perfcounters: fix refcounting bug, take 2

[deliverable/linux.git] / kernel / perf_counter.c

/*
 * Performance counter core code
 *
 *  Copyright(C) 2008 Thomas Gleixner <tglx@linutronix.de>
 *  Copyright(C) 2008 Red Hat, Inc., Ingo Molnar
 *
 *  For licencing details see kernel-base/COPYING
 */

#include <linux/fs.h>
#include <linux/cpu.h>
#include <linux/smp.h>
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/sysfs.h>
#include <linux/ptrace.h>
#include <linux/percpu.h>
#include <linux/uaccess.h>
#include <linux/syscalls.h>
#include <linux/anon_inodes.h>
#include <linux/kernel_stat.h>
#include <linux/perf_counter.h>
#include <linux/mm.h>
#include <linux/vmstat.h>

/*
 * Each CPU has a list of per CPU counters:
 */
DEFINE_PER_CPU(struct perf_cpu_context, perf_cpu_context);

int perf_max_counters __read_mostly = 1;
static int perf_reserved_percpu __read_mostly;
static int perf_overcommit __read_mostly = 1;

/*
 * Mutex for (sysadmin-configurable) counter reservations:
 */
static DEFINE_MUTEX(perf_resource_mutex);

/*
 * Architecture provided APIs - weak aliases:
 */
extern __weak const struct hw_perf_counter_ops *
hw_perf_counter_init(struct perf_counter *counter)
{
        return NULL;
}

u64 __weak hw_perf_save_disable(void)           { return 0; }
void __weak hw_perf_restore(u64 ctrl)           { barrier(); }
void __weak hw_perf_counter_setup(int cpu)      { barrier(); }
int __weak hw_perf_group_sched_in(struct perf_counter *group_leader,
               struct perf_cpu_context *cpuctx,
               struct perf_counter_context *ctx, int cpu)
{
        return 0;
}

void __weak perf_counter_print_debug(void)      { }

static void
list_add_counter(struct perf_counter *counter, struct perf_counter_context *ctx)
{
        struct perf_counter *group_leader = counter->group_leader;

        /*
         * Depending on whether it is a standalone or sibling counter,
         * add it straight to the context's counter list, or to the group
         * leader's sibling list:
         */
        if (counter->group_leader == counter)
                list_add_tail(&counter->list_entry, &ctx->counter_list);
        else
                list_add_tail(&counter->list_entry, &group_leader->sibling_list);
}

static void
list_del_counter(struct perf_counter *counter, struct perf_counter_context *ctx)
{
        struct perf_counter *sibling, *tmp;

        list_del_init(&counter->list_entry);

        /*
         * If this was a group counter with sibling counters then
         * upgrade the siblings to singleton counters by adding them
         * to the context list directly:
         */
        list_for_each_entry_safe(sibling, tmp,
                                 &counter->sibling_list, list_entry) {

                list_del_init(&sibling->list_entry);
                list_add_tail(&sibling->list_entry, &ctx->counter_list);
                sibling->group_leader = sibling;
        }
}

static void
counter_sched_out(struct perf_counter *counter,
                  struct perf_cpu_context *cpuctx,
                  struct perf_counter_context *ctx)
{
        if (counter->state != PERF_COUNTER_STATE_ACTIVE)
                return;

        counter->state = PERF_COUNTER_STATE_INACTIVE;
        counter->hw_ops->disable(counter);
        counter->oncpu = -1;

        if (!is_software_counter(counter))
                cpuctx->active_oncpu--;
        ctx->nr_active--;
        if (counter->hw_event.exclusive || !cpuctx->active_oncpu)
                cpuctx->exclusive = 0;
}

static void
group_sched_out(struct perf_counter *group_counter,
                struct perf_cpu_context *cpuctx,
                struct perf_counter_context *ctx)
{
        struct perf_counter *counter;

        if (group_counter->state != PERF_COUNTER_STATE_ACTIVE)
                return;

        counter_sched_out(group_counter, cpuctx, ctx);

        /*
         * Schedule out siblings (if any):
         */
        list_for_each_entry(counter, &group_counter->sibling_list, list_entry)
                counter_sched_out(counter, cpuctx, ctx);

        if (group_counter->hw_event.exclusive)
                cpuctx->exclusive = 0;
}

/*
 * Cross CPU call to remove a performance counter
 *
 * We disable the counter on the hardware level first. After that we
 * remove it from the context list.
 */
static void __perf_counter_remove_from_context(void *info)
{
        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
        struct perf_counter *counter = info;
        struct perf_counter_context *ctx = counter->ctx;
        unsigned long flags;
        u64 perf_flags;

        /*
         * If this is a task context, we need to check whether it is
         * the current task context of this cpu. If not it has been
         * scheduled out before the smp call arrived.
         */
        if (ctx->task && cpuctx->task_ctx != ctx)
                return;

        curr_rq_lock_irq_save(&flags);
        spin_lock(&ctx->lock);

        counter_sched_out(counter, cpuctx, ctx);

        counter->task = NULL;
        ctx->nr_counters--;

        /*
         * Protect the list operation against NMI by disabling the
         * counters on a global level. NOP for non NMI based counters.
         */
        perf_flags = hw_perf_save_disable();
        list_del_counter(counter, ctx);
        hw_perf_restore(perf_flags);

        if (!ctx->task) {
                /*
                 * Allow more per task counters with respect to the
                 * reservation:
                 */
                cpuctx->max_pertask =
                        min(perf_max_counters - ctx->nr_counters,
                            perf_max_counters - perf_reserved_percpu);
        }

        spin_unlock(&ctx->lock);
        curr_rq_unlock_irq_restore(&flags);
}


/*
 * Remove the counter from a task's (or a CPU's) list of counters.
 *
 * Must be called with counter->mutex and ctx->mutex held.
 *
 * CPU counters are removed with a smp call. For task counters we only
 * call when the task is on a CPU.
 */
static void perf_counter_remove_from_context(struct perf_counter *counter)
{
        struct perf_counter_context *ctx = counter->ctx;
        struct task_struct *task = ctx->task;

        if (!task) {
                /*
                 * Per cpu counters are removed via an smp call and
                 * the removal is always sucessful.
                 */
                smp_call_function_single(counter->cpu,
                                         __perf_counter_remove_from_context,
                                         counter, 1);
                return;
        }

retry:
        task_oncpu_function_call(task, __perf_counter_remove_from_context,
                                 counter);

        spin_lock_irq(&ctx->lock);
        /*
         * If the context is active we need to retry the smp call.
         */
        if (ctx->nr_active && !list_empty(&counter->list_entry)) {
                spin_unlock_irq(&ctx->lock);
                goto retry;
        }

        /*
         * The lock prevents that this context is scheduled in so we
         * can remove the counter safely, if the call above did not
         * succeed.
         */
        if (!list_empty(&counter->list_entry)) {
                ctx->nr_counters--;
                list_del_counter(counter, ctx);
                counter->task = NULL;
        }
        spin_unlock_irq(&ctx->lock);
}

/*
 * Cross CPU call to disable a performance counter
 */
static void __perf_counter_disable(void *info)
{
        struct perf_counter *counter = info;
        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
        struct perf_counter_context *ctx = counter->ctx;
        unsigned long flags;

        /*
         * If this is a per-task counter, need to check whether this
         * counter's task is the current task on this cpu.
         */
        if (ctx->task && cpuctx->task_ctx != ctx)
                return;

        curr_rq_lock_irq_save(&flags);
        spin_lock(&ctx->lock);

