/*
 * Performance events 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/vmalloc.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_event.h>
#include <linux/ftrace_event.h>
#include <linux/hw_breakpoint.h>

#include <asm/irq_regs.h>

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

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

static atomic_t nr_events __read_mostly;
static atomic_t nr_mmap_events __read_mostly;
static atomic_t nr_comm_events __read_mostly;
static atomic_t nr_task_events __read_mostly;

/*
 * perf event paranoia level:
 *  -1 - not paranoid at all
 *   0 - disallow raw tracepoint access for unpriv
 *   1 - disallow cpu events for unpriv
 *   2 - disallow kernel profiling for unpriv
 */
int sysctl_perf_event_paranoid __read_mostly = 1;

static inline bool perf_paranoid_tracepoint_raw(void)
{
	return sysctl_perf_event_paranoid > -1;
}

static inline bool perf_paranoid_cpu(void)
{
	return sysctl_perf_event_paranoid > 0;
}

static inline bool perf_paranoid_kernel(void)
{
	return sysctl_perf_event_paranoid > 1;
}

int sysctl_perf_event_mlock __read_mostly = 512; /* 'free' kb per user */

/*
 * max perf event sample rate
 */
int sysctl_perf_event_sample_rate __read_mostly = 100000;

static atomic64_t perf_event_id;

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

/*
 * Architecture provided APIs - weak aliases:
 */
extern __weak const struct pmu *hw_perf_event_init(struct perf_event *event)
{
	return NULL;
}

void __weak hw_perf_disable(void)		{ barrier(); }
void __weak hw_perf_enable(void)		{ barrier(); }

void __weak hw_perf_event_setup(int cpu)	{ barrier(); }
void __weak hw_perf_event_setup_online(int cpu)	{ barrier(); }

int __weak
hw_perf_group_sched_in(struct perf_event *group_leader,
	       struct perf_cpu_context *cpuctx,
	       struct perf_event_context *ctx, int cpu)
{
	return 0;
}

void __weak perf_event_print_debug(void)	{ }

static DEFINE_PER_CPU(int, perf_disable_count);

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

bool __perf_enable(void)
{
	return !--__get_cpu_var(perf_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_event_context *ctx)
{
	WARN_ON(!atomic_inc_not_zero(&ctx->refcount));
}

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

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

static void put_ctx(struct perf_event_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);
	}
}

static void unclone_ctx(struct perf_event_context *ctx)
{
	if (ctx->parent_ctx) {
		put_ctx(ctx->parent_ctx);
		ctx->parent_ctx = NULL;
	}
}

/*
 * If we inherit events we want to return the parent event id
 * to userspace.
 */
static u64 primary_event_id(struct perf_event *event)
{
	u64 id = event->id;

	if (event->parent)
		id = event->parent->id;

	return id;
}

/*
 * Get the perf_event_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_event_context *
perf_lock_task_context(struct task_struct *task, unsigned long *flags)
{
	struct perf_event_context *ctx;

	rcu_read_lock();
 retry:
	ctx = rcu_dereference(task->perf_event_ctxp);
	if (ctx) {
		/*
		 * If this context is a clone of another, it might
		 * get swapped for another underneath us by
		 * perf_event_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.
		 */
		raw_spin_lock_irqsave(&ctx->lock, *flags);
		if (ctx != rcu_dereference(task->perf_event_ctxp)) {
			raw_spin_unlock_irqrestore(&ctx->lock, *flags);
			goto retry;
		}

		if (!atomic_inc_not_zero(&ctx->refcount)) {
			raw_spin_unlock_irqrestore(&ctx->lock, *flags);
			ctx = NULL;
		}
	}
	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_event_context *perf_pin_task_context(struct task_struct *task)
{
	struct perf_event_context *ctx;
	unsigned long flags;

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

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

	raw_spin_lock_irqsave(&ctx->lock, flags);
	--ctx->pin_count;
	raw_spin_unlock_irqrestore(&ctx->lock, flags);
	put_ctx(ctx);
}

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_event_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 event.
 */
static void update_event_times(struct perf_event *event)
{
	struct perf_event_context *ctx = event->ctx;
	u64 run_end;

	if (event->state < PERF_EVENT_STATE_INACTIVE ||
	    event->group_leader->state < PERF_EVENT_STATE_INACTIVE)
		return;

	if (ctx->is_active)
		run_end = ctx->time;
	else
		run_end = event->tstamp_stopped;

	event->total_time_enabled = run_end - event->tstamp_enabled;

	if (event->state == PERF_EVENT_STATE_INACTIVE)
		run_end = event->tstamp_stopped;
	else
		run_end = ctx->time;

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

/*
 * Add a event from the lists for its context.
 * Must be called with ctx->mutex and ctx->lock held.
 */
static void
list_add_event(struct perf_event *event, struct perf_event_context *ctx)
{
	struct perf_event *group_leader = event->group_leader;

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

	list_add_rcu(&event->event_entry, &ctx->event_list);
	ctx->nr_events++;
	if (event->attr.inherit_stat)
		ctx->nr_stat++;
}

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

	if (list_empty(&event->group_entry))
		return;
	ctx->nr_events--;
	if (event->attr.inherit_stat)
		ctx->nr_stat--;

	list_del_init(&event->group_entry);
	list_del_rcu(&event->event_entry);

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

	update_event_times(event);

	/*
	 * If event was in error state, then keep it
	 * that way, otherwise bogus counts will be
	 * returned on read(). The only way to get out
	 * of error state is by explicit re-enabling
	 * of the event
	 */
	if (event->state > PERF_EVENT_STATE_OFF)
		event->state = PERF_EVENT_STATE_OFF;

