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

 /* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * Sleepable Read-Copy Update mechanism for mutual exclusion
  *
  * Copyright (C) IBM Corporation, 2006
  * Copyright (C) Fujitsu, 2012
  *
  * Author: Paul McKenney <[email protected]>
  *	   Lai Jiangshan <[email protected]>
  *
  * For detailed explanation of Read-Copy Update mechanism see -
  *		Documentation/RCU/ *.txt
  *
  */

 #ifndef _LINUX_SRCU_H
 #define _LINUX_SRCU_H

 #include <linux/mutex.h>
 #include <linux/rcupdate.h>
 #include <linux/workqueue.h>
 #include <linux/rcu_segcblist.h>

 struct srcu_struct;

 #ifdef CONFIG_DEBUG_LOCK_ALLOC

 int __init_srcu_struct(struct srcu_struct *ssp, const char *name,
 		       struct lock_class_key *key);

 #define init_srcu_struct(ssp) \
 ({ \
 	static struct lock_class_key __srcu_key; \
 	\
 	__init_srcu_struct((ssp), #ssp, &__srcu_key); \
 })

 #define __SRCU_DEP_MAP_INIT(srcu_name)	.dep_map = { .name = #srcu_name },
 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

 int init_srcu_struct(struct srcu_struct *ssp);

 #define __SRCU_DEP_MAP_INIT(srcu_name)
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */

 /* Values for SRCU Tree srcu_data ->srcu_reader_flavor, but also used by rcutorture. */
 #define SRCU_READ_FLAVOR_NORMAL	0x1		// srcu_read_lock().
 #define SRCU_READ_FLAVOR_NMI	0x2		// srcu_read_lock_nmisafe().
 #define SRCU_READ_FLAVOR_LITE	0x4		// srcu_read_lock_lite().
 #define SRCU_READ_FLAVOR_ALL	0x7		// All of the above.

 #ifdef CONFIG_TINY_SRCU
 #include <linux/srcutiny.h>
 #elif defined(CONFIG_TREE_SRCU)
 #include <linux/srcutree.h>
 #else
 #error "Unknown SRCU implementation specified to kernel configuration"
 #endif

 void call_srcu(struct srcu_struct *ssp, struct rcu_head *head,
 		void (*func)(struct rcu_head *head));
 void cleanup_srcu_struct(struct srcu_struct *ssp);
 int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp);
 void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
 #ifdef CONFIG_TINY_SRCU
 #define __srcu_read_lock_lite __srcu_read_lock
 #define __srcu_read_unlock_lite __srcu_read_unlock
 #else // #ifdef CONFIG_TINY_SRCU
 int __srcu_read_lock_lite(struct srcu_struct *ssp) __acquires(ssp);
 void __srcu_read_unlock_lite(struct srcu_struct *ssp, int idx) __releases(ssp);
 #endif // #else // #ifdef CONFIG_TINY_SRCU
 void synchronize_srcu(struct srcu_struct *ssp);

 #define SRCU_GET_STATE_COMPLETED 0x1

 /**
  * get_completed_synchronize_srcu - Return a pre-completed polled state cookie
  *
  * Returns a value that poll_state_synchronize_srcu() will always treat
  * as a cookie whose grace period has already completed.
  */
 static inline unsigned long get_completed_synchronize_srcu(void)
 {
 	return SRCU_GET_STATE_COMPLETED;
 }

 unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp);
 unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp);
 bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie);

 // Maximum number of unsigned long values corresponding to
 // not-yet-completed SRCU grace periods.
 #define NUM_ACTIVE_SRCU_POLL_OLDSTATE 2

 /**
  * same_state_synchronize_srcu - Are two old-state values identical?
  * @oldstate1: First old-state value.
  * @oldstate2: Second old-state value.
  *
  * The two old-state values must have been obtained from either
  * get_state_synchronize_srcu(), start_poll_synchronize_srcu(), or
  * get_completed_synchronize_srcu().  Returns @true if the two values are
  * identical and @false otherwise.  This allows structures whose lifetimes
  * are tracked by old-state values to push these values to a list header,
  * allowing those structures to be slightly smaller.
  */
 static inline bool same_state_synchronize_srcu(unsigned long oldstate1, unsigned long oldstate2)
 {
 	return oldstate1 == oldstate2;
 }