        /*
         * If the counter is on, turn it off.
         * If it is in error state, leave it in error state.
         */
        if (counter->state >= PERF_COUNTER_STATE_INACTIVE) {
                if (counter == counter->group_leader)
                        group_sched_out(counter, cpuctx, ctx);
                else
                        counter_sched_out(counter, cpuctx, ctx);
                counter->state = PERF_COUNTER_STATE_OFF;
        }

        spin_unlock(&ctx->lock);
        curr_rq_unlock_irq_restore(&flags);
}

/*
 * Disable a counter.
 */
static void perf_counter_disable(struct perf_counter *counter)
{
        struct perf_counter_context *ctx = counter->ctx;
        struct task_struct *task = ctx->task;

        if (!task) {
                /*
                 * Disable the counter on the cpu that it's on
                 */
                smp_call_function_single(counter->cpu, __perf_counter_disable,
                                         counter, 1);
                return;
        }

 retry:
        task_oncpu_function_call(task, __perf_counter_disable, counter);

        spin_lock_irq(&ctx->lock);
        /*
         * If the counter is still active, we need to retry the cross-call.
         */
        if (counter->state == PERF_COUNTER_STATE_ACTIVE) {
                spin_unlock_irq(&ctx->lock);
                goto retry;
        }

        /*
         * Since we have the lock this context can't be scheduled
         * in, so we can change the state safely.
         */
        if (counter->state == PERF_COUNTER_STATE_INACTIVE)
                counter->state = PERF_COUNTER_STATE_OFF;

        spin_unlock_irq(&ctx->lock);
}

/*
 * Disable a counter and all its children.
 */
static void perf_counter_disable_family(struct perf_counter *counter)
{
        struct perf_counter *child;

        perf_counter_disable(counter);

        /*
         * Lock the mutex to protect the list of children
         */
        mutex_lock(&counter->mutex);
        list_for_each_entry(child, &counter->child_list, child_list)
                perf_counter_disable(child);
        mutex_unlock(&counter->mutex);
}

static int
counter_sched_in(struct perf_counter *counter,
                 struct perf_cpu_context *cpuctx,
                 struct perf_counter_context *ctx,
                 int cpu)
{
        if (counter->state <= PERF_COUNTER_STATE_OFF)
                return 0;

        counter->state = PERF_COUNTER_STATE_ACTIVE;
        counter->oncpu = cpu;   /* TODO: put 'cpu' into cpuctx->cpu */
        /*
         * The new state must be visible before we turn it on in the hardware:
         */
        smp_wmb();

        if (counter->hw_ops->enable(counter)) {
                counter->state = PERF_COUNTER_STATE_INACTIVE;
                counter->oncpu = -1;
                return -EAGAIN;
        }

        if (!is_software_counter(counter))
                cpuctx->active_oncpu++;
        ctx->nr_active++;

        if (counter->hw_event.exclusive)
                cpuctx->exclusive = 1;

        return 0;
}

/*
 * Return 1 for a group consisting entirely of software counters,
 * 0 if the group contains any hardware counters.
 */
static int is_software_only_group(struct perf_counter *leader)
{
        struct perf_counter *counter;

        if (!is_software_counter(leader))
                return 0;
        list_for_each_entry(counter, &leader->sibling_list, list_entry)
                if (!is_software_counter(counter))
                        return 0;
        return 1;
}

/*
 * Work out whether we can put this counter group on the CPU now.
 */
static int group_can_go_on(struct perf_counter *counter,
                           struct perf_cpu_context *cpuctx,
                           int can_add_hw)
{
        /*
         * Groups consisting entirely of software counters can always go on.
         */
        if (is_software_only_group(counter))
                return 1;
        /*
         * If an exclusive group is already on, no other hardware
         * counters can go on.
         */
        if (cpuctx->exclusive)
                return 0;
        /*
         * If this group is exclusive and there are already
         * counters on the CPU, it can't go on.
         */
        if (counter->hw_event.exclusive && cpuctx->active_oncpu)
                return 0;
        /*
         * Otherwise, try to add it if all previous groups were able
         * to go on.
         */
        return can_add_hw;
}

/*
 * Cross CPU call to install and enable a performance counter
 */
static void __perf_install_in_context(void *info)
{
        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
        struct perf_counter *counter = info;
        struct perf_counter_context *ctx = counter->ctx;
        struct perf_counter *leader = counter->group_leader;
        int cpu = smp_processor_id();
        unsigned long flags;
        u64 perf_flags;
        int err;

        /*
         * If this is a task context, we need to check whether it is
         * the current task context of this cpu. If not it has been
         * scheduled out before the smp call arrived.
         */
        if (ctx->task && cpuctx->task_ctx != ctx)
                return;

        curr_rq_lock_irq_save(&flags);
        spin_lock(&ctx->lock);

        /*
         * Protect the list operation against NMI by disabling the
         * counters on a global level. NOP for non NMI based counters.
         */
        perf_flags = hw_perf_save_disable();

        list_add_counter(counter, ctx);
        ctx->nr_counters++;

        /*
         * Don't put the counter on if it is disabled or if
         * it is in a group and the group isn't on.
         */
        if (counter->state != PERF_COUNTER_STATE_INACTIVE ||
            (leader != counter && leader->state != PERF_COUNTER_STATE_ACTIVE))
                goto unlock;

        /*
         * An exclusive counter can't go on if there are already active
         * hardware counters, and no hardware counter can go on if there
         * is already an exclusive counter on.
         */
        if (!group_can_go_on(counter, cpuctx, 1))
                err = -EEXIST;
        else
                err = counter_sched_in(counter, cpuctx, ctx, cpu);

        if (err) {
                /*
                 * This counter couldn't go on.  If it is in a group
                 * then we have to pull the whole group off.
                 * If the counter group is pinned then put it in error state.
                 */
                if (leader != counter)
                        group_sched_out(leader, cpuctx, ctx);
                if (leader->hw_event.pinned)
                        leader->state = PERF_COUNTER_STATE_ERROR;
        }

        if (!err && !ctx->task && cpuctx->max_pertask)
                cpuctx->max_pertask--;

 unlock:
        hw_perf_restore(perf_flags);

        spin_unlock(&ctx->lock);
        curr_rq_unlock_irq_restore(&flags);
}

/*
 * Attach a performance counter to a context
 *
 * First we add the counter to the list with the hardware enable bit
 * in counter->hw_config cleared.
 *
 * If the counter is attached to a task which is on a CPU we use a smp
 * call to enable it in the task context. The task might have been
 * scheduled away, but we check this in the smp call again.
 *
 * Must be called with ctx->mutex held.
 */
static void
perf_install_in_context(struct perf_counter_context *ctx,
                        struct perf_counter *counter,
                        int cpu)
{
        struct task_struct *task = ctx->task;

        if (!task) {
                /*
                 * Per cpu counters are installed via an smp call and
                 * the install is always sucessful.
                 */
                smp_call_function_single(cpu, __perf_install_in_context,
                                         counter, 1);
                return;
        }

        counter->task = task;
retry:
        task_oncpu_function_call(task, __perf_install_in_context,
                                 counter);

        spin_lock_irq(&ctx->lock);
        /*
         * we need to retry the smp call.
         */
        if (ctx->is_active && list_empty(&counter->list_entry)) {
                spin_unlock_irq(&ctx->lock);
                goto retry;
        }

        /*
         * The lock prevents that this context is scheduled in so we
         * can add the counter safely, if it the call above did not
         * succeed.
         */
        if (list_empty(&counter->list_entry)) {
                list_add_counter(counter, ctx);
                ctx->nr_counters++;
        }
        spin_unlock_irq(&ctx->lock);
}

/*
 * Cross CPU call to enable a performance counter
 */
static void __perf_counter_enable(void *info)
{
        struct perf_counter *counter = info;
        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
        struct perf_counter_context *ctx = counter->ctx;
        struct perf_counter *leader = counter->group_leader;
        unsigned long flags;
        int err;