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

		list_move_tail(&sibling->group_entry, &ctx->group_list);
		sibling->group_leader = sibling;
	}
}

static void
event_sched_out(struct perf_event *event,
		  struct perf_cpu_context *cpuctx,
		  struct perf_event_context *ctx)
{
	if (event->state != PERF_EVENT_STATE_ACTIVE)
		return;

	event->state = PERF_EVENT_STATE_INACTIVE;
	if (event->pending_disable) {
		event->pending_disable = 0;
		event->state = PERF_EVENT_STATE_OFF;
	}
	event->tstamp_stopped = ctx->time;
	event->pmu->disable(event);
	event->oncpu = -1;

	if (!is_software_event(event))
		cpuctx->active_oncpu--;
	ctx->nr_active--;
	if (event->attr.exclusive || !cpuctx->active_oncpu)
		cpuctx->exclusive = 0;
}

static void
group_sched_out(struct perf_event *group_event,
		struct perf_cpu_context *cpuctx,
		struct perf_event_context *ctx)
{
	struct perf_event *event;

	if (group_event->state != PERF_EVENT_STATE_ACTIVE)
		return;

	event_sched_out(group_event, cpuctx, ctx);

	/*
	 * Schedule out siblings (if any):
	 */
	list_for_each_entry(event, &group_event->sibling_list, group_entry)
		event_sched_out(event, cpuctx, ctx);

	if (group_event->attr.exclusive)
		cpuctx->exclusive = 0;
}

/*
 * Cross CPU call to remove a performance event
 *
 * We disable the event on the hardware level first. After that we
 * remove it from the context list.
 */
static void __perf_event_remove_from_context(void *info)
{
	struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
	struct perf_event *event = info;
	struct perf_event_context *ctx = event->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;

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

	event_sched_out(event, cpuctx, ctx);

	list_del_event(event, ctx);

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

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


/*
 * Remove the event from a task's (or a CPU's) list of events.
 *
 * Must be called with ctx->mutex held.
 *
 * CPU events are removed with a smp call. For task events we only
 * call when the task is on a CPU.
 *
 * If event->ctx is a cloned context, callers must make sure that
 * every task struct that event->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_event_exit_task, it's OK because the
 * context has been detached from its task.
 */
static void perf_event_remove_from_context(struct perf_event *event)
{
	struct perf_event_context *ctx = event->ctx;
	struct task_struct *task = ctx->task;

	if (!task) {
		/*
		 * Per cpu events are removed via an smp call and
		 * the removal is always successful.
		 */
		smp_call_function_single(event->cpu,
					 __perf_event_remove_from_context,
					 event, 1);
		return;
	}

retry:
	task_oncpu_function_call(task, __perf_event_remove_from_context,
				 event);

	raw_spin_lock_irq(&ctx->lock);
	/*
	 * If the context is active we need to retry the smp call.
	 */
	if (ctx->nr_active && !list_empty(&event->group_entry)) {
		raw_spin_unlock_irq(&ctx->lock);
		goto retry;
	}

	/*
	 * The lock prevents that this context is scheduled in so we
	 * can remove the event safely, if the call above did not
	 * succeed.
	 */
	if (!list_empty(&event->group_entry))
		list_del_event(event, ctx);
	raw_spin_unlock_irq(&ctx->lock);
}

/*
 * Update total_time_enabled and total_time_running for all events in a group.
 */
static void update_group_times(struct perf_event *leader)
{
	struct perf_event *event;

	update_event_times(leader);
	list_for_each_entry(event, &leader->sibling_list, group_entry)
		update_event_times(event);
}

/*
 * Cross CPU call to disable a performance event
 */
static void __perf_event_disable(void *info)
{
	struct perf_event *event = info;
	struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
	struct perf_event_context *ctx = event->ctx;

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

	raw_spin_lock(&ctx->lock);

	/*
	 * If the event is on, turn it off.
	 * If it is in error state, leave it in error state.
	 */
	if (event->state >= PERF_EVENT_STATE_INACTIVE) {
		update_context_time(ctx);
		update_group_times(event);
		if (event == event->group_leader)
			group_sched_out(event, cpuctx, ctx);
		else
			event_sched_out(event, cpuctx, ctx);
		event->state = PERF_EVENT_STATE_OFF;
	}

	raw_spin_unlock(&ctx->lock);
}

/*
 * Disable a event.
 *
 * If event->ctx is a cloned context, callers must make sure that
 * every task struct that event->ctx->task could possibly point to
 * remains valid.  This condition is satisifed when called through
 * perf_event_for_each_child or perf_event_for_each because they
 * hold the top-level event's child_mutex, so any descendant that
 * goes to exit will block in sync_child_event.
 * When called from perf_pending_event it's OK because event->ctx
 * is the current context on this CPU and preemption is disabled,
 * hence we can't get into perf_event_task_sched_out for this context.
 */
void perf_event_disable(struct perf_event *event)
{
	struct perf_event_context *ctx = event->ctx;
	struct task_struct *task = ctx->task;

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

 retry:
	task_oncpu_function_call(task, __perf_event_disable, event);

	raw_spin_lock_irq(&ctx->lock);
	/*
	 * If the event is still active, we need to retry the cross-call.
	 */
	if (event->state == PERF_EVENT_STATE_ACTIVE) {
		raw_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 (event->state == PERF_EVENT_STATE_INACTIVE) {
		update_group_times(event);
		event->state = PERF_EVENT_STATE_OFF;
	}

	raw_spin_unlock_irq(&ctx->lock);
}

static int
event_sched_in(struct perf_event *event,
		 struct perf_cpu_context *cpuctx,
		 struct perf_event_context *ctx,
		 int cpu)
{
	if (event->state <= PERF_EVENT_STATE_OFF)
		return 0;

	event->state = PERF_EVENT_STATE_ACTIVE;
	event->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 (event->pmu->enable(event)) {
		event->state = PERF_EVENT_STATE_INACTIVE;
		event->oncpu = -1;
		return -EAGAIN;
	}

