include/linux/srcu.h - kernel/msm-4.9 - Gitiles

 /*
  * Sleepable 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, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *
  * Copyright (C) IBM Corporation, 2006
  *
  * Author: Paul McKenney <paulmck@us.ibm.com>
  *
  * For detailed explanation of Read-Copy Update mechanism see -
  * 		Documentation/RCU/ *.txt
  *
  */

 #ifndef _LINUX_SRCU_H
 #define _LINUX_SRCU_H

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

 struct srcu_struct_array {
 	int c[2];
 };

 struct srcu_struct {
 	int completed;
 	struct srcu_struct_array __percpu *per_cpu_ref;
 	struct mutex mutex;
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map dep_map;
 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 };

 #ifndef CONFIG_PREEMPT
 #define srcu_barrier() barrier()
 #else /* #ifndef CONFIG_PREEMPT */
 #define srcu_barrier()
 #endif /* #else #ifndef CONFIG_PREEMPT */

 #ifdef CONFIG_DEBUG_LOCK_ALLOC

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

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

 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

 int init_srcu_struct(struct srcu_struct *sp);

 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */

 void cleanup_srcu_struct(struct srcu_struct *sp);
 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
 void synchronize_srcu(struct srcu_struct *sp);
 void synchronize_srcu_expedited(struct srcu_struct *sp);
 long srcu_batches_completed(struct srcu_struct *sp);

 #ifdef CONFIG_DEBUG_LOCK_ALLOC

 /**
  * srcu_read_lock_held - might we be in SRCU read-side critical section?
  *
  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
  * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
  * this assumes we are in an SRCU read-side critical section unless it can
  * prove otherwise.
  *
  * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
  * and while lockdep is disabled.
  *
  * Note that if the CPU is in the idle loop from an RCU point of view
  * (ie: that we are in the section between rcu_idle_enter() and
  * rcu_idle_exit()) then srcu_read_lock_held() returns false even if
  * the CPU did an srcu_read_lock().  The reason for this is that RCU
  * ignores CPUs that are in such a section, considering these as in
  * extended quiescent state, so such a CPU is effectively never in an
  * RCU read-side critical section regardless of what RCU primitives it
  * invokes.  This state of affairs is required --- we need to keep an
  * RCU-free window in idle where the CPU may possibly enter into low
  * power mode. This way we can notice an extended quiescent state to
  * other CPUs that started a grace period. Otherwise we would delay any
  * grace period as long as we run in the idle task.
  *
  * Similarly, we avoid claiming an SRCU read lock held if the current
  * CPU is offline.
  */
 static inline int srcu_read_lock_held(struct srcu_struct *sp)
 {
 	if (!debug_lockdep_rcu_enabled())
 		return 1;
 	if (rcu_is_cpu_idle())
 		return 0;
 	if (!rcu_lockdep_current_cpu_online())
 		return 0;
 	return lock_is_held(&sp->dep_map);
 }

 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

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

 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */

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

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

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

 	rcu_lock_acquire(&(sp)->dep_map);
 	rcu_lockdep_assert(!rcu_is_cpu_idle(),
 			   "srcu_read_lock() used illegally while idle");
 	return retval;
 }

 /**
  * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
  * @sp: srcu_struct in which to unregister the old reader.
  * @idx: return value from corresponding srcu_read_lock().
  *
  * Exit an SRCU read-side critical section.
  */
 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
 	__releases(sp)
 {
 	rcu_lockdep_assert(!rcu_is_cpu_idle(),
 			   "srcu_read_unlock() used illegally while idle");
 	rcu_lock_release(&(sp)->dep_map);
 	__srcu_read_unlock(sp, idx);
 }

 /**
  * srcu_read_lock_raw - register a new reader for an SRCU-protected structure.
  * @sp: srcu_struct in which to register the new reader.
  *
  * Enter an SRCU read-side critical section.  Similar to srcu_read_lock(),
  * but avoids the RCU-lockdep checking.  This means that it is legal to
  * use srcu_read_lock_raw() in one context, for example, in an exception
  * handler, and then have the matching srcu_read_unlock_raw() in another
  * context, for example in the task that took the exception.
  *
  * However, the entire SRCU read-side critical section must reside within a
  * single task.  For example, beware of using srcu_read_lock_raw() in
  * a device interrupt handler and srcu_read_unlock() in the interrupted
  * task:  This will not work if interrupts are threaded.
  */
 static inline int srcu_read_lock_raw(struct srcu_struct *sp)
 {
 	unsigned long flags;
 	int ret;

 	local_irq_save(flags);
 	ret =  __srcu_read_lock(sp);
 	local_irq_restore(flags);
 	return ret;
 }

 /**
  * srcu_read_unlock_raw - unregister reader from an SRCU-protected structure.
  * @sp: srcu_struct in which to unregister the old reader.
  * @idx: return value from corresponding srcu_read_lock_raw().
  *
  * Exit an SRCU read-side critical section without lockdep-RCU checking.
  * See srcu_read_lock_raw() for more details.
  */
 static inline void srcu_read_unlock_raw(struct srcu_struct *sp, int idx)
 {
 	unsigned long flags;

 	local_irq_save(flags);
 	__srcu_read_unlock(sp, idx);
 	local_irq_restore(flags);
 }

