rcupdate.h 40.2 KB
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/*
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 * Read-Copy Update mechanism for mutual exclusion
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 *
 * 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
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 * along with this program; if not, you can access it online at
 * http://www.gnu.org/licenses/gpl-2.0.html.
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 *
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 * Copyright IBM Corporation, 2001
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 *
 * Author: Dipankar Sarma <dipankar@in.ibm.com>
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 *
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 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
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 * 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 -
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 *		http://lse.sourceforge.net/locking/rcupdate.html
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 *
 */

#ifndef __LINUX_RCUPDATE_H
#define __LINUX_RCUPDATE_H

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#include <linux/types.h>
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#include <linux/cache.h>
#include <linux/spinlock.h>
#include <linux/threads.h>
#include <linux/cpumask.h>
#include <linux/seqlock.h>
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#include <linux/lockdep.h>
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#include <linux/completion.h>
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#include <linux/debugobjects.h>
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#include <linux/bug.h>
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#include <linux/compiler.h>
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#include <linux/ktime.h>

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#include <asm/barrier.h>
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extern int rcu_expedited; /* for sysctl */
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#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_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_expedited(void);  /* Internal RCU use. */
void rcu_expedite_gp(void);
void rcu_unexpedite_gp(void);
#endif /* #else #ifdef CONFIG_TINY_RCU */

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enum rcutorture_type {
	RCU_FLAVOR,
	RCU_BH_FLAVOR,
	RCU_SCHED_FLAVOR,
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	RCU_TASKS_FLAVOR,
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	SRCU_FLAVOR,
	INVALID_RCU_FLAVOR
};

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#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
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void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
			    unsigned long *gpnum, unsigned long *completed);
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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);
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#else
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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;
}
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static inline void rcutorture_record_test_transition(void)
{
}
static inline void rcutorture_record_progress(unsigned long vernum)
{
}
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#ifdef CONFIG_RCU_TRACE
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void do_trace_rcu_torture_read(const char *rcutorturename,
			       struct rcu_head *rhp,
			       unsigned long secs,
			       unsigned long c_old,
			       unsigned long c);
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#else
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#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
	do { } while (0)
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#endif
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#endif

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#define UINT_CMP_GE(a, b)	(UINT_MAX / 2 >= (a) - (b))
#define UINT_CMP_LT(a, b)	(UINT_MAX / 2 < (a) - (b))
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#define ULONG_CMP_GE(a, b)	(ULONG_MAX / 2 >= (a) - (b))
#define ULONG_CMP_LT(a, b)	(ULONG_MAX / 2 < (a) - (b))
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#define ulong2long(a)		(*(long *)(&(a)))
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/* Exported common interfaces */
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#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.
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 *
 * 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).
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 */
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void call_rcu(struct rcu_head *head,
	      void (*func)(struct rcu_head *head));
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#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.
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 *
 * See the description of call_rcu() for more detailed information on
 * memory ordering guarantees.
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 */
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void call_rcu_bh(struct rcu_head *head,
		 void (*func)(struct rcu_head *head));
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/**
 * 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.
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 *
 * See the description of call_rcu() for more detailed information on
 * memory ordering guarantees.
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 */
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void call_rcu_sched(struct rcu_head *head,
		    void (*func)(struct rcu_head *rcu));
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void synchronize_sched(void);
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/*
 * Structure allowing asynchronous waiting on RCU.
 */
struct rcu_synchronize {
	struct rcu_head head;
	struct completion completion;
};
void wakeme_after_rcu(struct rcu_head *head);

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void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
		   struct rcu_synchronize *rs_array);

#define _wait_rcu_gp(checktiny, ...) \
do { \
	call_rcu_func_t __crcu_array[] = { __VA_ARGS__ }; \
	const int __n = ARRAY_SIZE(__crcu_array); \
	struct rcu_synchronize __rs_array[__n]; \
	\
	__wait_rcu_gp(checktiny, __n, __crcu_array, __rs_array); \
} while (0)

#define wait_rcu_gp(...) _wait_rcu_gp(false, __VA_ARGS__)