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

	if (!is_software_event(event))
		cpuctx->active_oncpu++;
	ctx->nr_active++;

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

	return 0;
}

static int
group_sched_in(struct perf_event *group_event,
	       struct perf_cpu_context *cpuctx,
	       struct perf_event_context *ctx,
	       int cpu)
{
	struct perf_event *event, *partial_group;
	int ret;

	if (group_event->state == PERF_EVENT_STATE_OFF)
		return 0;

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

	if (event_sched_in(group_event, cpuctx, ctx, cpu))
		return -EAGAIN;

	/*
	 * Schedule in siblings as one group (if any):
	 */
	list_for_each_entry(event, &group_event->sibling_list, group_entry) {
		if (event_sched_in(event, cpuctx, ctx, cpu)) {
			partial_group = event;
			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(event, &group_event->sibling_list, group_entry) {
		if (event == partial_group)
			break;
		event_sched_out(event, cpuctx, ctx);
	}
	event_sched_out(group_event, cpuctx, ctx);

	return -EAGAIN;
}

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

	if (!is_software_event(leader))
		return 0;

	list_for_each_entry(event, &leader->sibling_list, group_entry)
		if (!is_software_event(event))
			return 0;

	return 1;
}

/*
 * Work out whether we can put this event group on the CPU now.
 */
static int group_can_go_on(struct perf_event *event,
			   struct perf_cpu_context *cpuctx,
			   int can_add_hw)
{
	/*
	 * Groups consisting entirely of software events can always go on.
	 */
	if (is_software_only_group(event))
		return 1;
	/*
	 * If an exclusive group is already on, no other hardware
	 * events can go on.
	 */
	if (cpuctx->exclusive)
		return 0;
	/*
	 * If this group is exclusive and there are already
	 * events on the CPU, it can't go on.
	 */
	if (event->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_event_to_ctx(struct perf_event *event,
			       struct perf_event_context *ctx)
{
	list_add_event(event, ctx);
	event->tstamp_enabled = ctx->time;
	event->tstamp_running = ctx->time;
	event->tstamp_stopped = ctx->time;
}

/*
 * Cross CPU call to install and enable a performance event
 *
 * 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_event *event = info;
	struct perf_event_context *ctx = event->ctx;
	struct perf_event *leader = event->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 events.
	 */
	if (ctx->task && cpuctx->task_ctx != ctx) {
		if (cpuctx->task_ctx || ctx->task != current)
			return;
		cpuctx->task_ctx = ctx;
	}

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

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

	add_event_to_ctx(event, ctx);

	if (event->cpu != -1 && event->cpu != smp_processor_id())
		goto unlock;

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

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

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

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

 unlock:
	perf_enable();

	raw_spin_unlock(&ctx->lock);
}

/*
 * Attach a performance event to a context
 *
 * First we add the event to the list with the hardware enable bit
 * in event->hw_config cleared.
 *
 * If the event 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_event_context *ctx,
			struct perf_event *event,
			int cpu)
{
	struct task_struct *task = ctx->task;

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

retry:
	task_oncpu_function_call(task, __perf_install_in_context,
				 event);

	raw_spin_lock_irq(&ctx->lock);
	/*
	 * we need to retry the smp call.
	 */
	if (ctx->is_active && list_empty(&event->group_entry)) {
		raw_spin_unlock_irq(&ctx->lock);
		goto retry;
	}

	/*
	 * The lock prevents that this context is scheduled in so we
	 * can add the event safely, if it the call above did not
	 * succeed.
	 */
	if (list_empty(&event->group_entry))
		add_event_to_ctx(event, ctx);
	raw_spin_unlock_irq(&ctx->lock);
}

/*
 * Put a event into inactive state and update time fields.
 * Enabling the leader of a group effectively enables all
 * the group members that aren't explicitly disabled, so we
 * have to update their ->tstamp_enabled also.
 * Note: this works for group members as well as group leaders
 * since the non-leader members' sibling_lists will be empty.
 */
static void __perf_event_mark_enabled(struct perf_event *event,
					struct perf_event_context *ctx)
{
	struct perf_event *sub;

	event->state = PERF_EVENT_STATE_INACTIVE;
	event->tstamp_enabled = ctx->time - event->total_time_enabled;
	list_for_each_entry(sub, &event->sibling_list, group_entry)
		if (sub->state >= PERF_EVENT_STATE_INACTIVE)
			sub->tstamp_enabled =
				ctx->time - sub->total_time_enabled;
}

/*
 * Cross CPU call to enable a performance event
 */
static void __perf_event_enable(void *info)
{
	struct perf_event *event = info;
	struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
	struct perf_event_context *ctx = event->ctx;
	struct perf_event *leader = event->group_leader;
	int err;

	/*
	 * If this is a per-task event, need to check whether this
	 * event'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;
	}

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

	if (event->state >= PERF_EVENT_STATE_INACTIVE)
		goto unlock;
	__perf_event_mark_enabled(event, ctx);

	if (event->cpu != -1 && event->cpu != smp_processor_id())
		goto unlock;

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

	if (!group_can_go_on(event, cpuctx, 1)) {
		err = -EEXIST;
	} else {
		perf_disable();
		if (event == leader)
			err = group_sched_in(event, cpuctx, ctx,
					     smp_processor_id());
		else
			err = event_sched_in(event, cpuctx, ctx,
					       smp_processor_id());
		perf_enable();
	}

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

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

/*
 * Enable a event.
 *
 * If event->ctx is a cloned context, callers must make sure that
 * every task struct that event->ctx->task could possibly point to
 * remains valid.  This condition is satisfied when called through
 * perf_event_for_each_child or perf_event_for_each as described
 * for perf_event_disable.
 */
void perf_event_enable(struct perf_event *event)
{
	struct perf_event_context *ctx = event->ctx;
	struct task_struct *task = ctx->task;