 #ifdef CONFIG_NEED_SRCU_NMI_SAFE
 int __srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp);
 void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx) __releases(ssp);
 #else
 static inline int __srcu_read_lock_nmisafe(struct srcu_struct *ssp)
 {
 	return __srcu_read_lock(ssp);
 }
 static inline void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
 {
 	__srcu_read_unlock(ssp, idx);
 }
 #endif /* CONFIG_NEED_SRCU_NMI_SAFE */

 void srcu_init(void);

 #ifdef CONFIG_DEBUG_LOCK_ALLOC

 /**
  * srcu_read_lock_held - might we be in SRCU read-side critical section?
  * @ssp: The srcu_struct structure to check
  *
  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
  * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
  * this assumes we are in an SRCU read-side critical section unless it can
  * prove otherwise.
  *
  * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
  * and while lockdep is disabled.
  *
  * Note that SRCU is based on its own statemachine and it doesn't
  * relies on normal RCU, it can be called from the CPU which
  * is in the idle loop from an RCU point of view or offline.
  */
 static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
 {
 	if (!debug_lockdep_rcu_enabled())
 		return 1;
 	return lock_is_held(&ssp->dep_map);
 }

 /*
  * Annotations provide deadlock detection for SRCU.
  *
  * Similar to other lockdep annotations, except there is an additional
  * srcu_lock_sync(), which is basically an empty *write*-side critical section,
  * see lock_sync() for more information.
  */

 /* Annotates a srcu_read_lock() */
 static inline void srcu_lock_acquire(struct lockdep_map *map)
 {
 	lock_map_acquire_read(map);
 }

 /* Annotates a srcu_read_lock() */
 static inline void srcu_lock_release(struct lockdep_map *map)
 {
 	lock_map_release(map);
 }

 /* Annotates a synchronize_srcu() */
 static inline void srcu_lock_sync(struct lockdep_map *map)
 {
 	lock_map_sync(map);
 }

 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

 static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
 {
 	return 1;
 }

 #define srcu_lock_acquire(m) do { } while (0)
 #define srcu_lock_release(m) do { } while (0)
 #define srcu_lock_sync(m) do { } while (0)

 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */


 /**
  * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
  * @p: the pointer to fetch and protect for later dereferencing
  * @ssp: pointer to the srcu_struct, which is used to check that we
  *	really are in an SRCU read-side critical section.
  * @c: condition to check for update-side use
  *
  * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
  * critical section will result in an RCU-lockdep splat, unless @c evaluates
  * to 1.  The @c argument will normally be a logical expression containing
  * lockdep_is_held() calls.
  */
 #define srcu_dereference_check(p, ssp, c) \
 	__rcu_dereference_check((p), __UNIQUE_ID(rcu), \
 				(c) || srcu_read_lock_held(ssp), __rcu)

 /**
  * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
  * @p: the pointer to fetch and protect for later dereferencing
  * @ssp: pointer to the srcu_struct, which is used to check that we
  *	really are in an SRCU read-side critical section.
  *
  * Makes rcu_dereference_check() do the dirty work.  If PROVE_RCU
  * is enabled, invoking this outside of an RCU read-side critical
  * section will result in an RCU-lockdep splat.
  */
 #define srcu_dereference(p, ssp) srcu_dereference_check((p), (ssp), 0)

 /**
  * srcu_dereference_notrace - no tracing and no lockdep calls from here
  * @p: the pointer to fetch and protect for later dereferencing
  * @ssp: pointer to the srcu_struct, which is used to check that we
  *	really are in an SRCU read-side critical section.
  */
 #define srcu_dereference_notrace(p, ssp) srcu_dereference_check((p), (ssp), 1)

