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/*

 * Read-Copy Update mechanism for mutual exclusion

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; either version 2 of the License, or

 * (at your option) any later version.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, you can access it online at

 * http://www.gnu.org/licenses/gpl-2.0.html.

 *

 * Copyright IBM Corporation, 2001

 *

 * Author: Dipankar Sarma 

 *

 * Based on the original work by Paul McKenney 

 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.

 * Papers:

 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf

 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)

 *

 * For detailed explanation of Read-Copy Update mechanism see -

 *		http://lse.sourceforge.net/locking/rcupdate.html

 *

 */

#ifndef __LINUX_RCUPDATE_H

#define __LINUX_RCUPDATE_H

#include 

#include 

#include 

#include 

//#include 

#include 

#include 

#include 

//#include 

#include 

#include 

#include 

#include 

#ifndef CONFIG_TINY_RCU

extern int rcu_expedited; /* for sysctl */

extern int rcu_normal;    /* also for sysctl */

#endif /* #ifndef CONFIG_TINY_RCU */

#ifdef CONFIG_TINY_RCU

/* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny. */

static inline bool rcu_gp_is_normal(void)  /* Internal RCU use. */

{

	return true;

}

static inline bool rcu_gp_is_expedited(void)  /* Internal RCU use. */

{

	return false;

}

static inline void rcu_expedite_gp(void)

{

}

static inline void rcu_unexpedite_gp(void)

{

}

#else /* #ifdef CONFIG_TINY_RCU */

bool rcu_gp_is_normal(void);     /* Internal RCU use. */

bool rcu_gp_is_expedited(void);  /* Internal RCU use. */

void rcu_expedite_gp(void);

void rcu_unexpedite_gp(void);

#endif /* #else #ifdef CONFIG_TINY_RCU */

enum rcutorture_type {

	RCU_FLAVOR,

	RCU_BH_FLAVOR,

	RCU_SCHED_FLAVOR,

	RCU_TASKS_FLAVOR,

	SRCU_FLAVOR,

	INVALID_RCU_FLAVOR

};

#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)

void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,

			    unsigned long *gpnum, unsigned long *completed);

void rcutorture_record_test_transition(void);

void rcutorture_record_progress(unsigned long vernum);

void do_trace_rcu_torture_read(const char *rcutorturename,

			       struct rcu_head *rhp,

			       unsigned long secs,

			       unsigned long c_old,

			       unsigned long c);

#else

static inline void rcutorture_get_gp_data(enum rcutorture_type test_type,

					  int *flags,

					  unsigned long *gpnum,

					  unsigned long *completed)

{

	*flags = 0;

	*gpnum = 0;

	*completed = 0;

}

static inline void rcutorture_record_test_transition(void)

{

}

static inline void rcutorture_record_progress(unsigned long vernum)

{

}

#ifdef CONFIG_RCU_TRACE

void do_trace_rcu_torture_read(const char *rcutorturename,

			       struct rcu_head *rhp,

			       unsigned long secs,

			       unsigned long c_old,

			       unsigned long c);

#else

#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \

	do { } while (0)

#endif

#endif

#define UINT_CMP_GE(a, b)	(UINT_MAX / 2 >= (a) - (b))

#define UINT_CMP_LT(a, b)	(UINT_MAX / 2 < (a) - (b))

#define ULONG_CMP_GE(a, b)	(ULONG_MAX / 2 >= (a) - (b))

#define ULONG_CMP_LT(a, b)	(ULONG_MAX / 2 < (a) - (b))

#define ulong2long(a)		(*(long *)(&(a)))

/* Exported common interfaces */

#ifdef CONFIG_PREEMPT_RCU

/**

 * call_rcu() - Queue an RCU callback for invocation after a grace period.

 * @head: structure to be used for queueing the RCU updates.

 * @func: actual callback function to be invoked after the grace period

 *

 * The callback function will be invoked some time after a full grace

 * period elapses, in other words after all pre-existing RCU read-side

 * critical sections have completed.  However, the callback function

 * might well execute concurrently with RCU read-side critical sections

 * that started after call_rcu() was invoked.  RCU read-side critical

 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),

 * and may be nested.

 *

 * Note that all CPUs must agree that the grace period extended beyond

 * all pre-existing RCU read-side critical section.  On systems with more

 * than one CPU, this means that when "func()" is invoked, each CPU is

 * guaranteed to have executed a full memory barrier since the end of its

 * last RCU read-side critical section whose beginning preceded the call

 * to call_rcu().  It also means that each CPU executing an RCU read-side

 * critical section that continues beyond the start of "func()" must have

 * executed a memory barrier after the call_rcu() but before the beginning

 * of that RCU read-side critical section.  Note that these guarantees

 * include CPUs that are offline, idle, or executing in user mode, as

 * well as CPUs that are executing in the kernel.