/**
 * synchronize_rcu_mult - Wait concurrently for multiple grace periods
 * @...: List of call_rcu() functions for the flavors to wait on.
 *
 * This macro waits concurrently for multiple flavors of RCU grace periods.
 * For example, synchronize_rcu_mult(call_rcu, call_rcu_bh) would wait
 * on concurrent RCU and RCU-bh grace periods.  Waiting on a give SRCU
 * domain requires you to write a wrapper function for that SRCU domain's
 * call_srcu() function, supplying the corresponding srcu_struct.
 *
 * If Tiny RCU, tell _wait_rcu_gp() not to bother waiting for RCU
 * or RCU-bh, given that anywhere synchronize_rcu_mult() can be called
 * is automatically a grace period.
 */
#define synchronize_rcu_mult(...) \
	_wait_rcu_gp(IS_ENABLED(CONFIG_TINY_RCU), __VA_ARGS__)

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/**
 * 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, void (*func)(struct rcu_head *head));
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void synchronize_rcu_tasks(void);
void rcu_barrier_tasks(void);
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#ifdef CONFIG_PREEMPT_RCU

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void __rcu_read_lock(void);
void __rcu_read_unlock(void);
void rcu_read_unlock_special(struct task_struct *t);
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void synchronize_rcu(void);

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/*
 * 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)

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#else /* #ifdef CONFIG_PREEMPT_RCU */

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

static inline void __rcu_read_unlock(void)
{
	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 */
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void rcu_init(void);
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void rcu_end_inkernel_boot(void);
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void rcu_sched_qs(void);
void rcu_bh_qs(void);
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void rcu_check_callbacks(int user);
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struct notifier_block;
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int rcu_cpu_notify(struct notifier_block *self,
		   unsigned long action, void *hcpu);
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#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 */

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#ifdef CONFIG_NO_HZ_FULL
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void rcu_user_enter(void);
void rcu_user_exit(void);
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#else
static inline void rcu_user_enter(void) { }
static inline void rcu_user_exit(void) { }
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static inline void rcu_user_hooks_switch(struct task_struct *prev,
					 struct task_struct *next) { }
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#endif /* CONFIG_NO_HZ_FULL */
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#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 */

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/**
 * 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 { \
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		rcu_irq_enter(); \
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		do { a; } while (0); \
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		rcu_irq_exit(); \
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	} while (0)

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/*
 * 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
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#define TASKS_RCU(x) x
extern struct srcu_struct tasks_rcu_exit_srcu;
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#define rcu_note_voluntary_context_switch(t) \
	do { \
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		rcu_all_qs(); \
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		if (READ_ONCE((t)->rcu_tasks_holdout)) \
			WRITE_ONCE((t)->rcu_tasks_holdout, false); \
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	} while (0)
#else /* #ifdef CONFIG_TASKS_RCU */
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#define TASKS_RCU(x) do { } while (0)
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#define rcu_note_voluntary_context_switch(t)	rcu_all_qs()
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#endif /* #else #ifdef CONFIG_TASKS_RCU */

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/**
 * 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 { \
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	if (!cond_resched()) \
		rcu_note_voluntary_context_switch(current); \
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} while (0)

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#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP)
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bool __rcu_is_watching(void);
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#endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */

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

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#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
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#include <linux/rcutree.h>
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#elif defined(CONFIG_TINY_RCU)
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#include <linux/rcutiny.h>
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#else
#error "Unknown RCU implementation specified to kernel configuration"
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#endif
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/*
 * 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
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void init_rcu_head(struct rcu_head *head);
void destroy_rcu_head(struct rcu_head *head);
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void init_rcu_head_on_stack(struct rcu_head *head);
void destroy_rcu_head_on_stack(struct rcu_head *head);
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#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
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static inline void init_rcu_head(struct rcu_head *head)
{
}

static inline void destroy_rcu_head(struct rcu_head *head)
{
}

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static inline void init_rcu_head_on_stack(struct rcu_head *head)
{
}

static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
{
}
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#endif	/* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
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#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)
{
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	return true;
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}
#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */

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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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static inline void rcu_lock_acquire(struct lockdep_map *map)
{
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	lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
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}

static inline void rcu_lock_release(struct lockdep_map *map)
{
	lock_release(map, 1, _THIS_IP_);
}

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extern struct lockdep_map rcu_lock_map;
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extern struct lockdep_map rcu_bh_lock_map;
extern struct lockdep_map rcu_sched_lock_map;
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extern struct lockdep_map rcu_callback_map;
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int debug_lockdep_rcu_enabled(void);
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int rcu_read_lock_held(void);
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int rcu_read_lock_bh_held(void);
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/**
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 * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
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 *
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 * 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
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 * critical section unless it can prove otherwise.
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 */
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#ifdef CONFIG_PREEMPT_COUNT
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int rcu_read_lock_sched_held(void);
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#else /* #ifdef CONFIG_PREEMPT_COUNT */
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static inline int rcu_read_lock_sched_held(void)
{
	return 1;
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}
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#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
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#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

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# define rcu_lock_acquire(a)		do { } while (0)
# define rcu_lock_release(a)		do { } while (0)
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static inline int rcu_read_lock_held(void)
{
	return 1;
}

static inline int rcu_read_lock_bh_held(void)
{
	return 1;
}

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#ifdef CONFIG_PREEMPT_COUNT
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static inline int rcu_read_lock_sched_held(void)
{
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	return preempt_count() != 0 || irqs_disabled();
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}
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#else /* #ifdef CONFIG_PREEMPT_COUNT */
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static inline int rcu_read_lock_sched_held(void)
{
	return 1;
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}
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#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
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#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */

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/* Deprecate rcu_lockdep_assert():  Use RCU_LOCKDEP_WARN() instead. */
static inline void __attribute((deprecated)) deprecate_rcu_lockdep_assert(void)
{
}

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#ifdef CONFIG_PROVE_RCU

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/**
 * rcu_lockdep_assert - emit lockdep splat if specified condition not met
 * @c: condition to check
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 * @s: informative message
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 */
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#define rcu_lockdep_assert(c, s)					\
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	do {								\
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		static bool __section(.data.unlikely) __warned;		\
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		deprecate_rcu_lockdep_assert();				\
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		if (debug_lockdep_rcu_enabled() && !__warned && !(c)) {	\
			__warned = true;				\
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			lockdep_rcu_suspicious(__FILE__, __LINE__, s);	\
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		}							\
	} while (0)

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/**
 * 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)

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#if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
static inline void rcu_preempt_sleep_check(void)
{
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	RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
			 "Illegal context switch in RCU read-side critical section");
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}
#else /* #ifdef CONFIG_PROVE_RCU */
static inline void rcu_preempt_sleep_check(void)
{
}
#endif /* #else #ifdef CONFIG_PROVE_RCU */

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#define rcu_sleep_check()						\
	do {								\
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		rcu_preempt_sleep_check();				\
590 591 592 593
		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"); \
594 595
	} while (0)

596 597
#else /* #ifdef CONFIG_PROVE_RCU */

598 599
#define rcu_lockdep_assert(c, s) deprecate_rcu_lockdep_assert()
#define RCU_LOCKDEP_WARN(c, s) do { } while (0)
600
#define rcu_sleep_check() do { } while (0)
601 602 603 604 605 606 607 608 609 610 611

#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.
 */
612 613 614 615 616 617 618 619

#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__ */

620
#define __rcu_access_pointer(p, space) \
621
({ \
622
	typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \
623 624 625
	rcu_dereference_sparse(p, space); \
	((typeof(*p) __force __kernel *)(_________p1)); \
})
626
#define __rcu_dereference_check(p, c, space) \
627
({ \
628 629
	/* Dependency order vs. p above. */ \
	typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
630
	RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
631
	rcu_dereference_sparse(p, space); \
632
	((typeof(*p) __force __kernel *)(________p1)); \
633
})
634
#define __rcu_dereference_protected(p, c, space) \
635
({ \
636
	RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
637 638 639
	rcu_dereference_sparse(p, space); \
	((typeof(*p) __force __kernel *)(p)); \
})
640

