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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

 *

 * Authors: Dipankar Sarma <dipankar@in.ibm.com>

 *          Manfred Spraul <manfred@colorfullife.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

 *

 */

#include <linux/types.h>

#include <linux/kernel.h>

#include <linux/init.h>

#include <linux/spinlock.h>

#include <linux/smp.h>

#include <linux/rcupdate.h>

#include <linux/interrupt.h>

#include <linux/sched.h>

#include <asm/atomic.h>

#include <linux/bitops.h>

#include <linux/module.h>

#include <linux/completion.h>

#include <linux/moduleparam.h>

#include <linux/percpu.h>

#include <linux/notifier.h>

#include <linux/cpu.h>

#include <linux/mutex.h>

#ifdef CONFIG_DEBUG_LOCK_ALLOC

static struct lock_class_key rcu_lock_key;

struct lockdep_map rcu_lock_map =

        STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);

EXPORT_SYMBOL_GPL(rcu_lock_map);

#endif

/* Definition for rcupdate control block. */

static struct rcu_ctrlblk rcu_ctrlblk = {

        .cur = -300,

        .completed = -300,

        .lock = __SPIN_LOCK_UNLOCKED(&rcu_ctrlblk.lock),

        .cpumask = CPU_MASK_NONE,

};

static struct rcu_ctrlblk rcu_bh_ctrlblk = {

        .cur = -300,

        .completed = -300,

        .lock = __SPIN_LOCK_UNLOCKED(&rcu_bh_ctrlblk.lock),

        .cpumask = CPU_MASK_NONE,

};

DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L };

DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L };

/* Fake initialization required by compiler */

static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL};

static int blimit = 10;

static int qhimark = 10000;

static int qlowmark = 100;

static atomic_t rcu_barrier_cpu_count;

static DEFINE_MUTEX(rcu_barrier_mutex);

static struct completion rcu_barrier_completion;

#ifdef CONFIG_SMP

static void force_quiescent_state(struct rcu_data *rdp,

                        struct rcu_ctrlblk *rcp)

{

        int cpu;

        cpumask_t cpumask;

        set_need_resched();

        if (unlikely(!rcp->signaled)) {

                rcp->signaled = 1;

                /*

                 * Don't send IPI to itself. With irqs disabled,

                 * rdp->cpu is the current cpu.

                 */

                cpumask = rcp->cpumask;

                cpu_clear(rdp->cpu, cpumask);

                for_each_cpu_mask(cpu, cpumask)

                        smp_send_reschedule(cpu);

        }

}

#else

static inline void force_quiescent_state(struct rcu_data *rdp,

                        struct rcu_ctrlblk *rcp)

{

        set_need_resched();

}

#endif

/**

 * 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.

 */

void fastcall call_rcu(struct rcu_head *head,

                                void (*func)(struct rcu_head *rcu))

{

        unsigned long flags;

        struct rcu_data *rdp;

        head->func = func;

        head->next = NULL;

        local_irq_save(flags);

        rdp = &__get_cpu_var(rcu_data);

        *rdp->nxttail = head;

        rdp->nxttail = &head->next;

        if (unlikely(++rdp->qlen > qhimark)) {

                rdp->blimit = INT_MAX;

                force_quiescent_state(rdp, &rcu_ctrlblk);

        }

        local_irq_restore(flags);

}

/**

 * 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.

 */

void fastcall call_rcu_bh(struct rcu_head *head,

                                void (*func)(struct rcu_head *rcu))

{

        unsigned long flags;

        struct rcu_data *rdp;

        head->func = func;

        head->next = NULL;

        local_irq_save(flags);

        rdp = &__get_cpu_var(rcu_bh_data);

        *rdp->nxttail = head;

        rdp->nxttail = &head->next;

        if (unlikely(++rdp->qlen > qhimark)) {

                rdp->blimit = INT_MAX;

                force_quiescent_state(rdp, &rcu_bh_ctrlblk);

        }

        local_irq_restore(flags);

}

/*

 * Return the number of RCU batches processed thus far.  Useful

 * for debug and statistics.

 */

long rcu_batches_completed(void)

{

        return rcu_ctrlblk.completed;

}

/*

 * Return the number of RCU batches processed thus far.  Useful

 * for debug and statistics.

 */

long rcu_batches_completed_bh(void)

{

        return rcu_bh_ctrlblk.completed;

}

static void rcu_barrier_callback(struct rcu_head *notused)

{

        if (atomic_dec_and_test(&rcu_barrier_cpu_count))

                complete(&rcu_barrier_completion);

}

/*

 * Called with preemption disabled, and from cross-cpu IRQ context.

