include/linux/srcutree.h - kernel/common - Git at Google

 /* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * Sleepable Read-Copy Update mechanism for mutual exclusion,
  *	tree variant.
  *
  * Copyright (C) IBM Corporation, 2017
  *
  * Author: Paul McKenney <[email protected]>
  */

 #ifndef _LINUX_SRCU_TREE_H
 #define _LINUX_SRCU_TREE_H

 #include <linux/rcu_node_tree.h>
 #include <linux/completion.h>

 struct srcu_node;
 struct srcu_struct;

 /*
  * Per-CPU structure feeding into leaf srcu_node, similar in function
  * to rcu_node.
  */
 struct srcu_data {
 	/* Read-side state. */
 	atomic_long_t srcu_lock_count[2];	/* Locks per CPU. */
 	atomic_long_t srcu_unlock_count[2];	/* Unlocks per CPU. */
 	int srcu_reader_flavor;			/* Reader flavor for srcu_struct structure? */
 						/* Values: SRCU_READ_FLAVOR_.*  */

 	/* Update-side state. */
 	spinlock_t __private lock ____cacheline_internodealigned_in_smp;
 	struct rcu_segcblist srcu_cblist;	/* List of callbacks.*/
 	unsigned long srcu_gp_seq_needed;	/* Furthest future GP needed. */
 	unsigned long srcu_gp_seq_needed_exp;	/* Furthest future exp GP. */
 	bool srcu_cblist_invoking;		/* Invoking these CBs? */
 	struct timer_list delay_work;		/* Delay for CB invoking */
 	struct work_struct work;		/* Context for CB invoking. */
 	struct rcu_head srcu_barrier_head;	/* For srcu_barrier() use. */
 	struct srcu_node *mynode;		/* Leaf srcu_node. */
 	unsigned long grpmask;			/* Mask for leaf srcu_node */
 						/*  ->srcu_data_have_cbs[]. */
 	int cpu;
 	struct srcu_struct *ssp;
 };

 /*
  * Node in SRCU combining tree, similar in function to rcu_data.
  */
 struct srcu_node {
 	spinlock_t __private lock;
 	unsigned long srcu_have_cbs[4];		/* GP seq for children having CBs, but only */
 						/*  if greater than ->srcu_gp_seq. */
 	unsigned long srcu_data_have_cbs[4];	/* Which srcu_data structs have CBs for given GP? */
 	unsigned long srcu_gp_seq_needed_exp;	/* Furthest future exp GP. */
 	struct srcu_node *srcu_parent;		/* Next up in tree. */
 	int grplo;				/* Least CPU for node. */
 	int grphi;				/* Biggest CPU for node. */
 };

 /*
  * Per-SRCU-domain structure, update-side data linked from srcu_struct.
  */
 struct srcu_usage {
 	struct srcu_node *node;			/* Combining tree. */
 	struct srcu_node *level[RCU_NUM_LVLS + 1];
 						/* First node at each level. */
 	int srcu_size_state;			/* Small-to-big transition state. */
 	struct mutex srcu_cb_mutex;		/* Serialize CB preparation. */
 	spinlock_t __private lock;		/* Protect counters and size state. */
 	struct mutex srcu_gp_mutex;		/* Serialize GP work. */
 	unsigned long srcu_gp_seq;		/* Grace-period seq #. */
 	unsigned long srcu_gp_seq_needed;	/* Latest gp_seq needed. */
 	unsigned long srcu_gp_seq_needed_exp;	/* Furthest future exp GP. */
 	unsigned long srcu_gp_start;		/* Last GP start timestamp (jiffies) */
 	unsigned long srcu_last_gp_end;		/* Last GP end timestamp (ns) */
 	unsigned long srcu_size_jiffies;	/* Current contention-measurement interval. */
 	unsigned long srcu_n_lock_retries;	/* Contention events in current interval. */
 	unsigned long srcu_n_exp_nodelay;	/* # expedited no-delays in current GP phase. */
 	bool sda_is_static;			/* May ->sda be passed to free_percpu()? */
 	unsigned long srcu_barrier_seq;		/* srcu_barrier seq #. */
 	struct mutex srcu_barrier_mutex;	/* Serialize barrier ops. */
 	struct completion srcu_barrier_completion;
 						/* Awaken barrier rq at end. */
 	atomic_t srcu_barrier_cpu_cnt;		/* # CPUs not yet posting a */
 						/*  callback for the barrier */
 						/*  operation. */
 	unsigned long reschedule_jiffies;
 	unsigned long reschedule_count;
 	struct delayed_work work;
 	struct srcu_struct *srcu_ssp;
 };