 *

 * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the

 * resulting RCU callback function "func()", then both CPU A and CPU B are

 * guaranteed to execute a full memory barrier during the time interval

 * between the call to call_rcu() and the invocation of "func()" -- even

 * if CPU A and CPU B are the same CPU (but again only if the system has

 * more than one CPU).

 */

void call_rcu(struct rcu_head *head,

	      rcu_callback_t func);

#else /* #ifdef CONFIG_PREEMPT_RCU */

/* In classic RCU, call_rcu() is just call_rcu_sched(). */

#define	call_rcu	call_rcu_sched

#endif /* #else #ifdef CONFIG_PREEMPT_RCU */

/**

 * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.

 * @head: structure to be used for queueing the RCU updates.

 * @func: actual callback function to be invoked after the grace period

 *

 * The callback function will be invoked some time after a full grace

 * period elapses, in other words after all currently executing RCU

 * read-side critical sections have completed. call_rcu_bh() assumes

 * that the read-side critical sections end on completion of a softirq

 * handler. This means that read-side critical sections in process

 * context must not be interrupted by softirqs. This interface is to be

 * used when most of the read-side critical sections are in softirq context.

 * RCU read-side critical sections are delimited by :

 *  - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context.

 *  OR

 *  - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.

 *  These may be nested.

 *

 * See the description of call_rcu() for more detailed information on

 * memory ordering guarantees.

 */

void call_rcu_bh(struct rcu_head *head,

		 rcu_callback_t func);

/**

 * call_rcu_sched() - Queue an RCU for invocation after sched grace period.

 * @head: structure to be used for queueing the RCU updates.

 * @func: actual callback function to be invoked after the grace period

 *

 * The callback function will be invoked some time after a full grace

 * period elapses, in other words after all currently executing RCU

 * read-side critical sections have completed. call_rcu_sched() assumes

 * that the read-side critical sections end on enabling of preemption

 * or on voluntary preemption.

 * RCU read-side critical sections are delimited by :

 *  - rcu_read_lock_sched() and  rcu_read_unlock_sched(),

 *  OR

 *  anything that disables preemption.

 *  These may be nested.

 *

 * See the description of call_rcu() for more detailed information on

 * memory ordering guarantees.

 */

void call_rcu_sched(struct rcu_head *head,

		    rcu_callback_t func);

void synchronize_sched(void);

#define wait_rcu_gp(...)

/**

 * call_rcu_tasks() - Queue an RCU for invocation task-based grace period

 * @head: structure to be used for queueing the RCU updates.

 * @func: actual callback function to be invoked after the grace period

 *

 * The callback function will be invoked some time after a full grace

 * period elapses, in other words after all currently executing RCU

 * read-side critical sections have completed. call_rcu_tasks() assumes

 * that the read-side critical sections end at a voluntary context

 * switch (not a preemption!), entry into idle, or transition to usermode

 * execution.  As such, there are no read-side primitives analogous to

 * rcu_read_lock() and rcu_read_unlock() because this primitive is intended

 * to determine that all tasks have passed through a safe state, not so

 * much for data-strcuture synchronization.

 *

 * See the description of call_rcu() for more detailed information on

 * memory ordering guarantees.

 */

void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);

void synchronize_rcu_tasks(void);

void rcu_barrier_tasks(void);

#ifdef CONFIG_PREEMPT_RCU

void __rcu_read_lock(void);

void __rcu_read_unlock(void);

void rcu_read_unlock_special(struct task_struct *t);

void synchronize_rcu(void);

/*

 * Defined as a macro as it is a very low level header included from

 * areas that don't even know about current.  This gives the rcu_read_lock()

 * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other

 * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.

 */

#define rcu_preempt_depth() (current->rcu_read_lock_nesting)

#else /* #ifdef CONFIG_PREEMPT_RCU */

static inline void __rcu_read_lock(void)

{

	if (IS_ENABLED(CONFIG_PREEMPT_COUNT))

		preempt_disable();

}

static inline void __rcu_read_unlock(void)

{

	if (IS_ENABLED(CONFIG_PREEMPT_COUNT))

		preempt_enable();

}

static inline void synchronize_rcu(void)

{

	synchronize_sched();

}

static inline int rcu_preempt_depth(void)

{

	return 0;

}

#endif /* #else #ifdef CONFIG_PREEMPT_RCU */

/* Internal to kernel */

void rcu_init(void);

void rcu_sched_qs(void);

void rcu_bh_qs(void);

void rcu_check_callbacks(int user);

void rcu_report_dead(unsigned int cpu);