        /*
         * If this is a per-task counter, need to check whether this
         * counter's task is the current task on this cpu.
         */
        if (ctx->task && cpuctx->task_ctx != ctx)
                return;

        curr_rq_lock_irq_save(&flags);
        spin_lock(&ctx->lock);

        if (counter->state >= PERF_COUNTER_STATE_INACTIVE)
                goto unlock;
        counter->state = PERF_COUNTER_STATE_INACTIVE;

        /*
         * If the counter is in a group and isn't the group leader,
         * then don't put it on unless the group is on.
         */
        if (leader != counter && leader->state != PERF_COUNTER_STATE_ACTIVE)
                goto unlock;

        if (!group_can_go_on(counter, cpuctx, 1))
                err = -EEXIST;
        else
                err = counter_sched_in(counter, cpuctx, ctx,
                                       smp_processor_id());

        if (err) {
                /*
                 * If this counter can't go on and it's part of a
                 * group, then the whole group has to come off.
                 */
                if (leader != counter)
                        group_sched_out(leader, cpuctx, ctx);
                if (leader->hw_event.pinned)
                        leader->state = PERF_COUNTER_STATE_ERROR;
        }

 unlock:
        spin_unlock(&ctx->lock);
        curr_rq_unlock_irq_restore(&flags);
}

/*
 * Enable a counter.
 */
static void perf_counter_enable(struct perf_counter *counter)
{
        struct perf_counter_context *ctx = counter->ctx;
        struct task_struct *task = ctx->task;

        if (!task) {
                /*
                 * Enable the counter on the cpu that it's on
                 */
                smp_call_function_single(counter->cpu, __perf_counter_enable,
                                         counter, 1);
                return;
        }

        spin_lock_irq(&ctx->lock);
        if (counter->state >= PERF_COUNTER_STATE_INACTIVE)
                goto out;

        /*
         * If the counter is in error state, clear that first.
         * That way, if we see the counter in error state below, we
         * know that it has gone back into error state, as distinct
         * from the task having been scheduled away before the
         * cross-call arrived.
         */
        if (counter->state == PERF_COUNTER_STATE_ERROR)
                counter->state = PERF_COUNTER_STATE_OFF;

 retry:
        spin_unlock_irq(&ctx->lock);
        task_oncpu_function_call(task, __perf_counter_enable, counter);

        spin_lock_irq(&ctx->lock);

        /*
         * If the context is active and the counter is still off,
         * we need to retry the cross-call.
         */
        if (ctx->is_active && counter->state == PERF_COUNTER_STATE_OFF)
                goto retry;

        /*
         * Since we have the lock this context can't be scheduled
         * in, so we can change the state safely.
         */
        if (counter->state == PERF_COUNTER_STATE_OFF)
                counter->state = PERF_COUNTER_STATE_INACTIVE;
 out:
        spin_unlock_irq(&ctx->lock);
}

/*
 * Enable a counter and all its children.
 */
static void perf_counter_enable_family(struct perf_counter *counter)
{
        struct perf_counter *child;

        perf_counter_enable(counter);

        /*
         * Lock the mutex to protect the list of children
         */
        mutex_lock(&counter->mutex);
        list_for_each_entry(child, &counter->child_list, child_list)
                perf_counter_enable(child);
        mutex_unlock(&counter->mutex);
}

void __perf_counter_sched_out(struct perf_counter_context *ctx,
                              struct perf_cpu_context *cpuctx)
{
        struct perf_counter *counter;
        u64 flags;

        spin_lock(&ctx->lock);
        ctx->is_active = 0;
        if (likely(!ctx->nr_counters))
                goto out;

        flags = hw_perf_save_disable();
        if (ctx->nr_active) {
                list_for_each_entry(counter, &ctx->counter_list, list_entry)
                        group_sched_out(counter, cpuctx, ctx);
        }
        hw_perf_restore(flags);
 out:
        spin_unlock(&ctx->lock);
}

/*
 * Called from scheduler to remove the counters of the current task,
 * with interrupts disabled.
 *
 * We stop each counter and update the counter value in counter->count.
 *
 * This does not protect us against NMI, but disable()
 * sets the disabled bit in the control field of counter _before_
 * accessing the counter control register. If a NMI hits, then it will
 * not restart the counter.
 */
void perf_counter_task_sched_out(struct task_struct *task, int cpu)
{
        struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);
        struct perf_counter_context *ctx = &task->perf_counter_ctx;

        if (likely(!cpuctx->task_ctx))
                return;

        __perf_counter_sched_out(ctx, cpuctx);

        cpuctx->task_ctx = NULL;
}

static void perf_counter_cpu_sched_out(struct perf_cpu_context *cpuctx)
{
        __perf_counter_sched_out(&cpuctx->ctx, cpuctx);
}

static int
group_sched_in(struct perf_counter *group_counter,
               struct perf_cpu_context *cpuctx,
               struct perf_counter_context *ctx,
               int cpu)
{
        struct perf_counter *counter, *partial_group;
        int ret;

        if (group_counter->state == PERF_COUNTER_STATE_OFF)
                return 0;

        ret = hw_perf_group_sched_in(group_counter, cpuctx, ctx, cpu);
        if (ret)
                return ret < 0 ? ret : 0;

        if (counter_sched_in(group_counter, cpuctx, ctx, cpu))
                return -EAGAIN;

        /*
         * Schedule in siblings as one group (if any):
         */
        list_for_each_entry(counter, &group_counter->sibling_list, list_entry) {
                if (counter_sched_in(counter, cpuctx, ctx, cpu)) {
                        partial_group = counter;
                        goto group_error;
                }
        }

        return 0;

group_error:
        /*
         * Groups can be scheduled in as one unit only, so undo any
         * partial group before returning:
         */
        list_for_each_entry(counter, &group_counter->sibling_list, list_entry) {
                if (counter == partial_group)
                        break;
                counter_sched_out(counter, cpuctx, ctx);
        }
        counter_sched_out(group_counter, cpuctx, ctx);

        return -EAGAIN;
}

static void
__perf_counter_sched_in(struct perf_counter_context *ctx,
                        struct perf_cpu_context *cpuctx, int cpu)
{
        struct perf_counter *counter;
        u64 flags;
        int can_add_hw = 1;

        spin_lock(&ctx->lock);
        ctx->is_active = 1;
        if (likely(!ctx->nr_counters))
                goto out;

        flags = hw_perf_save_disable();

        /*
         * First go through the list and put on any pinned groups
         * in order to give them the best chance of going on.
         */
        list_for_each_entry(counter, &ctx->counter_list, list_entry) {
                if (counter->state <= PERF_COUNTER_STATE_OFF ||
                    !counter->hw_event.pinned)
                        continue;
                if (counter->cpu != -1 && counter->cpu != cpu)
                        continue;

                if (group_can_go_on(counter, cpuctx, 1))
                        group_sched_in(counter, cpuctx, ctx, cpu);

                /*
                 * If this pinned group hasn't been scheduled,
                 * put it in error state.
                 */
                if (counter->state == PERF_COUNTER_STATE_INACTIVE)
                        counter->state = PERF_COUNTER_STATE_ERROR;
        }

        list_for_each_entry(counter, &ctx->counter_list, list_entry) {
                /*
                 * Ignore counters in OFF or ERROR state, and
                 * ignore pinned counters since we did them already.
                 */
                if (counter->state <= PERF_COUNTER_STATE_OFF ||
                    counter->hw_event.pinned)
                        continue;

                /*
                 * Listen to the 'cpu' scheduling filter constraint
                 * of counters:
                 */
                if (counter->cpu != -1 && counter->cpu != cpu)
                        continue;

                if (group_can_go_on(counter, cpuctx, can_add_hw)) {
                        if (group_sched_in(counter, cpuctx, ctx, cpu))
                                can_add_hw = 0;
                }
        }
        hw_perf_restore(flags);
 out:
        spin_unlock(&ctx->lock);
}