 /**
  * srcu_read_lock - register a new reader for an SRCU-protected structure.
  * @ssp: srcu_struct in which to register the new reader.
  *
  * Enter an SRCU read-side critical section.  Note that SRCU read-side
  * critical sections may be nested.  However, it is illegal to
  * call anything that waits on an SRCU grace period for the same
  * srcu_struct, whether directly or indirectly.  Please note that
  * one way to indirectly wait on an SRCU grace period is to acquire
  * a mutex that is held elsewhere while calling synchronize_srcu() or
  * synchronize_srcu_expedited().
  *
  * The return value from srcu_read_lock() is guaranteed to be
  * non-negative.  This value must be passed unaltered to the matching
  * srcu_read_unlock().  Note that srcu_read_lock() and the matching
  * srcu_read_unlock() must occur in the same context, for example, it is
  * illegal to invoke srcu_read_unlock() in an irq handler if the matching
  * srcu_read_lock() was invoked in process context.  Or, for that matter to
  * invoke srcu_read_unlock() from one task and the matching srcu_read_lock()
  * from another.
  */
 static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
 {
 	int retval;

 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
 	retval = __srcu_read_lock(ssp);
 	srcu_lock_acquire(&ssp->dep_map);
 	return retval;
 }

 /**
  * srcu_read_lock_lite - register a new reader for an SRCU-protected structure.
  * @ssp: srcu_struct in which to register the new reader.
  *
  * Enter an SRCU read-side critical section, but for a light-weight
  * smp_mb()-free reader.  See srcu_read_lock() for more information.
  *
  * If srcu_read_lock_lite() is ever used on an srcu_struct structure,
  * then none of the other flavors may be used, whether before, during,
  * or after.  Note that grace-period auto-expediting is disabled for _lite
  * srcu_struct structures because auto-expedited grace periods invoke
  * synchronize_rcu_expedited(), IPIs and all.
  *
  * Note that srcu_read_lock_lite() can be invoked only from those contexts
  * where RCU is watching, that is, from contexts where it would be legal
  * to invoke rcu_read_lock().  Otherwise, lockdep will complain.
  */
 static inline int srcu_read_lock_lite(struct srcu_struct *ssp) __acquires(ssp)
 {
 	int retval;

 	srcu_check_read_flavor_lite(ssp);
 	retval = __srcu_read_lock_lite(ssp);
 	rcu_try_lock_acquire(&ssp->dep_map);
 	return retval;
 }

 /**
  * srcu_read_lock_nmisafe - register a new reader for an SRCU-protected structure.
  * @ssp: srcu_struct in which to register the new reader.
  *
  * Enter an SRCU read-side critical section, but in an NMI-safe manner.
  * See srcu_read_lock() for more information.
  *
  * If srcu_read_lock_nmisafe() is ever used on an srcu_struct structure,
  * then none of the other flavors may be used, whether before, during,
  * or after.
  */
 static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp)
 {
 	int retval;

 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NMI);
 	retval = __srcu_read_lock_nmisafe(ssp);
 	rcu_try_lock_acquire(&ssp->dep_map);
 	return retval;
 }

 /* Used by tracing, cannot be traced and cannot invoke lockdep. */
 static inline notrace int
 srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
 {
 	int retval;

 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
 	retval = __srcu_read_lock(ssp);
 	return retval;
 }

 /**
  * srcu_down_read - register a new reader for an SRCU-protected structure.
  * @ssp: srcu_struct in which to register the new reader.
  *
  * Enter a semaphore-like SRCU read-side critical section.  Note that
  * SRCU read-side critical sections may be nested.  However, it is
  * illegal to call anything that waits on an SRCU grace period for the
  * same srcu_struct, whether directly or indirectly.  Please note that
  * one way to indirectly wait on an SRCU grace period is to acquire
  * a mutex that is held elsewhere while calling synchronize_srcu() or
  * synchronize_srcu_expedited().  But if you want lockdep to help you
  * keep this stuff straight, you should instead use srcu_read_lock().
  *
  * The semaphore-like nature of srcu_down_read() means that the matching
  * srcu_up_read() can be invoked from some other context, for example,
  * from some other task or from an irq handler.  However, neither
  * srcu_down_read() nor srcu_up_read() may be invoked from an NMI handler.
  *
  * Calls to srcu_down_read() may be nested, similar to the manner in
  * which calls to down_read() may be nested.
  */
 static inline int srcu_down_read(struct srcu_struct *ssp) __acquires(ssp)
 {
 	WARN_ON_ONCE(in_nmi());
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
 	return __srcu_read_lock(ssp);
 }