#ifndef CONFIG_TINY_RCU

void rcu_end_inkernel_boot(void);

#else /* #ifndef CONFIG_TINY_RCU */

static inline void rcu_end_inkernel_boot(void) { }

#endif /* #ifndef CONFIG_TINY_RCU */

#ifdef CONFIG_RCU_STALL_COMMON

void rcu_sysrq_start(void);

void rcu_sysrq_end(void);

#else /* #ifdef CONFIG_RCU_STALL_COMMON */

static inline void rcu_sysrq_start(void)

{

}

static inline void rcu_sysrq_end(void)

{

}

#endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */

#ifdef CONFIG_NO_HZ_FULL

void rcu_user_enter(void);

void rcu_user_exit(void);

#else

static inline void rcu_user_enter(void) { }

static inline void rcu_user_exit(void) { }

#endif /* CONFIG_NO_HZ_FULL */

#ifdef CONFIG_RCU_NOCB_CPU

void rcu_init_nohz(void);

#else /* #ifdef CONFIG_RCU_NOCB_CPU */

static inline void rcu_init_nohz(void)

{

}

#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */

/**

 * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers

 * @a: Code that RCU needs to pay attention to.

 *

 * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden

 * in the inner idle loop, that is, between the rcu_idle_enter() and

 * the rcu_idle_exit() -- RCU will happily ignore any such read-side

 * critical sections.  However, things like powertop need tracepoints

 * in the inner idle loop.

 *

 * This macro provides the way out:  RCU_NONIDLE(do_something_with_RCU())

 * will tell RCU that it needs to pay attending, invoke its argument

 * (in this example, a call to the do_something_with_RCU() function),

 * and then tell RCU to go back to ignoring this CPU.  It is permissible

 * to nest RCU_NONIDLE() wrappers, but the nesting level is currently

 * quite limited.  If deeper nesting is required, it will be necessary

 * to adjust DYNTICK_TASK_NESTING_VALUE accordingly.

 */

#define RCU_NONIDLE(a) \

	do { \

		rcu_irq_enter_irqson(); \

		do { a; } while (0); \

		rcu_irq_exit_irqson(); \

	} while (0)

/*

 * Note a voluntary context switch for RCU-tasks benefit.  This is a

 * macro rather than an inline function to avoid #include hell.

 */

#ifdef CONFIG_TASKS_RCU

#define TASKS_RCU(x) x

extern struct srcu_struct tasks_rcu_exit_srcu;

#define rcu_note_voluntary_context_switch(t) \

	do { \

		rcu_all_qs(); \

		if (READ_ONCE((t)->rcu_tasks_holdout)) \

			WRITE_ONCE((t)->rcu_tasks_holdout, false); \

	} while (0)

#else /* #ifdef CONFIG_TASKS_RCU */

#define TASKS_RCU(x) do { } while (0)

#define rcu_note_voluntary_context_switch(t)	rcu_all_qs()

#endif /* #else #ifdef CONFIG_TASKS_RCU */

/**

 * cond_resched_rcu_qs - Report potential quiescent states to RCU

 *

 * This macro resembles cond_resched(), except that it is defined to

 * report potential quiescent states to RCU-tasks even if the cond_resched()

 * machinery were to be shut off, as some advocate for PREEMPT kernels.

 */

#define cond_resched_rcu_qs() \

do { \

	if (!cond_resched()) \

		rcu_note_voluntary_context_switch(current); \

} while (0)

#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP)

bool __rcu_is_watching(void);

#endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */

/*

 * Infrastructure to implement the synchronize_() primitives in

 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.

 */

#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)

#include 

#elif defined(CONFIG_TINY_RCU)

#include 

#else

#error "Unknown RCU implementation specified to kernel configuration"

#endif

/*

 * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic

 * initialization and destruction of rcu_head on the stack. rcu_head structures

 * allocated dynamically in the heap or defined statically don't need any

 * initialization.