/*
 * Called from scheduler to add the counters of the current task
 * with interrupts disabled.
 *
 * We restore the counter value and then enable it.
 *
 * This does not protect us against NMI, but enable()
 * sets the enabled bit in the control field of counter _before_
 * accessing the counter control register. If a NMI hits, then it will
 * keep the counter running.
 */
void perf_counter_task_sched_in(struct task_struct *task, int cpu)
{
        struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);
        struct perf_counter_context *ctx = &task->perf_counter_ctx;

        __perf_counter_sched_in(ctx, cpuctx, cpu);
        cpuctx->task_ctx = ctx;
}

static void perf_counter_cpu_sched_in(struct perf_cpu_context *cpuctx, int cpu)
{
        struct perf_counter_context *ctx = &cpuctx->ctx;

        __perf_counter_sched_in(ctx, cpuctx, cpu);
}

int perf_counter_task_disable(void)
{
        struct task_struct *curr = current;
        struct perf_counter_context *ctx = &curr->perf_counter_ctx;
        struct perf_counter *counter;
        unsigned long flags;
        u64 perf_flags;
        int cpu;

        if (likely(!ctx->nr_counters))
                return 0;

        curr_rq_lock_irq_save(&flags);
        cpu = smp_processor_id();

        /* force the update of the task clock: */
        __task_delta_exec(curr, 1);

        perf_counter_task_sched_out(curr, cpu);

        spin_lock(&ctx->lock);

        /*
         * Disable all the counters:
         */
        perf_flags = hw_perf_save_disable();

        list_for_each_entry(counter, &ctx->counter_list, list_entry) {
                if (counter->state != PERF_COUNTER_STATE_ERROR)
                        counter->state = PERF_COUNTER_STATE_OFF;
        }

        hw_perf_restore(perf_flags);

        spin_unlock(&ctx->lock);

        curr_rq_unlock_irq_restore(&flags);

        return 0;
}

int perf_counter_task_enable(void)
{
        struct task_struct *curr = current;
        struct perf_counter_context *ctx = &curr->perf_counter_ctx;
        struct perf_counter *counter;
        unsigned long flags;
        u64 perf_flags;
        int cpu;

        if (likely(!ctx->nr_counters))
                return 0;

        curr_rq_lock_irq_save(&flags);
        cpu = smp_processor_id();

        /* force the update of the task clock: */
        __task_delta_exec(curr, 1);

        perf_counter_task_sched_out(curr, cpu);

        spin_lock(&ctx->lock);

        /*
         * Disable all the counters:
         */
        perf_flags = hw_perf_save_disable();

        list_for_each_entry(counter, &ctx->counter_list, list_entry) {
                if (counter->state > PERF_COUNTER_STATE_OFF)
                        continue;
                counter->state = PERF_COUNTER_STATE_INACTIVE;
                counter->hw_event.disabled = 0;
        }
        hw_perf_restore(perf_flags);

        spin_unlock(&ctx->lock);

        perf_counter_task_sched_in(curr, cpu);

        curr_rq_unlock_irq_restore(&flags);

        return 0;
}

/*
 * Round-robin a context's counters:
 */
static void rotate_ctx(struct perf_counter_context *ctx)
{
        struct perf_counter *counter;
        u64 perf_flags;

        if (!ctx->nr_counters)
                return;

        spin_lock(&ctx->lock);
        /*
         * Rotate the first entry last (works just fine for group counters too):
         */
        perf_flags = hw_perf_save_disable();
        list_for_each_entry(counter, &ctx->counter_list, list_entry) {
                list_del(&counter->list_entry);
                list_add_tail(&counter->list_entry, &ctx->counter_list);
                break;
        }
        hw_perf_restore(perf_flags);

        spin_unlock(&ctx->lock);
}

void perf_counter_task_tick(struct task_struct *curr, int cpu)
{
        struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);
        struct perf_counter_context *ctx = &curr->perf_counter_ctx;
        const int rotate_percpu = 0;

        if (rotate_percpu)
                perf_counter_cpu_sched_out(cpuctx);
        perf_counter_task_sched_out(curr, cpu);

        if (rotate_percpu)
                rotate_ctx(&cpuctx->ctx);
        rotate_ctx(ctx);

        if (rotate_percpu)
                perf_counter_cpu_sched_in(cpuctx, cpu);
        perf_counter_task_sched_in(curr, cpu);
}

/*
 * Cross CPU call to read the hardware counter
 */
static void __read(void *info)
{
        struct perf_counter *counter = info;
        unsigned long flags;

        curr_rq_lock_irq_save(&flags);
        counter->hw_ops->read(counter);
        curr_rq_unlock_irq_restore(&flags);
}

static u64 perf_counter_read(struct perf_counter *counter)
{
        /*
         * If counter is enabled and currently active on a CPU, update the
         * value in the counter structure:
         */
        if (counter->state == PERF_COUNTER_STATE_ACTIVE) {
                smp_call_function_single(counter->oncpu,
                                         __read, counter, 1);
        }

        return atomic64_read(&counter->count);
}

/*
 * Cross CPU call to switch performance data pointers
 */
static void __perf_switch_irq_data(void *info)
{
        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
        struct perf_counter *counter = info;
        struct perf_counter_context *ctx = counter->ctx;
        struct perf_data *oldirqdata = counter->irqdata;

        /*
         * If this is a task context, we need to check whether it is
         * the current task context of this cpu. If not it has been
         * scheduled out before the smp call arrived.
         */
        if (ctx->task) {
                if (cpuctx->task_ctx != ctx)
                        return;
                spin_lock(&ctx->lock);
        }

        /* Change the pointer NMI safe */
        atomic_long_set((atomic_long_t *)&counter->irqdata,
                        (unsigned long) counter->usrdata);
        counter->usrdata = oldirqdata;

        if (ctx->task)
                spin_unlock(&ctx->lock);
}

static struct perf_data *perf_switch_irq_data(struct perf_counter *counter)
{
        struct perf_counter_context *ctx = counter->ctx;
        struct perf_data *oldirqdata = counter->irqdata;
        struct task_struct *task = ctx->task;

        if (!task) {
                smp_call_function_single(counter->cpu,
                                         __perf_switch_irq_data,
                                         counter, 1);
                return counter->usrdata;
        }

retry:
        spin_lock_irq(&ctx->lock);
        if (counter->state != PERF_COUNTER_STATE_ACTIVE) {
                counter->irqdata = counter->usrdata;
                counter->usrdata = oldirqdata;
                spin_unlock_irq(&ctx->lock);
                return oldirqdata;
        }
        spin_unlock_irq(&ctx->lock);
        task_oncpu_function_call(task, __perf_switch_irq_data, counter);
        /* Might have failed, because task was scheduled out */
        if (counter->irqdata == oldirqdata)
                goto retry;

        return counter->usrdata;
}

static void put_context(struct perf_counter_context *ctx)
{
        if (ctx->task)
                put_task_struct(ctx->task);
}

static struct perf_counter_context *find_get_context(pid_t pid, int cpu)
{
        struct perf_cpu_context *cpuctx;
        struct perf_counter_context *ctx;
        struct task_struct *task;

        /*
         * If cpu is not a wildcard then this is a percpu counter:
         */
        if (cpu != -1) {
                /* Must be root to operate on a CPU counter: */
                if (!capable(CAP_SYS_ADMIN))
                        return ERR_PTR(-EACCES);

                if (cpu < 0 || cpu > num_possible_cpus())
                        return ERR_PTR(-EINVAL);