 /**
  * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
  * @ssp: srcu_struct in which to unregister the old reader.
  * @idx: return value from corresponding srcu_read_lock().
  *
  * Exit an SRCU read-side critical section.
  */
 static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
 	__releases(ssp)
 {
 	WARN_ON_ONCE(idx & ~0x1);
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
 	srcu_lock_release(&ssp->dep_map);
 	__srcu_read_unlock(ssp, idx);
 }

 /**
  * srcu_read_unlock_lite - unregister a old reader from an SRCU-protected structure.
  * @ssp: srcu_struct in which to unregister the old reader.
  * @idx: return value from corresponding srcu_read_lock().
  *
  * Exit a light-weight SRCU read-side critical section.
  */
 static inline void srcu_read_unlock_lite(struct srcu_struct *ssp, int idx)
 	__releases(ssp)
 {
 	WARN_ON_ONCE(idx & ~0x1);
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_LITE);
 	srcu_lock_release(&ssp->dep_map);
 	__srcu_read_unlock_lite(ssp, idx);
 }

 /**
  * srcu_read_unlock_nmisafe - unregister a old reader from an SRCU-protected structure.
  * @ssp: srcu_struct in which to unregister the old reader.
  * @idx: return value from corresponding srcu_read_lock().
  *
  * Exit an SRCU read-side critical section, but in an NMI-safe manner.
  */
 static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
 	__releases(ssp)
 {
 	WARN_ON_ONCE(idx & ~0x1);
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NMI);
 	rcu_lock_release(&ssp->dep_map);
 	__srcu_read_unlock_nmisafe(ssp, idx);
 }

 /* Used by tracing, cannot be traced and cannot call lockdep. */
 static inline notrace void
 srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp)
 {
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
 	__srcu_read_unlock(ssp, idx);
 }

 /**
  * srcu_up_read - unregister a old reader from an SRCU-protected structure.
  * @ssp: srcu_struct in which to unregister the old reader.
  * @idx: return value from corresponding srcu_read_lock().
  *
  * Exit an SRCU read-side critical section, but not necessarily from
  * the same context as the maching srcu_down_read().
  */
 static inline void srcu_up_read(struct srcu_struct *ssp, int idx)
 	__releases(ssp)
 {
 	WARN_ON_ONCE(idx & ~0x1);
 	WARN_ON_ONCE(in_nmi());
 	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
 	__srcu_read_unlock(ssp, idx);
 }

 /**
  * smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
  *
  * Converts the preceding srcu_read_unlock into a two-way memory barrier.
  *
  * Call this after srcu_read_unlock, to guarantee that all memory operations
  * that occur after smp_mb__after_srcu_read_unlock will appear to happen after
  * the preceding srcu_read_unlock.
  */
 static inline void smp_mb__after_srcu_read_unlock(void)
 {
 	/* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
 }

 /**
  * smp_mb__after_srcu_read_lock - ensure full ordering after srcu_read_lock
  *
  * Converts the preceding srcu_read_lock into a two-way memory barrier.
  *
  * Call this after srcu_read_lock, to guarantee that all memory operations
  * that occur after smp_mb__after_srcu_read_lock will appear to happen after
  * the preceding srcu_read_lock.
  */
 static inline void smp_mb__after_srcu_read_lock(void)
 {
 	/* __srcu_read_lock has smp_mb() internally so nothing to do here. */
 }

 DEFINE_LOCK_GUARD_1(srcu, struct srcu_struct,
 		    _T->idx = srcu_read_lock(_T->lock),
 		    srcu_read_unlock(_T->lock, _T->idx),
 		    int idx)

