include/linux/rcupdate.h - kernel/msm - Gitiles

 /*
  * 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 IBM Corporation, 2001
  *
  * Author: Dipankar Sarma <dipankar@in.ibm.com>
  *
  * Based on the original work by Paul McKenney <paulmck@us.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

 #ifdef __KERNEL__

 #include <linux/cache.h>
 #include <linux/spinlock.h>
 #include <linux/threads.h>
 #include <linux/percpu.h>
 #include <linux/cpumask.h>
 #include <linux/seqlock.h>
 #include <linux/lockdep.h>

 /**
  * struct rcu_head - callback structure for use with RCU
  * @next: next update requests in a list
  * @func: actual update function to call after the grace period.
  */
 struct rcu_head {
 	struct rcu_head *next;
 	void (*func)(struct rcu_head *head);
 };

 #ifdef CONFIG_CLASSIC_RCU
 #include <linux/rcuclassic.h>
 #else /* #ifdef CONFIG_CLASSIC_RCU */
 #include <linux/rcupreempt.h>
 #endif /* #else #ifdef CONFIG_CLASSIC_RCU */

 #define RCU_HEAD_INIT 	{ .next = NULL, .func = NULL }
 #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
 #define INIT_RCU_HEAD(ptr) do { \
        (ptr)->next = NULL; (ptr)->func = NULL; \
 } while (0)

 /**
  * rcu_read_lock - mark the beginning of an RCU read-side critical section.
  *
  * When synchronize_rcu() is invoked on one CPU while other CPUs
  * are within RCU read-side critical sections, then the
  * synchronize_rcu() is guaranteed to block until after all the other
  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
  * on one CPU while other CPUs are within RCU read-side critical
  * sections, invocation of the corresponding RCU callback is deferred
  * until after the all the other CPUs exit their critical sections.
  *
  * Note, however, that RCU callbacks are permitted to run concurrently
  * with RCU read-side critical sections.  One way that this can happen
  * is via the following sequence of events: (1) CPU 0 enters an RCU
  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
  * callback is invoked.  This is legal, because the RCU read-side critical
  * section that was running concurrently with the call_rcu() (and which
  * therefore might be referencing something that the corresponding RCU
  * callback would free up) has completed before the corresponding
  * RCU callback is invoked.
  *
  * RCU read-side critical sections may be nested.  Any deferred actions
  * will be deferred until the outermost RCU read-side critical section
  * completes.
  *
  * It is illegal to block while in an RCU read-side critical section.
  */
 #define rcu_read_lock() __rcu_read_lock()

 /**
  * rcu_read_unlock - marks the end of an RCU read-side critical section.
  *
  * See rcu_read_lock() for more information.
  */

 /*
  * 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.
  */
 #define rcu_read_unlock() __rcu_read_unlock()

 /**
  * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
  *
  * This is equivalent of rcu_read_lock(), but to be used when updates
  * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
  * 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().
  *
  */
 #define rcu_read_lock_bh() __rcu_read_lock_bh()

 /*
  * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
  *
  * See rcu_read_lock_bh() for more information.
  */
 #define rcu_read_unlock_bh() __rcu_read_unlock_bh()

 /*
  * Prevent the compiler from merging or refetching accesses.  The compiler
  * is also forbidden from reordering successive instances of ACCESS_ONCE(),
  * but only when the compiler is aware of some particular ordering.  One way
  * to make the compiler aware of ordering is to put the two invocations of
  * ACCESS_ONCE() in different C statements.
  *
  * This macro does absolutely -nothing- to prevent the CPU from reordering,
  * merging, or refetching absolutely anything at any time.
  */
 #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))

 /**
  * rcu_dereference - fetch an RCU-protected pointer in an
  * RCU read-side critical section.  This pointer may later
  * be safely dereferenced.
  *
  * Inserts memory barriers on architectures that require them
  * (currently only the Alpha), and, more importantly, documents
  * exactly which pointers are protected by RCU.
  */

 #define rcu_dereference(p)     ({ \
 				typeof(p) _________p1 = ACCESS_ONCE(p); \
 				smp_read_barrier_depends(); \
 				(_________p1); \
 				})