 */

#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD

void init_rcu_head(struct rcu_head *head);

void destroy_rcu_head(struct rcu_head *head);

void init_rcu_head_on_stack(struct rcu_head *head);

void destroy_rcu_head_on_stack(struct rcu_head *head);

#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */

static inline void init_rcu_head(struct rcu_head *head)

{

}

static inline void destroy_rcu_head(struct rcu_head *head)

{

}

static inline void init_rcu_head_on_stack(struct rcu_head *head)

{

}

static inline void destroy_rcu_head_on_stack(struct rcu_head *head)

{

}

#endif	/* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */

#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)

bool rcu_lockdep_current_cpu_online(void);

#else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */

static inline bool rcu_lockdep_current_cpu_online(void)

{

	return true;

}

#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */

#ifdef CONFIG_DEBUG_LOCK_ALLOC

static inline void rcu_lock_acquire(struct lockdep_map *map)

{

	lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);

}

static inline void rcu_lock_release(struct lockdep_map *map)

{

	lock_release(map, 1, _THIS_IP_);

}

extern struct lockdep_map rcu_lock_map;

extern struct lockdep_map rcu_bh_lock_map;

extern struct lockdep_map rcu_sched_lock_map;

extern struct lockdep_map rcu_callback_map;

int debug_lockdep_rcu_enabled(void);

int rcu_read_lock_held(void);

int rcu_read_lock_bh_held(void);

/**

 * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?

 *

 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an

 * RCU-sched read-side critical section.  In absence of

 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side

 * critical section unless it can prove otherwise.

 */

#ifdef CONFIG_PREEMPT_COUNT

int rcu_read_lock_sched_held(void);

#else /* #ifdef CONFIG_PREEMPT_COUNT */

static inline int rcu_read_lock_sched_held(void)

{

	return 1;

}

#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */

#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

# define rcu_lock_acquire(a)		do { } while (0)

# define rcu_lock_release(a)		do { } while (0)

static inline int rcu_read_lock_held(void)

{

	return 1;

}

static inline int rcu_read_lock_bh_held(void)

{

	return 1;

}

#ifdef CONFIG_PREEMPT_COUNT

static inline int rcu_read_lock_sched_held(void)

{

	return preempt_count() != 0 || irqs_disabled();

}

#else /* #ifdef CONFIG_PREEMPT_COUNT */

static inline int rcu_read_lock_sched_held(void)

{

	return 1;

}

#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */

#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */

#ifdef CONFIG_PROVE_RCU

/**

 * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met

 * @c: condition to check

 * @s: informative message

 */

#define RCU_LOCKDEP_WARN(c, s)						\

	do {								\

		static bool __section(.data.unlikely) __warned;		\

		if (debug_lockdep_rcu_enabled() && !__warned && (c)) {	\

			__warned = true;				\

			lockdep_rcu_suspicious(__FILE__, __LINE__, s);	\

		}							\

	} while (0)

#if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)

static inline void rcu_preempt_sleep_check(void)

{

	RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),

			 "Illegal context switch in RCU read-side critical section");

}

#else /* #ifdef CONFIG_PROVE_RCU */

static inline void rcu_preempt_sleep_check(void)

{

}

#endif /* #else #ifdef CONFIG_PROVE_RCU */

#define rcu_sleep_check()						\

	do {								\

		rcu_preempt_sleep_check();				\

		RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map),	\

				 "Illegal context switch in RCU-bh read-side critical section"); \

		RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map),	\

				 "Illegal context switch in RCU-sched read-side critical section"); \

	} while (0)

#else /* #ifdef CONFIG_PROVE_RCU */

#define RCU_LOCKDEP_WARN(c, s) do { } while (0)

#define rcu_sleep_check() do { } while (0)

#endif /* #else #ifdef CONFIG_PROVE_RCU */

/*

 * Helper functions for rcu_dereference_check(), rcu_dereference_protected()

 * and rcu_assign_pointer().  Some of these could be folded into their

 * callers, but they are left separate in order to ease introduction of

 * multiple flavors of pointers to match the multiple flavors of RCU

 * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in

 * the future.

 */

#ifdef __CHECKER__

#define rcu_dereference_sparse(p, space) \

	((void)(((typeof(*p) space *)p) == p))

#else /* #ifdef __CHECKER__ */

#define rcu_dereference_sparse(p, space)

#endif /* #else #ifdef __CHECKER__ */

#define __rcu_access_pointer(p, space) \

({ \

	typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \

	rcu_dereference_sparse(p, space); \

	((typeof(*p) __force __kernel *)(_________p1)); \

})

#define __rcu_dereference_check(p, c, space) \

({ \

	/* Dependency order vs. p above. */ \

	typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \

	RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \

	rcu_dereference_sparse(p, space); \

	((typeof(*p) __force __kernel *)(________p1)); \

})

#define __rcu_dereference_protected(p, c, space) \

({ \

	RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \

	rcu_dereference_sparse(p, space); \

	((typeof(*p) __force __kernel *)(p)); \

})

/**

 * RCU_INITIALIZER() - statically initialize an RCU-protected global variable

 * @v: The value to statically initialize with.