 */

static void rcu_barrier_func(void *notused)

{

        int cpu = smp_processor_id();

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

        struct rcu_head *head;

        head = &rdp->barrier;

        atomic_inc(&rcu_barrier_cpu_count);

        call_rcu(head, rcu_barrier_callback);

}

/**

 * rcu_barrier - Wait until all the in-flight RCUs are complete.

 */

void rcu_barrier(void)

{

        BUG_ON(in_interrupt());

        /* Take cpucontrol mutex to protect against CPU hotplug */

        mutex_lock(&rcu_barrier_mutex);

        init_completion(&rcu_barrier_completion);

        atomic_set(&rcu_barrier_cpu_count, 0);

        on_each_cpu(rcu_barrier_func, NULL, 0, 1);

        wait_for_completion(&rcu_barrier_completion);

        mutex_unlock(&rcu_barrier_mutex);

}

EXPORT_SYMBOL_GPL(rcu_barrier);

/*

 * Invoke the completed RCU callbacks. They are expected to be in

 * a per-cpu list.

 */

static void rcu_do_batch(struct rcu_data *rdp)

{

        struct rcu_head *next, *list;

        int count = 0;

        list = rdp->donelist;

        while (list) {

                next = list->next;

                prefetch(next);

                list->func(list);

                list = next;

                if (++count >= rdp->blimit)

                        break;

        }

        rdp->donelist = list;

        local_irq_disable();

        rdp->qlen -= count;

        local_irq_enable();

        if (rdp->blimit == INT_MAX && rdp->qlen <= qlowmark)

                rdp->blimit = blimit;

        if (!rdp->donelist)

                rdp->donetail = &rdp->donelist;

        else

                tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu));

}

/*

 * Grace period handling:

 * The grace period handling consists out of two steps:

 * - A new grace period is started.

 *   This is done by rcu_start_batch. The start is not broadcasted to

 *   all cpus, they must pick this up by comparing rcp->cur with

 *   rdp->quiescbatch. All cpus are recorded  in the

 *   rcu_ctrlblk.cpumask bitmap.

 * - All cpus must go through a quiescent state.

 *   Since the start of the grace period is not broadcasted, at least two

 *   calls to rcu_check_quiescent_state are required:

 *   The first call just notices that a new grace period is running. The

 *   following calls check if there was a quiescent state since the beginning

 *   of the grace period. If so, it updates rcu_ctrlblk.cpumask. If

 *   the bitmap is empty, then the grace period is completed.

 *   rcu_check_quiescent_state calls rcu_start_batch(0) to start the next grace

 *   period (if necessary).

 */

/*

 * Register a new batch of callbacks, and start it up if there is currently no

 * active batch and the batch to be registered has not already occurred.

 * Caller must hold rcu_ctrlblk.lock.

 */

static void rcu_start_batch(struct rcu_ctrlblk *rcp)

{

        if (rcp->next_pending &&

                        rcp->completed == rcp->cur) {

                rcp->next_pending = 0;

                /*

                 * next_pending == 0 must be visible in

                 * __rcu_process_callbacks() before it can see new value of cur.

                 */

                smp_wmb();

                rcp->cur++;

                /*

                 * Accessing nohz_cpu_mask before incrementing rcp->cur needs a

                 * Barrier  Otherwise it can cause tickless idle CPUs to be

                 * included in rcp->cpumask, which will extend graceperiods

                 * unnecessarily.

                 */

                smp_mb();

                cpus_andnot(rcp->cpumask, cpu_online_map, nohz_cpu_mask);

                rcp->signaled = 0;

        }

}

/*

 * cpu went through a quiescent state since the beginning of the grace period.

 * Clear it from the cpu mask and complete the grace period if it was the last

 * cpu. Start another grace period if someone has further entries pending

 */

static void cpu_quiet(int cpu, struct rcu_ctrlblk *rcp)

{

        cpu_clear(cpu, rcp->cpumask);

        if (cpus_empty(rcp->cpumask)) {

                /* batch completed ! */

                rcp->completed = rcp->cur;

                rcu_start_batch(rcp);

        }

}

/*

 * Check if the cpu has gone through a quiescent state (say context

 * switch). If so and if it already hasn't done so in this RCU

 * quiescent cycle, then indicate that it has done so.

 */

static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp,

                                        struct rcu_data *rdp)

{

        if (rdp->quiescbatch != rcp->cur) {

                /* start new grace period: */

                rdp->qs_pending = 1;

                rdp->passed_quiesc = 0;

                rdp->quiescbatch = rcp->cur;

                return;

        }

        /* Grace period already completed for this cpu?