 /**
  * rcu_assign_pointer - assign (publicize) a pointer to a newly
  * initialized structure that will be dereferenced by RCU read-side
  * critical sections.  Returns the value assigned.
  *
  * Inserts memory barriers on architectures that require them
  * (pretty much all of them other than x86), 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.
  */

 #define rcu_assign_pointer(p, v)	({ \
 						smp_wmb(); \
 						(p) = (v); \
 					})

 /**
  * synchronize_sched - block until all CPUs have exited any non-preemptive
  * kernel code sequences.
  *
  * This means that all preempt_disable code sequences, including NMI and
  * hardware-interrupt handlers, in progress on entry will have completed
  * before this primitive returns.  However, this does not guarantee that
  * softirq handlers will have completed, since in some kernels, these
  * handlers can run in process context, and can block.
  *
  * This primitive provides the guarantees made by the (now removed)
  * synchronize_kernel() API.  In contrast, synchronize_rcu() only
  * guarantees that rcu_read_lock() sections will have completed.
  * In "classic RCU", these two guarantees happen to be one and
  * the same, but can differ in realtime RCU implementations.
  */
 #define synchronize_sched() __synchronize_sched()

 /**
  * call_rcu - Queue an RCU callback for invocation after a grace period.
  * @head: structure to be used for queueing the RCU updates.
  * @func: actual update function to be invoked after the grace period
  *
  * The update 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.  RCU read-side critical
  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
  * and may be nested.
  */
 extern void call_rcu(struct rcu_head *head,
 			      void (*func)(struct rcu_head *head));

 /**
  * 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 update function to be invoked after the grace period
  *
  * The update 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.
  */
 extern void call_rcu_bh(struct rcu_head *head,
 			void (*func)(struct rcu_head *head));

 /* Exported common interfaces */
 extern void synchronize_rcu(void);
 extern void rcu_barrier(void);
 extern long rcu_batches_completed(void);
 extern long rcu_batches_completed_bh(void);

 /* Internal to kernel */
 extern void rcu_init(void);
 extern int rcu_needs_cpu(int cpu);

 #endif /* __KERNEL__ */
 #endif /* __LINUX_RCUPDATE_H */
	/*
	* 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 IBM Corporation, 2001
	*
	* Author: Dipankar Sarma <dipankar@in.ibm.com>
	*
	* Based on the original work by Paul McKenney <paulmck@us.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

	#ifdef __KERNEL__

	#include <linux/cache.h>
	#include <linux/spinlock.h>
	#include <linux/threads.h>
	#include <linux/percpu.h>
	#include <linux/cpumask.h>
	#include <linux/seqlock.h>
	#include <linux/lockdep.h>

	/**
	* struct rcu_head - callback structure for use with RCU
	* @next: next update requests in a list
	* @func: actual update function to call after the grace period.
	*/
	struct rcu_head {
	struct rcu_head *next;
	void (func)(struct rcu_head head);
	};

	#ifdef CONFIG_CLASSIC_RCU
	#include <linux/rcuclassic.h>
	#else /* #ifdef CONFIG_CLASSIC_RCU */
	#include <linux/rcupreempt.h>
	#endif /* #else #ifdef CONFIG_CLASSIC_RCU */

	#define RCU_HEAD_INIT { .next = NULL, .func = NULL }
	#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
	#define INIT_RCU_HEAD(ptr) do { \
	(ptr)->next = NULL; (ptr)->func = NULL; \
	} while (0)

	/**
	* rcu_read_lock - mark the beginning of an RCU read-side critical section.
	*
	* When synchronize_rcu() is invoked on one CPU while other CPUs
	* are within RCU read-side critical sections, then the
	* synchronize_rcu() is guaranteed to block until after all the other
	* CPUs exit their critical sections. Similarly, if call_rcu() is invoked
	* on one CPU while other CPUs are within RCU read-side critical
	* sections, invocation of the corresponding RCU callback is deferred
	* until after the all the other CPUs exit their critical sections.
	*
	* Note, however, that RCU callbacks are permitted to run concurrently
	* with RCU read-side critical sections. One way that this can happen
	* is via the following sequence of events: (1) CPU 0 enters an RCU
	* read-side critical section, (2) CPU 1 invokes call_rcu() to register
	* an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
	* (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
	* callback is invoked. This is legal, because the RCU read-side critical
	* section that was running concurrently with the call_rcu() (and which
	* therefore might be referencing something that the corresponding RCU
	* callback would free up) has completed before the corresponding
	* RCU callback is invoked.
	*
	* RCU read-side critical sections may be nested. Any deferred actions
	* will be deferred until the outermost RCU read-side critical section
	* completes.
	*
	* It is illegal to block while in an RCU read-side critical section.
	*/
	#define rcu_read_lock() __rcu_read_lock()

