perf_counter: Add PERF_SAMPLE_PERIOD

[pandora-kernel.git] / kernel / perf_counter.c

/*
 * Performance counter core code
 *
 *  Copyright (C) 2008 Thomas Gleixner <tglx@linutronix.de>
 *  Copyright (C) 2008-2009 Red Hat, Inc., Ingo Molnar
 *  Copyright (C) 2008-2009 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
 *  Copyright  ©  2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
 *
 *  For licensing details see kernel-base/COPYING
 */

#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/cpu.h>
#include <linux/smp.h>
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/sysfs.h>
#include <linux/dcache.h>
#include <linux/percpu.h>
#include <linux/ptrace.h>
#include <linux/vmstat.h>
#include <linux/hardirq.h>
#include <linux/rculist.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 <asm/irq_regs.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;

static atomic_t nr_counters __read_mostly;
static atomic_t nr_mmap_counters __read_mostly;
static atomic_t nr_comm_counters __read_mostly;

int sysctl_perf_counter_priv __read_mostly; /* do we need to be privileged */
int sysctl_perf_counter_mlock __read_mostly = 512; /* 'free' kb per user */
int sysctl_perf_counter_limit __read_mostly = 100000; /* max NMIs per second */

static atomic64_t perf_counter_id;

/*
 * Lock for (sysadmin-configurable) counter reservations:
 */
static DEFINE_SPINLOCK(perf_resource_lock);

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

void __weak hw_perf_disable(void)               { barrier(); }
void __weak hw_perf_enable(void)                { 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 DEFINE_PER_CPU(int, disable_count);

void __perf_disable(void)
{
        __get_cpu_var(disable_count)++;
}

bool __perf_enable(void)
{
        return !--__get_cpu_var(disable_count);
}

void perf_disable(void)
{
        __perf_disable();
        hw_perf_disable();
}

void perf_enable(void)
{
        if (__perf_enable())
                hw_perf_enable();
}

static void get_ctx(struct perf_counter_context *ctx)
{
        atomic_inc(&ctx->refcount);
}

static void free_ctx(struct rcu_head *head)
{
        struct perf_counter_context *ctx;

        ctx = container_of(head, struct perf_counter_context, rcu_head);
        kfree(ctx);
}

static void put_ctx(struct perf_counter_context *ctx)
{
        if (atomic_dec_and_test(&ctx->refcount)) {
                if (ctx->parent_ctx)
                        put_ctx(ctx->parent_ctx);
                if (ctx->task)
                        put_task_struct(ctx->task);
                call_rcu(&ctx->rcu_head, free_ctx);
        }
}

/*
 * Get the perf_counter_context for a task and lock it.
 * This has to cope with with the fact that until it is locked,
 * the context could get moved to another task.
 */
static struct perf_counter_context *
perf_lock_task_context(struct task_struct *task, unsigned long *flags)
{
        struct perf_counter_context *ctx;

        rcu_read_lock();
 retry:
        ctx = rcu_dereference(task->perf_counter_ctxp);
        if (ctx) {
                /*
                 * If this context is a clone of another, it might
                 * get swapped for another underneath us by
                 * perf_counter_task_sched_out, though the
                 * rcu_read_lock() protects us from any context
                 * getting freed.  Lock the context and check if it
                 * got swapped before we could get the lock, and retry
                 * if so.  If we locked the right context, then it
                 * can't get swapped on us any more.
                 */
                spin_lock_irqsave(&ctx->lock, *flags);
                if (ctx != rcu_dereference(task->perf_counter_ctxp)) {
                        spin_unlock_irqrestore(&ctx->lock, *flags);
                        goto retry;
                }
        }
        rcu_read_unlock();
        return ctx;
}

/*
 * Get the context for a task and increment its pin_count so it
 * can't get swapped to another task.  This also increments its
 * reference count so that the context can't get freed.
 */
static struct perf_counter_context *perf_pin_task_context(struct task_struct *task)
{
        struct perf_counter_context *ctx;
        unsigned long flags;

        ctx = perf_lock_task_context(task, &flags);
        if (ctx) {
                ++ctx->pin_count;
                get_ctx(ctx);
                spin_unlock_irqrestore(&ctx->lock, flags);
        }
        return ctx;
}

static void perf_unpin_context(struct perf_counter_context *ctx)
{
        unsigned long flags;

        spin_lock_irqsave(&ctx->lock, flags);
        --ctx->pin_count;
        spin_unlock_irqrestore(&ctx->lock, flags);
        put_ctx(ctx);
}

/*
 * Add a counter from the lists for its context.
 * Must be called with ctx->mutex and ctx->lock held.
 */
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 (group_leader == counter)
                list_add_tail(&counter->list_entry, &ctx->counter_list);
        else {
                list_add_tail(&counter->list_entry, &group_leader->sibling_list);
                group_leader->nr_siblings++;
        }

        list_add_rcu(&counter->event_entry, &ctx->event_list);
        ctx->nr_counters++;
}

/*
 * Remove a counter from the lists for its context.
 * Must be called with ctx->mutex and ctx->lock held.
 */
static void
list_del_counter(struct perf_counter *counter, struct perf_counter_context *ctx)
{
        struct perf_counter *sibling, *tmp;

        if (list_empty(&counter->list_entry))
                return;
        ctx->nr_counters--;

        list_del_init(&counter->list_entry);
        list_del_rcu(&counter->event_entry);

        if (counter->group_leader != counter)
                counter->group_leader->nr_siblings--;

        /*
         * 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_move_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->tstamp_stopped = ctx->time;
        counter->pmu->disable(counter);
        counter->oncpu = -1;

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

        /*
         * 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;

        spin_lock(&ctx->lock);
        /*
         * Protect the list operation against NMI by disabling the
         * counters on a global level.
         */
        perf_disable();

        counter_sched_out(counter, cpuctx, ctx);

        list_del_counter(counter, ctx);

        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);
        }

        perf_enable();
        spin_unlock(&ctx->lock);
}


/*
 * Remove the counter from a task's (or a CPU's) list of counters.
 *
 * Must be called with ctx->mutex held.
 *
 * CPU counters are removed with a smp call. For task counters we only
 * call when the task is on a CPU.
 *
 * If counter->ctx is a cloned context, callers must make sure that
 * every task struct that counter->ctx->task could possibly point to
 * remains valid.  This is OK when called from perf_release since
 * that only calls us on the top-level context, which can't be a clone.
 * When called from perf_counter_exit_task, it's OK because the
 * context has been detached from its task.
 */
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)) {
                list_del_counter(counter, ctx);
        }
        spin_unlock_irq(&ctx->lock);
}

static inline u64 perf_clock(void)
{
        return cpu_clock(smp_processor_id());
}

/*
 * Update the record of the current time in a context.
 */
static void update_context_time(struct perf_counter_context *ctx)
{
        u64 now = perf_clock();

        ctx->time += now - ctx->timestamp;
        ctx->timestamp = now;
}

/*
 * Update the total_time_enabled and total_time_running fields for a counter.
 */
static void update_counter_times(struct perf_counter *counter)
{
        struct perf_counter_context *ctx = counter->ctx;
        u64 run_end;

        if (counter->state < PERF_COUNTER_STATE_INACTIVE)
                return;

        counter->total_time_enabled = ctx->time - counter->tstamp_enabled;

        if (counter->state == PERF_COUNTER_STATE_INACTIVE)
                run_end = counter->tstamp_stopped;
        else
                run_end = ctx->time;

        counter->total_time_running = run_end - counter->tstamp_running;
}

/*
 * Update total_time_enabled and total_time_running for all counters in a group.
 */
static void update_group_times(struct perf_counter *leader)
{
        struct perf_counter *counter;

        update_counter_times(leader);
        list_for_each_entry(counter, &leader->sibling_list, list_entry)
                update_counter_times(counter);
}

/*
 * 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;

        /*
         * 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;

        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) {
                update_context_time(ctx);
                update_counter_times(counter);
                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);
}

/*
 * Disable a counter.
 *
 * If counter->ctx is a cloned context, callers must make sure that
 * every task struct that counter->ctx->task could possibly point to
 * remains valid.  This condition is satisifed when called through
 * perf_counter_for_each_child or perf_counter_for_each because they
 * hold the top-level counter's child_mutex, so any descendant that
 * goes to exit will block in sync_child_counter.
 * When called from perf_pending_counter it's OK because counter->ctx
 * is the current context on this CPU and preemption is disabled,
 * hence we can't get into perf_counter_task_sched_out for this context.
 */
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) {
                update_counter_times(counter);
                counter->state = PERF_COUNTER_STATE_OFF;
        }

        spin_unlock_irq(&ctx->lock);
}

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

        counter->tstamp_running += ctx->time - counter->tstamp_stopped;

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

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

        return 0;
}

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;
}

/*
 * 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->attr.exclusive && cpuctx->active_oncpu)
                return 0;
        /*
         * Otherwise, try to add it if all previous groups were able
         * to go on.
         */
        return can_add_hw;
}

static void add_counter_to_ctx(struct perf_counter *counter,
                               struct perf_counter_context *ctx)
{
        list_add_counter(counter, ctx);
        counter->tstamp_enabled = ctx->time;
        counter->tstamp_running = ctx->time;
        counter->tstamp_stopped = ctx->time;
}

/*
 * Cross CPU call to install and enable a performance counter
 *
 * Must be called with ctx->mutex held
 */
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();
        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.
         * Or possibly this is the right context but it isn't
         * on this cpu because it had no counters.
         */
        if (ctx->task && cpuctx->task_ctx != ctx) {
                if (cpuctx->task_ctx || ctx->task != current)
                        return;
                cpuctx->task_ctx = ctx;
        }

        spin_lock(&ctx->lock);
        ctx->is_active = 1;
        update_context_time(ctx);

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

        add_counter_to_ctx(counter, ctx);

        /*
         * 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->attr.pinned) {
                        update_group_times(leader);
                        leader->state = PERF_COUNTER_STATE_ERROR;
                }
        }

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

 unlock:
        perf_enable();

        spin_unlock(&ctx->lock);
}

/*
 * 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;
        }

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))
                add_counter_to_ctx(counter, ctx);
        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;
        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) {
                if (cpuctx->task_ctx || ctx->task != current)
                        return;
                cpuctx->task_ctx = ctx;
        }

        spin_lock(&ctx->lock);
        ctx->is_active = 1;
        update_context_time(ctx);

        if (counter->state >= PERF_COUNTER_STATE_INACTIVE)
                goto unlock;
        counter->state = PERF_COUNTER_STATE_INACTIVE;
        counter->tstamp_enabled = ctx->time - counter->total_time_enabled;