641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677
/**
 * 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.
 */
678
#define rcu_assign_pointer(p, v) smp_store_release(&p, RCU_INITIALIZER(v))
679 680 681 682 683 684

/**
 * 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
685
 * smp_read_barrier_depends() and keep the READ_ONCE().  This is useful
686 687 688 689 690
 * 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.
691 692 693 694 695 696 697
 *
 * 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.
698 699 700
 */
#define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)

701
/**
702
 * rcu_dereference_check() - rcu_dereference with debug checking
703 704
 * @p: The pointer to read, prior to dereferencing
 * @c: The conditions under which the dereference will take place
705
 *
706
 * Do an rcu_dereference(), but check that the conditions under which the
707 708 709 710 711
 * 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.
712 713 714
 *
 * For example:
 *
715
 *	bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
716 717
 *
 * could be used to indicate to lockdep that foo->bar may only be dereferenced
718
 * if either rcu_read_lock() is held, or that the lock required to replace
719 720 721 722 723 724
 * 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:
 *
725
 *	bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
726
 *					      atomic_read(&foo->usage) == 0);
727 728 729 730 731 732
 *
 * 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.
733 734
 */
#define rcu_dereference_check(p, c) \
735
	__rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
736 737 738 739 740 741 742 743 744

/**
 * 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) \
745
	__rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu)
746

747
/**
748 749 750 751 752 753 754
 * 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) \
755
	__rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \
756 757 758 759
				__rcu)

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

760 761 762 763 764 765 766 767 768
/*
 * The tracing infrastructure traces RCU (we want that), but unfortunately
 * some of the RCU checks causes tracing to lock up the system.
 *
 * The 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)

769 770 771 772
/**
 * 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
773 774
 *
 * Return the value of the specified RCU-protected pointer, but omit
775
 * both the smp_read_barrier_depends() and the READ_ONCE().  This
776 777 778 779 780
 * 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.
781 782 783 784
 *
 * 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.
785 786
 */
#define rcu_dereference_protected(p, c) \
787
	__rcu_dereference_protected((p), (c), __rcu)
788

789

790
/**
791 792
 * rcu_dereference() - fetch RCU-protected pointer for dereferencing
 * @p: The pointer to read, prior to dereferencing
793
 *
794
 * This is a simple wrapper around rcu_dereference_check().
795
 */
796
#define rcu_dereference(p) rcu_dereference_check(p, 0)
797

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/**
799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815
 * 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_read_lock() - mark the beginning of an RCU read-side critical section
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 *
817
 * When synchronize_rcu() is invoked on one CPU while other CPUs
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 * are within RCU read-side critical sections, then the
819
 * synchronize_rcu() is guaranteed to block until after all the other
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 * 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
826
 * with new RCU read-side critical sections.  One way that this can happen
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 * 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.
 *
841 842 843 844 845
 * 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!
 *
846 847
 * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU),
 * it is illegal to block while in an RCU read-side critical section.
848
 * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPT
849 850 851 852 853
 * 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.
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 */
855 856 857 858
static inline void rcu_read_lock(void)
{
	__rcu_read_lock();
	__acquire(RCU);
859
	rcu_lock_acquire(&rcu_lock_map);
860 861
	RCU_LOCKDEP_WARN(!rcu_is_watching(),
			 "rcu_read_lock() used illegally while idle");
862
}
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/*
 * 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.
 */
873 874