	/**
	* rcu_read_unlock - marks the end of an RCU read-side critical section.
	*
	* See rcu_read_lock() for more information.
	*/

	/*
	* 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.
	*/
	#define rcu_read_unlock() __rcu_read_unlock()

	/**
	* rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
	*
	* This is equivalent of rcu_read_lock(), but to be used when updates
	* are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
	* 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().
	*
	*/
	#define rcu_read_lock_bh() __rcu_read_lock_bh()

	/*
	* rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
	*
	* See rcu_read_lock_bh() for more information.
	*/
	#define rcu_read_unlock_bh() __rcu_read_unlock_bh()

	/*
	* Prevent the compiler from merging or refetching accesses. The compiler
	* is also forbidden from reordering successive instances of ACCESS_ONCE(),
	* but only when the compiler is aware of some particular ordering. One way
	* to make the compiler aware of ordering is to put the two invocations of
	* ACCESS_ONCE() in different C statements.
	*
	* This macro does absolutely -nothing- to prevent the CPU from reordering,
	* merging, or refetching absolutely anything at any time.
	*/
	#define ACCESS_ONCE(x) ((volatile typeof(x) )&(x))

	/**
	* rcu_dereference - fetch an RCU-protected pointer in an
	* RCU read-side critical section. This pointer may later
	* be safely dereferenced.
	*
	* Inserts memory barriers on architectures that require them
	* (currently only the Alpha), and, more importantly, documents
	* exactly which pointers are protected by RCU.
	*/

	#define rcu_dereference(p) ({ \
	typeof(p) _________p1 = ACCESS_ONCE(p); \
	smp_read_barrier_depends(); \
	(_________p1); \
	})

	/**
	* rcu_assign_pointer - assign (publicize) a pointer to a newly
	* initialized structure that will be dereferenced by RCU read-side
	* critical sections. Returns the value assigned.
	*
	* Inserts memory barriers on architectures that require them
	* (pretty much all of them other than x86), 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.
	*/

	#define rcu_assign_pointer(p, v) ({ \
	smp_wmb(); \
	(p) = (v); \
	})

	/**
	* synchronize_sched - block until all CPUs have exited any non-preemptive
	* kernel code sequences.
	*
	* This means that all preempt_disable code sequences, including NMI and
	* hardware-interrupt handlers, in progress on entry will have completed
	* before this primitive returns. However, this does not guarantee that
	* softirq handlers will have completed, since in some kernels, these
	* handlers can run in process context, and can block.
	*
	* This primitive provides the guarantees made by the (now removed)
	* synchronize_kernel() API. In contrast, synchronize_rcu() only
	* guarantees that rcu_read_lock() sections will have completed.
	* In "classic RCU", these two guarantees happen to be one and
	* the same, but can differ in realtime RCU implementations.
	*/
	#define synchronize_sched() __synchronize_sched()

	/**
	* call_rcu - Queue an RCU callback for invocation after a grace period.
	* @head: structure to be used for queueing the RCU updates.
	* @func: actual update function to be invoked after the grace period
	*
	* The update 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. RCU read-side critical
	* sections are delimited by rcu_read_lock() and rcu_read_unlock(),
	* and may be nested.
	*/
	extern void call_rcu(struct rcu_head *head,
	void (func)(struct rcu_head head));

	/**
	* 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 update function to be invoked after the grace period
	*
	* The update 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.
	*/
	extern void call_rcu_bh(struct rcu_head *head,
	void (func)(struct rcu_head head));

	/* Exported common interfaces */
	extern void synchronize_rcu(void);
	extern void rcu_barrier(void);
	extern long rcu_batches_completed(void);
	extern long rcu_batches_completed_bh(void);

	/* Internal to kernel */
	extern void rcu_init(void);
	extern int rcu_needs_cpu(int cpu);

	#endif /* __KERNEL__ */
	#endif /* __LINUX_RCUPDATE_H */