        /*
         * 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 {
                perf_disable();
                if (counter == leader)
                        err = group_sched_in(counter, cpuctx, ctx,
                                             smp_processor_id());
                else
                        err = counter_sched_in(counter, cpuctx, ctx,
                                               smp_processor_id());
                perf_enable();
        }

        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->attr.pinned) {
                        update_group_times(leader);
                        leader->state = PERF_COUNTER_STATE_ERROR;
                }
        }

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

/*
 * Enable a counter.
 *
 * If counter->ctx is a cloned context, callers must make sure that
 * every task struct that counter->ctx->task could possibly point to
 * remains valid.  This condition is satisfied when called through
 * perf_counter_for_each_child or perf_counter_for_each as described
 * for perf_counter_disable.
 */
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;
                counter->tstamp_enabled =
                        ctx->time - counter->total_time_enabled;
        }
 out:
        spin_unlock_irq(&ctx->lock);
}

static int perf_counter_refresh(struct perf_counter *counter, int refresh)
{
        /*
         * not supported on inherited counters
         */
        if (counter->attr.inherit)
                return -EINVAL;

        atomic_add(refresh, &counter->event_limit);
        perf_counter_enable(counter);

        return 0;
}

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

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

        perf_disable();
        if (ctx->nr_active) {
                list_for_each_entry(counter, &ctx->counter_list, list_entry) {
                        if (counter != counter->group_leader)
                                counter_sched_out(counter, cpuctx, ctx);
                        else
                                group_sched_out(counter, cpuctx, ctx);
                }
        }
        perf_enable();
 out:
        spin_unlock(&ctx->lock);
}

/*
 * Test whether two contexts are equivalent, i.e. whether they
 * have both been cloned from the same version of the same context
 * and they both have the same number of enabled counters.
 * If the number of enabled counters is the same, then the set
 * of enabled counters should be the same, because these are both
 * inherited contexts, therefore we can't access individual counters
 * in them directly with an fd; we can only enable/disable all
 * counters via prctl, or enable/disable all counters in a family
 * via ioctl, which will have the same effect on both contexts.
 */
static int context_equiv(struct perf_counter_context *ctx1,
                         struct perf_counter_context *ctx2)
{
        return ctx1->parent_ctx && ctx1->parent_ctx == ctx2->parent_ctx
                && ctx1->parent_gen == ctx2->parent_gen
                && !ctx1->pin_count && !ctx2->pin_count;
}

/*
 * 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,
                                 struct task_struct *next, int cpu)
{
        struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);
        struct perf_counter_context *ctx = task->perf_counter_ctxp;
        struct perf_counter_context *next_ctx;
        struct perf_counter_context *parent;
        struct pt_regs *regs;
        int do_switch = 1;

        regs = task_pt_regs(task);
        perf_swcounter_event(PERF_COUNT_CONTEXT_SWITCHES, 1, 1, regs, 0);

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

        update_context_time(ctx);

        rcu_read_lock();
        parent = rcu_dereference(ctx->parent_ctx);
        next_ctx = next->perf_counter_ctxp;
        if (parent && next_ctx &&
            rcu_dereference(next_ctx->parent_ctx) == parent) {
                /*
                 * Looks like the two contexts are clones, so we might be
                 * able to optimize the context switch.  We lock both
                 * contexts and check that they are clones under the
                 * lock (including re-checking that neither has been
                 * uncloned in the meantime).  It doesn't matter which
                 * order we take the locks because no other cpu could
                 * be trying to lock both of these tasks.
                 */
                spin_lock(&ctx->lock);
                spin_lock_nested(&next_ctx->lock, SINGLE_DEPTH_NESTING);
                if (context_equiv(ctx, next_ctx)) {
                        /*
                         * XXX do we need a memory barrier of sorts
                         * wrt to rcu_dereference() of perf_counter_ctxp
                         */
                        task->perf_counter_ctxp = next_ctx;
                        next->perf_counter_ctxp = ctx;
                        ctx->task = next;
                        next_ctx->task = task;
                        do_switch = 0;
                }
                spin_unlock(&next_ctx->lock);
                spin_unlock(&ctx->lock);
        }
        rcu_read_unlock();

        if (do_switch) {
                __perf_counter_sched_out(ctx, cpuctx);
                cpuctx->task_ctx = NULL;
        }
}

/*
 * Called with IRQs disabled
 */
static void __perf_counter_task_sched_out(struct perf_counter_context *ctx)
{
        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);

        if (!cpuctx->task_ctx)
                return;

        if (WARN_ON_ONCE(ctx != cpuctx->task_ctx))
                return;

        __perf_counter_sched_out(ctx, cpuctx);
        cpuctx->task_ctx = NULL;
}

/*
 * Called with IRQs disabled
 */
static void perf_counter_cpu_sched_out(struct perf_cpu_context *cpuctx)
{
        __perf_counter_sched_out(&cpuctx->ctx, cpuctx);
}

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

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

        ctx->timestamp = perf_clock();

        perf_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->attr.pinned)
                        continue;
                if (counter->cpu != -1 && counter->cpu != cpu)
                        continue;

                if (counter != counter->group_leader)
                        counter_sched_in(counter, cpuctx, ctx, cpu);
                else {
                        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) {
                        update_group_times(counter);
                        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->attr.pinned)
                        continue;

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

                if (counter != counter->group_leader) {
                        if (counter_sched_in(counter, cpuctx, ctx, cpu))
                                can_add_hw = 0;
                } else {
                        if (group_can_go_on(counter, cpuctx, can_add_hw)) {
                                if (group_sched_in(counter, cpuctx, ctx, cpu))
                                        can_add_hw = 0;
                        }
                }
        }
        perf_enable();
 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_ctxp;

        if (likely(!ctx))
                return;
        if (cpuctx->task_ctx == ctx)
                return;
        __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);
}

#define MAX_INTERRUPTS (~0ULL)

static void perf_log_throttle(struct perf_counter *counter, int enable);
static void perf_log_period(struct perf_counter *counter, u64 period);

static void perf_adjust_freq(struct perf_counter_context *ctx)
{
        struct perf_counter *counter;
        u64 interrupts, sample_period;
        u64 events, period;
        s64 delta;

        spin_lock(&ctx->lock);
        list_for_each_entry(counter, &ctx->counter_list, list_entry) {
                if (counter->state != PERF_COUNTER_STATE_ACTIVE)
                        continue;

                interrupts = counter->hw.interrupts;
                counter->hw.interrupts = 0;

                if (interrupts == MAX_INTERRUPTS) {
                        perf_log_throttle(counter, 1);
                        counter->pmu->unthrottle(counter);
                        interrupts = 2*sysctl_perf_counter_limit/HZ;
                }

                if (!counter->attr.freq || !counter->attr.sample_freq)
                        continue;

                events = HZ * interrupts * counter->hw.sample_period;
                period = div64_u64(events, counter->attr.sample_freq);

                delta = (s64)(1 + period - counter->hw.sample_period);
                delta >>= 1;

                sample_period = counter->hw.sample_period + delta;

                if (!sample_period)
                        sample_period = 1;

                perf_log_period(counter, sample_period);

                counter->hw.sample_period = sample_period;
        }
        spin_unlock(&ctx->lock);
}

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

        if (!ctx->nr_counters)
                return;

        spin_lock(&ctx->lock);
        /*
         * Rotate the first entry last (works just fine for group counters too):
         */
        perf_disable();
        list_for_each_entry(counter, &ctx->counter_list, list_entry) {
                list_move_tail(&counter->list_entry, &ctx->counter_list);
                break;
        }
        perf_enable();

        spin_unlock(&ctx->lock);
}

void perf_counter_task_tick(struct task_struct *curr, int cpu)
{
        struct perf_cpu_context *cpuctx;
        struct perf_counter_context *ctx;

        if (!atomic_read(&nr_counters))
                return;

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

        perf_adjust_freq(&cpuctx->ctx);
        if (ctx)
                perf_adjust_freq(ctx);

        perf_counter_cpu_sched_out(cpuctx);
        if (ctx)
                __perf_counter_task_sched_out(ctx);

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

        perf_counter_cpu_sched_in(cpuctx, cpu);
        if (ctx)
                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;
        struct perf_counter_context *ctx = counter->ctx;
        unsigned long flags;

        local_irq_save(flags);
        if (ctx->is_active)
                update_context_time(ctx);
        counter->pmu->read(counter);
        update_counter_times(counter);
        local_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);
        } else if (counter->state == PERF_COUNTER_STATE_INACTIVE) {
                update_counter_times(counter);
        }

        return atomic64_read(&counter->count);
}

/*
 * 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);
        INIT_LIST_HEAD(&ctx->event_list);
        atomic_set(&ctx->refcount, 1);
        ctx->task = task;
}

static struct perf_counter_context *find_get_context(pid_t pid, int cpu)
{
        struct perf_counter_context *parent_ctx;
        struct perf_counter_context *ctx;
        struct perf_cpu_context *cpuctx;
        struct task_struct *task;
        unsigned long flags;
        int err;

        /*
         * 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 (sysctl_perf_counter_priv && !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;
                get_ctx(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);

        /*
         * Can't attach counters to a dying task.
         */
        err = -ESRCH;
        if (task->flags & PF_EXITING)
                goto errout;

        /* Reuse ptrace permission checks for now. */
        err = -EACCES;
        if (!ptrace_may_access(task, PTRACE_MODE_READ))
                goto errout;

 retry:
        ctx = perf_lock_task_context(task, &flags);
        if (ctx) {
                parent_ctx = ctx->parent_ctx;
                if (parent_ctx) {
                        put_ctx(parent_ctx);
                        ctx->parent_ctx = NULL;         /* no longer a clone */
                }
                /*
                 * Get an extra reference before dropping the lock so that
                 * this context won't get freed if the task exits.
                 */
                get_ctx(ctx);
                spin_unlock_irqrestore(&ctx->lock, flags);
        }

        if (!ctx) {
                ctx = kmalloc(sizeof(struct perf_counter_context), GFP_KERNEL);
                err = -ENOMEM;
                if (!ctx)
                        goto errout;
                __perf_counter_init_context(ctx, task);
                get_ctx(ctx);
                if (cmpxchg(&task->perf_counter_ctxp, NULL, ctx)) {
                        /*
                         * We raced with some other task; use
                         * the context they set.
                         */
                        kfree(ctx);
                        goto retry;
                }
                get_task_struct(task);
        }

        put_task_struct(task);
        return ctx;

 errout:
        put_task_struct(task);
        return ERR_PTR(err);
}

static void free_counter_rcu(struct rcu_head *head)
{
        struct perf_counter *counter;

        counter = container_of(head, struct perf_counter, rcu_head);
        if (counter->ns)
                put_pid_ns(counter->ns);
        kfree(counter);
}

static void perf_pending_sync(struct perf_counter *counter);

static void free_counter(struct perf_counter *counter)
{
        perf_pending_sync(counter);

        atomic_dec(&nr_counters);
        if (counter->attr.mmap)
                atomic_dec(&nr_mmap_counters);
        if (counter->attr.comm)
                atomic_dec(&nr_comm_counters);

        if (counter->destroy)
                counter->destroy(counter);

        put_ctx(counter->ctx);
        call_rcu(&counter->rcu_head, free_counter_rcu);
}

/*
 * 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;