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

	raw_spin_lock_irq(&ctx->lock);
	if (event->state >= PERF_EVENT_STATE_INACTIVE)
		goto out;

	/*
	 * If the event is in error state, clear that first.
	 * That way, if we see the event 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 (event->state == PERF_EVENT_STATE_ERROR)
		event->state = PERF_EVENT_STATE_OFF;

 retry:
	raw_spin_unlock_irq(&ctx->lock);
	task_oncpu_function_call(task, __perf_event_enable, event);

	raw_spin_lock_irq(&ctx->lock);

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

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

 out:
	raw_spin_unlock_irq(&ctx->lock);
}

static int perf_event_refresh(struct perf_event *event, int refresh)
{
	/*
	 * not supported on inherited events
	 */
	if (event->attr.inherit)
		return -EINVAL;

	atomic_add(refresh, &event->event_limit);
	perf_event_enable(event);

	return 0;
}

void __perf_event_sched_out(struct perf_event_context *ctx,
			      struct perf_cpu_context *cpuctx)
{
	struct perf_event *event;

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

	perf_disable();
	if (ctx->nr_active) {
		list_for_each_entry(event, &ctx->group_list, group_entry)
			group_sched_out(event, cpuctx, ctx);
	}
	perf_enable();
 out:
	raw_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 events.
 * If the number of enabled events is the same, then the set
 * of enabled events should be the same, because these are both
 * inherited contexts, therefore we can't access individual events
 * in them directly with an fd; we can only enable/disable all
 * events via prctl, or enable/disable all events in a family
 * via ioctl, which will have the same effect on both contexts.
 */
static int context_equiv(struct perf_event_context *ctx1,
			 struct perf_event_context *ctx2)
{
	return ctx1->parent_ctx && ctx1->parent_ctx == ctx2->parent_ctx
		&& ctx1->parent_gen == ctx2->parent_gen
		&& !ctx1->pin_count && !ctx2->pin_count;
}

static void __perf_event_sync_stat(struct perf_event *event,
				     struct perf_event *next_event)
{
	u64 value;

	if (!event->attr.inherit_stat)
		return;

	/*
	 * Update the event value, we cannot use perf_event_read()
	 * because we're in the middle of a context switch and have IRQs
	 * disabled, which upsets smp_call_function_single(), however
	 * we know the event must be on the current CPU, therefore we
	 * don't need to use it.
	 */
	switch (event->state) {
	case PERF_EVENT_STATE_ACTIVE:
		event->pmu->read(event);
		/* fall-through */

	case PERF_EVENT_STATE_INACTIVE:
		update_event_times(event);
		break;

	default:
		break;
	}

	/*
	 * In order to keep per-task stats reliable we need to flip the event
	 * values when we flip the contexts.
	 */
	value = atomic64_read(&next_event->count);
	value = atomic64_xchg(&event->count, value);
	atomic64_set(&next_event->count, value);

	swap(event->total_time_enabled, next_event->total_time_enabled);
	swap(event->total_time_running, next_event->total_time_running);

	/*
	 * Since we swizzled the values, update the user visible data too.
	 */
	perf_event_update_userpage(event);
	perf_event_update_userpage(next_event);
}

#define list_next_entry(pos, member) \
	list_entry(pos->member.next, typeof(*pos), member)

static void perf_event_sync_stat(struct perf_event_context *ctx,
				   struct perf_event_context *next_ctx)
{
	struct perf_event *event, *next_event;

	if (!ctx->nr_stat)
		return;

	update_context_time(ctx);

	event = list_first_entry(&ctx->event_list,
				   struct perf_event, event_entry);

	next_event = list_first_entry(&next_ctx->event_list,
					struct perf_event, event_entry);

	while (&event->event_entry != &ctx->event_list &&
	       &next_event->event_entry != &next_ctx->event_list) {

		__perf_event_sync_stat(event, next_event);

		event = list_next_entry(event, event_entry);
		next_event = list_next_entry(next_event, event_entry);
	}
}

/*
 * Called from scheduler to remove the events of the current task,
 * with interrupts disabled.
 *
 * We stop each event and update the event value in event->count.
 *
 * This does not protect us against NMI, but disable()
 * sets the disabled bit in the control field of event _before_
 * accessing the event control register. If a NMI hits, then it will
 * not restart the event.
 */
void perf_event_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_event_context *ctx = task->perf_event_ctxp;
	struct perf_event_context *next_ctx;
	struct perf_event_context *parent;
	struct pt_regs *regs;
	int do_switch = 1;

	regs = task_pt_regs(task);
	perf_sw_event(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, 1, regs, 0);

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

	rcu_read_lock();
	parent = rcu_dereference(ctx->parent_ctx);
	next_ctx = next->perf_event_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.
		 */
		raw_spin_lock(&ctx->lock);
		raw_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_event_ctxp
			 */
			task->perf_event_ctxp = next_ctx;
			next->perf_event_ctxp = ctx;
			ctx->task = next;
			next_ctx->task = task;
			do_switch = 0;

			perf_event_sync_stat(ctx, next_ctx);
		}
		raw_spin_unlock(&next_ctx->lock);
		raw_spin_unlock(&ctx->lock);
	}
	rcu_read_unlock();

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

/*
 * Called with IRQs disabled
 */
static void __perf_event_task_sched_out(struct perf_event_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_event_sched_out(ctx, cpuctx);
	cpuctx->task_ctx = NULL;
}

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

static void
__perf_event_sched_in(struct perf_event_context *ctx,
			struct perf_cpu_context *cpuctx, int cpu)
{
	struct perf_event *event;
	int can_add_hw = 1;

	raw_spin_lock(&ctx->lock);
	ctx->is_active = 1;
	if (likely(!ctx->nr_events))
		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(event, &ctx->group_list, group_entry) {
		if (event->state <= PERF_EVENT_STATE_OFF ||
		    !event->attr.pinned)
			continue;
		if (event->cpu != -1 && event->cpu != cpu)
			continue;