 #endif
	/*
	* Sleepable 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, write to the Free Software
	* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
	*
	* Copyright (C) IBM Corporation, 2006
	*
	* Author: Paul McKenney <paulmck@us.ibm.com>
	*
	* For detailed explanation of Read-Copy Update mechanism see -
	* Documentation/RCU/ *.txt
	*
	*/

	#ifndef _LINUX_SRCU_H
	#define _LINUX_SRCU_H

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

	struct srcu_struct_array {
	int c[2];
	};

	struct srcu_struct {
	int completed;
	struct srcu_struct_array __percpu *per_cpu_ref;
	struct mutex mutex;
	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	struct lockdep_map dep_map;
	#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
	};

	#ifndef CONFIG_PREEMPT
	#define srcu_barrier() barrier()
	#else /* #ifndef CONFIG_PREEMPT */
	#define srcu_barrier()
	#endif /* #else #ifndef CONFIG_PREEMPT */

	#ifdef CONFIG_DEBUG_LOCK_ALLOC

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

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

	#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

	int init_srcu_struct(struct srcu_struct *sp);

	#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */

	void cleanup_srcu_struct(struct srcu_struct *sp);
	int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
	void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
	void synchronize_srcu(struct srcu_struct *sp);
	void synchronize_srcu_expedited(struct srcu_struct *sp);
	long srcu_batches_completed(struct srcu_struct *sp);

	#ifdef CONFIG_DEBUG_LOCK_ALLOC

	/**
	* srcu_read_lock_held - might we be in SRCU read-side critical section?
	*
	* If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
	* read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
	* this assumes we are in an SRCU read-side critical section unless it can
	* prove otherwise.
	*
	* Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
	* and while lockdep is disabled.
	*
	* Note that if the CPU is in the idle loop from an RCU point of view
	* (ie: that we are in the section between rcu_idle_enter() and
	* rcu_idle_exit()) then srcu_read_lock_held() returns false even if
	* the CPU did an srcu_read_lock(). The reason for this is that RCU
	* ignores CPUs that are in such a section, considering these as in
	* extended quiescent state, so such a CPU is effectively never in an
	* RCU read-side critical section regardless of what RCU primitives it
	* invokes. This state of affairs is required --- we need to keep an
	* RCU-free window in idle where the CPU may possibly enter into low
	* power mode. This way we can notice an extended quiescent state to
	* other CPUs that started a grace period. Otherwise we would delay any
	* grace period as long as we run in the idle task.
	*
	* Similarly, we avoid claiming an SRCU read lock held if the current
	* CPU is offline.
	*/
	static inline int srcu_read_lock_held(struct srcu_struct *sp)
	{
	if (!debug_lockdep_rcu_enabled())
	return 1;
	if (rcu_is_cpu_idle())
	return 0;
	if (!rcu_lockdep_current_cpu_online())
	return 0;
	return lock_is_held(&sp->dep_map);
	}

	#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

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

	#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */

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

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

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

	rcu_lock_acquire(&(sp)->dep_map);
	rcu_lockdep_assert(!rcu_is_cpu_idle(),
	"srcu_read_lock() used illegally while idle");
	return retval;
	}

	/**
	* srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
	* @sp: srcu_struct in which to unregister the old reader.
	* @idx: return value from corresponding srcu_read_lock().
	*
	* Exit an SRCU read-side critical section.
	*/
	static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
	__releases(sp)
	{
	rcu_lockdep_assert(!rcu_is_cpu_idle(),
	"srcu_read_unlock() used illegally while idle");
	rcu_lock_release(&(sp)->dep_map);
	__srcu_read_unlock(sp, idx);
	}

	/**
	* srcu_read_lock_raw - register a new reader for an SRCU-protected structure.
	* @sp: srcu_struct in which to register the new reader.
	*
	* Enter an SRCU read-side critical section. Similar to srcu_read_lock(),
	* but avoids the RCU-lockdep checking. This means that it is legal to
	* use srcu_read_lock_raw() in one context, for example, in an exception
	* handler, and then have the matching srcu_read_unlock_raw() in another
	* context, for example in the task that took the exception.
	*
	* However, the entire SRCU read-side critical section must reside within a
	* single task. For example, beware of using srcu_read_lock_raw() in
	* a device interrupt handler and srcu_read_unlock() in the interrupted
	* task: This will not work if interrupts are threaded.
	*/
	static inline int srcu_read_lock_raw(struct srcu_struct *sp)
	{
	unsigned long flags;
	int ret;

	local_irq_save(flags);
	ret = __srcu_read_lock(sp);
	local_irq_restore(flags);
	return ret;
	}

	/**
	* srcu_read_unlock_raw - unregister reader from an SRCU-protected structure.
	* @sp: srcu_struct in which to unregister the old reader.
	* @idx: return value from corresponding srcu_read_lock_raw().
	*
	* Exit an SRCU read-side critical section without lockdep-RCU checking.
	* See srcu_read_lock_raw() for more details.
	*/
	static inline void srcu_read_unlock_raw(struct srcu_struct *sp, int idx)
	{
	unsigned long flags;

	local_irq_save(flags);
	__srcu_read_unlock(sp, idx);
	local_irq_restore(flags);
	}

	#endif