 #endif
	/* SPDX-License-Identifier: GPL-2.0+ */
	/*
	* Sleepable Read-Copy Update mechanism for mutual exclusion
	*
	* Copyright (C) IBM Corporation, 2006
	* Copyright (C) Fujitsu, 2012
	*
	* Author: Paul McKenney <[email protected]>
	* Lai Jiangshan <[email protected]>
	*
	* For detailed explanation of Read-Copy Update mechanism see -
	* Documentation/RCU/ *.txt
	*
	*/

	#ifndef _LINUX_SRCU_H
	#define _LINUX_SRCU_H

	#include <linux/mutex.h>
	#include <linux/rcupdate.h>
	#include <linux/workqueue.h>
	#include <linux/rcu_segcblist.h>

	struct srcu_struct;

	#ifdef CONFIG_DEBUG_LOCK_ALLOC

	int __init_srcu_struct(struct srcu_struct ssp, const char name,
	struct lock_class_key *key);

	#define init_srcu_struct(ssp) \
	({ \
	static struct lock_class_key __srcu_key; \
	\
	__init_srcu_struct((ssp), #ssp, &__srcu_key); \
	})

	#define __SRCU_DEP_MAP_INIT(srcu_name) .dep_map = { .name = #srcu_name },
	#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

	int init_srcu_struct(struct srcu_struct *ssp);

	#define __SRCU_DEP_MAP_INIT(srcu_name)
	#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */

	/* Values for SRCU Tree srcu_data ->srcu_reader_flavor, but also used by rcutorture. */
	#define SRCU_READ_FLAVOR_NORMAL 0x1 // srcu_read_lock().
	#define SRCU_READ_FLAVOR_NMI 0x2 // srcu_read_lock_nmisafe().
	#define SRCU_READ_FLAVOR_LITE 0x4 // srcu_read_lock_lite().
	#define SRCU_READ_FLAVOR_ALL 0x7 // All of the above.

	#ifdef CONFIG_TINY_SRCU
	#include <linux/srcutiny.h>
	#elif defined(CONFIG_TREE_SRCU)
	#include <linux/srcutree.h>
	#else
	#error "Unknown SRCU implementation specified to kernel configuration"
	#endif

	void call_srcu(struct srcu_struct ssp, struct rcu_head head,
	void (func)(struct rcu_head head));
	void cleanup_srcu_struct(struct srcu_struct *ssp);
	int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp);
	void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
	#ifdef CONFIG_TINY_SRCU
	#define __srcu_read_lock_lite __srcu_read_lock
	#define __srcu_read_unlock_lite __srcu_read_unlock
	#else // #ifdef CONFIG_TINY_SRCU
	int __srcu_read_lock_lite(struct srcu_struct *ssp) __acquires(ssp);
	void __srcu_read_unlock_lite(struct srcu_struct *ssp, int idx) __releases(ssp);
	#endif // #else // #ifdef CONFIG_TINY_SRCU
	void synchronize_srcu(struct srcu_struct *ssp);

	#define SRCU_GET_STATE_COMPLETED 0x1

	/**
	* get_completed_synchronize_srcu - Return a pre-completed polled state cookie
	*
	* Returns a value that poll_state_synchronize_srcu() will always treat
	* as a cookie whose grace period has already completed.
	*/
	static inline unsigned long get_completed_synchronize_srcu(void)
	{
	return SRCU_GET_STATE_COMPLETED;
	}

	unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp);
	unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp);
	bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie);

	// Maximum number of unsigned long values corresponding to
	// not-yet-completed SRCU grace periods.
	#define NUM_ACTIVE_SRCU_POLL_OLDSTATE 2

	/**
	* same_state_synchronize_srcu - Are two old-state values identical?
	* @oldstate1: First old-state value.
	* @oldstate2: Second old-state value.
	*
	* The two old-state values must have been obtained from either
	* get_state_synchronize_srcu(), start_poll_synchronize_srcu(), or
	* get_completed_synchronize_srcu(). Returns @true if the two values are
	* identical and @false otherwise. This allows structures whose lifetimes
	* are tracked by old-state values to push these values to a list header,
	* allowing those structures to be slightly smaller.
	*/
	static inline bool same_state_synchronize_srcu(unsigned long oldstate1, unsigned long oldstate2)
	{
	return oldstate1 == oldstate2;
	}