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

		/*
		 * If this pinned group hasn't been scheduled,
		 * put it in error state.
		 */
		if (event->state == PERF_EVENT_STATE_INACTIVE) {
			update_group_times(event);
			event->state = PERF_EVENT_STATE_ERROR;
		}
	}

	list_for_each_entry(event, &ctx->group_list, group_entry) {
		/*
		 * Ignore events in OFF or ERROR state, and
		 * ignore pinned events since we did them already.
		 */
		if (event->state <= PERF_EVENT_STATE_OFF ||
		    event->attr.pinned)
			continue;

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

		if (group_can_go_on(event, cpuctx, can_add_hw))
			if (group_sched_in(event, cpuctx, ctx, cpu))
				can_add_hw = 0;
	}
	perf_enable();
 out:
	raw_spin_unlock(&ctx->lock);
}

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

	if (likely(!ctx))
		return;
	if (cpuctx->task_ctx == ctx)
		return;
	__perf_event_sched_in(ctx, cpuctx, cpu);
	cpuctx->task_ctx = ctx;
}

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

	__perf_event_sched_in(ctx, cpuctx, cpu);
}

#define MAX_INTERRUPTS (~0ULL)

static void perf_log_throttle(struct perf_event *event, int enable);

static void perf_adjust_period(struct perf_event *event, u64 events)
{
	struct hw_perf_event *hwc = &event->hw;
	u64 period, sample_period;
	s64 delta;

	events *= hwc->sample_period;
	period = div64_u64(events, event->attr.sample_freq);

	delta = (s64)(period - hwc->sample_period);
	delta = (delta + 7) / 8; /* low pass filter */

	sample_period = hwc->sample_period + delta;

	if (!sample_period)
		sample_period = 1;

	hwc->sample_period = sample_period;
}

static void perf_ctx_adjust_freq(struct perf_event_context *ctx)
{
	struct perf_event *event;
	struct hw_perf_event *hwc;
	u64 interrupts, freq;

	raw_spin_lock(&ctx->lock);
	list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {
		if (event->state != PERF_EVENT_STATE_ACTIVE)
			continue;

		hwc = &event->hw;

		interrupts = hwc->interrupts;
		hwc->interrupts = 0;

		/*
		 * unthrottle events on the tick
		 */
		if (interrupts == MAX_INTERRUPTS) {
			perf_log_throttle(event, 1);
			event->pmu->unthrottle(event);
			interrupts = 2*sysctl_perf_event_sample_rate/HZ;
		}

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

		/*
		 * if the specified freq < HZ then we need to skip ticks
		 */
		if (event->attr.sample_freq < HZ) {
			freq = event->attr.sample_freq;

			hwc->freq_count += freq;
			hwc->freq_interrupts += interrupts;

			if (hwc->freq_count < HZ)
				continue;

			interrupts = hwc->freq_interrupts;
			hwc->freq_interrupts = 0;
			hwc->freq_count -= HZ;
		} else
			freq = HZ;

		perf_adjust_period(event, freq * interrupts);

		/*
		 * In order to avoid being stalled by an (accidental) huge
		 * sample period, force reset the sample period if we didn't
		 * get any events in this freq period.
		 */
		if (!interrupts) {
			perf_disable();
			event->pmu->disable(event);
			atomic64_set(&hwc->period_left, 0);
			event->pmu->enable(event);
			perf_enable();
		}
	}
	raw_spin_unlock(&ctx->lock);
}

/*
 * Round-robin a context's events:
 */
static void rotate_ctx(struct perf_event_context *ctx)
{
	struct perf_event *event;

	if (!ctx->nr_events)
		return;

	raw_spin_lock(&ctx->lock);
	/*
	 * Rotate the first entry last (works just fine for group events too):
	 */
	perf_disable();
	list_for_each_entry(event, &ctx->group_list, group_entry) {
		list_move_tail(&event->group_entry, &ctx->group_list);
		break;
	}
	perf_enable();

	raw_spin_unlock(&ctx->lock);
}

void perf_event_task_tick(struct task_struct *curr, int cpu)
{
	struct perf_cpu_context *cpuctx;
	struct perf_event_context *ctx;

	if (!atomic_read(&nr_events))
		return;

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

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

	perf_event_cpu_sched_out(cpuctx);
	if (ctx)
		__perf_event_task_sched_out(ctx);

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

	perf_event_cpu_sched_in(cpuctx, cpu);
	if (ctx)
		perf_event_task_sched_in(curr, cpu);
}

/*
 * Enable all of a task's events that have been marked enable-on-exec.
 * This expects task == current.
 */
static void perf_event_enable_on_exec(struct task_struct *task)
{
	struct perf_event_context *ctx;
	struct perf_event *event;
	unsigned long flags;
	int enabled = 0;

	local_irq_save(flags);
	ctx = task->perf_event_ctxp;
	if (!ctx || !ctx->nr_events)
		goto out;

	__perf_event_task_sched_out(ctx);

	raw_spin_lock(&ctx->lock);

	list_for_each_entry(event, &ctx->group_list, group_entry) {
		if (!event->attr.enable_on_exec)
			continue;
		event->attr.enable_on_exec = 0;
		if (event->state >= PERF_EVENT_STATE_INACTIVE)
			continue;
		__perf_event_mark_enabled(event, ctx);
		enabled = 1;
	}

	/*
	 * Unclone this context if we enabled any event.
	 */
	if (enabled)
		unclone_ctx(ctx);

	raw_spin_unlock(&ctx->lock);

	perf_event_task_sched_in(task, smp_processor_id());
 out:
	local_irq_restore(flags);
}