        WARN_ON_ONCE(ctx->parent_ctx);
        mutex_lock(&ctx->mutex);
        perf_counter_remove_from_context(counter);
        mutex_unlock(&ctx->mutex);

        mutex_lock(&counter->owner->perf_counter_mutex);
        list_del_init(&counter->owner_entry);
        mutex_unlock(&counter->owner->perf_counter_mutex);
        put_task_struct(counter->owner);

        free_counter(counter);

        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 values[3];
        int n;

        /*
         * 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;

        WARN_ON_ONCE(counter->ctx->parent_ctx);
        mutex_lock(&counter->child_mutex);
        values[0] = perf_counter_read(counter);
        n = 1;
        if (counter->attr.read_format & PERF_FORMAT_TOTAL_TIME_ENABLED)
                values[n++] = counter->total_time_enabled +
                        atomic64_read(&counter->child_total_time_enabled);
        if (counter->attr.read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
                values[n++] = counter->total_time_running +
                        atomic64_read(&counter->child_total_time_running);
        if (counter->attr.read_format & PERF_FORMAT_ID)
                values[n++] = counter->id;
        mutex_unlock(&counter->child_mutex);

        if (count < n * sizeof(u64))
                return -EINVAL;
        count = n * sizeof(u64);

        if (copy_to_user(buf, values, count))
                return -EFAULT;

        return count;
}

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

        return perf_read_hw(counter, buf, count);
}

static unsigned int perf_poll(struct file *file, poll_table *wait)
{
        struct perf_counter *counter = file->private_data;
        struct perf_mmap_data *data;
        unsigned int events = POLL_HUP;

        rcu_read_lock();
        data = rcu_dereference(counter->data);
        if (data)
                events = atomic_xchg(&data->poll, 0);
        rcu_read_unlock();

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

        return events;
}

static void perf_counter_reset(struct perf_counter *counter)
{
        (void)perf_counter_read(counter);
        atomic64_set(&counter->count, 0);
        perf_counter_update_userpage(counter);
}

static void perf_counter_for_each_sibling(struct perf_counter *counter,
                                          void (*func)(struct perf_counter *))
{
        struct perf_counter_context *ctx = counter->ctx;
        struct perf_counter *sibling;

        WARN_ON_ONCE(ctx->parent_ctx);
        mutex_lock(&ctx->mutex);
        counter = counter->group_leader;

        func(counter);
        list_for_each_entry(sibling, &counter->sibling_list, list_entry)
                func(sibling);
        mutex_unlock(&ctx->mutex);
}

/*
 * Holding the top-level counter's child_mutex means that any
 * descendant process that has inherited this counter will block
 * in sync_child_counter if it goes to exit, thus satisfying the
 * task existence requirements of perf_counter_enable/disable.
 */
static void perf_counter_for_each_child(struct perf_counter *counter,
                                        void (*func)(struct perf_counter *))
{
        struct perf_counter *child;

        WARN_ON_ONCE(counter->ctx->parent_ctx);
        mutex_lock(&counter->child_mutex);
        func(counter);
        list_for_each_entry(child, &counter->child_list, child_list)
                func(child);
        mutex_unlock(&counter->child_mutex);
}

static void perf_counter_for_each(struct perf_counter *counter,
                                  void (*func)(struct perf_counter *))
{
        struct perf_counter *child;

        WARN_ON_ONCE(counter->ctx->parent_ctx);
        mutex_lock(&counter->child_mutex);
        perf_counter_for_each_sibling(counter, func);
        list_for_each_entry(child, &counter->child_list, child_list)
                perf_counter_for_each_sibling(child, func);
        mutex_unlock(&counter->child_mutex);
}

static int perf_counter_period(struct perf_counter *counter, u64 __user *arg)
{
        struct perf_counter_context *ctx = counter->ctx;
        unsigned long size;
        int ret = 0;
        u64 value;

        if (!counter->attr.sample_period)
                return -EINVAL;

        size = copy_from_user(&value, arg, sizeof(value));
        if (size != sizeof(value))
                return -EFAULT;

        if (!value)
                return -EINVAL;

        spin_lock_irq(&ctx->lock);
        if (counter->attr.freq) {
                if (value > sysctl_perf_counter_limit) {
                        ret = -EINVAL;
                        goto unlock;
                }

                counter->attr.sample_freq = value;
        } else {
                counter->attr.sample_period = value;
                counter->hw.sample_period = value;

                perf_log_period(counter, value);
        }
unlock:
        spin_unlock_irq(&ctx->lock);

        return ret;
}

static long perf_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
        struct perf_counter *counter = file->private_data;
        void (*func)(struct perf_counter *);
        u32 flags = arg;

        switch (cmd) {
        case PERF_COUNTER_IOC_ENABLE:
                func = perf_counter_enable;
                break;
        case PERF_COUNTER_IOC_DISABLE:
                func = perf_counter_disable;
                break;
        case PERF_COUNTER_IOC_RESET:
                func = perf_counter_reset;
                break;

        case PERF_COUNTER_IOC_REFRESH:
                return perf_counter_refresh(counter, arg);

        case PERF_COUNTER_IOC_PERIOD:
                return perf_counter_period(counter, (u64 __user *)arg);

        default:
                return -ENOTTY;
        }

        if (flags & PERF_IOC_FLAG_GROUP)
                perf_counter_for_each(counter, func);
        else
                perf_counter_for_each_child(counter, func);

        return 0;
}

int perf_counter_task_enable(void)
{
        struct perf_counter *counter;

        mutex_lock(&current->perf_counter_mutex);
        list_for_each_entry(counter, &current->perf_counter_list, owner_entry)
                perf_counter_for_each_child(counter, perf_counter_enable);
        mutex_unlock(&current->perf_counter_mutex);

        return 0;
}

int perf_counter_task_disable(void)
{
        struct perf_counter *counter;

        mutex_lock(&current->perf_counter_mutex);
        list_for_each_entry(counter, &current->perf_counter_list, owner_entry)
                perf_counter_for_each_child(counter, perf_counter_disable);
        mutex_unlock(&current->perf_counter_mutex);

        return 0;
}

/*
 * Callers need to ensure there can be no nesting of this function, otherwise
 * the seqlock logic goes bad. We can not serialize this because the arch
 * code calls this from NMI context.
 */
void perf_counter_update_userpage(struct perf_counter *counter)
{
        struct perf_counter_mmap_page *userpg;
        struct perf_mmap_data *data;

        rcu_read_lock();
        data = rcu_dereference(counter->data);
        if (!data)
                goto unlock;

        userpg = data->user_page;

        /*
         * Disable preemption so as to not let the corresponding user-space
         * spin too long if we get preempted.
         */
        preempt_disable();
        ++userpg->lock;
        barrier();
        userpg->index = counter->hw.idx;
        userpg->offset = atomic64_read(&counter->count);
        if (counter->state == PERF_COUNTER_STATE_ACTIVE)
                userpg->offset -= atomic64_read(&counter->hw.prev_count);

        barrier();
        ++userpg->lock;
        preempt_enable();
unlock:
        rcu_read_unlock();
}

static int perf_mmap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
{
        struct perf_counter *counter = vma->vm_file->private_data;
        struct perf_mmap_data *data;
        int ret = VM_FAULT_SIGBUS;

        rcu_read_lock();
        data = rcu_dereference(counter->data);
        if (!data)
                goto unlock;

        if (vmf->pgoff == 0) {
                vmf->page = virt_to_page(data->user_page);
        } else {
                int nr = vmf->pgoff - 1;

                if ((unsigned)nr > data->nr_pages)
                        goto unlock;

                vmf->page = virt_to_page(data->data_pages[nr]);
        }
        get_page(vmf->page);
        ret = 0;
unlock:
        rcu_read_unlock();

        return ret;
}

static int perf_mmap_data_alloc(struct perf_counter *counter, int nr_pages)
{
        struct perf_mmap_data *data;
        unsigned long size;
        int i;

        WARN_ON(atomic_read(&counter->mmap_count));

        size = sizeof(struct perf_mmap_data);
        size += nr_pages * sizeof(void *);

        data = kzalloc(size, GFP_KERNEL);
        if (!data)
                goto fail;

        data->user_page = (void *)get_zeroed_page(GFP_KERNEL);
        if (!data->user_page)
                goto fail_user_page;

        for (i = 0; i < nr_pages; i++) {
                data->data_pages[i] = (void *)get_zeroed_page(GFP_KERNEL);
                if (!data->data_pages[i])
                        goto fail_data_pages;
        }

        data->nr_pages = nr_pages;
        atomic_set(&data->lock, -1);

        rcu_assign_pointer(counter->data, data);

        return 0;

fail_data_pages:
        for (i--; i >= 0; i--)
                free_page((unsigned long)data->data_pages[i]);

        free_page((unsigned long)data->user_page);

fail_user_page:
        kfree(data);

fail:
        return -ENOMEM;
}

static void __perf_mmap_data_free(struct rcu_head *rcu_head)
{
        struct perf_mmap_data *data;
        int i;

        data = container_of(rcu_head, struct perf_mmap_data, rcu_head);

        free_page((unsigned long)data->user_page);
        for (i = 0; i < data->nr_pages; i++)
                free_page((unsigned long)data->data_pages[i]);
        kfree(data);
}

static void perf_mmap_data_free(struct perf_counter *counter)
{
        struct perf_mmap_data *data = counter->data;

        WARN_ON(atomic_read(&counter->mmap_count));

        rcu_assign_pointer(counter->data, NULL);
        call_rcu(&data->rcu_head, __perf_mmap_data_free);
}

static void perf_mmap_open(struct vm_area_struct *vma)
{
        struct perf_counter *counter = vma->vm_file->private_data;

        atomic_inc(&counter->mmap_count);
}

static void perf_mmap_close(struct vm_area_struct *vma)
{
        struct perf_counter *counter = vma->vm_file->private_data;