 */

#define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)

/**

 * rcu_assign_pointer() - assign to RCU-protected pointer

 * @p: pointer to assign to

 * @v: value to assign (publish)

 *

 * Assigns the specified value to the specified RCU-protected

 * pointer, ensuring that any concurrent RCU readers will see

 * any prior initialization.

 *

 * Inserts memory barriers on architectures that require them

 * (which is most of them), and also prevents the compiler from

 * reordering the code that initializes the structure after the pointer

 * assignment.  More importantly, this call documents which pointers

 * will be dereferenced by RCU read-side code.

 *

 * In some special cases, you may use RCU_INIT_POINTER() instead

 * of rcu_assign_pointer().  RCU_INIT_POINTER() is a bit faster due

 * to the fact that it does not constrain either the CPU or the compiler.

 * That said, using RCU_INIT_POINTER() when you should have used

 * rcu_assign_pointer() is a very bad thing that results in

 * impossible-to-diagnose memory corruption.  So please be careful.

 * See the RCU_INIT_POINTER() comment header for details.

 *

 * Note that rcu_assign_pointer() evaluates each of its arguments only

 * once, appearances notwithstanding.  One of the "extra" evaluations

 * is in typeof() and the other visible only to sparse (__CHECKER__),

 * neither of which actually execute the argument.  As with most cpp

 * macros, this execute-arguments-only-once property is important, so

 * please be careful when making changes to rcu_assign_pointer() and the

 * other macros that it invokes.

 */

#define rcu_assign_pointer(p, v) smp_store_release(&p, RCU_INITIALIZER(v))

/**

 * rcu_access_pointer() - fetch RCU pointer with no dereferencing

 * @p: The pointer to read

 *

 * Return the value of the specified RCU-protected pointer, but omit the

 * smp_read_barrier_depends() and keep the READ_ONCE().  This is useful

 * when the value of this pointer is accessed, but the pointer is not

 * dereferenced, for example, when testing an RCU-protected pointer against

 * NULL.  Although rcu_access_pointer() may also be used in cases where

 * update-side locks prevent the value of the pointer from changing, you

 * should instead use rcu_dereference_protected() for this use case.

 *

 * It is also permissible to use rcu_access_pointer() when read-side

 * access to the pointer was removed at least one grace period ago, as

 * is the case in the context of the RCU callback that is freeing up

 * the data, or after a synchronize_rcu() returns.  This can be useful

 * when tearing down multi-linked structures after a grace period

 * has elapsed.

 */

#define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)

/**

 * rcu_dereference_check() - rcu_dereference with debug checking

 * @p: The pointer to read, prior to dereferencing

 * @c: The conditions under which the dereference will take place

 *

 * Do an rcu_dereference(), but check that the conditions under which the

 * dereference will take place are correct.  Typically the conditions

 * indicate the various locking conditions that should be held at that

 * point.  The check should return true if the conditions are satisfied.

 * An implicit check for being in an RCU read-side critical section

 * (rcu_read_lock()) is included.

 *

 * For example:

 *

 *	bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));

 *

 * could be used to indicate to lockdep that foo->bar may only be dereferenced

 * if either rcu_read_lock() is held, or that the lock required to replace

 * the bar struct at foo->bar is held.

 *

 * Note that the list of conditions may also include indications of when a lock

 * need not be held, for example during initialisation or destruction of the

 * target struct:

 *

 *	bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||

 *					      atomic_read(&foo->usage) == 0);

 *

 * Inserts memory barriers on architectures that require them

 * (currently only the Alpha), prevents the compiler from refetching

 * (and from merging fetches), and, more importantly, documents exactly

 * which pointers are protected by RCU and checks that the pointer is

 * annotated as __rcu.

 */

#define rcu_dereference_check(p, c) \

	__rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)

/**

 * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking

 * @p: The pointer to read, prior to dereferencing

 * @c: The conditions under which the dereference will take place

 *

 * This is the RCU-bh counterpart to rcu_dereference_check().

 */

#define rcu_dereference_bh_check(p, c) \

	__rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu)

/**

 * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking

 * @p: The pointer to read, prior to dereferencing

 * @c: The conditions under which the dereference will take place

 *

 * This is the RCU-sched counterpart to rcu_dereference_check().

 */

#define rcu_dereference_sched_check(p, c) \

	__rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \

				__rcu)

#define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/

/*

 * The tracing infrastructure traces RCU (we want that), but unfortunately

 * some of the RCU checks causes tracing to lock up the system.

 *

 * The no-tracing version of rcu_dereference_raw() must not call

 * rcu_read_lock_held().