 /*
  * Per-SRCU-domain structure, similar in function to rcu_state.
  */
 struct srcu_struct {
 	unsigned int srcu_idx;			/* Current rdr array element. */
 	struct srcu_data __percpu *sda;		/* Per-CPU srcu_data array. */
 	struct lockdep_map dep_map;
 	struct srcu_usage *srcu_sup;		/* Update-side data. */
 };

 // Values for size state variable (->srcu_size_state).  Once the state
 // has been set to SRCU_SIZE_ALLOC, the grace-period code advances through
 // this state machine one step per grace period until the SRCU_SIZE_BIG state
 // is reached.  Otherwise, the state machine remains in the SRCU_SIZE_SMALL
 // state indefinitely.
 #define SRCU_SIZE_SMALL		0	// No srcu_node combining tree, ->node == NULL
 #define SRCU_SIZE_ALLOC		1	// An srcu_node tree is being allocated, initialized,
 					//  and then referenced by ->node.  It will not be used.
 #define SRCU_SIZE_WAIT_BARRIER	2	// The srcu_node tree starts being used by everything
 					//  except call_srcu(), especially by srcu_barrier().
 					//  By the end of this state, all CPUs and threads
 					//  are aware of this tree's existence.
 #define SRCU_SIZE_WAIT_CALL	3	// The srcu_node tree starts being used by call_srcu().
 					//  By the end of this state, all of the call_srcu()
 					//  invocations that were running on a non-boot CPU
 					//  and using the boot CPU's callback queue will have
 					//  completed.
 #define SRCU_SIZE_WAIT_CBS1	4	// Don't trust the ->srcu_have_cbs[] grace-period
 #define SRCU_SIZE_WAIT_CBS2	5	//  sequence elements or the ->srcu_data_have_cbs[]
 #define SRCU_SIZE_WAIT_CBS3	6	//  CPU-bitmask elements until all four elements of
 #define SRCU_SIZE_WAIT_CBS4	7	//  each array have been initialized.
 #define SRCU_SIZE_BIG		8	// The srcu_node combining tree is fully initialized
 					//  and all aspects of it are being put to use.

 /* Values for state variable (bottom bits of ->srcu_gp_seq). */
 #define SRCU_STATE_IDLE		0
 #define SRCU_STATE_SCAN1	1
 #define SRCU_STATE_SCAN2	2

 /*
  * Values for initializing gp sequence fields. Higher values allow wrap arounds to
  * occur earlier.
  * The second value with state is useful in the case of static initialization of
  * srcu_usage where srcu_gp_seq_needed is expected to have some state value in its
  * lower bits (or else it will appear to be already initialized within
  * the call check_init_srcu_struct()).
  */
 #define SRCU_GP_SEQ_INITIAL_VAL ((0UL - 100UL) << RCU_SEQ_CTR_SHIFT)
 #define SRCU_GP_SEQ_INITIAL_VAL_WITH_STATE (SRCU_GP_SEQ_INITIAL_VAL - 1)

 #define __SRCU_USAGE_INIT(name)									\
 {												\
 	.lock = __SPIN_LOCK_UNLOCKED(name.lock),						\
 	.srcu_gp_seq = SRCU_GP_SEQ_INITIAL_VAL,							\
 	.srcu_gp_seq_needed = SRCU_GP_SEQ_INITIAL_VAL_WITH_STATE,				\
 	.srcu_gp_seq_needed_exp = SRCU_GP_SEQ_INITIAL_VAL,					\
 	.work = __DELAYED_WORK_INITIALIZER(name.work, NULL, 0),					\
 }

 #define __SRCU_STRUCT_INIT_COMMON(name, usage_name)						\
 	.srcu_sup = &usage_name,								\
 	__SRCU_DEP_MAP_INIT(name)