                /*
                 * We could be clever and allow to attach a counter to an
                 * offline CPU and activate it when the CPU comes up, but
                 * that's for later.
                 */
                if (!cpu_isset(cpu, cpu_online_map))
                        return ERR_PTR(-ENODEV);

                cpuctx = &per_cpu(perf_cpu_context, cpu);
                ctx = &cpuctx->ctx;

                return ctx;
        }

        rcu_read_lock();
        if (!pid)
                task = current;
        else
                task = find_task_by_vpid(pid);
        if (task)
                get_task_struct(task);
        rcu_read_unlock();

        if (!task)
                return ERR_PTR(-ESRCH);

        ctx = &task->perf_counter_ctx;
        ctx->task = task;

        /* Reuse ptrace permission checks for now. */
        if (!ptrace_may_access(task, PTRACE_MODE_READ)) {
                put_context(ctx);
                return ERR_PTR(-EACCES);
        }

        return ctx;
}

/*
 * Called when the last reference to the file is gone.
 */
static int perf_release(struct inode *inode, struct file *file)
{
        struct perf_counter *counter = file->private_data;
        struct perf_counter_context *ctx = counter->ctx;

        file->private_data = NULL;

        mutex_lock(&ctx->mutex);
        mutex_lock(&counter->mutex);

        perf_counter_remove_from_context(counter);

        mutex_unlock(&counter->mutex);
        mutex_unlock(&ctx->mutex);

        kfree(counter);
        put_context(ctx);

        return 0;
}

/*
 * Read the performance counter - simple non blocking version for now
 */
static ssize_t
perf_read_hw(struct perf_counter *counter, char __user *buf, size_t count)
{
        u64 cntval;

        if (count != sizeof(cntval))
                return -EINVAL;

        /*
         * Return end-of-file for a read on a counter that is in
         * error state (i.e. because it was pinned but it couldn't be
         * scheduled on to the CPU at some point).
         */
        if (counter->state == PERF_COUNTER_STATE_ERROR)
                return 0;

        mutex_lock(&counter->mutex);
        cntval = perf_counter_read(counter);
        mutex_unlock(&counter->mutex);

        return put_user(cntval, (u64 __user *) buf) ? -EFAULT : sizeof(cntval);
}

static ssize_t
perf_copy_usrdata(struct perf_data *usrdata, char __user *buf, size_t count)
{
        if (!usrdata->len)
                return 0;

        count = min(count, (size_t)usrdata->len);
        if (copy_to_user(buf, usrdata->data + usrdata->rd_idx, count))
                return -EFAULT;

        /* Adjust the counters */
        usrdata->len -= count;
        if (!usrdata->len)
                usrdata->rd_idx = 0;
        else
                usrdata->rd_idx += count;

        return count;
}

static ssize_t
perf_read_irq_data(struct perf_counter  *counter,
                   char __user          *buf,
                   size_t               count,
                   int                  nonblocking)
{
        struct perf_data *irqdata, *usrdata;
        DECLARE_WAITQUEUE(wait, current);
        ssize_t res, res2;

        irqdata = counter->irqdata;
        usrdata = counter->usrdata;

        if (usrdata->len + irqdata->len >= count)
                goto read_pending;

        if (nonblocking)
                return -EAGAIN;

        spin_lock_irq(&counter->waitq.lock);
        __add_wait_queue(&counter->waitq, &wait);
        for (;;) {
                set_current_state(TASK_INTERRUPTIBLE);
                if (usrdata->len + irqdata->len >= count)
                        break;

                if (signal_pending(current))
                        break;

                if (counter->state == PERF_COUNTER_STATE_ERROR)
                        break;

                spin_unlock_irq(&counter->waitq.lock);
                schedule();
                spin_lock_irq(&counter->waitq.lock);
        }
        __remove_wait_queue(&counter->waitq, &wait);
        __set_current_state(TASK_RUNNING);
        spin_unlock_irq(&counter->waitq.lock);

        if (usrdata->len + irqdata->len < count &&
            counter->state != PERF_COUNTER_STATE_ERROR)
                return -ERESTARTSYS;
read_pending:
        mutex_lock(&counter->mutex);

        /* Drain pending data first: */
        res = perf_copy_usrdata(usrdata, buf, count);
        if (res < 0 || res == count)
                goto out;

        /* Switch irq buffer: */
        usrdata = perf_switch_irq_data(counter);
        res2 = perf_copy_usrdata(usrdata, buf + res, count - res);
        if (res2 < 0) {
                if (!res)
                        res = -EFAULT;
        } else {
                res += res2;
        }
out:
        mutex_unlock(&counter->mutex);

        return res;
}

static ssize_t
perf_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{
        struct perf_counter *counter = file->private_data;

        switch (counter->hw_event.record_type) {
        case PERF_RECORD_SIMPLE:
                return perf_read_hw(counter, buf, count);

        case PERF_RECORD_IRQ:
        case PERF_RECORD_GROUP:
                return perf_read_irq_data(counter, buf, count,
                                          file->f_flags & O_NONBLOCK);
        }
        return -EINVAL;
}

static unsigned int perf_poll(struct file *file, poll_table *wait)
{
        struct perf_counter *counter = file->private_data;
        unsigned int events = 0;
        unsigned long flags;

        poll_wait(file, &counter->waitq, wait);

        spin_lock_irqsave(&counter->waitq.lock, flags);
        if (counter->usrdata->len || counter->irqdata->len)
                events |= POLLIN;
        spin_unlock_irqrestore(&counter->waitq.lock, flags);

        return events;
}

static long perf_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
        struct perf_counter *counter = file->private_data;
        int err = 0;

        switch (cmd) {
        case PERF_COUNTER_IOC_ENABLE:
                perf_counter_enable_family(counter);
                break;
        case PERF_COUNTER_IOC_DISABLE:
                perf_counter_disable_family(counter);
                break;
        default:
                err = -ENOTTY;
        }
        return err;
}

static const struct file_operations perf_fops = {
        .release                = perf_release,
        .read                   = perf_read,
        .poll                   = perf_poll,
        .unlocked_ioctl         = perf_ioctl,
        .compat_ioctl           = perf_ioctl,
};

static int cpu_clock_perf_counter_enable(struct perf_counter *counter)
{
        int cpu = raw_smp_processor_id();

        atomic64_set(&counter->hw.prev_count, cpu_clock(cpu));
        return 0;
}

static void cpu_clock_perf_counter_update(struct perf_counter *counter)
{
        int cpu = raw_smp_processor_id();
        s64 prev;
        u64 now;

        now = cpu_clock(cpu);
        prev = atomic64_read(&counter->hw.prev_count);
        atomic64_set(&counter->hw.prev_count, now);
        atomic64_add(now - prev, &counter->count);
}

static void cpu_clock_perf_counter_disable(struct perf_counter *counter)
{
        cpu_clock_perf_counter_update(counter);
}

static void cpu_clock_perf_counter_read(struct perf_counter *counter)
{
        cpu_clock_perf_counter_update(counter);
}

static const struct hw_perf_counter_ops perf_ops_cpu_clock = {
        .enable         = cpu_clock_perf_counter_enable,
        .disable        = cpu_clock_perf_counter_disable,
        .read           = cpu_clock_perf_counter_read,
};