 */

#define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu)

/**

 * rcu_dereference_protected() - fetch RCU pointer when updates prevented

 * @p: The pointer to read, prior to dereferencing

 * @c: The conditions under which the dereference will take place

 *

 * Return the value of the specified RCU-protected pointer, but omit

 * both the smp_read_barrier_depends() and the READ_ONCE().  This

 * is useful in cases where update-side locks prevent the value of the

 * pointer from changing.  Please note that this primitive does -not-

 * prevent the compiler from repeating this reference or combining it

 * with other references, so it should not be used without protection

 * of appropriate locks.

 *

 * This function is only for update-side use.  Using this function

 * when protected only by rcu_read_lock() will result in infrequent

 * but very ugly failures.

 */

#define rcu_dereference_protected(p, c) \

	__rcu_dereference_protected((p), (c), __rcu)

/**

 * rcu_dereference() - fetch RCU-protected pointer for dereferencing

 * @p: The pointer to read, prior to dereferencing

 *

 * This is a simple wrapper around rcu_dereference_check().

 */

#define rcu_dereference(p) rcu_dereference_check(p, 0)

/**

 * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing

 * @p: The pointer to read, prior to dereferencing

 *

 * Makes rcu_dereference_check() do the dirty work.

 */

#define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)

/**

 * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing

 * @p: The pointer to read, prior to dereferencing

 *

 * Makes rcu_dereference_check() do the dirty work.

 */

#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)

/**

 * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism

 * @p: The pointer to hand off

 *

 * This is simply an identity function, but it documents where a pointer

 * is handed off from RCU to some other synchronization mechanism, for

 * example, reference counting or locking.  In C11, it would map to

 * kill_dependency().  It could be used as follows:

 *

 *	rcu_read_lock();

 *	p = rcu_dereference(gp);

 *	long_lived = is_long_lived(p);

 *	if (long_lived) {

 *		if (!atomic_inc_not_zero(p->refcnt))

 *			long_lived = false;

 *		else

 *			p = rcu_pointer_handoff(p);

 *	}

 *	rcu_read_unlock();

 */

#define rcu_pointer_handoff(p) (p)

/**

 * rcu_read_lock() - mark the beginning of an RCU read-side critical section

 *

 * When synchronize_rcu() is invoked on one CPU while other CPUs

 * are within RCU read-side critical sections, then the

 * synchronize_rcu() is guaranteed to block until after all the other

 * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked

 * on one CPU while other CPUs are within RCU read-side critical

 * sections, invocation of the corresponding RCU callback is deferred

 * until after the all the other CPUs exit their critical sections.

 *

 * Note, however, that RCU callbacks are permitted to run concurrently

 * with new RCU read-side critical sections.  One way that this can happen

 * is via the following sequence of events: (1) CPU 0 enters an RCU

 * read-side critical section, (2) CPU 1 invokes call_rcu() to register

 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,

 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU

 * callback is invoked.  This is legal, because the RCU read-side critical

 * section that was running concurrently with the call_rcu() (and which

 * therefore might be referencing something that the corresponding RCU

 * callback would free up) has completed before the corresponding

 * RCU callback is invoked.

 *

 * RCU read-side critical sections may be nested.  Any deferred actions

 * will be deferred until the outermost RCU read-side critical section

 * completes.

 *

 * You can avoid reading and understanding the next paragraph by

 * following this rule: don't put anything in an rcu_read_lock() RCU

 * read-side critical section that would block in a !PREEMPT kernel.

 * But if you want the full story, read on!

 *

 * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU),

 * it is illegal to block while in an RCU read-side critical section.

 * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPT

 * kernel builds, RCU read-side critical sections may be preempted,

 * but explicit blocking is illegal.  Finally, in preemptible RCU

 * implementations in real-time (with -rt patchset) kernel builds, RCU

 * read-side critical sections may be preempted and they may also block, but

 * only when acquiring spinlocks that are subject to priority inheritance.

 */

static inline void rcu_read_lock(void)

{

	__rcu_read_lock();

	__acquire(RCU);

	rcu_lock_acquire(&rcu_lock_map);

	RCU_LOCKDEP_WARN(!rcu_is_watching(),

			 "rcu_read_lock() used illegally while idle");

}

/*

 * So where is rcu_write_lock()?  It does not exist, as there is no

 * way for writers to lock out RCU readers.  This is a feature, not

 * a bug -- this property is what provides RCU's performance benefits.

 * Of course, writers must coordinate with each other.  The normal

 * spinlock primitives work well for this, but any other technique may be

 * used as well.  RCU does not care how the writers keep out of each

 * others' way, as long as they do so.

 */

/**

 * rcu_read_unlock() - marks the end of an RCU read-side critical section.

 *

 * In most situations, rcu_read_unlock() is immune from deadlock.

 * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()

 * is responsible for deboosting, which it does via rt_mutex_unlock().

 * Unfortunately, this function acquires the scheduler's runqueue and

 * priority-inheritance spinlocks.  This means that deadlock could result

 * if the caller of rcu_read_unlock() already holds one of these locks or

 * any lock that is ever acquired while holding them; or any lock which

 * can be taken from interrupt context because rcu_boost()->rt_mutex_lock()

 * does not disable irqs while taking ->wait_lock.

 *

 * That said, RCU readers are never priority boosted unless they were

 * preempted.  Therefore, one way to avoid deadlock is to make sure

 * that preemption never happens within any RCU read-side critical

 * section whose outermost rcu_read_unlock() is called with one of

 * rt_mutex_unlock()'s locks held.  Such preemption can be avoided in

 * a number of ways, for example, by invoking preempt_disable() before

 * critical section's outermost rcu_read_lock().

 *

 * Given that the set of locks acquired by rt_mutex_unlock() might change

 * at any time, a somewhat more future-proofed approach is to make sure

 * that that preemption never happens within any RCU read-side critical

 * section whose outermost rcu_read_unlock() is called with irqs disabled.

 * This approach relies on the fact that rt_mutex_unlock() currently only

 * acquires irq-disabled locks.

 *

 * The second of these two approaches is best in most situations,

 * however, the first approach can also be useful, at least to those

 * developers willing to keep abreast of the set of locks acquired by

 * rt_mutex_unlock().

 *

 * See rcu_read_lock() for more information.

 */

static inline void rcu_read_unlock(void)

{

	RCU_LOCKDEP_WARN(!rcu_is_watching(),

			 "rcu_read_unlock() used illegally while idle");

	__release(RCU);

	__rcu_read_unlock();

	rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */

}

/**

 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section

 *

 * This is equivalent of rcu_read_lock(), but to be used when updates

 * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since

 * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a

 * softirq handler to be a quiescent state, a process in RCU read-side

 * critical section must be protected by disabling softirqs. Read-side

 * critical sections in interrupt context can use just rcu_read_lock(),

 * though this should at least be commented to avoid confusing people

 * reading the code.

 *

 * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()

 * must occur in the same context, for example, it is illegal to invoke

 * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()

 * was invoked from some other task.

 */

static inline void rcu_read_lock_bh(void)

{

	local_bh_disable();

	__acquire(RCU_BH);

	rcu_lock_acquire(&rcu_bh_lock_map);

	RCU_LOCKDEP_WARN(!rcu_is_watching(),

			 "rcu_read_lock_bh() used illegally while idle");

}

/*

 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section

 *

 * See rcu_read_lock_bh() for more information.

 */

static inline void rcu_read_unlock_bh(void)

{

	RCU_LOCKDEP_WARN(!rcu_is_watching(),

			 "rcu_read_unlock_bh() used illegally while idle");

	rcu_lock_release(&rcu_bh_lock_map);

	__release(RCU_BH);

	local_bh_enable();

}

/**

 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section

 *

 * This is equivalent of rcu_read_lock(), but to be used when updates

 * are being done using call_rcu_sched() or synchronize_rcu_sched().

 * Read-side critical sections can also be introduced by anything that

 * disables preemption, including local_irq_disable() and friends.

 *

 * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()

 * must occur in the same context, for example, it is illegal to invoke

 * rcu_read_unlock_sched() from process context if the matching

 * rcu_read_lock_sched() was invoked from an NMI handler.

 */

static inline void rcu_read_lock_sched(void)

{

	preempt_disable();

	__acquire(RCU_SCHED);

	rcu_lock_acquire(&rcu_sched_lock_map);

	RCU_LOCKDEP_WARN(!rcu_is_watching(),

			 "rcu_read_lock_sched() used illegally while idle");

}

/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */

static inline notrace void rcu_read_lock_sched_notrace(void)

{

	preempt_disable_notrace();

	__acquire(RCU_SCHED);

}

/*

 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section

 *

 * See rcu_read_lock_sched for more information.