        WARN_ON_ONCE(counter->ctx->parent_ctx);
        if (atomic_dec_and_mutex_lock(&counter->mmap_count, &counter->mmap_mutex)) {
                struct user_struct *user = current_user();

                atomic_long_sub(counter->data->nr_pages + 1, &user->locked_vm);
                vma->vm_mm->locked_vm -= counter->data->nr_locked;
                perf_mmap_data_free(counter);
                mutex_unlock(&counter->mmap_mutex);
        }
}

static struct vm_operations_struct perf_mmap_vmops = {
        .open  = perf_mmap_open,
        .close = perf_mmap_close,
        .fault = perf_mmap_fault,
};

static int perf_mmap(struct file *file, struct vm_area_struct *vma)
{
        struct perf_counter *counter = file->private_data;
        unsigned long user_locked, user_lock_limit;
        struct user_struct *user = current_user();
        unsigned long locked, lock_limit;
        unsigned long vma_size;
        unsigned long nr_pages;
        long user_extra, extra;
        int ret = 0;

        if (!(vma->vm_flags & VM_SHARED) || (vma->vm_flags & VM_WRITE))
                return -EINVAL;

        vma_size = vma->vm_end - vma->vm_start;
        nr_pages = (vma_size / PAGE_SIZE) - 1;

        /*
         * If we have data pages ensure they're a power-of-two number, so we
         * can do bitmasks instead of modulo.
         */
        if (nr_pages != 0 && !is_power_of_2(nr_pages))
                return -EINVAL;

        if (vma_size != PAGE_SIZE * (1 + nr_pages))
                return -EINVAL;

        if (vma->vm_pgoff != 0)
                return -EINVAL;

        WARN_ON_ONCE(counter->ctx->parent_ctx);
        mutex_lock(&counter->mmap_mutex);
        if (atomic_inc_not_zero(&counter->mmap_count)) {
                if (nr_pages != counter->data->nr_pages)
                        ret = -EINVAL;
                goto unlock;
        }

        user_extra = nr_pages + 1;
        user_lock_limit = sysctl_perf_counter_mlock >> (PAGE_SHIFT - 10);

        /*
         * Increase the limit linearly with more CPUs:
         */
        user_lock_limit *= num_online_cpus();

        user_locked = atomic_long_read(&user->locked_vm) + user_extra;

        extra = 0;
        if (user_locked > user_lock_limit)
                extra = user_locked - user_lock_limit;

        lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
        lock_limit >>= PAGE_SHIFT;
        locked = vma->vm_mm->locked_vm + extra;

        if ((locked > lock_limit) && !capable(CAP_IPC_LOCK)) {
                ret = -EPERM;
                goto unlock;
        }

        WARN_ON(counter->data);
        ret = perf_mmap_data_alloc(counter, nr_pages);
        if (ret)
                goto unlock;

        atomic_set(&counter->mmap_count, 1);
        atomic_long_add(user_extra, &user->locked_vm);
        vma->vm_mm->locked_vm += extra;
        counter->data->nr_locked = extra;
unlock:
        mutex_unlock(&counter->mmap_mutex);

        vma->vm_flags &= ~VM_MAYWRITE;
        vma->vm_flags |= VM_RESERVED;
        vma->vm_ops = &perf_mmap_vmops;

        return ret;
}

static int perf_fasync(int fd, struct file *filp, int on)
{
        struct inode *inode = filp->f_path.dentry->d_inode;
        struct perf_counter *counter = filp->private_data;
        int retval;

        mutex_lock(&inode->i_mutex);
        retval = fasync_helper(fd, filp, on, &counter->fasync);
        mutex_unlock(&inode->i_mutex);

        if (retval < 0)
                return retval;

        return 0;
}

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

/*
 * Perf counter wakeup
 *
 * If there's data, ensure we set the poll() state and publish everything
 * to user-space before waking everybody up.
 */

void perf_counter_wakeup(struct perf_counter *counter)
{
        wake_up_all(&counter->waitq);

        if (counter->pending_kill) {
                kill_fasync(&counter->fasync, SIGIO, counter->pending_kill);
                counter->pending_kill = 0;
        }
}

/*
 * Pending wakeups
 *
 * Handle the case where we need to wakeup up from NMI (or rq->lock) context.
 *
 * The NMI bit means we cannot possibly take locks. Therefore, maintain a
 * single linked list and use cmpxchg() to add entries lockless.
 */

static void perf_pending_counter(struct perf_pending_entry *entry)
{
        struct perf_counter *counter = container_of(entry,
                        struct perf_counter, pending);

        if (counter->pending_disable) {
                counter->pending_disable = 0;
                perf_counter_disable(counter);
        }

        if (counter->pending_wakeup) {
                counter->pending_wakeup = 0;
                perf_counter_wakeup(counter);
        }
}

#define PENDING_TAIL ((struct perf_pending_entry *)-1UL)

static DEFINE_PER_CPU(struct perf_pending_entry *, perf_pending_head) = {
        PENDING_TAIL,
};

static void perf_pending_queue(struct perf_pending_entry *entry,
                               void (*func)(struct perf_pending_entry *))
{
        struct perf_pending_entry **head;

        if (cmpxchg(&entry->next, NULL, PENDING_TAIL) != NULL)
                return;

        entry->func = func;

        head = &get_cpu_var(perf_pending_head);

        do {
                entry->next = *head;
        } while (cmpxchg(head, entry->next, entry) != entry->next);

        set_perf_counter_pending();

        put_cpu_var(perf_pending_head);
}

static int __perf_pending_run(void)
{
        struct perf_pending_entry *list;
        int nr = 0;

        list = xchg(&__get_cpu_var(perf_pending_head), PENDING_TAIL);
        while (list != PENDING_TAIL) {
                void (*func)(struct perf_pending_entry *);
                struct perf_pending_entry *entry = list;

                list = list->next;

                func = entry->func;
                entry->next = NULL;
                /*
                 * Ensure we observe the unqueue before we issue the wakeup,
                 * so that we won't be waiting forever.
                 * -- see perf_not_pending().
                 */
                smp_wmb();

                func(entry);
                nr++;
        }

        return nr;
}

static inline int perf_not_pending(struct perf_counter *counter)
{
        /*
         * If we flush on whatever cpu we run, there is a chance we don't
         * need to wait.
         */
        get_cpu();
        __perf_pending_run();
        put_cpu();

        /*
         * Ensure we see the proper queue state before going to sleep
         * so that we do not miss the wakeup. -- see perf_pending_handle()
         */
        smp_rmb();
        return counter->pending.next == NULL;
}

static void perf_pending_sync(struct perf_counter *counter)
{
        wait_event(counter->waitq, perf_not_pending(counter));
}

void perf_counter_do_pending(void)
{
        __perf_pending_run();
}

/*
 * Callchain support -- arch specific
 */

__weak struct perf_callchain_entry *perf_callchain(struct pt_regs *regs)
{
        return NULL;
}

/*
 * Output
 */

struct perf_output_handle {
        struct perf_counter     *counter;
        struct perf_mmap_data   *data;
        unsigned long           head;
        unsigned long           offset;
        int                     nmi;
        int                     overflow;
        int                     locked;
        unsigned long           flags;
};

static void perf_output_wakeup(struct perf_output_handle *handle)
{
        atomic_set(&handle->data->poll, POLL_IN);

        if (handle->nmi) {
                handle->counter->pending_wakeup = 1;
                perf_pending_queue(&handle->counter->pending,
                                   perf_pending_counter);
        } else
                perf_counter_wakeup(handle->counter);
}

/*
 * Curious locking construct.
 *
 * We need to ensure a later event doesn't publish a head when a former
 * event isn't done writing. However since we need to deal with NMIs we
 * cannot fully serialize things.
 *
 * What we do is serialize between CPUs so we only have to deal with NMI
 * nesting on a single CPU.
 *
 * We only publish the head (and generate a wakeup) when the outer-most
 * event completes.
 */
static void perf_output_lock(struct perf_output_handle *handle)
{
        struct perf_mmap_data *data = handle->data;
        int cpu;

        handle->locked = 0;

        local_irq_save(handle->flags);
        cpu = smp_processor_id();

        if (in_nmi() && atomic_read(&data->lock) == cpu)
                return;

        while (atomic_cmpxchg(&data->lock, -1, cpu) != -1)
                cpu_relax();

        handle->locked = 1;
}

static void perf_output_unlock(struct perf_output_handle *handle)
{
        struct perf_mmap_data *data = handle->data;
        unsigned long head;
        int cpu;

        data->done_head = data->head;

        if (!handle->locked)
                goto out;

again:
        /*
         * The xchg implies a full barrier that ensures all writes are done
         * before we publish the new head, matched by a rmb() in userspace when
         * reading this position.
         */
        while ((head = atomic_long_xchg(&data->done_head, 0)))
                data->user_page->data_head = head;

        /*
         * NMI can happen here, which means we can miss a done_head update.
         */

        cpu = atomic_xchg(&data->lock, -1);
        WARN_ON_ONCE(cpu != smp_processor_id());

        /*
         * Therefore we have to validate we did not indeed do so.
         */
        if (unlikely(atomic_long_read(&data->done_head))) {
                /*
                 * Since we had it locked, we can lock it again.
                 */
                while (atomic_cmpxchg(&data->lock, -1, cpu) != -1)
                        cpu_relax();

                goto again;
        }

        if (atomic_xchg(&data->wakeup, 0))
                perf_output_wakeup(handle);
out:
        local_irq_restore(handle->flags);
}

static int perf_output_begin(struct perf_output_handle *handle,
                             struct perf_counter *counter, unsigned int size,
                             int nmi, int overflow)
{
        struct perf_mmap_data *data;
        unsigned int offset, head;

        /*
         * For inherited counters we send all the output towards the parent.
         */
        if (counter->parent)
                counter = counter->parent;

        rcu_read_lock();
        data = rcu_dereference(counter->data);
        if (!data)
                goto out;

        handle->data     = data;
        handle->counter  = counter;
        handle->nmi      = nmi;
        handle->overflow = overflow;

        if (!data->nr_pages)
                goto fail;

        perf_output_lock(handle);

        do {
                offset = head = atomic_long_read(&data->head);
                head += size;
        } while (atomic_long_cmpxchg(&data->head, offset, head) != offset);

        handle->offset  = offset;
        handle->head    = head;

        if ((offset >> PAGE_SHIFT) != (head >> PAGE_SHIFT))
                atomic_set(&data->wakeup, 1);

        return 0;

fail:
        perf_output_wakeup(handle);
out:
        rcu_read_unlock();

        return -ENOSPC;
}

static void perf_output_copy(struct perf_output_handle *handle,
                             const void *buf, unsigned int len)
{
        unsigned int pages_mask;
        unsigned int offset;
        unsigned int size;
        void **pages;

        offset          = handle->offset;
        pages_mask      = handle->data->nr_pages - 1;
        pages           = handle->data->data_pages;

        do {
                unsigned int page_offset;
                int nr;

                nr          = (offset >> PAGE_SHIFT) & pages_mask;
                page_offset = offset & (PAGE_SIZE - 1);
                size        = min_t(unsigned int, PAGE_SIZE - page_offset, len);

                memcpy(pages[nr] + page_offset, buf, size);

                len         -= size;
                buf         += size;
                offset      += size;
        } while (len);

        handle->offset = offset;

