path: root/include/linux/rcupdate.h

/* SPDX-License-Identifier: GPL-2.0+ */
/*
 * Read-Copy Update mechanism for mutual exclusion
 *
 * Copyright IBM Corporation, 2001
 *
 * Author: Dipankar Sarma <dipankar@in.ibm.com>
 *
 * Based on the original work by Paul McKenney <paulmck@vnet.ibm.com>
 * 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 <linux/types.h>
#include <linux/compiler.h>
#include <linux/atomic.h>
#include <linux/irqflags.h>
#include <linux/preempt.h>
#include <linux/bottom_half.h>
#include <linux/lockdep.h>
#include <linux/cleanup.h>
#include <asm/processor.h>
#include <linux/cpumask.h>
#include <linux/context_tracking_irq.h>

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

/* Exported common interfaces */
void call_rcu(struct rcu_head *head, rcu_callback_t func);
void rcu_barrier_tasks(void);
void rcu_barrier_tasks_rude(void);
void synchronize_rcu(void);

struct rcu_gp_oldstate;
unsigned long get_completed_synchronize_rcu(void);
void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp);

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

/**
 * same_state_synchronize_rcu - 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_rcu(), start_poll_synchronize_rcu(), or
 * get_completed_synchronize_rcu().  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_rcu(unsigned long oldstate1, unsigned long oldstate2)
{
	return oldstate1 == oldstate2;
}

#ifdef CONFIG_PREEMPT_RCU

void __rcu_read_lock(void);
void __rcu_read_unlock(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() READ_ONCE(current->rcu_read_lock_nesting)

#else /* #ifdef CONFIG_PREEMPT_RCU */

#ifdef CONFIG_TINY_RCU
#define rcu_read_unlock_strict() do { } while (0)
#else
void rcu_read_unlock_strict(void);
#endif

static inline void __rcu_read_lock(void)
{
	preempt_disable();
}

static inline void __rcu_read_unlock(void)
{
	preempt_enable();
	if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
		rcu_read_unlock_strict();
}

static inline int rcu_preempt_depth(void)
{
	return 0;
}

#endif /* #else #ifdef CONFIG_PREEMPT_RCU */

#ifdef CONFIG_RCU_LAZY
void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func);
#else
static inline void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func)
{
	call_rcu(head, func);
}
#endif

/* Internal to kernel */
void rcu_init(void);
extern int rcu_scheduler_active;
void rcu_sched_clock_irq(int user);

#ifdef CONFIG_TASKS_RCU_GENERIC
void rcu_init_tasks_generic(void);
#else
static inline void rcu_init_tasks_generic(void) { }
#endif

#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 */

#if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK))
void rcu_irq_work_resched(void);
#else
static inline void rcu_irq_work_resched(void) { }
#endif

#ifdef CONFIG_RCU_NOCB_CPU
void rcu_init_nohz(void);
int rcu_nocb_cpu_offload(int cpu);
int rcu_nocb_cpu_deoffload(int cpu);
void rcu_nocb_flush_deferred_wakeup(void);
#else /* #ifdef CONFIG_RCU_NOCB_CPU */
static inline void rcu_init_nohz(void) { }
static inline int rcu_nocb_cpu_offload(int cpu) { return -EINVAL; }
static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; }
static inline void rcu_nocb_flush_deferred_wakeup(void) { }
#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */

/*
 * Note a quasi-voluntary context switch for RCU-tasks's benefit.
 * This is a macro rather than an inline function to avoid #include hell.
 */
#ifdef CONFIG_TASKS_RCU_GENERIC

# ifdef CONFIG_TASKS_RCU
# define rcu_tasks_classic_qs(t, preempt)				\
	do {								\
		if (!(preempt) && READ_ONCE((t)->rcu_tasks_holdout))	\
			WRITE_ONCE((t)->rcu_tasks_holdout, false);	\
	} while (0)
void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
void synchronize_rcu_tasks(void);
# else
# define rcu_tasks_classic_qs(t, preempt) do { } while (0)
# define call_rcu_tasks call_rcu
# define synchronize_rcu_tasks synchronize_rcu
# endif

# ifdef CONFIG_TASKS_TRACE_RCU
// Bits for ->trc_reader_special.b.need_qs field.
#define TRC_NEED_QS		0x1  // Task needs a quiescent state.
#define TRC_NEED_QS_CHECKED	0x2  // Task has been checked for needing quiescent state.

u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new);
void rcu_tasks_trace_qs_blkd(struct task_struct *t);