 #define __SRCU_STRUCT_INIT_MODULE(name, usage_name)						\
 {												\
 	__SRCU_STRUCT_INIT_COMMON(name, usage_name)						\
 }

 #define __SRCU_STRUCT_INIT(name, usage_name, pcpu_name)						\
 {												\
 	.sda = &pcpu_name,									\
 	__SRCU_STRUCT_INIT_COMMON(name, usage_name)						\
 }

 /*
  * Define and initialize a srcu struct at build time.
  * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it.
  *
  * Note that although DEFINE_STATIC_SRCU() hides the name from other
  * files, the per-CPU variable rules nevertheless require that the
  * chosen name be globally unique.  These rules also prohibit use of
  * DEFINE_STATIC_SRCU() within a function.  If these rules are too
  * restrictive, declare the srcu_struct manually.  For example, in
  * each file:
  *
  *	static struct srcu_struct my_srcu;
  *
  * Then, before the first use of each my_srcu, manually initialize it:
  *
  *	init_srcu_struct(&my_srcu);
  *
  * See include/linux/percpu-defs.h for the rules on per-CPU variables.
  */
 #ifdef MODULE
 # define __DEFINE_SRCU(name, is_static)								\
 	static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage);	\
 	is_static struct srcu_struct name = __SRCU_STRUCT_INIT_MODULE(name, name##_srcu_usage);	\
 	extern struct srcu_struct * const __srcu_struct_##name;					\
 	struct srcu_struct * const __srcu_struct_##name						\
 		__section("___srcu_struct_ptrs") = &name
 #else
 # define __DEFINE_SRCU(name, is_static)								\
 	static DEFINE_PER_CPU(struct srcu_data, name##_srcu_data);				\
 	static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage);	\
 	is_static struct srcu_struct name =							\
 		__SRCU_STRUCT_INIT(name, name##_srcu_usage, name##_srcu_data)
 #endif
 #define DEFINE_SRCU(name)		__DEFINE_SRCU(name, /* not static */)
 #define DEFINE_STATIC_SRCU(name)	__DEFINE_SRCU(name, static)

 void synchronize_srcu_expedited(struct srcu_struct *ssp);
 void srcu_barrier(struct srcu_struct *ssp);
 void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf);

 /*
  * Counts the new reader in the appropriate per-CPU element of the
  * srcu_struct.  Returns an index that must be passed to the matching
  * srcu_read_unlock_lite().
  *
  * Note that this_cpu_inc() is an RCU read-side critical section either
  * because it disables interrupts, because it is a single instruction,
  * or because it is a read-modify-write atomic operation, depending on
  * the whims of the architecture.
  */
 static inline int __srcu_read_lock_lite(struct srcu_struct *ssp)
 {
 	int idx;

 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_lock_lite().");
 	idx = READ_ONCE(ssp->srcu_idx) & 0x1;
 	this_cpu_inc(ssp->sda->srcu_lock_count[idx].counter); /* Y */
 	barrier(); /* Avoid leaking the critical section. */
 	return idx;
 }

 /*
  * Removes the count for the old reader from the appropriate
  * per-CPU element of the srcu_struct.  Note that this may well be a
  * different CPU than that which was incremented by the corresponding
  * srcu_read_lock_lite(), but it must be within the same task.
  *
  * Note that this_cpu_inc() is an RCU read-side critical section either
  * because it disables interrupts, because it is a single instruction,
  * or because it is a read-modify-write atomic operation, depending on
  * the whims of the architecture.
  */
 static inline void __srcu_read_unlock_lite(struct srcu_struct *ssp, int idx)
 {
 	barrier();  /* Avoid leaking the critical section. */
 	this_cpu_inc(ssp->sda->srcu_unlock_count[idx].counter);  /* Z */
 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_lite().");
 }

 void __srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor);

 // Record _lite() usage even for CONFIG_PROVE_RCU=n kernels.
 static inline void srcu_check_read_flavor_lite(struct srcu_struct *ssp)
 {
 	struct srcu_data *sdp = raw_cpu_ptr(ssp->sda);

 	if (likely(READ_ONCE(sdp->srcu_reader_flavor) & SRCU_READ_FLAVOR_LITE))
 		return;

 	// Note that the cmpxchg() in __srcu_check_read_flavor() is fully ordered.
 	__srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_LITE);
 }

