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/*

 * Read-Copy Update mechanism for mutual exclusion

 *

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

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

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

 * (at your option) any later version.

 *

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

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

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

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

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

 *

 * Copyright (C) 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);

};

#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)

/* Global control variables for rcupdate callback mechanism. */

struct rcu_ctrlblk {

        long    cur;            /* Current batch number.                      */

        long    completed;      /* Number of the last completed batch         */

        int     next_pending;   /* Is the next batch already waiting?         */

        int     signaled;

        spinlock_t      lock    ____cacheline_internodealigned_in_smp;

        cpumask_t       cpumask; /* CPUs that need to switch in order    */

                                 /* for current batch to proceed.        */

} ____cacheline_internodealigned_in_smp;

/* Is batch a before batch b ? */

static inline int rcu_batch_before(long a, long b)

{

        return (a - b) < 0;

}

/* Is batch a after batch b ? */

static inline int rcu_batch_after(long a, long b)

{

        return (a - b) > 0;

}

/*

 * Per-CPU data for Read-Copy UPdate.

 * nxtlist - new callbacks are added here

 * curlist - current batch for which quiescent cycle started if any

 */

struct rcu_data {

        /* 1) quiescent state handling : */

        long            quiescbatch;     /* Batch # for grace period */

        int             passed_quiesc;   /* User-mode/idle loop etc. */

        int             qs_pending;      /* core waits for quiesc state */

        /* 2) batch handling */

        long            batch;           /* Batch # for current RCU batch */

        struct rcu_head *nxtlist;

        struct rcu_head **nxttail;

        long            qlen;            /* # of queued callbacks */

        struct rcu_head *curlist;

        struct rcu_head **curtail;

        struct rcu_head *donelist;

        struct rcu_head **donetail;

        long            blimit;          /* Upper limit on a processed batch */

        int cpu;

        struct rcu_head barrier;

};

DECLARE_PER_CPU(struct rcu_data, rcu_data);

DECLARE_PER_CPU(struct rcu_data, rcu_bh_data);

/*

 * Increment the quiescent state counter.

 * The counter is a bit degenerated: We do not need to know

 * how many quiescent states passed, just if there was at least

 * one since the start of the grace period. Thus just a flag.

 */

static inline void rcu_qsctr_inc(int cpu)

{

        struct rcu_data *rdp = &per_cpu(rcu_data, cpu);

        rdp->passed_quiesc = 1;

}

static inline void rcu_bh_qsctr_inc(int cpu)

{

        struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);

        rdp->passed_quiesc = 1;

}

extern int rcu_pending(int cpu);

extern int rcu_needs_cpu(int cpu);

#ifdef CONFIG_DEBUG_LOCK_ALLOC

extern struct lockdep_map rcu_lock_map;

# define rcu_read_acquire()     lock_acquire(&rcu_lock_map, 0, 0, 2, 1, _THIS_IP_)

# define rcu_read_release()     lock_release(&rcu_lock_map, 1, _THIS_IP_)

#else

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

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

#endif

/**

 * 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() \

        do { \

                preempt_disable(); \

                __acquire(RCU); \

                rcu_read_acquire(); \

        } while(0)

/**

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

 *

 * See rcu_read_lock() for more information.

 */

#define rcu_read_unlock() \

        do { \

                rcu_read_release(); \

                __release(RCU); \

                preempt_enable(); \

        } while(0)

/*

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

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

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

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

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

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

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

 */

/**

 * rcu_read_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() \

        do { \

                local_bh_disable(); \

                __acquire(RCU_BH); \

                rcu_read_acquire(); \

        } while(0)

/*

 * 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() \

        do { \

                rcu_read_release(); \

                __release(RCU_BH); \

                local_bh_enable(); \

        } while(0)

/*

 * 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_rcu()

extern void rcu_init(void);

extern void rcu_check_callbacks(int cpu, int user);

extern void rcu_restart_cpu(int cpu);

extern long rcu_batches_completed(void);

extern long rcu_batches_completed_bh(void);

/* Exported interfaces */

extern void FASTCALL(call_rcu(struct rcu_head *head,

                                void (*func)(struct rcu_head *head)));

extern void FASTCALL(call_rcu_bh(struct rcu_head *head,

                                void (*func)(struct rcu_head *head)));

extern void synchronize_rcu(void);

extern void rcu_barrier(void);

#endif /* __KERNEL__ */

#endif /* __LINUX_RCUPDATE_H */