/*
 * Called from within the scheduler:
 */
static u64 task_clock_perf_counter_val(struct perf_counter *counter, int update)
{
        struct task_struct *curr = counter->task;
        u64 delta;

        delta = __task_delta_exec(curr, update);

        return curr->se.sum_exec_runtime + delta;
}

static void task_clock_perf_counter_update(struct perf_counter *counter, u64 now)
{
        u64 prev;
        s64 delta;

        prev = atomic64_read(&counter->hw.prev_count);

        atomic64_set(&counter->hw.prev_count, now);

        delta = now - prev;

        atomic64_add(delta, &counter->count);
}

static void task_clock_perf_counter_read(struct perf_counter *counter)
{
        u64 now = task_clock_perf_counter_val(counter, 1);

        task_clock_perf_counter_update(counter, now);
}

static int task_clock_perf_counter_enable(struct perf_counter *counter)
{
        u64 now = task_clock_perf_counter_val(counter, 0);

        atomic64_set(&counter->hw.prev_count, now);

        return 0;
}

static void task_clock_perf_counter_disable(struct perf_counter *counter)
{
        u64 now = task_clock_perf_counter_val(counter, 0);

        task_clock_perf_counter_update(counter, now);
}

static const struct hw_perf_counter_ops perf_ops_task_clock = {
        .enable         = task_clock_perf_counter_enable,
        .disable        = task_clock_perf_counter_disable,
        .read           = task_clock_perf_counter_read,
};

#ifdef CONFIG_VM_EVENT_COUNTERS
#define cpu_page_faults()       __get_cpu_var(vm_event_states).event[PGFAULT]
#else
#define cpu_page_faults()       0
#endif

static u64 get_page_faults(struct perf_counter *counter)
{
        struct task_struct *curr = counter->ctx->task;

        if (curr)
                return curr->maj_flt + curr->min_flt;
        return cpu_page_faults();
}

static void page_faults_perf_counter_update(struct perf_counter *counter)
{
        u64 prev, now;
        s64 delta;

        prev = atomic64_read(&counter->hw.prev_count);
        now = get_page_faults(counter);

        atomic64_set(&counter->hw.prev_count, now);

        delta = now - prev;

        atomic64_add(delta, &counter->count);
}

static void page_faults_perf_counter_read(struct perf_counter *counter)
{
        page_faults_perf_counter_update(counter);
}

static int page_faults_perf_counter_enable(struct perf_counter *counter)
{
        atomic64_set(&counter->hw.prev_count, get_page_faults(counter));
        return 0;
}

static void page_faults_perf_counter_disable(struct perf_counter *counter)
{
        page_faults_perf_counter_update(counter);
}

static const struct hw_perf_counter_ops perf_ops_page_faults = {
        .enable         = page_faults_perf_counter_enable,
        .disable        = page_faults_perf_counter_disable,
        .read           = page_faults_perf_counter_read,
};

static u64 get_context_switches(struct perf_counter *counter)
{
        struct task_struct *curr = counter->ctx->task;

        if (curr)
                return curr->nvcsw + curr->nivcsw;
        return cpu_nr_switches(smp_processor_id());
}

static void context_switches_perf_counter_update(struct perf_counter *counter)
{
        u64 prev, now;
        s64 delta;

        prev = atomic64_read(&counter->hw.prev_count);
        now = get_context_switches(counter);

        atomic64_set(&counter->hw.prev_count, now);

        delta = now - prev;

        atomic64_add(delta, &counter->count);
}

static void context_switches_perf_counter_read(struct perf_counter *counter)
{
        context_switches_perf_counter_update(counter);
}

static int context_switches_perf_counter_enable(struct perf_counter *counter)
{
        atomic64_set(&counter->hw.prev_count, get_context_switches(counter));
        return 0;
}

static void context_switches_perf_counter_disable(struct perf_counter *counter)
{
        context_switches_perf_counter_update(counter);
}

static const struct hw_perf_counter_ops perf_ops_context_switches = {
        .enable         = context_switches_perf_counter_enable,
        .disable        = context_switches_perf_counter_disable,
        .read           = context_switches_perf_counter_read,
};

static inline u64 get_cpu_migrations(struct perf_counter *counter)
{
        struct task_struct *curr = counter->ctx->task;

        if (curr)
                return curr->se.nr_migrations;
        return cpu_nr_migrations(smp_processor_id());
}

static void cpu_migrations_perf_counter_update(struct perf_counter *counter)
{
        u64 prev, now;
        s64 delta;

        prev = atomic64_read(&counter->hw.prev_count);
        now = get_cpu_migrations(counter);

        atomic64_set(&counter->hw.prev_count, now);

        delta = now - prev;

        atomic64_add(delta, &counter->count);
}

static void cpu_migrations_perf_counter_read(struct perf_counter *counter)
{
        cpu_migrations_perf_counter_update(counter);
}

static int cpu_migrations_perf_counter_enable(struct perf_counter *counter)
{
        atomic64_set(&counter->hw.prev_count, get_cpu_migrations(counter));
        return 0;
}

static void cpu_migrations_perf_counter_disable(struct perf_counter *counter)
{
        cpu_migrations_perf_counter_update(counter);
}

static const struct hw_perf_counter_ops perf_ops_cpu_migrations = {
        .enable         = cpu_migrations_perf_counter_enable,
        .disable        = cpu_migrations_perf_counter_disable,
        .read           = cpu_migrations_perf_counter_read,
};

static const struct hw_perf_counter_ops *
sw_perf_counter_init(struct perf_counter *counter)
{
        const struct hw_perf_counter_ops *hw_ops = NULL;

        /*
         * Software counters (currently) can't in general distinguish
         * between user, kernel and hypervisor events.
         * However, context switches and cpu migrations are considered
         * to be kernel events, and page faults are never hypervisor
         * events.
         */
        switch (counter->hw_event.type) {
        case PERF_COUNT_CPU_CLOCK:
                if (!(counter->hw_event.exclude_user ||
                      counter->hw_event.exclude_kernel ||
                      counter->hw_event.exclude_hv))
                        hw_ops = &perf_ops_cpu_clock;
                break;
        case PERF_COUNT_TASK_CLOCK:
                if (counter->hw_event.exclude_user ||
                    counter->hw_event.exclude_kernel ||
                    counter->hw_event.exclude_hv)
                        break;
                /*
                 * If the user instantiates this as a per-cpu counter,
                 * use the cpu_clock counter instead.
                 */
                if (counter->ctx->task)
                        hw_ops = &perf_ops_task_clock;
                else
                        hw_ops = &perf_ops_cpu_clock;
                break;
        case PERF_COUNT_PAGE_FAULTS:
                if (!(counter->hw_event.exclude_user ||
                      counter->hw_event.exclude_kernel))
                        hw_ops = &perf_ops_page_faults;
                break;
        case PERF_COUNT_CONTEXT_SWITCHES:
                if (!counter->hw_event.exclude_kernel)
                        hw_ops = &perf_ops_context_switches;
                break;
        case PERF_COUNT_CPU_MIGRATIONS:
                if (!counter->hw_event.exclude_kernel)
                        hw_ops = &perf_ops_cpu_migrations;
                break;
        default:
                break;
        }
        return hw_ops;
}

/*
 * Allocate and initialize a counter structure
 */
static struct perf_counter *
perf_counter_alloc(struct perf_counter_hw_event *hw_event,
                   int cpu,
                   struct perf_counter_context *ctx,
                   struct perf_counter *group_leader,
                   gfp_t gfpflags)
{
        const struct hw_perf_counter_ops *hw_ops;
        struct perf_counter *counter;

        counter = kzalloc(sizeof(*counter), gfpflags);
        if (!counter)
                return NULL;

        /*
         * Single counters are their own group leaders, with an
         * empty sibling list:
         */
        if (!group_leader)
                group_leader = counter;

        mutex_init(&counter->mutex);
        INIT_LIST_HEAD(&counter->list_entry);
        INIT_LIST_HEAD(&counter->sibling_list);
        init_waitqueue_head(&counter->waitq);