         * qs_pending is checked instead of the actual bitmap to avoid

         * cacheline trashing.

         */

        if (!rdp->qs_pending)

                return;

        /*

         * Was there a quiescent state since the beginning of the grace

         * period? If no, then exit and wait for the next call.

         */

        if (!rdp->passed_quiesc)

                return;

        rdp->qs_pending = 0;

        spin_lock(&rcp->lock);

        /*

         * rdp->quiescbatch/rcp->cur and the cpu bitmap can come out of sync

         * during cpu startup. Ignore the quiescent state.

         */

        if (likely(rdp->quiescbatch == rcp->cur))

                cpu_quiet(rdp->cpu, rcp);

        spin_unlock(&rcp->lock);

}

#ifdef CONFIG_HOTPLUG_CPU

/* warning! helper for rcu_offline_cpu. do not use elsewhere without reviewing

 * locking requirements, the list it's pulling from has to belong to a cpu

 * which is dead and hence not processing interrupts.

 */

static void rcu_move_batch(struct rcu_data *this_rdp, struct rcu_head *list,

                                struct rcu_head **tail)

{

        local_irq_disable();

        *this_rdp->nxttail = list;

        if (list)

                this_rdp->nxttail = tail;

        local_irq_enable();

}

static void __rcu_offline_cpu(struct rcu_data *this_rdp,

                                struct rcu_ctrlblk *rcp, struct rcu_data *rdp)

{

        /* if the cpu going offline owns the grace period

         * we can block indefinitely waiting for it, so flush

         * it here

         */

        spin_lock_bh(&rcp->lock);

        if (rcp->cur != rcp->completed)

                cpu_quiet(rdp->cpu, rcp);

        spin_unlock_bh(&rcp->lock);

        rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail);

        rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail);

        rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail);

}

static void rcu_offline_cpu(int cpu)

{

        struct rcu_data *this_rdp = &get_cpu_var(rcu_data);

        struct rcu_data *this_bh_rdp = &get_cpu_var(rcu_bh_data);

        __rcu_offline_cpu(this_rdp, &rcu_ctrlblk,

                                        &per_cpu(rcu_data, cpu));

        __rcu_offline_cpu(this_bh_rdp, &rcu_bh_ctrlblk,

                                        &per_cpu(rcu_bh_data, cpu));

        put_cpu_var(rcu_data);

        put_cpu_var(rcu_bh_data);

        tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu);

}

#else

static void rcu_offline_cpu(int cpu)

{

}

#endif

/*

 * This does the RCU processing work from tasklet context.

 */

static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,

                                        struct rcu_data *rdp)

{

        if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) {

                *rdp->donetail = rdp->curlist;

                rdp->donetail = rdp->curtail;

                rdp->curlist = NULL;

                rdp->curtail = &rdp->curlist;

        }

        if (rdp->nxtlist && !rdp->curlist) {

                local_irq_disable();

                rdp->curlist = rdp->nxtlist;

                rdp->curtail = rdp->nxttail;

                rdp->nxtlist = NULL;

                rdp->nxttail = &rdp->nxtlist;

                local_irq_enable();

                /*

                 * start the next batch of callbacks

                 */

                /* determine batch number */

                rdp->batch = rcp->cur + 1;

                /* see the comment and corresponding wmb() in

                 * the rcu_start_batch()

                 */

                smp_rmb();

                if (!rcp->next_pending) {

                        /* and start it/schedule start if it's a new batch */

                        spin_lock(&rcp->lock);

                        rcp->next_pending = 1;

                        rcu_start_batch(rcp);

                        spin_unlock(&rcp->lock);

                }

        }

        rcu_check_quiescent_state(rcp, rdp);

        if (rdp->donelist)

                rcu_do_batch(rdp);

}

static void rcu_process_callbacks(unsigned long unused)

{

        __rcu_process_callbacks(&rcu_ctrlblk, &__get_cpu_var(rcu_data));

        __rcu_process_callbacks(&rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data));

}

static int __rcu_pending(struct rcu_ctrlblk *rcp, struct rcu_data *rdp)

{

        /* This cpu has pending rcu entries and the grace period

         * for them has completed.