# define rcu_tasks_trace_qs(t)							\
	do {									\
		int ___rttq_nesting = READ_ONCE((t)->trc_reader_nesting);	\
										\
		if (unlikely(READ_ONCE((t)->trc_reader_special.b.need_qs) == TRC_NEED_QS) &&	\
		    likely(!___rttq_nesting)) {					\
			rcu_trc_cmpxchg_need_qs((t), TRC_NEED_QS, TRC_NEED_QS_CHECKED);	\
		} else if (___rttq_nesting && ___rttq_nesting != INT_MIN &&	\
			   !READ_ONCE((t)->trc_reader_special.b.blocked)) {	\
			rcu_tasks_trace_qs_blkd(t);				\
		}								\
	} while (0)
# else
# define rcu_tasks_trace_qs(t) do { } while (0)
# endif

#define rcu_tasks_qs(t, preempt)					\
do {									\
	rcu_tasks_classic_qs((t), (preempt));				\
	rcu_tasks_trace_qs(t);						\
} while (0)

# ifdef CONFIG_TASKS_RUDE_RCU
void call_rcu_tasks_rude(struct rcu_head *head, rcu_callback_t func);
void synchronize_rcu_tasks_rude(void);
# endif

#define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t, false)
void exit_tasks_rcu_start(void);
void exit_tasks_rcu_stop(void);
void exit_tasks_rcu_finish(void);
#else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
#define rcu_tasks_classic_qs(t, preempt) do { } while (0)
#define rcu_tasks_qs(t, preempt) do { } while (0)
#define rcu_note_voluntary_context_switch(t) do { } while (0)
#define call_rcu_tasks call_rcu
#define synchronize_rcu_tasks synchronize_rcu
static inline void exit_tasks_rcu_start(void) { }
static inline void exit_tasks_rcu_stop(void) { }
static inline void exit_tasks_rcu_finish(void) { }
#endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */

/**
 * rcu_trace_implies_rcu_gp - does an RCU Tasks Trace grace period imply an RCU grace period?
 *
 * As an accident of implementation, an RCU Tasks Trace grace period also
 * acts as an RCU grace period.  However, this could change at any time.
 * Code relying on this accident must call this function to verify that
 * this accident is still happening.
 *
 * You have been warned!
 */
static inline bool rcu_trace_implies_rcu_gp(void) { return true; }

/**
 * cond_resched_tasks_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 PREEMPTION kernels.
 */
#define cond_resched_tasks_rcu_qs() \
do { \
	rcu_tasks_qs(current, false); \
	cond_resched(); \
} while (0)

/*
 * Infrastructure to implement the synchronize_() primitives in
 * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
 */

#if defined(CONFIG_TREE_RCU)
#include <linux/rcutree.h>
#elif defined(CONFIG_TINY_RCU)
#include <linux/rcutiny.h>
#else
#error "Unknown RCU implementation specified to kernel configuration"
#endif

/*
 * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls
 * are needed for dynamic initialization and destruction of rcu_head
 * on the stack, and init_rcu_head()/destroy_rcu_head() are needed for
 * dynamic initialization and destruction of statically allocated rcu_head
 * structures.  However, rcu_head structures allocated dynamically in the
 * heap 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) */

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;

#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_try_lock_acquire(struct lockdep_map *map)
{
	lock_acquire(map, 0, 1, 2, 0, NULL, _THIS_IP_);
}

static inline void rcu_lock_release(struct lockdep_map *map)
{
	lock_release(map, _THIS_IP_);
}

int debug_lockdep_rcu_enabled(void);
int rcu_read_lock_held(void);
int rcu_read_lock_bh_held(void);
int rcu_read_lock_sched_held(void);
int rcu_read_lock_any_held(void);

#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

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

static inline int rcu_read_lock_sched_held(void)
{
	return !preemptible();
}

static inline int rcu_read_lock_any_held(void)
{
	return !preemptible();
}

static inline int debug_lockdep_rcu_enabled(void)
{
	return 0;
}

#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
 *
 * This checks debug_lockdep_rcu_enabled() before checking (c) to
 * prevent early boot splats due to lockdep not yet being initialized,
 * and rechecks it after checking (c) to prevent false-positive splats
 * due to races with lockdep being disabled.  See commit 3066820034b5dd
 * ("rcu: Reject RCU_LOCKDEP_WARN() false positives") for more detail.
 */
#define RCU_LOCKDEP_WARN(c, s)						\
	do {								\
		static bool __section(".data.unlikely") __warned;	\
		if (debug_lockdep_rcu_enabled() && (c) &&		\
		    debug_lockdep_rcu_enabled() && !__warned) {		\
			__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();				\
		if (!IS_ENABLED(CONFIG_PREEMPT_RT))			\
		    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 && (c))
#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 pointers markings to match different RCU implementations
 * (e.g., __srcu), should this make sense in the future.
 */

#ifdef __CHECKER__
#define rcu_check_sparse(p, space) \
	((void)(((typeof(*p) space *)p) == p))
#else /* #ifdef __CHECKER__ */
#define rcu_check_sparse(p, space)
#endif /* #else #ifdef __CHECKER__ */

