include/linux/srcu.h

   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
  64 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  65
  66 /**
  67  * srcu_read_lock_held - might we be in SRCU read-side critical section?
  68  * @ssp: The srcu_struct structure to check
  69  *
  70  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
  71  * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
  72  * this assumes we are in an SRCU read-side critical section unless it can
  73  * prove otherwise.
  74  *
  75  * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
  76  * and while lockdep is disabled.
  77  *
  78  * Note that SRCU is based on its own statemachine and it doesn't
  79  * relies on normal RCU, it can be called from the CPU which
  80  * is in the idle loop from an RCU point of view or offline.
  81  */
  82 static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
  83 {
  84         if (!debug_lockdep_rcu_enabled())
  85                 return 1;
  86         return lock_is_held(&ssp->dep_map);
  87 }
  88
  89 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  90
  91 static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
  92 {
  93         return 1;
  94 }
  95
  96 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  97
  98 /**
  99  * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
 100  * @p: the pointer to fetch and protect for later dereferencing
 101  * @ssp: pointer to the srcu_struct, which is used to check that we
 102  *      really are in an SRCU read-side critical section.
 103  * @c: condition to check for update-side use
 104  *
 105  * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
 106  * critical section will result in an RCU-lockdep splat, unless @c evaluates
 107  * to 1.  The @c argument will normally be a logical expression containing
 108  * lockdep_is_held() calls.
 109  */
 110 #define srcu_dereference_check(p, ssp, c) \
 111         __rcu_dereference_check((p), (c) || srcu_read_lock_held(ssp), __rcu)
 112
 113 /**
 114  * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
 115  * @p: the pointer to fetch and protect for later dereferencing
 116  * @ssp: pointer to the srcu_struct, which is used to check that we
 117  *      really are in an SRCU read-side critical section.
 118  *
 119  * Makes rcu_dereference_check() do the dirty work.  If PROVE_RCU
 120  * is enabled, invoking this outside of an RCU read-side critical
 121  * section will result in an RCU-lockdep splat.
 122  */
 123 #define srcu_dereference(p, ssp) srcu_dereference_check((p), (ssp), 0)
 124
 125 /**
 126  * srcu_dereference_notrace - no tracing and no lockdep calls from here
 127  * @p: the pointer to fetch and protect for later dereferencing
 128  * @ssp: pointer to the srcu_struct, which is used to check that we
 129  *      really are in an SRCU read-side critical section.
 130  */
 131 #define srcu_dereference_notrace(p, ssp) srcu_dereference_check((p), (ssp), 1)
 132
 133 /**
 134  * srcu_read_lock - register a new reader for an SRCU-protected structure.
 135  * @ssp: srcu_struct in which to register the new reader.
 136  *
 137  * Enter an SRCU read-side critical section.  Note that SRCU read-side
 138  * critical sections may be nested.  However, it is illegal to
 139  * call anything that waits on an SRCU grace period for the same
 140  * srcu_struct, whether directly or indirectly.  Please note that
 141  * one way to indirectly wait on an SRCU grace period is to acquire
 142  * a mutex that is held elsewhere while calling synchronize_srcu() or
 143  * synchronize_srcu_expedited().
 144  *
 145  * Note that srcu_read_lock() and the matching srcu_read_unlock() must
 146  * occur in the same context, for example, it is illegal to invoke
 147  * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
 148  * was invoked in process context.
 149  */
 150 static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
 151 {
 152         int retval;
 153
 154         retval = __srcu_read_lock(ssp);
 155         rcu_lock_acquire(&(ssp)->dep_map);
 156         return retval;
 157 }
 158
 159 /* Used by tracing, cannot be traced and cannot invoke lockdep. */
 160 static inline notrace int
 161 srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
 162 {
 163         int retval;
 164
 165         retval = __srcu_read_lock(ssp);
 166         return retval;
 167 }
 168
 169 /**
 170  * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
 171  * @ssp: srcu_struct in which to unregister the old reader.
 172  * @idx: return value from corresponding srcu_read_lock().
 173  *
 174  * Exit an SRCU read-side critical section.
 175  */
 176 static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
 177         __releases(ssp)
 178 {
 179         WARN_ON_ONCE(idx & ~0x1);
 180         rcu_lock_release(&(ssp)->dep_map);
 181         __srcu_read_unlock(ssp, idx);
 182 }
 183
 184 /* Used by tracing, cannot be traced and cannot call lockdep. */
 185 static inline notrace void
 186 srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp)
 187 {
 188         __srcu_read_unlock(ssp, idx);
 189 }
 190
 191 /**
 192  * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
 193  *
 194  * Converts the preceding srcu_read_unlock into a two-way memory barrier.
 195  *
 196  * Call this after srcu_read_unlock, to guarantee that all memory operations
 197  * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
 198  * the preceding srcu_read_unlock.
 199  */
 200 static inline void smp_mb__after_srcu_read_unlock(void)
 201 {
 202         /* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
 203 }
 204
 205 #endif