	#ifdef CONFIG_NEED_SRCU_NMI_SAFE
	int __srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp);
	void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx) __releases(ssp);
	#else
	static inline int __srcu_read_lock_nmisafe(struct srcu_struct *ssp)
	{
	return __srcu_read_lock(ssp);
	}
	static inline void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
	{
	__srcu_read_unlock(ssp, idx);
	}
	#endif /* CONFIG_NEED_SRCU_NMI_SAFE */

	void srcu_init(void);

	#ifdef CONFIG_DEBUG_LOCK_ALLOC

	/**
	* srcu_read_lock_held - might we be in SRCU read-side critical section?
	* @ssp: The srcu_struct structure to check
	*
	* If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
	* read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
	* this assumes we are in an SRCU read-side critical section unless it can
	* prove otherwise.
	*
	* Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
	* and while lockdep is disabled.
	*
	* Note that SRCU is based on its own statemachine and it doesn't
	* relies on normal RCU, it can be called from the CPU which
	* is in the idle loop from an RCU point of view or offline.
	*/
	static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
	{
	if (!debug_lockdep_rcu_enabled())
	return 1;
	return lock_is_held(&ssp->dep_map);
	}

	/*
	* Annotations provide deadlock detection for SRCU.
	*
	* Similar to other lockdep annotations, except there is an additional
	* srcu_lock_sync(), which is basically an empty write-side critical section,
	* see lock_sync() for more information.
	*/

	/* Annotates a srcu_read_lock() */
	static inline void srcu_lock_acquire(struct lockdep_map *map)
	{
	lock_map_acquire_read(map);
	}

	/* Annotates a srcu_read_lock() */
	static inline void srcu_lock_release(struct lockdep_map *map)
	{
	lock_map_release(map);
	}

	/* Annotates a synchronize_srcu() */
	static inline void srcu_lock_sync(struct lockdep_map *map)
	{
	lock_map_sync(map);
	}

	#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

	static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
	{
	return 1;
	}

	#define srcu_lock_acquire(m) do { } while (0)
	#define srcu_lock_release(m) do { } while (0)
	#define srcu_lock_sync(m) do { } while (0)

	#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */


	/**
	* srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
	* @p: the pointer to fetch and protect for later dereferencing
	* @ssp: pointer to the srcu_struct, which is used to check that we
	* really are in an SRCU read-side critical section.
	* @c: condition to check for update-side use
	*
	* If PROVE_RCU is enabled, invoking this outside of an RCU read-side
	* critical section will result in an RCU-lockdep splat, unless @c evaluates
	* to 1. The @c argument will normally be a logical expression containing
	* lockdep_is_held() calls.
	*/
	#define srcu_dereference_check(p, ssp, c) \
	__rcu_dereference_check((p), __UNIQUE_ID(rcu), \
	(c) \|\| srcu_read_lock_held(ssp), __rcu)

	/**
	* srcu_dereference - fetch SRCU-protected pointer for later dereferencing
	* @p: the pointer to fetch and protect for later dereferencing
	* @ssp: pointer to the srcu_struct, which is used to check that we
	* really are in an SRCU read-side critical section.
	*
	* Makes rcu_dereference_check() do the dirty work. If PROVE_RCU
	* is enabled, invoking this outside of an RCU read-side critical
	* section will result in an RCU-lockdep splat.
	*/
	#define srcu_dereference(p, ssp) srcu_dereference_check((p), (ssp), 0)

	/**
	* srcu_dereference_notrace - no tracing and no lockdep calls from here
	* @p: the pointer to fetch and protect for later dereferencing
	* @ssp: pointer to the srcu_struct, which is used to check that we
	* really are in an SRCU read-side critical section.
	*/
	#define srcu_dereference_notrace(p, ssp) srcu_dereference_check((p), (ssp), 1)