/**
875
 * rcu_read_unlock() - marks the end of an RCU read-side critical section.
876
 *
877 878 879 880 881 882
 * 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
883 884 885
 * 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.
886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906
 *
 * 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().
 *
907 908
 * See rcu_read_lock() for more information.
 */
909 910
static inline void rcu_read_unlock(void)
{
911 912
	RCU_LOCKDEP_WARN(!rcu_is_watching(),
			 "rcu_read_unlock() used illegally while idle");
913 914
	__release(RCU);
	__rcu_read_unlock();
915
	rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
916
}
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/**
919
 * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
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 *
 * This is equivalent of rcu_read_lock(), but to be used when updates
922 923 924 925 926 927 928
 * 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.
929 930 931 932 933
 *
 * 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.
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 */
935 936
static inline void rcu_read_lock_bh(void)
{
937
	local_bh_disable();
938
	__acquire(RCU_BH);
939
	rcu_lock_acquire(&rcu_bh_lock_map);
940 941
	RCU_LOCKDEP_WARN(!rcu_is_watching(),
			 "rcu_read_lock_bh() used illegally while idle");
942
}
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/*
 * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
 *
 * See rcu_read_lock_bh() for more information.
 */
949 950
static inline void rcu_read_unlock_bh(void)
{
951 952
	RCU_LOCKDEP_WARN(!rcu_is_watching(),
			 "rcu_read_unlock_bh() used illegally while idle");
953
	rcu_lock_release(&rcu_bh_lock_map);
954
	__release(RCU_BH);
955
	local_bh_enable();
956
}
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958
/**
959
 * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
960
 *
961 962 963 964
 * 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.
965 966 967 968 969
 *
 * 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.
970
 */
971 972 973
static inline void rcu_read_lock_sched(void)
{
	preempt_disable();
974
	__acquire(RCU_SCHED);
975
	rcu_lock_acquire(&rcu_sched_lock_map);
976 977
	RCU_LOCKDEP_WARN(!rcu_is_watching(),
			 "rcu_read_lock_sched() used illegally while idle");
978
}
979 980

/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
981
static inline notrace void rcu_read_lock_sched_notrace(void)
982 983
{
	preempt_disable_notrace();
984
	__acquire(RCU_SCHED);
985
}
986 987 988 989 990 991

/*
 * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
 *
 * See rcu_read_lock_sched for more information.
 */
992 993
static inline void rcu_read_unlock_sched(void)
{
994 995
	RCU_LOCKDEP_WARN(!rcu_is_watching(),
			 "rcu_read_unlock_sched() used illegally while idle");
996
	rcu_lock_release(&rcu_sched_lock_map);
997
	__release(RCU_SCHED);
998 999
	preempt_enable();
}
1000 1001

/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
1002
static inline notrace void rcu_read_unlock_sched_notrace(void)
1003
{
1004
	__release(RCU_SCHED);
1005 1006
	preempt_enable_notrace();
}
1007

1008 1009 1010
/**
 * RCU_INIT_POINTER() - initialize an RCU protected pointer
 *
1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038
 * 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.
1039 1040 1041
 *
 * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
 * ordering guarantees for either the CPU or the compiler.
1042 1043
 */
#define RCU_INIT_POINTER(p, v) \
1044
	do { \
1045
		rcu_dereference_sparse(p, __rcu); \
1046
		WRITE_ONCE(p, RCU_INITIALIZER(v)); \
1047
	} while (0)
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1049 1050 1051 1052 1053 1054
/**
 * 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) \
1055
		.p = RCU_INITIALIZER(v)
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1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068
/*
 * 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)); \
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		kfree_call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \
1070 1071
	} while (0)

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/**
 * 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().
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 *
 * The BUILD_BUG_ON check must not involve any function calls, hence the
 * checks are done in macros here.
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Lai Jiangshan 已提交
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 */
#define kfree_rcu(ptr, rcu_head)					\
	__kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))

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#ifdef CONFIG_TINY_RCU
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static inline int rcu_needs_cpu(u64 basemono, u64 *nextevt)
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{
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	*nextevt = KTIME_MAX;
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	return 0;
}
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#endif /* #ifdef CONFIG_TINY_RCU */
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#if defined(CONFIG_RCU_NOCB_CPU_ALL)
static inline bool rcu_is_nocb_cpu(int cpu) { return true; }
#elif defined(CONFIG_RCU_NOCB_CPU)
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bool rcu_is_nocb_cpu(int cpu);
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#else
static inline bool rcu_is_nocb_cpu(int cpu) { return false; }
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#endif
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/* Only for use by adaptive-ticks code. */
#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
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bool rcu_sys_is_idle(void);
void rcu_sysidle_force_exit(void);
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#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 */


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Linus Torvalds 已提交
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#endif /* __LINUX_RCUPDATE_H */