 */

static inline void rcu_read_unlock_sched(void)

{

	RCU_LOCKDEP_WARN(!rcu_is_watching(),

			 "rcu_read_unlock_sched() used illegally while idle");

	rcu_lock_release(&rcu_sched_lock_map);

	__release(RCU_SCHED);

	preempt_enable();

}

/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */

static inline notrace void rcu_read_unlock_sched_notrace(void)

{

	__release(RCU_SCHED);

	preempt_enable_notrace();

}

/**

 * RCU_INIT_POINTER() - initialize an RCU protected pointer

 *

 * Initialize an RCU-protected pointer in special cases where readers

 * do not need ordering constraints on the CPU or the compiler.  These

 * special cases are:

 *

 * 1.	This use of RCU_INIT_POINTER() is NULLing out the pointer -or-

 * 2.	The caller has taken whatever steps are required to prevent

 *	RCU readers from concurrently accessing this pointer -or-

 * 3.	The referenced data structure has already been exposed to

 *	readers either at compile time or via rcu_assign_pointer() -and-

 *	a.	You have not made -any- reader-visible changes to

 *		this structure since then -or-

 *	b.	It is OK for readers accessing this structure from its

 *		new location to see the old state of the structure.  (For

 *		example, the changes were to statistical counters or to

 *		other state where exact synchronization is not required.)

 *

 * Failure to follow these rules governing use of RCU_INIT_POINTER() will

 * result in impossible-to-diagnose memory corruption.  As in the structures

 * will look OK in crash dumps, but any concurrent RCU readers might

 * see pre-initialized values of the referenced data structure.  So

 * please be very careful how you use RCU_INIT_POINTER()!!!

 *

 * If you are creating an RCU-protected linked structure that is accessed

 * by a single external-to-structure RCU-protected pointer, then you may

 * use RCU_INIT_POINTER() to initialize the internal RCU-protected

 * pointers, but you must use rcu_assign_pointer() to initialize the

 * external-to-structure pointer -after- you have completely initialized

 * the reader-accessible portions of the linked structure.

 *

 * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no

 * ordering guarantees for either the CPU or the compiler.

 */

#define RCU_INIT_POINTER(p, v) \

	do { \

		rcu_dereference_sparse(p, __rcu); \

		WRITE_ONCE(p, RCU_INITIALIZER(v)); \

	} while (0)

/**

 * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer

 *

 * GCC-style initialization for an RCU-protected pointer in a structure field.

 */

#define RCU_POINTER_INITIALIZER(p, v) \

		.p = RCU_INITIALIZER(v)

/*

 * Does the specified offset indicate that the corresponding rcu_head

 * structure can be handled by kfree_rcu()?

 */

#define __is_kfree_rcu_offset(offset) ((offset) < 4096)

/*

 * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.

 */

#define __kfree_rcu(head, offset) \

	do { \

		BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \

		kfree_call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \

	} while (0)

/**

 * kfree_rcu() - kfree an object after a grace period.

 * @ptr:	pointer to kfree

 * @rcu_head:	the name of the struct rcu_head within the type of @ptr.

 *

 * Many rcu callbacks functions just call kfree() on the base structure.

 * These functions are trivial, but their size adds up, and furthermore

 * when they are used in a kernel module, that module must invoke the

 * high-latency rcu_barrier() function at module-unload time.

 *

 * The kfree_rcu() function handles this issue.  Rather than encoding a

 * function address in the embedded rcu_head structure, kfree_rcu() instead

 * encodes the offset of the rcu_head structure within the base structure.

 * Because the functions are not allowed in the low-order 4096 bytes of

 * kernel virtual memory, offsets up to 4095 bytes can be accommodated.

 * If the offset is larger than 4095 bytes, a compile-time error will

 * be generated in __kfree_rcu().  If this error is triggered, you can

 * either fall back to use of call_rcu() or rearrange the structure to

 * position the rcu_head structure into the first 4096 bytes.

 *

 * Note that the allowable offset might decrease in the future, for example,

 * to allow something like kmem_cache_free_rcu().

 *

 * The BUILD_BUG_ON check must not involve any function calls, hence the

 * checks are done in macros here.

 */

#define kfree_rcu(ptr, rcu_head)					\

	__kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))

#ifdef CONFIG_TINY_RCU

static inline int rcu_needs_cpu(u64 basemono, u64 *nextevt)

{

	*nextevt = KTIME_MAX;

	return 0;

}

#endif /* #ifdef CONFIG_TINY_RCU */

#if defined(CONFIG_RCU_NOCB_CPU_ALL)

static inline bool rcu_is_nocb_cpu(int cpu) { return true; }

#elif defined(CONFIG_RCU_NOCB_CPU)

bool rcu_is_nocb_cpu(int cpu);

#else

static inline bool rcu_is_nocb_cpu(int cpu) { return false; }

#endif

/* Only for use by adaptive-ticks code. */

#ifdef CONFIG_NO_HZ_FULL_SYSIDLE

bool rcu_sys_is_idle(void);

void rcu_sysidle_force_exit(void);

#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */

static inline bool rcu_sys_is_idle(void)

{

	return false;

}

static inline void rcu_sysidle_force_exit(void)

{

}

#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */

#endif /* __LINUX_RCUPDATE_H */