        INIT_LIST_HEAD(&counter->child_list);

        counter->irqdata                = &counter->data[0];
        counter->usrdata                = &counter->data[1];
        counter->cpu                    = cpu;
        counter->hw_event               = *hw_event;
        counter->wakeup_pending         = 0;
        counter->group_leader           = group_leader;
        counter->hw_ops                 = NULL;
        counter->ctx                    = ctx;

        counter->state = PERF_COUNTER_STATE_INACTIVE;
        if (hw_event->disabled)
                counter->state = PERF_COUNTER_STATE_OFF;

        hw_ops = NULL;
        if (!hw_event->raw && hw_event->type < 0)
                hw_ops = sw_perf_counter_init(counter);
        else
                hw_ops = hw_perf_counter_init(counter);

        if (!hw_ops) {
                kfree(counter);
                return NULL;
        }
        counter->hw_ops = hw_ops;

        return counter;
}

/**
 * sys_perf_task_open - open a performance counter, associate it to a task/cpu
 *
 * @hw_event_uptr:      event type attributes for monitoring/sampling
 * @pid:                target pid
 * @cpu:                target cpu
 * @group_fd:           group leader counter fd
 */
asmlinkage int
sys_perf_counter_open(struct perf_counter_hw_event *hw_event_uptr __user,
                      pid_t pid, int cpu, int group_fd)
{
        struct perf_counter *counter, *group_leader;
        struct perf_counter_hw_event hw_event;
        struct perf_counter_context *ctx;
        struct file *counter_file = NULL;
        struct file *group_file = NULL;
        int fput_needed = 0;
        int fput_needed2 = 0;
        int ret;

        if (copy_from_user(&hw_event, hw_event_uptr, sizeof(hw_event)) != 0)
                return -EFAULT;

        /*
         * Get the target context (task or percpu):
         */
        ctx = find_get_context(pid, cpu);
        if (IS_ERR(ctx))
                return PTR_ERR(ctx);

        /*
         * Look up the group leader (we will attach this counter to it):
         */
        group_leader = NULL;
        if (group_fd != -1) {
                ret = -EINVAL;
                group_file = fget_light(group_fd, &fput_needed);
                if (!group_file)
                        goto err_put_context;
                if (group_file->f_op != &perf_fops)
                        goto err_put_context;

                group_leader = group_file->private_data;
                /*
                 * Do not allow a recursive hierarchy (this new sibling
                 * becoming part of another group-sibling):
                 */
                if (group_leader->group_leader != group_leader)
                        goto err_put_context;
                /*
                 * Do not allow to attach to a group in a different
                 * task or CPU context:
                 */
                if (group_leader->ctx != ctx)
                        goto err_put_context;
                /*
                 * Only a group leader can be exclusive or pinned
                 */
                if (hw_event.exclusive || hw_event.pinned)
                        goto err_put_context;
        }

        ret = -EINVAL;
        counter = perf_counter_alloc(&hw_event, cpu, ctx, group_leader,
                                     GFP_KERNEL);
        if (!counter)
                goto err_put_context;

        ret = anon_inode_getfd("[perf_counter]", &perf_fops, counter, 0);
        if (ret < 0)
                goto err_free_put_context;

        counter_file = fget_light(ret, &fput_needed2);
        if (!counter_file)
                goto err_free_put_context;

        counter->filp = counter_file;
        mutex_lock(&ctx->mutex);
        perf_install_in_context(ctx, counter, cpu);
        mutex_unlock(&ctx->mutex);

        fput_light(counter_file, fput_needed2);

out_fput:
        fput_light(group_file, fput_needed);

        return ret;

err_free_put_context:
        kfree(counter);

err_put_context:
        put_context(ctx);

        goto out_fput;
}

/*
 * Initialize the perf_counter context in a task_struct:
 */
static void
__perf_counter_init_context(struct perf_counter_context *ctx,
                            struct task_struct *task)
{
        memset(ctx, 0, sizeof(*ctx));
        spin_lock_init(&ctx->lock);
        mutex_init(&ctx->mutex);
        INIT_LIST_HEAD(&ctx->counter_list);
        ctx->task = task;
}

/*
 * inherit a counter from parent task to child task:
 */
static struct perf_counter *
inherit_counter(struct perf_counter *parent_counter,
              struct task_struct *parent,
              struct perf_counter_context *parent_ctx,
              struct task_struct *child,
              struct perf_counter *group_leader,
              struct perf_counter_context *child_ctx)
{
        struct perf_counter *child_counter;

        /*
         * Instead of creating recursive hierarchies of counters,
         * we link inherited counters back to the original parent,
         * which has a filp for sure, which we use as the reference
         * count:
         */
        if (parent_counter->parent)
                parent_counter = parent_counter->parent;

        child_counter = perf_counter_alloc(&parent_counter->hw_event,
                                           parent_counter->cpu, child_ctx,
                                           group_leader, GFP_KERNEL);
        if (!child_counter)
                return NULL;

        /*
         * Link it up in the child's context:
         */
        child_counter->task = child;
        list_add_counter(child_counter, child_ctx);
        child_ctx->nr_counters++;

        child_counter->parent = parent_counter;
        /*
         * inherit into child's child as well:
         */
        child_counter->hw_event.inherit = 1;

        /*
         * Get a reference to the parent filp - we will fput it
         * when the child counter exits. This is safe to do because
         * we are in the parent and we know that the filp still
         * exists and has a nonzero count:
         */
        atomic_long_inc(&parent_counter->filp->f_count);

        /*
         * Link this into the parent counter's child list
         */
        mutex_lock(&parent_counter->mutex);
        list_add_tail(&child_counter->child_list, &parent_counter->child_list);

        /*
         * Make the child state follow the state of the parent counter,
         * not its hw_event.disabled bit.  We hold the parent's mutex,
         * so we won't race with perf_counter_{en,dis}able_family.
         */
        if (parent_counter->state >= PERF_COUNTER_STATE_INACTIVE)
                child_counter->state = PERF_COUNTER_STATE_INACTIVE;
        else
                child_counter->state = PERF_COUNTER_STATE_OFF;

        mutex_unlock(&parent_counter->mutex);

        return child_counter;
}

static int inherit_group(struct perf_counter *parent_counter,
              struct task_struct *parent,
              struct perf_counter_context *parent_ctx,
              struct task_struct *child,
              struct perf_counter_context *child_ctx)
{
        struct perf_counter *leader;
        struct perf_counter *sub;

        leader = inherit_counter(parent_counter, parent, parent_ctx,
                                 child, NULL, child_ctx);
        if (!leader)
                return -ENOMEM;
        list_for_each_entry(sub, &parent_counter->sibling_list, list_entry) {
                if (!inherit_counter(sub, parent, parent_ctx,
                                     child, leader, child_ctx))
                        return -ENOMEM;
        }
        return 0;
}

static void sync_child_counter(struct perf_counter *child_counter,
                               struct perf_counter *parent_counter)
{
        u64 parent_val, child_val;

        parent_val = atomic64_read(&parent_counter->count);
        child_val = atomic64_read(&child_counter->count);

        /*
         * Add back the child's count to the parent's count:
         */
        atomic64_add(child_val, &parent_counter->count);

        /*
         * Remove this counter from the parent's list
         */
        mutex_lock(&parent_counter->mutex);
        list_del_init(&child_counter->child_list);
        mutex_unlock(&parent_counter->mutex);

        /*
         * Release the parent counter, if this was the last
         * reference to it.
         */
        fput(parent_counter->filp);
}

static void
__perf_counter_exit_task(struct task_struct *child,
                         struct perf_counter *child_counter,
                         struct perf_counter_context *child_ctx)
{
        struct perf_counter *parent_counter;
        struct perf_counter *sub, *tmp;

        /*
         * If we do not self-reap then we have to wait for the
         * child task to unschedule (it will happen for sure),
         * so that its counter is at its final count. (This
         * condition triggers rarely - child tasks usually get
         * off their CPU before the parent has a chance to
         * get this far into the reaping action)
         */
        if (child != current) {
                wait_task_inactive(child, 0);
                list_del_init(&child_counter->list_entry);
        } else {
                struct perf_cpu_context *cpuctx;
                unsigned long flags;
                u64 perf_flags;