	/**
	* srcu_read_lock - register a new reader for an SRCU-protected structure.
	* @ssp: srcu_struct in which to register the new reader.
	*
	* Enter an SRCU read-side critical section. Note that SRCU read-side
	* critical sections may be nested. However, it is illegal to
	* call anything that waits on an SRCU grace period for the same
	* srcu_struct, whether directly or indirectly. Please note that
	* one way to indirectly wait on an SRCU grace period is to acquire
	* a mutex that is held elsewhere while calling synchronize_srcu() or
	* synchronize_srcu_expedited().
	*
	* The return value from srcu_read_lock() is guaranteed to be
	* non-negative. This value must be passed unaltered to the matching
	* srcu_read_unlock(). Note that srcu_read_lock() and the matching
	* srcu_read_unlock() must occur in the same context, for example, it is
	* illegal to invoke srcu_read_unlock() in an irq handler if the matching
	* srcu_read_lock() was invoked in process context. Or, for that matter to
	* invoke srcu_read_unlock() from one task and the matching srcu_read_lock()
	* from another.
	*/
	static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
	{
	int retval;

	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
	retval = __srcu_read_lock(ssp);
	srcu_lock_acquire(&ssp->dep_map);
	return retval;
	}

	/**
	* srcu_read_lock_lite - register a new reader for an SRCU-protected structure.
	* @ssp: srcu_struct in which to register the new reader.
	*
	* Enter an SRCU read-side critical section, but for a light-weight
	* smp_mb()-free reader. See srcu_read_lock() for more information.
	*
	* If srcu_read_lock_lite() is ever used on an srcu_struct structure,
	* then none of the other flavors may be used, whether before, during,
	* or after. Note that grace-period auto-expediting is disabled for _lite
	* srcu_struct structures because auto-expedited grace periods invoke
	* synchronize_rcu_expedited(), IPIs and all.
	*
	* Note that srcu_read_lock_lite() can be invoked only from those contexts
	* where RCU is watching, that is, from contexts where it would be legal
	* to invoke rcu_read_lock(). Otherwise, lockdep will complain.
	*/
	static inline int srcu_read_lock_lite(struct srcu_struct *ssp) __acquires(ssp)
	{
	int retval;

	srcu_check_read_flavor_lite(ssp);
	retval = __srcu_read_lock_lite(ssp);
	rcu_try_lock_acquire(&ssp->dep_map);
	return retval;
	}

	/**
	* srcu_read_lock_nmisafe - register a new reader for an SRCU-protected structure.
	* @ssp: srcu_struct in which to register the new reader.
	*
	* Enter an SRCU read-side critical section, but in an NMI-safe manner.
	* See srcu_read_lock() for more information.
	*
	* If srcu_read_lock_nmisafe() is ever used on an srcu_struct structure,
	* then none of the other flavors may be used, whether before, during,
	* or after.
	*/
	static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp)
	{
	int retval;

	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NMI);
	retval = __srcu_read_lock_nmisafe(ssp);
	rcu_try_lock_acquire(&ssp->dep_map);
	return retval;
	}

	/* Used by tracing, cannot be traced and cannot invoke lockdep. */
	static inline notrace int
	srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
	{
	int retval;

	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
	retval = __srcu_read_lock(ssp);
	return retval;
	}

	/**
	* srcu_down_read - register a new reader for an SRCU-protected structure.
	* @ssp: srcu_struct in which to register the new reader.
	*
	* Enter a semaphore-like SRCU read-side critical section. Note that
	* SRCU read-side critical sections may be nested. However, it is
	* illegal to call anything that waits on an SRCU grace period for the
	* same srcu_struct, whether directly or indirectly. Please note that
	* one way to indirectly wait on an SRCU grace period is to acquire
	* a mutex that is held elsewhere while calling synchronize_srcu() or
	* synchronize_srcu_expedited(). But if you want lockdep to help you
	* keep this stuff straight, you should instead use srcu_read_lock().
	*
	* The semaphore-like nature of srcu_down_read() means that the matching
	* srcu_up_read() can be invoked from some other context, for example,
	* from some other task or from an irq handler. However, neither
	* srcu_down_read() nor srcu_up_read() may be invoked from an NMI handler.
	*
	* Calls to srcu_down_read() may be nested, similar to the manner in
	* which calls to down_read() may be nested.
	*/
	static inline int srcu_down_read(struct srcu_struct *ssp) __acquires(ssp)
	{
	WARN_ON_ONCE(in_nmi());
	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
	return __srcu_read_lock(ssp);
	}