        /*
         * Check we didn't copy past our reservation window, taking the
         * possible unsigned int wrap into account.
         */
        WARN_ON_ONCE(((long)(handle->head - handle->offset)) < 0);
}

#define perf_output_put(handle, x) \
        perf_output_copy((handle), &(x), sizeof(x))

static void perf_output_end(struct perf_output_handle *handle)
{
        struct perf_counter *counter = handle->counter;
        struct perf_mmap_data *data = handle->data;

        int wakeup_events = counter->attr.wakeup_events;

        if (handle->overflow && wakeup_events) {
                int events = atomic_inc_return(&data->events);
                if (events >= wakeup_events) {
                        atomic_sub(wakeup_events, &data->events);
                        atomic_set(&data->wakeup, 1);
                }
        }

        perf_output_unlock(handle);
        rcu_read_unlock();
}

static u32 perf_counter_pid(struct perf_counter *counter, struct task_struct *p)
{
        /*
         * only top level counters have the pid namespace they were created in
         */
        if (counter->parent)
                counter = counter->parent;

        return task_tgid_nr_ns(p, counter->ns);
}

static u32 perf_counter_tid(struct perf_counter *counter, struct task_struct *p)
{
        /*
         * only top level counters have the pid namespace they were created in
         */
        if (counter->parent)
                counter = counter->parent;

        return task_pid_nr_ns(p, counter->ns);
}

static void perf_counter_output(struct perf_counter *counter,
                                int nmi, struct pt_regs *regs, u64 addr)
{
        int ret;
        u64 sample_type = counter->attr.sample_type;
        struct perf_output_handle handle;
        struct perf_event_header header;
        u64 ip;
        struct {
                u32 pid, tid;
        } tid_entry;
        struct {
                u64 id;
                u64 counter;
        } group_entry;
        struct perf_callchain_entry *callchain = NULL;
        int callchain_size = 0;
        u64 time;
        struct {
                u32 cpu, reserved;
        } cpu_entry;

        header.type = 0;
        header.size = sizeof(header);

        header.misc = PERF_EVENT_MISC_OVERFLOW;
        header.misc |= perf_misc_flags(regs);

        if (sample_type & PERF_SAMPLE_IP) {
                ip = perf_instruction_pointer(regs);
                header.type |= PERF_SAMPLE_IP;
                header.size += sizeof(ip);
        }

        if (sample_type & PERF_SAMPLE_TID) {
                /* namespace issues */
                tid_entry.pid = perf_counter_pid(counter, current);
                tid_entry.tid = perf_counter_tid(counter, current);

                header.type |= PERF_SAMPLE_TID;
                header.size += sizeof(tid_entry);
        }

        if (sample_type & PERF_SAMPLE_TIME) {
                /*
                 * Maybe do better on x86 and provide cpu_clock_nmi()
                 */
                time = sched_clock();

                header.type |= PERF_SAMPLE_TIME;
                header.size += sizeof(u64);
        }

        if (sample_type & PERF_SAMPLE_ADDR) {
                header.type |= PERF_SAMPLE_ADDR;
                header.size += sizeof(u64);
        }

        if (sample_type & PERF_SAMPLE_ID) {
                header.type |= PERF_SAMPLE_ID;
                header.size += sizeof(u64);
        }

        if (sample_type & PERF_SAMPLE_CPU) {
                header.type |= PERF_SAMPLE_CPU;
                header.size += sizeof(cpu_entry);

                cpu_entry.cpu = raw_smp_processor_id();
        }

        if (sample_type & PERF_SAMPLE_PERIOD) {
                header.type |= PERF_SAMPLE_PERIOD;
                header.size += sizeof(u64);
        }

        if (sample_type & PERF_SAMPLE_GROUP) {
                header.type |= PERF_SAMPLE_GROUP;
                header.size += sizeof(u64) +
                        counter->nr_siblings * sizeof(group_entry);
        }

        if (sample_type & PERF_SAMPLE_CALLCHAIN) {
                callchain = perf_callchain(regs);

                if (callchain) {
                        callchain_size = (1 + callchain->nr) * sizeof(u64);

                        header.type |= PERF_SAMPLE_CALLCHAIN;
                        header.size += callchain_size;
                }
        }

        ret = perf_output_begin(&handle, counter, header.size, nmi, 1);
        if (ret)
                return;

        perf_output_put(&handle, header);

        if (sample_type & PERF_SAMPLE_IP)
                perf_output_put(&handle, ip);

        if (sample_type & PERF_SAMPLE_TID)
                perf_output_put(&handle, tid_entry);

        if (sample_type & PERF_SAMPLE_TIME)
                perf_output_put(&handle, time);

        if (sample_type & PERF_SAMPLE_ADDR)
                perf_output_put(&handle, addr);

        if (sample_type & PERF_SAMPLE_ID)
                perf_output_put(&handle, counter->id);

        if (sample_type & PERF_SAMPLE_CPU)
                perf_output_put(&handle, cpu_entry);

        if (sample_type & PERF_SAMPLE_PERIOD)
                perf_output_put(&handle, counter->hw.sample_period);

        /*
         * XXX PERF_SAMPLE_GROUP vs inherited counters seems difficult.
         */
        if (sample_type & PERF_SAMPLE_GROUP) {
                struct perf_counter *leader, *sub;
                u64 nr = counter->nr_siblings;

                perf_output_put(&handle, nr);

                leader = counter->group_leader;
                list_for_each_entry(sub, &leader->sibling_list, list_entry) {
                        if (sub != counter)
                                sub->pmu->read(sub);

                        group_entry.id = sub->id;
                        group_entry.counter = atomic64_read(&sub->count);

                        perf_output_put(&handle, group_entry);
                }
        }

        if (callchain)
                perf_output_copy(&handle, callchain, callchain_size);

        perf_output_end(&handle);
}

/*
 * fork tracking
 */

struct perf_fork_event {
        struct task_struct      *task;

        struct {
                struct perf_event_header        header;

                u32                             pid;
                u32                             ppid;
        } event;
};

static void perf_counter_fork_output(struct perf_counter *counter,
                                     struct perf_fork_event *fork_event)
{
        struct perf_output_handle handle;
        int size = fork_event->event.header.size;
        struct task_struct *task = fork_event->task;
        int ret = perf_output_begin(&handle, counter, size, 0, 0);

        if (ret)
                return;

        fork_event->event.pid = perf_counter_pid(counter, task);
        fork_event->event.ppid = perf_counter_pid(counter, task->real_parent);

        perf_output_put(&handle, fork_event->event);
        perf_output_end(&handle);
}

static int perf_counter_fork_match(struct perf_counter *counter)
{
        if (counter->attr.comm || counter->attr.mmap)
                return 1;

        return 0;
}

static void perf_counter_fork_ctx(struct perf_counter_context *ctx,
                                  struct perf_fork_event *fork_event)
{
        struct perf_counter *counter;

        if (system_state != SYSTEM_RUNNING || list_empty(&ctx->event_list))
                return;

        rcu_read_lock();
        list_for_each_entry_rcu(counter, &ctx->event_list, event_entry) {
                if (perf_counter_fork_match(counter))
                        perf_counter_fork_output(counter, fork_event);
        }
        rcu_read_unlock();
}

static void perf_counter_fork_event(struct perf_fork_event *fork_event)
{
        struct perf_cpu_context *cpuctx;
        struct perf_counter_context *ctx;

        cpuctx = &get_cpu_var(perf_cpu_context);
        perf_counter_fork_ctx(&cpuctx->ctx, fork_event);
        put_cpu_var(perf_cpu_context);

        rcu_read_lock();
        /*
         * doesn't really matter which of the child contexts the
         * events ends up in.
         */
        ctx = rcu_dereference(current->perf_counter_ctxp);
        if (ctx)
                perf_counter_fork_ctx(ctx, fork_event);
        rcu_read_unlock();
}

void perf_counter_fork(struct task_struct *task)
{
        struct perf_fork_event fork_event;

        if (!atomic_read(&nr_comm_counters) &&
            !atomic_read(&nr_mmap_counters))
                return;

        fork_event = (struct perf_fork_event){
                .task   = task,
                .event  = {
                        .header = {
                                .type = PERF_EVENT_FORK,
                                .size = sizeof(fork_event.event),
                        },
                },
        };

        perf_counter_fork_event(&fork_event);
}

/*
 * comm tracking
 */

struct perf_comm_event {
        struct task_struct      *task;
        char                    *comm;
        int                     comm_size;

        struct {
                struct perf_event_header        header;

                u32                             pid;
                u32                             tid;
        } event;
};

static void perf_counter_comm_output(struct perf_counter *counter,
                                     struct perf_comm_event *comm_event)
{
        struct perf_output_handle handle;
        int size = comm_event->event.header.size;
        int ret = perf_output_begin(&handle, counter, size, 0, 0);

        if (ret)
                return;

        comm_event->event.pid = perf_counter_pid(counter, comm_event->task);
        comm_event->event.tid = perf_counter_tid(counter, comm_event->task);

        perf_output_put(&handle, comm_event->event);
        perf_output_copy(&handle, comm_event->comm,
                                   comm_event->comm_size);
        perf_output_end(&handle);
}

static int perf_counter_comm_match(struct perf_counter *counter)
{
        if (counter->attr.comm)
                return 1;

        return 0;
}

static void perf_counter_comm_ctx(struct perf_counter_context *ctx,
                                  struct perf_comm_event *comm_event)
{
        struct perf_counter *counter;

        if (system_state != SYSTEM_RUNNING || list_empty(&ctx->event_list))
                return;

        rcu_read_lock();
        list_for_each_entry_rcu(counter, &ctx->event_list, event_entry) {
                if (perf_counter_comm_match(counter))
                        perf_counter_comm_output(counter, comm_event);
        }
        rcu_read_unlock();
}

static void perf_counter_comm_event(struct perf_comm_event *comm_event)
{
        struct perf_cpu_context *cpuctx;
        struct perf_counter_context *ctx;
        unsigned int size;
        char *comm = comm_event->task->comm;

        size = ALIGN(strlen(comm)+1, sizeof(u64));

        comm_event->comm = comm;
        comm_event->comm_size = size;

        comm_event->event.header.size = sizeof(comm_event->event) + size;