 // Record non-_lite() usage only for CONFIG_PROVE_RCU=y kernels.
 static inline void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor)
 {
 	if (IS_ENABLED(CONFIG_PROVE_RCU))
 		__srcu_check_read_flavor(ssp, read_flavor);
 }

 #endif
	/* SPDX-License-Identifier: GPL-2.0+ */
	/*
	* Sleepable Read-Copy Update mechanism for mutual exclusion,
	* tree variant.
	*
	* Copyright (C) IBM Corporation, 2017
	*
	* Author: Paul McKenney <[email protected]>
	*/

	#ifndef _LINUX_SRCU_TREE_H
	#define _LINUX_SRCU_TREE_H

	#include <linux/rcu_node_tree.h>
	#include <linux/completion.h>

	struct srcu_node;
	struct srcu_struct;

	/*
	* Per-CPU structure feeding into leaf srcu_node, similar in function
	* to rcu_node.
	*/
	struct srcu_data {
	/* Read-side state. */
	atomic_long_t srcu_lock_count[2]; /* Locks per CPU. */
	atomic_long_t srcu_unlock_count[2]; /* Unlocks per CPU. */
	int srcu_reader_flavor; /* Reader flavor for srcu_struct structure? */
	/* Values: SRCU_READ_FLAVOR_.* */

	/* Update-side state. */
	spinlock_t __private lock ____cacheline_internodealigned_in_smp;
	struct rcu_segcblist srcu_cblist; /* List of callbacks.*/
	unsigned long srcu_gp_seq_needed; /* Furthest future GP needed. */
	unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */
	bool srcu_cblist_invoking; /* Invoking these CBs? */
	struct timer_list delay_work; /* Delay for CB invoking */
	struct work_struct work; /* Context for CB invoking. */
	struct rcu_head srcu_barrier_head; /* For srcu_barrier() use. */
	struct srcu_node mynode; / Leaf srcu_node. */
	unsigned long grpmask; /* Mask for leaf srcu_node */
	/* ->srcu_data_have_cbs[]. */
	int cpu;
	struct srcu_struct *ssp;
	};

	/*
	* Node in SRCU combining tree, similar in function to rcu_data.
	*/
	struct srcu_node {
	spinlock_t __private lock;
	unsigned long srcu_have_cbs[4]; /* GP seq for children having CBs, but only */
	/* if greater than ->srcu_gp_seq. */
	unsigned long srcu_data_have_cbs[4]; /* Which srcu_data structs have CBs for given GP? */
	unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */
	struct srcu_node srcu_parent; / Next up in tree. */
	int grplo; /* Least CPU for node. */
	int grphi; /* Biggest CPU for node. */
	};

	/*
	* Per-SRCU-domain structure, update-side data linked from srcu_struct.
	*/
	struct srcu_usage {
	struct srcu_node node; / Combining tree. */
	struct srcu_node *level[RCU_NUM_LVLS + 1];
	/* First node at each level. */
	int srcu_size_state; /* Small-to-big transition state. */
	struct mutex srcu_cb_mutex; /* Serialize CB preparation. */
	spinlock_t __private lock; /* Protect counters and size state. */
	struct mutex srcu_gp_mutex; /* Serialize GP work. */
	unsigned long srcu_gp_seq; /* Grace-period seq #. */
	unsigned long srcu_gp_seq_needed; /* Latest gp_seq needed. */
	unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */
	unsigned long srcu_gp_start; /* Last GP start timestamp (jiffies) */
	unsigned long srcu_last_gp_end; /* Last GP end timestamp (ns) */
	unsigned long srcu_size_jiffies; /* Current contention-measurement interval. */
	unsigned long srcu_n_lock_retries; /* Contention events in current interval. */
	unsigned long srcu_n_exp_nodelay; /* # expedited no-delays in current GP phase. */
	bool sda_is_static; /* May ->sda be passed to free_percpu()? */
	unsigned long srcu_barrier_seq; /* srcu_barrier seq #. */
	struct mutex srcu_barrier_mutex; /* Serialize barrier ops. */
	struct completion srcu_barrier_completion;
	/* Awaken barrier rq at end. */
	atomic_t srcu_barrier_cpu_cnt; /* # CPUs not yet posting a */
	/* callback for the barrier */
	/* operation. */
	unsigned long reschedule_jiffies;
	unsigned long reschedule_count;
	struct delayed_work work;
	struct srcu_struct *srcu_ssp;
	};