/*
 * Cross CPU call to read the hardware event
 */
static void __perf_event_read(void *info)
{
	struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
	struct perf_event *event = info;
	struct perf_event_context *ctx = event->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.  In that case
	 * event->count would have been updated to a recent sample
	 * when the event was scheduled out.
	 */
	if (ctx->task && cpuctx->task_ctx != ctx)
		return;

	raw_spin_lock(&ctx->lock);
	update_context_time(ctx);
	update_event_times(event);
	raw_spin_unlock(&ctx->lock);

	event->pmu->read(event);
}

static u64 perf_event_read(struct perf_event *event)
{
	/*
	 * If event is enabled and currently active on a CPU, update the
	 * value in the event structure:
	 */
	if (event->state == PERF_EVENT_STATE_ACTIVE) {
		smp_call_function_single(event->oncpu,
					 __perf_event_read, event, 1);
	} else if (event->state == PERF_EVENT_STATE_INACTIVE) {
		struct perf_event_context *ctx = event->ctx;
		unsigned long flags;

		raw_spin_lock_irqsave(&ctx->lock, flags);
		update_context_time(ctx);
		update_event_times(event);
		raw_spin_unlock_irqrestore(&ctx->lock, flags);
	}

	return atomic64_read(&event->count);
}

/*
 * Initialize the perf_event context in a task_struct:
 */
static void
__perf_event_init_context(struct perf_event_context *ctx,
			    struct task_struct *task)
{
	raw_spin_lock_init(&ctx->lock);
	mutex_init(&ctx->mutex);
	INIT_LIST_HEAD(&ctx->group_list);
	INIT_LIST_HEAD(&ctx->event_list);
	atomic_set(&ctx->refcount, 1);
	ctx->task = task;
}

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

	if (pid == -1 && cpu != -1) {
		/* Must be root to operate on a CPU event: */
		if (perf_paranoid_cpu() && !capable(CAP_SYS_ADMIN))
			return ERR_PTR(-EACCES);

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

		/*
		 * We could be clever and allow to attach a event to an
		 * offline CPU and activate it when the CPU comes up, but
		 * that's for later.
		 */
		if (!cpu_online(cpu))
			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 events 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) {
		unclone_ctx(ctx);
		raw_spin_unlock_irqrestore(&ctx->lock, flags);
	}

	if (!ctx) {
		ctx = kzalloc(sizeof(struct perf_event_context), GFP_KERNEL);
		err = -ENOMEM;
		if (!ctx)
			goto errout;
		__perf_event_init_context(ctx, task);
		get_ctx(ctx);
		if (cmpxchg(&task->perf_event_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 perf_event_free_filter(struct perf_event *event);

static void free_event_rcu(struct rcu_head *head)
{
	struct perf_event *event;

	event = container_of(head, struct perf_event, rcu_head);
	if (event->ns)
		put_pid_ns(event->ns);
	perf_event_free_filter(event);
	kfree(event);
}

static void perf_pending_sync(struct perf_event *event);

static void free_event(struct perf_event *event)
{
	perf_pending_sync(event);

	if (!event->parent) {
		atomic_dec(&nr_events);
		if (event->attr.mmap)
			atomic_dec(&nr_mmap_events);
		if (event->attr.comm)
			atomic_dec(&nr_comm_events);
		if (event->attr.task)
			atomic_dec(&nr_task_events);
	}

	if (event->output) {
		fput(event->output->filp);
		event->output = NULL;
	}

	if (event->destroy)
		event->destroy(event);

	put_ctx(event->ctx);
	call_rcu(&event->rcu_head, free_event_rcu);
}

int perf_event_release_kernel(struct perf_event *event)
{
	struct perf_event_context *ctx = event->ctx;

	WARN_ON_ONCE(ctx->parent_ctx);
	mutex_lock(&ctx->mutex);
	perf_event_remove_from_context(event);
	mutex_unlock(&ctx->mutex);

	mutex_lock(&event->owner->perf_event_mutex);
	list_del_init(&event->owner_entry);
	mutex_unlock(&event->owner->perf_event_mutex);
	put_task_struct(event->owner);

	free_event(event);

	return 0;
}
EXPORT_SYMBOL_GPL(perf_event_release_kernel);

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

	file->private_data = NULL;

	return perf_event_release_kernel(event);
}

static int perf_event_read_size(struct perf_event *event)
{
	int entry = sizeof(u64); /* value */
	int size = 0;
	int nr = 1;

	if (event->attr.read_format & PERF_FORMAT_TOTAL_TIME_ENABLED)
		size += sizeof(u64);

	if (event->attr.read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
		size += sizeof(u64);

	if (event->attr.read_format & PERF_FORMAT_ID)
		entry += sizeof(u64);

	if (event->attr.read_format & PERF_FORMAT_GROUP) {
		nr += event->group_leader->nr_siblings;
		size += sizeof(u64);
	}

	size += entry * nr;

	return size;
}

u64 perf_event_read_value(struct perf_event *event, u64 *enabled, u64 *running)
{
	struct perf_event *child;
	u64 total = 0;