         */

        if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch))

                return 1;

        /* This cpu has no pending entries, but there are new entries */

        if (!rdp->curlist && rdp->nxtlist)

                return 1;

        /* This cpu has finished callbacks to invoke */

        if (rdp->donelist)

                return 1;

        /* The rcu core waits for a quiescent state from the cpu */

        if (rdp->quiescbatch != rcp->cur || rdp->qs_pending)

                return 1;

        /* nothing to do */

        return 0;

}

/*

 * Check to see if there is any immediate RCU-related work to be done

 * by the current CPU, returning 1 if so.  This function is part of the

 * RCU implementation; it is -not- an exported member of the RCU API.

 */

int rcu_pending(int cpu)

{

        return __rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu)) ||

                __rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu));

}

/*

 * Check to see if any future RCU-related work will need to be done

 * by the current CPU, even if none need be done immediately, returning

 * 1 if so.  This function is part of the RCU implementation; it is -not-

 * an exported member of the RCU API.

 */

int rcu_needs_cpu(int cpu)

{

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

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

        return (!!rdp->curlist || !!rdp_bh->curlist || rcu_pending(cpu));

}

void rcu_check_callbacks(int cpu, int user)

{

        if (user ||

            (idle_cpu(cpu) && !in_softirq() &&

                                hardirq_count() <= (1 << HARDIRQ_SHIFT))) {

                rcu_qsctr_inc(cpu);

                rcu_bh_qsctr_inc(cpu);

        } else if (!in_softirq())

                rcu_bh_qsctr_inc(cpu);

        tasklet_schedule(&per_cpu(rcu_tasklet, cpu));

}

static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,

                                                struct rcu_data *rdp)

{

        memset(rdp, 0, sizeof(*rdp));

        rdp->curtail = &rdp->curlist;

        rdp->nxttail = &rdp->nxtlist;

        rdp->donetail = &rdp->donelist;

        rdp->quiescbatch = rcp->completed;

        rdp->qs_pending = 0;

        rdp->cpu = cpu;

        rdp->blimit = blimit;

}

static void __cpuinit rcu_online_cpu(int cpu)

{

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

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

        rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp);

        rcu_init_percpu_data(cpu, &rcu_bh_ctrlblk, bh_rdp);

        tasklet_init(&per_cpu(rcu_tasklet, cpu), rcu_process_callbacks, 0UL);

}

static int __cpuinit rcu_cpu_notify(struct notifier_block *self,

                                unsigned long action, void *hcpu)

{

        long cpu = (long)hcpu;

        switch (action) {

        case CPU_UP_PREPARE:

        case CPU_UP_PREPARE_FROZEN:

                rcu_online_cpu(cpu);

                break;

        case CPU_DEAD:

        case CPU_DEAD_FROZEN:

                rcu_offline_cpu(cpu);

                break;

        default:

                break;

        }

        return NOTIFY_OK;

}

static struct notifier_block __cpuinitdata rcu_nb = {

        .notifier_call  = rcu_cpu_notify,

};

/*

 * Initializes rcu mechanism.  Assumed to be called early.

 * That is before local timer(SMP) or jiffie timer (uniproc) is setup.

 * Note that rcu_qsctr and friends are implicitly

 * initialized due to the choice of ``0'' for RCU_CTR_INVALID.

 */

void __init rcu_init(void)

{

        rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE,

                        (void *)(long)smp_processor_id());

        /* Register notifier for non-boot CPUs */

        register_cpu_notifier(&rcu_nb);

}

struct rcu_synchronize {

        struct rcu_head head;

        struct completion completion;

};

/* Because of FASTCALL declaration of complete, we use this wrapper */

static void wakeme_after_rcu(struct rcu_head  *head)

{

        struct rcu_synchronize *rcu;

        rcu = container_of(head, struct rcu_synchronize, head);

        complete(&rcu->completion);

}

/**

 * synchronize_rcu - wait until a grace period has elapsed.

 *

 * Control will return to the caller some time after a full grace

 * period has elapsed, 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.

 *

 * If your read-side code is not protected by rcu_read_lock(), do -not-

 * use synchronize_rcu().

 */

void synchronize_rcu(void)

{

        struct rcu_synchronize rcu;

        init_completion(&rcu.completion);

        /* Will wake me after RCU finished */

        call_rcu(&rcu.head, wakeme_after_rcu);

        /* Wait for it */

        wait_for_completion(&rcu.completion);

}

module_param(blimit, int, 0);

module_param(qhimark, int, 0);

module_param(qlowmark, int, 0);

EXPORT_SYMBOL_GPL(rcu_batches_completed);

EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);

EXPORT_SYMBOL_GPL(call_rcu);

EXPORT_SYMBOL_GPL(call_rcu_bh);

EXPORT_SYMBOL_GPL(synchronize_rcu);