                /*
                 * Disable and unlink this counter.
                 *
                 * Be careful about zapping the list - IRQ/NMI context
                 * could still be processing it:
                 */
                curr_rq_lock_irq_save(&flags);
                perf_flags = hw_perf_save_disable();

                cpuctx = &__get_cpu_var(perf_cpu_context);

                group_sched_out(child_counter, cpuctx, child_ctx);

                list_del_init(&child_counter->list_entry);

                child_ctx->nr_counters--;

                hw_perf_restore(perf_flags);
                curr_rq_unlock_irq_restore(&flags);
        }

        parent_counter = child_counter->parent;
        /*
         * It can happen that parent exits first, and has counters
         * that are still around due to the child reference. These
         * counters need to be zapped - but otherwise linger.
         */
        if (parent_counter) {
                sync_child_counter(child_counter, parent_counter);
                list_for_each_entry_safe(sub, tmp, &child_counter->sibling_list,
                                         list_entry) {
                        if (sub->parent) {
                                sync_child_counter(sub, sub->parent);
                                kfree(sub);
                        }
                }
                kfree(child_counter);
        }
}

/*
 * When a child task exits, feed back counter values to parent counters.
 *
 * Note: we may be running in child context, but the PID is not hashed
 * anymore so new counters will not be added.
 */
void perf_counter_exit_task(struct task_struct *child)
{
        struct perf_counter *child_counter, *tmp;
        struct perf_counter_context *child_ctx;

        child_ctx = &child->perf_counter_ctx;

        if (likely(!child_ctx->nr_counters))
                return;

        list_for_each_entry_safe(child_counter, tmp, &child_ctx->counter_list,
                                 list_entry)
                __perf_counter_exit_task(child, child_counter, child_ctx);
}

/*
 * Initialize the perf_counter context in task_struct
 */
void perf_counter_init_task(struct task_struct *child)
{
        struct perf_counter_context *child_ctx, *parent_ctx;
        struct perf_counter *counter;
        struct task_struct *parent = current;

        child_ctx  =  &child->perf_counter_ctx;
        parent_ctx = &parent->perf_counter_ctx;

        __perf_counter_init_context(child_ctx, child);

        /*
         * This is executed from the parent task context, so inherit
         * counters that have been marked for cloning:
         */

        if (likely(!parent_ctx->nr_counters))
                return;

        /*
         * Lock the parent list. No need to lock the child - not PID
         * hashed yet and not running, so nobody can access it.
         */
        mutex_lock(&parent_ctx->mutex);

        /*
         * We dont have to disable NMIs - we are only looking at
         * the list, not manipulating it:
         */
        list_for_each_entry(counter, &parent_ctx->counter_list, list_entry) {
                if (!counter->hw_event.inherit)
                        continue;

                if (inherit_group(counter, parent,
                                  parent_ctx, child, child_ctx))
                        break;
        }

        mutex_unlock(&parent_ctx->mutex);
}

static void __cpuinit perf_counter_init_cpu(int cpu)
{
        struct perf_cpu_context *cpuctx;

        cpuctx = &per_cpu(perf_cpu_context, cpu);
        __perf_counter_init_context(&cpuctx->ctx, NULL);

        mutex_lock(&perf_resource_mutex);
        cpuctx->max_pertask = perf_max_counters - perf_reserved_percpu;
        mutex_unlock(&perf_resource_mutex);

        hw_perf_counter_setup(cpu);
}

#ifdef CONFIG_HOTPLUG_CPU
static void __perf_counter_exit_cpu(void *info)
{
        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
        struct perf_counter_context *ctx = &cpuctx->ctx;
        struct perf_counter *counter, *tmp;

        list_for_each_entry_safe(counter, tmp, &ctx->counter_list, list_entry)
                __perf_counter_remove_from_context(counter);
}
static void perf_counter_exit_cpu(int cpu)
{
        struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);
        struct perf_counter_context *ctx = &cpuctx->ctx;

        mutex_lock(&ctx->mutex);
        smp_call_function_single(cpu, __perf_counter_exit_cpu, NULL, 1);
        mutex_unlock(&ctx->mutex);
}
#else
static inline void perf_counter_exit_cpu(int cpu) { }
#endif

static int __cpuinit
perf_cpu_notify(struct notifier_block *self, unsigned long action, void *hcpu)
{
        unsigned int cpu = (long)hcpu;

        switch (action) {

        case CPU_UP_PREPARE:
        case CPU_UP_PREPARE_FROZEN:
                perf_counter_init_cpu(cpu);
                break;

        case CPU_DOWN_PREPARE:
        case CPU_DOWN_PREPARE_FROZEN:
                perf_counter_exit_cpu(cpu);
                break;

        default:
                break;
        }

        return NOTIFY_OK;
}

static struct notifier_block __cpuinitdata perf_cpu_nb = {
        .notifier_call          = perf_cpu_notify,
};

static int __init perf_counter_init(void)
{
        perf_cpu_notify(&perf_cpu_nb, (unsigned long)CPU_UP_PREPARE,
                        (void *)(long)smp_processor_id());
        register_cpu_notifier(&perf_cpu_nb);

        return 0;
}
early_initcall(perf_counter_init);

static ssize_t perf_show_reserve_percpu(struct sysdev_class *class, char *buf)
{
        return sprintf(buf, "%d\n", perf_reserved_percpu);
}

static ssize_t
perf_set_reserve_percpu(struct sysdev_class *class,
                        const char *buf,
                        size_t count)
{
        struct perf_cpu_context *cpuctx;
        unsigned long val;
        int err, cpu, mpt;

        err = strict_strtoul(buf, 10, &val);
        if (err)
                return err;
        if (val > perf_max_counters)
                return -EINVAL;

        mutex_lock(&perf_resource_mutex);
        perf_reserved_percpu = val;
        for_each_online_cpu(cpu) {
                cpuctx = &per_cpu(perf_cpu_context, cpu);
                spin_lock_irq(&cpuctx->ctx.lock);
                mpt = min(perf_max_counters - cpuctx->ctx.nr_counters,
                          perf_max_counters - perf_reserved_percpu);
                cpuctx->max_pertask = mpt;
                spin_unlock_irq(&cpuctx->ctx.lock);
        }
        mutex_unlock(&perf_resource_mutex);

        return count;
}

static ssize_t perf_show_overcommit(struct sysdev_class *class, char *buf)
{
        return sprintf(buf, "%d\n", perf_overcommit);
}

static ssize_t
perf_set_overcommit(struct sysdev_class *class, const char *buf, size_t count)
{
        unsigned long val;
        int err;

        err = strict_strtoul(buf, 10, &val);
        if (err)
                return err;
        if (val > 1)
                return -EINVAL;

        mutex_lock(&perf_resource_mutex);
        perf_overcommit = val;
        mutex_unlock(&perf_resource_mutex);

        return count;
}

static SYSDEV_CLASS_ATTR(
                                reserve_percpu,
                                0644,
                                perf_show_reserve_percpu,
                                perf_set_reserve_percpu
                        );

static SYSDEV_CLASS_ATTR(
                                overcommit,
                                0644,
                                perf_show_overcommit,
                                perf_set_overcommit
                        );

static struct attribute *perfclass_attrs[] = {
        &attr_reserve_percpu.attr,
        &attr_overcommit.attr,
        NULL
};

static struct attribute_group perfclass_attr_group = {
        .attrs                  = perfclass_attrs,
        .name                   = "perf_counters",
};

static int __init perf_counter_sysfs_init(void)
{
        return sysfs_create_group(&cpu_sysdev_class.kset.kobj,
                                  &perfclass_attr_group);
}
device_initcall(perf_counter_sysfs_init);