	*enabled = 0;
	*running = 0;

	mutex_lock(&event->child_mutex);
	total += perf_event_read(event);
	*enabled += event->total_time_enabled +
			atomic64_read(&event->child_total_time_enabled);
	*running += event->total_time_running +
			atomic64_read(&event->child_total_time_running);

	list_for_each_entry(child, &event->child_list, child_list) {
		total += perf_event_read(child);
		*enabled += child->total_time_enabled;
		*running += child->total_time_running;
	}
	mutex_unlock(&event->child_mutex);

	return total;
}
EXPORT_SYMBOL_GPL(perf_event_read_value);

static int perf_event_read_group(struct perf_event *event,
				   u64 read_format, char __user *buf)
{
	struct perf_event *leader = event->group_leader, *sub;
	int n = 0, size = 0, ret = -EFAULT;
	struct perf_event_context *ctx = leader->ctx;
	u64 values[5];
	u64 count, enabled, running;

	mutex_lock(&ctx->mutex);
	count = perf_event_read_value(leader, &enabled, &running);

	values[n++] = 1 + leader->nr_siblings;
	if (read_format & PERF_FORMAT_TOTAL_TIME_ENABLED)
		values[n++] = enabled;
	if (read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
		values[n++] = running;
	values[n++] = count;
	if (read_format & PERF_FORMAT_ID)
		values[n++] = primary_event_id(leader);

	size = n * sizeof(u64);

	if (copy_to_user(buf, values, size))
		goto unlock;

	ret = size;

	list_for_each_entry(sub, &leader->sibling_list, group_entry) {
		n = 0;

		values[n++] = perf_event_read_value(sub, &enabled, &running);
		if (read_format & PERF_FORMAT_ID)
			values[n++] = primary_event_id(sub);

		size = n * sizeof(u64);

		if (copy_to_user(buf + ret, values, size)) {
			ret = -EFAULT;
			goto unlock;
		}

		ret += size;
	}
unlock:
	mutex_unlock(&ctx->mutex);

	return ret;
}

static int perf_event_read_one(struct perf_event *event,
				 u64 read_format, char __user *buf)
{
	u64 enabled, running;
	u64 values[4];
	int n = 0;

	values[n++] = perf_event_read_value(event, &enabled, &running);
	if (read_format & PERF_FORMAT_TOTAL_TIME_ENABLED)
		values[n++] = enabled;
	if (read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
		values[n++] = running;
	if (read_format & PERF_FORMAT_ID)
		values[n++] = primary_event_id(event);

	if (copy_to_user(buf, values, n * sizeof(u64)))
		return -EFAULT;

	return n * sizeof(u64);
}

/*
 * Read the performance event - simple non blocking version for now
 */
static ssize_t
perf_read_hw(struct perf_event *event, char __user *buf, size_t count)
{
	u64 read_format = event->attr.read_format;
	int ret;

	/*
	 * Return end-of-file for a read on a event 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 (event->state == PERF_EVENT_STATE_ERROR)
		return 0;

	if (count < perf_event_read_size(event))
		return -ENOSPC;

	WARN_ON_ONCE(event->ctx->parent_ctx);
	if (read_format & PERF_FORMAT_GROUP)
		ret = perf_event_read_group(event, read_format, buf);
	else
		ret = perf_event_read_one(event, read_format, buf);

	return ret;
}

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

	return perf_read_hw(event, buf, count);
}

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

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

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

	return events;
}

static void perf_event_reset(struct perf_event *event)
{
	(void)perf_event_read(event);
	atomic64_set(&event->count, 0);
	perf_event_update_userpage(event);
}

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

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

static void perf_event_for_each(struct perf_event *event,
				  void (*func)(struct perf_event *))
{
	struct perf_event_context *ctx = event->ctx;
	struct perf_event *sibling;

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

	perf_event_for_each_child(event, func);
	func(event);
	list_for_each_entry(sibling, &event->sibling_list, group_entry)
		perf_event_for_each_child(event, func);
	mutex_unlock(&ctx->mutex);
}

static int perf_event_period(struct perf_event *event, u64 __user *arg)
{
	struct perf_event_context *ctx = event->ctx;
	unsigned long size;
	int ret = 0;
	u64 value;

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

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

	if (!value)
		return -EINVAL;

	raw_spin_lock_irq(&ctx->lock);
	if (event->attr.freq) {
		if (value > sysctl_perf_event_sample_rate) {
			ret = -EINVAL;
			goto unlock;
		}

		event->attr.sample_freq = value;
	} else {
		event->attr.sample_period = value;
		event->hw.sample_period = value;
	}
unlock:
	raw_spin_unlock_irq(&ctx->lock);

	return ret;
}

static int perf_event_set_output(struct perf_event *event, int output_fd);
static int perf_event_set_filter(struct perf_event *event, void __user *arg);

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

	switch (cmd) {
	case PERF_EVENT_IOC_ENABLE:
		func = perf_event_enable;
		break;
	case PERF_EVENT_IOC_DISABLE:
		func = perf_event_disable;
		break;
	case PERF_EVENT_IOC_RESET:
		func = perf_event_reset;
		break;

	case PERF_EVENT_IOC_REFRESH:
		return perf_event_refresh(event, arg);

	case PERF_EVENT_IOC_PERIOD:
		return perf_event_period(event, (u64 __user *)arg);

	case PERF_EVENT_IOC_SET_OUTPUT:
		return perf_event_set_output(event, arg);

	case PERF_EVENT_IOC_SET_FILTER:
		return perf_event_set_filter(event, (void __user *)arg);

	default:
		return -ENOTTY;
	}

	if (flags & PERF_IOC_FLAG_GROUP)
		perf_event_for_each(event, func);
	else
		perf_event_for_each_child(event, func);

	return 0;
}

int perf_event_task_enable(void)
{
	struct perf_event *event;

	mutex_lock(&current->perf_event_mutex);
	list_for_each_entry(event, &current->perf_event_list, owner_entry)
		perf_event_for_each_child(event, perf_event_enable);
	mutex_unlock(&current->perf_event_mutex);

	return 0;
}

int perf_event_task_disable(void)
{
	struct perf_event *event;

	mutex_lock(&current->perf_event_mutex);
	list_for_each_entry(event, &current->perf_event_list, owner_entry)
		perf_event_for_each_child(event, perf_event_disable);
	mutex_unlock(&current->perf_event_mutex);

	return 0;
}

#ifndef PERF_EVENT_INDEX_OFFSET
# define PERF_EVENT_INDEX_OFFSET 0
#endif

static int perf_event_index(struct perf_event *event)
{
	if (event->state != PERF_EVENT_STATE_ACTIVE)
		return 0;

	return event->hw.idx + 1 - PERF_EVENT_INDEX_OFFSET;
}

/*
 * 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_event_update_userpage(struct perf_event *event)
{
	struct perf_event_mmap_page *userpg;
	struct perf_mmap_data *data;

	rcu_read_lock();
	data = rcu_dereference(event->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 = perf_event_index(event);
	userpg->offset = atomic64_read(&event->count);
	if (event->state == PERF_EVENT_STATE_ACTIVE)
		userpg->offset -= atomic64_read(&event->hw.prev_count);

	userpg->time_enabled = event->total_time_enabled +
			atomic64_read(&event->child_total_time_enabled);

	userpg->time_running = event->total_time_running +
			atomic64_read(&event->child_total_time_running);