        cpuctx = &get_cpu_var(perf_cpu_context);
        perf_counter_comm_ctx(&cpuctx->ctx, comm_event);
        put_cpu_var(perf_cpu_context);

        rcu_read_lock();
        /*
         * doesn't really matter which of the child contexts the
         * events ends up in.
         */
        ctx = rcu_dereference(current->perf_counter_ctxp);
        if (ctx)
                perf_counter_comm_ctx(ctx, comm_event);
        rcu_read_unlock();
}

void perf_counter_comm(struct task_struct *task)
{
        struct perf_comm_event comm_event;

        if (!atomic_read(&nr_comm_counters))
                return;

        comm_event = (struct perf_comm_event){
                .task   = task,
                .event  = {
                        .header = { .type = PERF_EVENT_COMM, },
                },
        };

        perf_counter_comm_event(&comm_event);
}

/*
 * mmap tracking
 */

struct perf_mmap_event {
        struct vm_area_struct   *vma;

        const char              *file_name;
        int                     file_size;

        struct {
                struct perf_event_header        header;

                u32                             pid;
                u32                             tid;
                u64                             start;
                u64                             len;
                u64                             pgoff;
        } event;
};

static void perf_counter_mmap_output(struct perf_counter *counter,
                                     struct perf_mmap_event *mmap_event)
{
        struct perf_output_handle handle;
        int size = mmap_event->event.header.size;
        int ret = perf_output_begin(&handle, counter, size, 0, 0);

        if (ret)
                return;

        mmap_event->event.pid = perf_counter_pid(counter, current);
        mmap_event->event.tid = perf_counter_tid(counter, current);

        perf_output_put(&handle, mmap_event->event);
        perf_output_copy(&handle, mmap_event->file_name,
                                   mmap_event->file_size);
        perf_output_end(&handle);
}

static int perf_counter_mmap_match(struct perf_counter *counter,
                                   struct perf_mmap_event *mmap_event)
{
        if (counter->attr.mmap)
                return 1;

        return 0;
}

static void perf_counter_mmap_ctx(struct perf_counter_context *ctx,
                                  struct perf_mmap_event *mmap_event)
{
        struct perf_counter *counter;

        if (system_state != SYSTEM_RUNNING || list_empty(&ctx->event_list))
                return;

        rcu_read_lock();
        list_for_each_entry_rcu(counter, &ctx->event_list, event_entry) {
                if (perf_counter_mmap_match(counter, mmap_event))
                        perf_counter_mmap_output(counter, mmap_event);
        }
        rcu_read_unlock();
}

static void perf_counter_mmap_event(struct perf_mmap_event *mmap_event)
{
        struct perf_cpu_context *cpuctx;
        struct perf_counter_context *ctx;
        struct vm_area_struct *vma = mmap_event->vma;
        struct file *file = vma->vm_file;
        unsigned int size;
        char tmp[16];
        char *buf = NULL;
        const char *name;

        if (file) {
                buf = kzalloc(PATH_MAX, GFP_KERNEL);
                if (!buf) {
                        name = strncpy(tmp, "//enomem", sizeof(tmp));
                        goto got_name;
                }
                name = d_path(&file->f_path, buf, PATH_MAX);
                if (IS_ERR(name)) {
                        name = strncpy(tmp, "//toolong", sizeof(tmp));
                        goto got_name;
                }
        } else {
                name = arch_vma_name(mmap_event->vma);
                if (name)
                        goto got_name;

                if (!vma->vm_mm) {
                        name = strncpy(tmp, "[vdso]", sizeof(tmp));
                        goto got_name;
                }

                name = strncpy(tmp, "//anon", sizeof(tmp));
                goto got_name;
        }

got_name:
        size = ALIGN(strlen(name)+1, sizeof(u64));

        mmap_event->file_name = name;
        mmap_event->file_size = size;

        mmap_event->event.header.size = sizeof(mmap_event->event) + size;

        cpuctx = &get_cpu_var(perf_cpu_context);
        perf_counter_mmap_ctx(&cpuctx->ctx, mmap_event);
        put_cpu_var(perf_cpu_context);

        rcu_read_lock();
        /*
         * doesn't really matter which of the child contexts the
         * events ends up in.
         */
        ctx = rcu_dereference(current->perf_counter_ctxp);
        if (ctx)
                perf_counter_mmap_ctx(ctx, mmap_event);
        rcu_read_unlock();

        kfree(buf);
}

void __perf_counter_mmap(struct vm_area_struct *vma)
{
        struct perf_mmap_event mmap_event;

        if (!atomic_read(&nr_mmap_counters))
                return;

        mmap_event = (struct perf_mmap_event){
                .vma    = vma,
                .event  = {
                        .header = { .type = PERF_EVENT_MMAP, },
                        .start  = vma->vm_start,
                        .len    = vma->vm_end - vma->vm_start,
                        .pgoff  = vma->vm_pgoff,
                },
        };

        perf_counter_mmap_event(&mmap_event);
}

/*
 * Log sample_period changes so that analyzing tools can re-normalize the
 * event flow.
 */

static void perf_log_period(struct perf_counter *counter, u64 period)
{
        struct perf_output_handle handle;
        int ret;

        struct {
                struct perf_event_header        header;
                u64                             time;
                u64                             id;
                u64                             period;
        } freq_event = {
                .header = {
                        .type = PERF_EVENT_PERIOD,
                        .misc = 0,
                        .size = sizeof(freq_event),
                },
                .time = sched_clock(),
                .id = counter->id,
                .period = period,
        };

        if (counter->hw.sample_period == period)
                return;

        ret = perf_output_begin(&handle, counter, sizeof(freq_event), 0, 0);
        if (ret)
                return;

        perf_output_put(&handle, freq_event);
        perf_output_end(&handle);
}

/*
 * IRQ throttle logging
 */

static void perf_log_throttle(struct perf_counter *counter, int enable)
{
        struct perf_output_handle handle;
        int ret;

        struct {
                struct perf_event_header        header;
                u64                             time;
        } throttle_event = {
                .header = {
                        .type = PERF_EVENT_THROTTLE + 1,
                        .misc = 0,
                        .size = sizeof(throttle_event),
                },
                .time = sched_clock(),
        };

        ret = perf_output_begin(&handle, counter, sizeof(throttle_event), 1, 0);
        if (ret)
                return;

        perf_output_put(&handle, throttle_event);
        perf_output_end(&handle);
}

/*
 * Generic counter overflow handling.
 */

int perf_counter_overflow(struct perf_counter *counter,
                          int nmi, struct pt_regs *regs, u64 addr)
{
        int events = atomic_read(&counter->event_limit);
        int throttle = counter->pmu->unthrottle != NULL;
        int ret = 0;

        if (!throttle) {
                counter->hw.interrupts++;
        } else {
                if (counter->hw.interrupts != MAX_INTERRUPTS) {
                        counter->hw.interrupts++;
                        if (HZ*counter->hw.interrupts > (u64)sysctl_perf_counter_limit) {
                                counter->hw.interrupts = MAX_INTERRUPTS;
                                perf_log_throttle(counter, 0);
                                ret = 1;
                        }
                } else {
                        /*
                         * Keep re-disabling counters even though on the previous
                         * pass we disabled it - just in case we raced with a
                         * sched-in and the counter got enabled again:
                         */
                        ret = 1;
                }
        }

        /*
         * XXX event_limit might not quite work as expected on inherited
         * counters
         */

        counter->pending_kill = POLL_IN;
        if (events && atomic_dec_and_test(&counter->event_limit)) {
                ret = 1;
                counter->pending_kill = POLL_HUP;
                if (nmi) {
                        counter->pending_disable = 1;
                        perf_pending_queue(&counter->pending,
                                           perf_pending_counter);
                } else
                        perf_counter_disable(counter);
        }

        perf_counter_output(counter, nmi, regs, addr);
        return ret;
}

/*
 * Generic software counter infrastructure
 */

static void perf_swcounter_update(struct perf_counter *counter)
{
        struct hw_perf_counter *hwc = &counter->hw;
        u64 prev, now;
        s64 delta;

again:
        prev = atomic64_read(&hwc->prev_count);
        now = atomic64_read(&hwc->count);
        if (atomic64_cmpxchg(&hwc->prev_count, prev, now) != prev)
                goto again;

        delta = now - prev;

        atomic64_add(delta, &counter->count);
        atomic64_sub(delta, &hwc->period_left);
}

static void perf_swcounter_set_period(struct perf_counter *counter)
{
        struct hw_perf_counter *hwc = &counter->hw;
        s64 left = atomic64_read(&hwc->period_left);
        s64 period = hwc->sample_period;

        if (unlikely(left <= -period)) {
                left = period;
                atomic64_set(&hwc->period_left, left);
        }

        if (unlikely(left <= 0)) {
                left += period;
                atomic64_add(period, &hwc->period_left);
        }

        atomic64_set(&hwc->prev_count, -left);
        atomic64_set(&hwc->count, -left);
}

static enum hrtimer_restart perf_swcounter_hrtimer(struct hrtimer *hrtimer)
{
        enum hrtimer_restart ret = HRTIMER_RESTART;
        struct perf_counter *counter;
        struct pt_regs *regs;
        u64 period;

        counter = container_of(hrtimer, struct perf_counter, hw.hrtimer);
        counter->pmu->read(counter);

        regs = get_irq_regs();
        /*
         * In case we exclude kernel IPs or are somehow not in interrupt
         * context, provide the next best thing, the user IP.
         */
        if ((counter->attr.exclude_kernel || !regs) &&
                        !counter->attr.exclude_user)
                regs = task_pt_regs(current);

        if (regs) {
                if (perf_counter_overflow(counter, 0, regs, 0))
                        ret = HRTIMER_NORESTART;
        }

        period = max_t(u64, 10000, counter->hw.sample_period);
        hrtimer_forward_now(hrtimer, ns_to_ktime(period));

        return ret;
}

static void perf_swcounter_overflow(struct perf_counter *counter,
                                    int nmi, struct pt_regs *regs, u64 addr)
{
        perf_swcounter_update(counter);
        perf_swcounter_set_period(counter);
        if (perf_counter_overflow(counter, nmi, regs, addr))
                /* soft-disable the counter */
                ;

}

static int perf_swcounter_is_counting(struct perf_counter *counter)
{
        struct perf_counter_context *ctx;
        unsigned long flags;
        int count;

        if (counter->state == PERF_COUNTER_STATE_ACTIVE)
                return 1;

        if (counter->state != PERF_COUNTER_STATE_INACTIVE)
                return 0;