	/**
	* srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
	* @ssp: srcu_struct in which to unregister the old reader.
	* @idx: return value from corresponding srcu_read_lock().
	*
	* Exit an SRCU read-side critical section.
	*/
	static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
	__releases(ssp)
	{
	WARN_ON_ONCE(idx & ~0x1);
	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
	srcu_lock_release(&ssp->dep_map);
	__srcu_read_unlock(ssp, idx);
	}

	/**
	* srcu_read_unlock_lite - unregister a old reader from an SRCU-protected structure.
	* @ssp: srcu_struct in which to unregister the old reader.
	* @idx: return value from corresponding srcu_read_lock().
	*
	* Exit a light-weight SRCU read-side critical section.
	*/
	static inline void srcu_read_unlock_lite(struct srcu_struct *ssp, int idx)
	__releases(ssp)
	{
	WARN_ON_ONCE(idx & ~0x1);
	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_LITE);
	srcu_lock_release(&ssp->dep_map);
	__srcu_read_unlock_lite(ssp, idx);
	}

	/**
	* srcu_read_unlock_nmisafe - unregister a old reader from an SRCU-protected structure.
	* @ssp: srcu_struct in which to unregister the old reader.
	* @idx: return value from corresponding srcu_read_lock().
	*
	* Exit an SRCU read-side critical section, but in an NMI-safe manner.
	*/
	static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
	__releases(ssp)
	{
	WARN_ON_ONCE(idx & ~0x1);
	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NMI);
	rcu_lock_release(&ssp->dep_map);
	__srcu_read_unlock_nmisafe(ssp, idx);
	}

	/* Used by tracing, cannot be traced and cannot call lockdep. */
	static inline notrace void
	srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp)
	{
	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
	__srcu_read_unlock(ssp, idx);
	}

	/**
	* srcu_up_read - unregister a old reader from an SRCU-protected structure.
	* @ssp: srcu_struct in which to unregister the old reader.
	* @idx: return value from corresponding srcu_read_lock().
	*
	* Exit an SRCU read-side critical section, but not necessarily from
	* the same context as the maching srcu_down_read().
	*/
	static inline void srcu_up_read(struct srcu_struct *ssp, int idx)
	__releases(ssp)
	{
	WARN_ON_ONCE(idx & ~0x1);
	WARN_ON_ONCE(in_nmi());
	srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
	__srcu_read_unlock(ssp, idx);
	}

	/**
	* smp_mb__after_srcu_read_unlock - ensure full ordering after srcu_read_unlock
	*
	* Converts the preceding srcu_read_unlock into a two-way memory barrier.
	*
	* Call this after srcu_read_unlock, to guarantee that all memory operations
	* that occur after smp_mb__after_srcu_read_unlock will appear to happen after
	* the preceding srcu_read_unlock.
	*/
	static inline void smp_mb__after_srcu_read_unlock(void)
	{
	/* __srcu_read_unlock has smp_mb() internally so nothing to do here. */
	}

	/**
	* smp_mb__after_srcu_read_lock - ensure full ordering after srcu_read_lock
	*
	* Converts the preceding srcu_read_lock into a two-way memory barrier.
	*
	* Call this after srcu_read_lock, to guarantee that all memory operations
	* that occur after smp_mb__after_srcu_read_lock will appear to happen after
	* the preceding srcu_read_lock.
	*/
	static inline void smp_mb__after_srcu_read_lock(void)
	{
	/* __srcu_read_lock has smp_mb() internally so nothing to do here. */
	}

	DEFINE_LOCK_GUARD_1(srcu, struct srcu_struct,
	_T->idx = srcu_read_lock(_T->lock),
	srcu_read_unlock(_T->lock, _T->idx),
	int idx)

	#endif