#define __unrcu_pointer(p, local)					\
({									\
	typeof(*p) *local = (typeof(*p) *__force)(p);			\
	rcu_check_sparse(p, __rcu);					\
	((typeof(*p) __force __kernel *)(local)); 			\
})
/**
 * unrcu_pointer - mark a pointer as not being RCU protected
 * @p: pointer needing to lose its __rcu property
 *
 * Converts @p from an __rcu pointer to a __kernel pointer.
 * This allows an __rcu pointer to be used with xchg() and friends.
 */
#define unrcu_pointer(p) __unrcu_pointer(p, __UNIQUE_ID(rcu))

#define __rcu_access_pointer(p, local, space) \
({ \
	typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
	rcu_check_sparse(p, space); \
	((typeof(*p) __force __kernel *)(local)); \
})
#define __rcu_dereference_check(p, local, c, space) \
({ \
	/* Dependency order vs. p above. */ \
	typeof(*p) *local = (typeof(*p) *__force)READ_ONCE(p); \
	RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
	rcu_check_sparse(p, space); \
	((typeof(*p) __force __kernel *)(local)); \
})
#define __rcu_dereference_protected(p, local, c, space) \
({ \
	RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
	rcu_check_sparse(p, space); \
	((typeof(*p) __force __kernel *)(p)); \
})
#define __rcu_dereference_raw(p, local) \
({ \
	/* Dependency order vs. p above. */ \
	typeof(p) local = READ_ONCE(p); \
	((typeof(*p) __force __kernel *)(local)); \
})
#define rcu_dereference_raw(p) __rcu_dereference_raw(p, __UNIQUE_ID(rcu))

/**
 * 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)					      \
do {									      \
	uintptr_t _r_a_p__v = (uintptr_t)(v);				      \
	rcu_check_sparse(p, __rcu);					      \
									      \
	if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL)	      \
		WRITE_ONCE((p), (typeof(p))(_r_a_p__v));		      \
	else								      \
		smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
} while (0)

/**
 * rcu_replace_pointer() - replace an RCU pointer, returning its old value
 * @rcu_ptr: RCU pointer, whose old value is returned
 * @ptr: regular pointer
 * @c: the lockdep conditions under which the dereference will take place
 *
 * Perform a replacement, where @rcu_ptr is an RCU-annotated
 * pointer and @c is the lockdep argument that is passed to the
 * rcu_dereference_protected() call used to read that pointer.  The old
 * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr.
 */
#define rcu_replace_pointer(rcu_ptr, ptr, c)				\
({									\
	typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c));	\
	rcu_assign_pointer((rcu_ptr), (ptr));				\
	__tmp;								\
})

/**
 * 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
 * lockdep checks for being in an RCU read-side critical section.  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.
 * Within an RCU read-side critical section, there is little reason to
 * use rcu_access_pointer().
 *
 * It is usually best to test the rcu_access_pointer() return value
 * directly in order to avoid accidental dereferences being introduced
 * by later inattentive changes.  In other words, assigning the
 * rcu_access_pointer() return value to a local variable results in an
 * accident waiting to happen.
 *
 * 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.  However,
 * rcu_dereference_protected() is normally preferred for this use case.
 */
#define rcu_access_pointer(p) __rcu_access_pointer((p), __UNIQUE_ID(rcu), __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), __UNIQUE_ID(rcu), \
				(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().  However,
 * please note that starting in v5.0 kernels, vanilla RCU grace periods
 * wait for local_bh_disable() regions of code in addition to regions of
 * code demarked by rcu_read_lock() and rcu_read_unlock().  This means
 * that synchronize_rcu(), call_rcu, and friends all take not only
 * rcu_read_lock() but also rcu_read_lock_bh() into account.
 */
#define rcu_dereference_bh_check(p, c) \
	__rcu_dereference_check((p), __UNIQUE_ID(rcu), \
				(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().
 * However, please note that starting in v5.0 kernels, vanilla RCU grace
 * periods wait for preempt_disable() regions of code in addition to
 * regions of code demarked by rcu_read_lock() and rcu_read_unlock().
 * This means that synchronize_rcu(), call_rcu, and friends all take not
 * only rcu_read_lock() but also rcu_read_lock_sched() into account.
 */
#define rcu_dereference_sched_check(p, c) \
	__rcu_dereference_check((p), __UNIQUE_ID(rcu), \
				(c) || rcu_read_lock_sched_held(), \
				__rcu)

/*
 * 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_check(p) \
	__rcu_dereference_check((p), __UNIQUE_ID(rcu), 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
 * 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), __UNIQUE_ID(rcu), (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_l