        /*
         * If the counter is inactive, it could be just because
         * its task is scheduled out, or because it's in a group
         * which could not go on the PMU.  We want to count in
         * the first case but not the second.  If the context is
         * currently active then an inactive software counter must
         * be the second case.  If it's not currently active then
         * we need to know whether the counter was active when the
         * context was last active, which we can determine by
         * comparing counter->tstamp_stopped with ctx->time.
         *
         * We are within an RCU read-side critical section,
         * which protects the existence of *ctx.
         */
        ctx = counter->ctx;
        spin_lock_irqsave(&ctx->lock, flags);
        count = 1;
        /* Re-check state now we have the lock */
        if (counter->state < PERF_COUNTER_STATE_INACTIVE ||
            counter->ctx->is_active ||
            counter->tstamp_stopped < ctx->time)
                count = 0;
        spin_unlock_irqrestore(&ctx->lock, flags);
        return count;
}

static int perf_swcounter_match(struct perf_counter *counter,
                                enum perf_event_types type,
                                u32 event, struct pt_regs *regs)
{
        u64 event_config;

        event_config = ((u64) type << PERF_COUNTER_TYPE_SHIFT) | event;

        if (!perf_swcounter_is_counting(counter))
                return 0;

        if (counter->attr.config != event_config)
                return 0;

        if (regs) {
                if (counter->attr.exclude_user && user_mode(regs))
                        return 0;

                if (counter->attr.exclude_kernel && !user_mode(regs))
                        return 0;
        }

        return 1;
}

static void perf_swcounter_add(struct perf_counter *counter, u64 nr,
                               int nmi, struct pt_regs *regs, u64 addr)
{
        int neg = atomic64_add_negative(nr, &counter->hw.count);

        if (counter->hw.sample_period && !neg && regs)
                perf_swcounter_overflow(counter, nmi, regs, addr);
}

static void perf_swcounter_ctx_event(struct perf_counter_context *ctx,
                                     enum perf_event_types type, u32 event,
                                     u64 nr, int nmi, struct pt_regs *regs,
                                     u64 addr)
{
        struct perf_counter *counter;

        if (system_state != SYSTEM_RUNNING || list_empty(&ctx->event_list))
                return;

        rcu_read_lock();
        list_for_each_entry_rcu(counter, &ctx->event_list, event_entry) {
                if (perf_swcounter_match(counter, type, event, regs))
                        perf_swcounter_add(counter, nr, nmi, regs, addr);
        }
        rcu_read_unlock();
}

static int *perf_swcounter_recursion_context(struct perf_cpu_context *cpuctx)
{
        if (in_nmi())
                return &cpuctx->recursion[3];

        if (in_irq())
                return &cpuctx->recursion[2];

        if (in_softirq())
                return &cpuctx->recursion[1];

        return &cpuctx->recursion[0];
}

static void __perf_swcounter_event(enum perf_event_types type, u32 event,
                                   u64 nr, int nmi, struct pt_regs *regs,
                                   u64 addr)
{
        struct perf_cpu_context *cpuctx = &get_cpu_var(perf_cpu_context);
        int *recursion = perf_swcounter_recursion_context(cpuctx);
        struct perf_counter_context *ctx;

        if (*recursion)
                goto out;

        (*recursion)++;
        barrier();

        perf_swcounter_ctx_event(&cpuctx->ctx, type, event,
                                 nr, nmi, regs, addr);
        rcu_read_lock();
        /*
         * doesn't really matter which of the child contexts the
         * events ends up in.
         */
        ctx = rcu_dereference(current->perf_counter_ctxp);
        if (ctx)
                perf_swcounter_ctx_event(ctx, type, event, nr, nmi, regs, addr);
        rcu_read_unlock();

        barrier();
        (*recursion)--;

out:
        put_cpu_var(perf_cpu_context);
}

void
perf_swcounter_event(u32 event, u64 nr, int nmi, struct pt_regs *regs, u64 addr)
{
        __perf_swcounter_event(PERF_TYPE_SOFTWARE, event, nr, nmi, regs, addr);
}

static void perf_swcounter_read(struct perf_counter *counter)
{
        perf_swcounter_update(counter);
}

static int perf_swcounter_enable(struct perf_counter *counter)
{
        perf_swcounter_set_period(counter);
        return 0;
}

static void perf_swcounter_disable(struct perf_counter *counter)
{
        perf_swcounter_update(counter);
}

static const struct pmu perf_ops_generic = {
        .enable         = perf_swcounter_enable,
        .disable        = perf_swcounter_disable,
        .read           = perf_swcounter_read,
};

/*
 * Software counter: cpu wall time clock
 */

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 int cpu_clock_perf_counter_enable(struct perf_counter *counter)
{
        struct hw_perf_counter *hwc = &counter->hw;
        int cpu = raw_smp_processor_id();

        atomic64_set(&hwc->prev_count, cpu_clock(cpu));
        hrtimer_init(&hwc->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
        hwc->hrtimer.function = perf_swcounter_hrtimer;
        if (hwc->sample_period) {
                u64 period = max_t(u64, 10000, hwc->sample_period);
                __hrtimer_start_range_ns(&hwc->hrtimer,
                                ns_to_ktime(period), 0,
                                HRTIMER_MODE_REL, 0);
        }

        return 0;
}

static void cpu_clock_perf_counter_disable(struct perf_counter *counter)
{
        if (counter->hw.sample_period)
                hrtimer_cancel(&counter->hw.hrtimer);
        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 pmu perf_ops_cpu_clock = {
        .enable         = cpu_clock_perf_counter_enable,
        .disable        = cpu_clock_perf_counter_disable,
        .read           = cpu_clock_perf_counter_read,
};

/*
 * Software counter: task time clock
 */

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

        prev = atomic64_xchg(&counter->hw.prev_count, now);
        delta = now - prev;
        atomic64_add(delta, &counter->count);
}

static int task_clock_perf_counter_enable(struct perf_counter *counter)
{
        struct hw_perf_counter *hwc = &counter->hw;
        u64 now;

        now = counter->ctx->time;

        atomic64_set(&hwc->prev_count, now);
        hrtimer_init(&hwc->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
        hwc->hrtimer.function = perf_swcounter_hrtimer;
        if (hwc->sample_period) {
                u64 period = max_t(u64, 10000, hwc->sample_period);
                __hrtimer_start_range_ns(&hwc->hrtimer,
                                ns_to_ktime(period), 0,
                                HRTIMER_MODE_REL, 0);
        }

        return 0;
}

static void task_clock_perf_counter_disable(struct perf_counter *counter)
{
        if (counter->hw.sample_period)
                hrtimer_cancel(&counter->hw.hrtimer);
        task_clock_perf_counter_update(counter, counter->ctx->time);

}

static void task_clock_perf_counter_read(struct perf_counter *counter)
{
        u64 time;

        if (!in_nmi()) {
                update_context_time(counter->ctx);
                time = counter->ctx->time;
        } else {
                u64 now = perf_clock();
                u64 delta = now - counter->ctx->timestamp;
                time = counter->ctx->time + delta;
        }

        task_clock_perf_counter_update(counter, time);
}

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

/*
 * Software counter: cpu migrations
 */
void perf_counter_task_migration(struct task_struct *task, int cpu)
{
        struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);
        struct perf_counter_context *ctx;

        perf_swcounter_ctx_event(&cpuctx->ctx, PERF_TYPE_SOFTWARE,
                                 PERF_COUNT_CPU_MIGRATIONS,
                                 1, 1, NULL, 0);

        ctx = perf_pin_task_context(task);
        if (ctx) {
                perf_swcounter_ctx_event(ctx, PERF_TYPE_SOFTWARE,
                                         PERF_COUNT_CPU_MIGRATIONS,
                                         1, 1, NULL, 0);
                perf_unpin_context(ctx);
        }
}

#ifdef CONFIG_EVENT_PROFILE
void perf_tpcounter_event(int event_id)
{
        struct pt_regs *regs = get_irq_regs();

        if (!regs)
                regs = task_pt_regs(current);

        __perf_swcounter_event(PERF_TYPE_TRACEPOINT, event_id, 1, 1, regs, 0);
}
EXPORT_SYMBOL_GPL(perf_tpcounter_event);

extern int ftrace_profile_enable(int);
extern void ftrace_profile_disable(int);

static void tp_perf_counter_destroy(struct perf_counter *counter)
{
        ftrace_profile_disable(perf_event_id(&counter->attr));
}

static const struct pmu *tp_perf_counter_init(struct perf_counter *counter)
{
        int event_id = perf_event_id(&counter->attr);
        int ret;

        ret = ftrace_profile_enable(event_id);
        if (ret)
                return NULL;

        counter->destroy = tp_perf_counter_destroy;
        counter->hw.sample_period = counter->attr.sample_period;

        return &perf_ops_generic;
}
#else
static const struct pmu *tp_perf_counter_init(struct perf_counter *counter)
{
        return NULL;
}
#endif

static const struct pmu *sw_perf_counter_init(struct perf_counter *counter)
{
        const struct pmu *pmu = 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 (perf_event_id(&counter->attr)) {
        case PERF_COUNT_CPU_CLOCK:
                pmu = &perf_ops_cpu_clock;

                break;
        case PERF_COUNT_TASK_CLOCK:
                /*
                 * If the user instantiates this as a per-cpu counter,
                 * use the cpu_clock counter instead.
                 */
                if (counter->ctx->task)
                        pmu = &perf_ops_task_clock;
                else
                        pmu = &perf_ops_cpu_clock;

                break;
        case PERF_COUNT_PAGE_FAULTS:
        case PERF_COUNT_PAGE_FAULTS_MIN:
        case PERF_COUNT_PAGE_FAULTS_MAJ:
        case PERF_COUNT_CONTEXT_SWITCHES:
        case PERF_COUNT_CPU_MIGRATIONS:
                pmu = &perf_ops_generic;
                break;
        }

        return pmu;
}

/*
 * Allocate and initialize a counter structure
 */
static struct perf_counter *
perf_counter_alloc(struct perf_counter_attr *attr,
                   int cpu,
                   struct perf_counter_context *ctx,
                   struct perf_counter *group_leader,
                   gfp_t gfpflags)
{
        const struct pmu *pmu;
        struct perf_counter *counter;
        struct hw_perf_counter *hwc;
        long err;

        counter = kzalloc(sizeof(*counter), gfpflags);
        if (!counter)
                return ERR_PTR(-ENOMEM);

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

        mutex_init(&counter->child_mutex);
        INIT_LIST_HEAD(&counter->child_list);