	/*
	* Per-SRCU-domain structure, similar in function to rcu_state.
	*/
	struct srcu_struct {
	unsigned int srcu_idx; /* Current rdr array element. */
	struct srcu_data __percpu sda; / Per-CPU srcu_data array. */
	struct lockdep_map dep_map;
	struct srcu_usage srcu_sup; / Update-side data. */
	};

	// Values for size state variable (->srcu_size_state). Once the state
	// has been set to SRCU_SIZE_ALLOC, the grace-period code advances through
	// this state machine one step per grace period until the SRCU_SIZE_BIG state
	// is reached. Otherwise, the state machine remains in the SRCU_SIZE_SMALL
	// state indefinitely.
	#define SRCU_SIZE_SMALL 0 // No srcu_node combining tree, ->node == NULL
	#define SRCU_SIZE_ALLOC 1 // An srcu_node tree is being allocated, initialized,
	// and then referenced by ->node. It will not be used.
	#define SRCU_SIZE_WAIT_BARRIER 2 // The srcu_node tree starts being used by everything
	// except call_srcu(), especially by srcu_barrier().
	// By the end of this state, all CPUs and threads
	// are aware of this tree's existence.
	#define SRCU_SIZE_WAIT_CALL 3 // The srcu_node tree starts being used by call_srcu().
	// By the end of this state, all of the call_srcu()
	// invocations that were running on a non-boot CPU
	// and using the boot CPU's callback queue will have
	// completed.
	#define SRCU_SIZE_WAIT_CBS1 4 // Don't trust the ->srcu_have_cbs[] grace-period
	#define SRCU_SIZE_WAIT_CBS2 5 // sequence elements or the ->srcu_data_have_cbs[]
	#define SRCU_SIZE_WAIT_CBS3 6 // CPU-bitmask elements until all four elements of
	#define SRCU_SIZE_WAIT_CBS4 7 // each array have been initialized.
	#define SRCU_SIZE_BIG 8 // The srcu_node combining tree is fully initialized
	// and all aspects of it are being put to use.

	/* Values for state variable (bottom bits of ->srcu_gp_seq). */
	#define SRCU_STATE_IDLE 0
	#define SRCU_STATE_SCAN1 1
	#define SRCU_STATE_SCAN2 2

	/*
	* Values for initializing gp sequence fields. Higher values allow wrap arounds to
	* occur earlier.
	* The second value with state is useful in the case of static initialization of
	* srcu_usage where srcu_gp_seq_needed is expected to have some state value in its
	* lower bits (or else it will appear to be already initialized within
	* the call check_init_srcu_struct()).
	*/
	#define SRCU_GP_SEQ_INITIAL_VAL ((0UL - 100UL) << RCU_SEQ_CTR_SHIFT)
	#define SRCU_GP_SEQ_INITIAL_VAL_WITH_STATE (SRCU_GP_SEQ_INITIAL_VAL - 1)

	#define __SRCU_USAGE_INIT(name) \
	{ \
	.lock = __SPIN_LOCK_UNLOCKED(name.lock), \
	.srcu_gp_seq = SRCU_GP_SEQ_INITIAL_VAL, \
	.srcu_gp_seq_needed = SRCU_GP_SEQ_INITIAL_VAL_WITH_STATE, \
	.srcu_gp_seq_needed_exp = SRCU_GP_SEQ_INITIAL_VAL, \
	.work = __DELAYED_WORK_INITIALIZER(name.work, NULL, 0), \
	}

	#define __SRCU_STRUCT_INIT_COMMON(name, usage_name) \
	.srcu_sup = &usage_name, \
	__SRCU_DEP_MAP_INIT(name)

	#define __SRCU_STRUCT_INIT_MODULE(name, usage_name) \
	{ \
	__SRCU_STRUCT_INIT_COMMON(name, usage_name) \
	}

	#define __SRCU_STRUCT_INIT(name, usage_name, pcpu_name) \
	{ \
	.sda = &pcpu_name, \
	__SRCU_STRUCT_INIT_COMMON(name, usage_name) \
	}

