after_srcu_read_unlock(void)
236 /* __srcu_read_unlock has smp_mb() internally so nothing to do here. */