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

        mutex_init(&counter->mmap_mutex);

        counter->cpu            = cpu;
        counter->attr           = *attr;
        counter->group_leader   = group_leader;
        counter->pmu            = NULL;
        counter->ctx            = ctx;
        counter->oncpu          = -1;

        counter->ns             = get_pid_ns(current->nsproxy->pid_ns);
        counter->id             = atomic64_inc_return(&perf_counter_id);

        counter->state          = PERF_COUNTER_STATE_INACTIVE;

        if (attr->disabled)
                counter->state = PERF_COUNTER_STATE_OFF;

        pmu = NULL;

        hwc = &counter->hw;
        if (attr->freq && attr->sample_freq)
                hwc->sample_period = div64_u64(TICK_NSEC, attr->sample_freq);
        else
                hwc->sample_period = attr->sample_period;

        /*
         * we currently do not support PERF_SAMPLE_GROUP on inherited counters
         */
        if (attr->inherit && (attr->sample_type & PERF_SAMPLE_GROUP))
                goto done;

        if (perf_event_raw(attr)) {
                pmu = hw_perf_counter_init(counter);
                goto done;
        }

        switch (perf_event_type(attr)) {
        case PERF_TYPE_HARDWARE:
                pmu = hw_perf_counter_init(counter);
                break;

        case PERF_TYPE_SOFTWARE:
                pmu = sw_perf_counter_init(counter);
                break;

        case PERF_TYPE_TRACEPOINT:
                pmu = tp_perf_counter_init(counter);
                break;
        }
done:
        err = 0;
        if (!pmu)
                err = -EINVAL;
        else if (IS_ERR(pmu))
                err = PTR_ERR(pmu);

        if (err) {
                if (counter->ns)
                        put_pid_ns(counter->ns);
                kfree(counter);
                return ERR_PTR(err);
        }

        counter->pmu = pmu;

        atomic_inc(&nr_counters);
        if (counter->attr.mmap)
                atomic_inc(&nr_mmap_counters);
        if (counter->attr.comm)
                atomic_inc(&nr_comm_counters);

        return counter;
}

/**
 * sys_perf_counter_open - open a performance counter, associate it to a task/cpu
 *
 * @attr_uptr:  event type attributes for monitoring/sampling
 * @pid:                target pid
 * @cpu:                target cpu
 * @group_fd:           group leader counter fd
 */
SYSCALL_DEFINE5(perf_counter_open,
                const struct perf_counter_attr __user *, attr_uptr,
                pid_t, pid, int, cpu, int, group_fd, unsigned long, flags)
{
        struct perf_counter *counter, *group_leader;
        struct perf_counter_attr attr;
        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;

        /* for future expandability... */
        if (flags)
                return -EINVAL;

        if (copy_from_user(&attr, attr_uptr, sizeof(attr)) != 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 (attr.exclusive || attr.pinned)
                        goto err_put_context;
        }

        counter = perf_counter_alloc(&attr, cpu, ctx, group_leader,
                                     GFP_KERNEL);
        ret = PTR_ERR(counter);
        if (IS_ERR(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;
        WARN_ON_ONCE(ctx->parent_ctx);
        mutex_lock(&ctx->mutex);
        perf_install_in_context(ctx, counter, cpu);
        ++ctx->generation;
        mutex_unlock(&ctx->mutex);

        counter->owner = current;
        get_task_struct(current);
        mutex_lock(&current->perf_counter_mutex);
        list_add_tail(&counter->owner_entry, &current->perf_counter_list);
        mutex_unlock(&current->perf_counter_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_ctx(ctx);

        goto out_fput;
}

/*
 * 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->attr,
                                           parent_counter->cpu, child_ctx,
                                           group_leader, GFP_KERNEL);
        if (IS_ERR(child_counter))
                return child_counter;
        get_ctx(child_ctx);

        /*
         * Make the child state follow the state of the parent counter,
         * not its attr.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;

        /*
         * Link it up in the child's context:
         */
        add_counter_to_ctx(child_counter, child_ctx);

        child_counter->parent = parent_counter;
        /*
         * inherit into child's child as well:
         */
        child_counter->attr.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
         */
        WARN_ON_ONCE(parent_counter->ctx->parent_ctx);
        mutex_lock(&parent_counter->child_mutex);
        list_add_tail(&child_counter->child_list, &parent_counter->child_list);
        mutex_unlock(&parent_counter->child_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;
        struct perf_counter *child_ctr;

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

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

        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);
        atomic64_add(child_counter->total_time_enabled,
                     &parent_counter->child_total_time_enabled);
        atomic64_add(child_counter->total_time_running,
                     &parent_counter->child_total_time_running);

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

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

static void
__perf_counter_exit_task(struct perf_counter *child_counter,
                         struct perf_counter_context *child_ctx)
{
        struct perf_counter *parent_counter;

        update_counter_times(child_counter);
        perf_counter_remove_from_context(child_counter);

        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);
                free_counter(child_counter);
        }
}

/*
 * When a child task exits, feed back counter values to parent counters.
 */
void perf_counter_exit_task(struct task_struct *child)
{
        struct perf_counter *child_counter, *tmp;
        struct perf_counter_context *child_ctx;
        unsigned long flags;

        if (likely(!child->perf_counter_ctxp))
                return;

        local_irq_save(flags);
        /*
         * We can't reschedule here because interrupts are disabled,
         * and either child is current or it is a task that can't be
         * scheduled, so we are now safe from rescheduling changing
         * our context.
         */
        child_ctx = child->perf_counter_ctxp;
        __perf_counter_task_sched_out(child_ctx);

        /*
         * Take the context lock here so that if find_get_context is
         * reading child->perf_counter_ctxp, we wait until it has
         * incremented the context's refcount before we do put_ctx below.
         */
        spin_lock(&child_ctx->lock);
        child->perf_counter_ctxp = NULL;
        if (child_ctx->parent_ctx) {
                /*
                 * This context is a clone; unclone it so it can't get
                 * swapped to another process while we're removing all
                 * the counters from it.
                 */
                put_ctx(child_ctx->parent_ctx);
                child_ctx->parent_ctx = NULL;
        }
        spin_unlock(&child_ctx->lock);
        local_irq_restore(flags);

        mutex_lock(&child_ctx->mutex);

again:
        list_for_each_entry_safe(child_counter, tmp, &child_ctx->counter_list,
                                 list_entry)
                __perf_counter_exit_task(child_counter, child_ctx);

        /*
         * If the last counter was a group counter, it will have appended all
         * its siblings to the list, but we obtained 'tmp' before that which
         * will still point to the list head terminating the iteration.
         */
        if (!list_empty(&child_ctx->counter_list))
                goto again;

        mutex_unlock(&child_ctx->mutex);

        put_ctx(child_ctx);
}

/*
 * free an unexposed, unused context as created by inheritance by
 * init_task below, used by fork() in case of fail.
 */
void perf_counter_free_task(struct task_struct *task)
{
        struct perf_counter_context *ctx = task->perf_counter_ctxp;
        struct perf_counter *counter, *tmp;

        if (!ctx)
                return;

        mutex_lock(&ctx->mutex);
again:
        list_for_each_entry_safe(counter, tmp, &ctx->counter_list, list_entry) {
                struct perf_counter *parent = counter->parent;

                if (WARN_ON_ONCE(!parent))
                        continue;

                mutex_lock(&parent->child_mutex);
                list_del_init(&counter->child_list);
                mutex_unlock(&parent->child_mutex);

                fput(parent->filp);

                list_del_counter(counter, ctx);
                free_counter(counter);
        }

        if (!list_empty(&ctx->counter_list))
                goto again;

        mutex_unlock(&ctx->mutex);

        put_ctx(ctx);
}

/*
 * Initialize the perf_counter context in task_struct
 */
int perf_counter_init_task(struct task_struct *child)
{
        struct perf_counter_context *child_ctx, *parent_ctx;
        struct perf_counter_context *cloned_ctx;
        struct perf_counter *counter;
        struct task_struct *parent = current;
        int inherited_all = 1;
        int ret = 0;

        child->perf_counter_ctxp = NULL;

        mutex_init(&child->perf_counter_mutex);
        INIT_LIST_HEAD(&child->perf_counter_list);

        if (likely(!parent->perf_counter_ctxp))
                return 0;

        /*
         * This is executed from the parent task context, so inherit
         * counters that have been marked for cloning.
         * First allocate and initialize a context for the child.
         */

        child_ctx = kmalloc(sizeof(struct perf_counter_context), GFP_KERNEL);
        if (!child_ctx)
                return -ENOMEM;

        __perf_counter_init_context(child_ctx, child);
        child->perf_counter_ctxp = child_ctx;
        get_task_struct(child);

        /*
         * If the parent's context is a clone, pin it so it won't get
         * swapped under us.
         */
        parent_ctx = perf_pin_task_context(parent);

        /*
         * No need to check if parent_ctx != NULL here; since we saw
         * it non-NULL earlier, the only reason for it to become NULL
         * is if we exit, and since we're currently in the middle of
         * a fork we can't be exiting at the same time.
         */

        /*
         * 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_rcu(counter, &parent_ctx->event_list, event_entry) {
                if (counter != counter->group_leader)
                        continue;

                if (!counter->attr.inherit) {
                        inherited_all = 0;
                        continue;
                }

                ret = inherit_group(counter, parent, parent_ctx,
                                             child, child_ctx);
                if (ret) {
                        inherited_all = 0;
                        break;
                }
        }

        if (inherited_all) {
                /*
                 * Mark the child context as a clone of the parent
                 * context, or of whatever the parent is a clone of.
                 * Note that if the parent is a clone, it could get
                 * uncloned at any point, but that doesn't matter
                 * because the list of counters and the generation
                 * count can't have changed since we took the mutex.
                 */
                cloned_ctx = rcu_dereference(parent_ctx->parent_ctx);
                if (cloned_ctx) {
                        child_ctx->parent_ctx = cloned_ctx;
                        child_ctx->parent_gen = parent_ctx->parent_gen;
                } else {
                        child_ctx->parent_ctx = parent_ctx;
                        child_ctx->parent_gen = parent_ctx->generation;
                }
                get_ctx(child_ctx->parent_ctx);
        }

        mutex_unlock(&parent_ctx->mutex);

        perf_unpin_context(parent_ctx);

        return ret;
}

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);

        spin_lock(&perf_resource_lock);
        cpuctx->max_pertask = perf_max_counters - perf_reserved_percpu;
        spin_unlock(&perf_resource_lock);

        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;
}

/*
 * This has to have a higher priority than migration_notifier in sched.c.
 */
static struct notifier_block __cpuinitdata perf_cpu_nb = {
        .notifier_call          = perf_cpu_notify,
        .priority               = 20,
};

void __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);
}

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;

        spin_lock(&perf_resource_lock);
        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);
        }
        spin_unlock(&perf_resource_lock);

        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;

        spin_lock(&perf_resource_lock);
        perf_overcommit = val;
        spin_unlock(&perf_resource_lock);

        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);