	/*
	* Define and initialize a srcu struct at build time.
	* Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it.
	*
	* Note that although DEFINE_STATIC_SRCU() hides the name from other
	* files, the per-CPU variable rules nevertheless require that the
	* chosen name be globally unique. These rules also prohibit use of
	* DEFINE_STATIC_SRCU() within a function. If these rules are too
	* restrictive, declare the srcu_struct manually. For example, in
	* each file:
	*
	* static struct srcu_struct my_srcu;
	*
	* Then, before the first use of each my_srcu, manually initialize it:
	*
	* init_srcu_struct(&my_srcu);
	*
	* See include/linux/percpu-defs.h for the rules on per-CPU variables.
	*/
	#ifdef MODULE
	# define __DEFINE_SRCU(name, is_static) \
	static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage); \
	is_static struct srcu_struct name = __SRCU_STRUCT_INIT_MODULE(name, name##_srcu_usage); \
	extern struct srcu_struct * const __srcu_struct_##name; \
	struct srcu_struct * const __srcu_struct_##name \
	__section("___srcu_struct_ptrs") = &name
	#else
	# define __DEFINE_SRCU(name, is_static) \
	static DEFINE_PER_CPU(struct srcu_data, name##_srcu_data); \
	static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage); \
	is_static struct srcu_struct name = \
	__SRCU_STRUCT_INIT(name, name##_srcu_usage, name##_srcu_data)
	#endif
	#define DEFINE_SRCU(name) __DEFINE_SRCU(name, /* not static */)
	#define DEFINE_STATIC_SRCU(name) __DEFINE_SRCU(name, static)

	void synchronize_srcu_expedited(struct srcu_struct *ssp);
	void srcu_barrier(struct srcu_struct *ssp);
	void srcu_torture_stats_print(struct srcu_struct ssp, char tt, char *tf);

	/*
	* Counts the new reader in the appropriate per-CPU element of the
	* srcu_struct. Returns an index that must be passed to the matching
	* srcu_read_unlock_lite().
	*
	* Note that this_cpu_inc() is an RCU read-side critical section either
	* because it disables interrupts, because it is a single instruction,
	* or because it is a read-modify-write atomic operation, depending on
	* the whims of the architecture.
	*/
	static inline int __srcu_read_lock_lite(struct srcu_struct *ssp)
	{
	int idx;

	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_lock_lite().");
	idx = READ_ONCE(ssp->srcu_idx) & 0x1;
	this_cpu_inc(ssp->sda->srcu_lock_count[idx].counter); /* Y */
	barrier(); /* Avoid leaking the critical section. */
	return idx;
	}

	/*
	* Removes the count for the old reader from the appropriate
	* per-CPU element of the srcu_struct. Note that this may well be a
	* different CPU than that which was incremented by the corresponding
	* srcu_read_lock_lite(), but it must be within the same task.
	*
	* Note that this_cpu_inc() is an RCU read-side critical section either
	* because it disables interrupts, because it is a single instruction,
	* or because it is a read-modify-write atomic operation, depending on
	* the whims of the architecture.
	*/
	static inline void __srcu_read_unlock_lite(struct srcu_struct *ssp, int idx)
	{
	barrier(); /* Avoid leaking the critical section. */
	this_cpu_inc(ssp->sda->srcu_unlock_count[idx].counter); /* Z */
	RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_lite().");
	}

	void __srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor);

	// Record _lite() usage even for CONFIG_PROVE_RCU=n kernels.
	static inline void srcu_check_read_flavor_lite(struct srcu_struct *ssp)
	{
	struct srcu_data *sdp = raw_cpu_ptr(ssp->sda);

	if (likely(READ_ONCE(sdp->srcu_reader_flavor) & SRCU_READ_FLAVOR_LITE))
	return;

	// Note that the cmpxchg() in __srcu_check_read_flavor() is fully ordered.
	__srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_LITE);
	}

	// Record non-_lite() usage only for CONFIG_PROVE_RCU=y kernels.
	static inline void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor)
	{
	if (IS_ENABLED(CONFIG_PROVE_RCU))
	__srcu_check_read_flavor(ssp, read_flavor);
	}

	#endif