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

static unsigned long perf_data_size(struct perf_mmap_data *data)
{
	return data->nr_pages << (PAGE_SHIFT + data->data_order);
}

#ifndef CONFIG_PERF_USE_VMALLOC

/*
 * Back perf_mmap() with regular GFP_KERNEL-0 pages.
 */

static struct page *
perf_mmap_to_page(struct perf_mmap_data *data, unsigned long pgoff)
{
	if (pgoff > data->nr_pages)
		return NULL;

	if (pgoff == 0)
		return virt_to_page(data->user_page);

	return virt_to_page(data->data_pages[pgoff - 1]);
}

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

	WARN_ON(atomic_read(&event->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->data_order = 0;
	data->nr_pages = nr_pages;

	return data;

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 NULL;
}

static void perf_mmap_free_page(unsigned long addr)
{
	struct page *page = virt_to_page((void *)addr);

	page->mapping = NULL;
	__free_page(page);
}

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

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

#else

/*
 * Back perf_mmap() with vmalloc memory.
 *
 * Required for architectures that have d-cache aliasing issues.
 */

static struct page *
perf_mmap_to_page(struct perf_mmap_data *data, unsigned long pgoff)
{
	if (pgoff > (1UL << data->data_order))
		return NULL;

	return vmalloc_to_page((void *)data->user_page + pgoff * PAGE_SIZE);
}

static void perf_mmap_unmark_page(void *addr)
{
	struct page *page = vmalloc_to_page(addr);

	page->mapping = NULL;
}

static void perf_mmap_data_free_work(struct work_struct *work)
{
	struct perf_mmap_data *data;
	void *base;
	int i, nr;

	data = container_of(work, struct perf_mmap_data, work);
	nr = 1 << data->data_order;

	base = data->user_page;
	for (i = 0; i < nr + 1; i++)
		perf_mmap_unmark_page(base + (i * PAGE_SIZE));

	vfree(base);
	kfree(data);
}

static void perf_mmap_data_free(struct perf_mmap_data *data)
{
	schedule_work(&data->work);
}

static struct perf_mmap_data *
perf_mmap_data_alloc(struct perf_event *event, int nr_pages)
{
	struct perf_mmap_data *data;
	unsigned long size;
	void *all_buf;

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

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

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

	INIT_WORK(&data->work, perf_mmap_data_free_work);

	all_buf = vmalloc_user((nr_pages + 1) * PAGE_SIZE);
	if (!all_buf)
		goto fail_all_buf;

	data->user_page = all_buf;
	data->data_pages[0] = all_buf + PAGE_SIZE;
	data->data_order = ilog2(nr_pages);
	data->nr_pages = 1;

	return data;

fail_all_buf:
	kfree(data);

fail:
	return NULL;
}

#endif

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

	if (vmf->flags & FAULT_FLAG_MKWRITE) {
		if (vmf->pgoff == 0)
			ret = 0;
		return ret;
	}

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

	if (vmf->pgoff && (vmf->flags & FAULT_FLAG_WRITE))
		goto unlock;

	vmf->page = perf_mmap_to_page(data, vmf->pgoff);
	if (!vmf->page)
		goto unlock;

	get_page(vmf->page);
	vmf->page->mapping = vma->vm_file->f_mapping;
	vmf->page->index   = vmf->pgoff;

	ret = 0;
unlock:
	rcu_read_unlock();

	return ret;
}

static void
perf_mmap_data_init(struct perf_event *event, struct perf_mmap_data *data)
{
	long max_size = perf_data_size(data);

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

	if (event->attr.watermark) {
		data->watermark = min_t(long, max_size,
					event->attr.wakeup_watermark);
	}

	if (!data->watermark)
		data->watermark = max_size / 2;


	rcu_assign_pointer(event->data, data);
}

static void perf_mmap_data_free_rcu(struct rcu_head *rcu_head)
{
	struct perf_mmap_data *data;

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

static void perf_mmap_data_release(struct perf_event *event)
{
	struct perf_mmap_data *data = event->data;

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

	rcu_assign_pointer(event->data, NULL);
	call_rcu(&data->rcu_head, perf_mmap_data_free_rcu);
}

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

	atomic_inc(&event->mmap_count);
}

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

	WARN_ON_ONCE(event->ctx->parent_ctx);
	if (atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex)) {
		unsigned long size = perf_data_size(event->data);
		struct user_struct *user = current_user();

		atomic_long_sub((size >> PAGE_SHIFT) + 1, &user->locked_vm);
		vma->vm_mm->locked_vm -= event->data->nr_locked;
		perf_mmap_data_release(event);
		mutex_unlock(&event->mmap_mutex);
	}
}

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

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

	if (!(vma->vm_flags & VM_SHARED))
		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(event->ctx->parent_ctx);
	mutex_lock(&event->mmap_mutex);
	if (event->output) {
		ret = -EINVAL;
		goto unlock;
	}

	if (atomic_inc_not_zero(&event->mmap_count)) {
		if (nr_pages != event->data->nr_pages)
			ret = -EINVAL;
		goto unlock;
	}

	user_extra = nr_pages + 1;
	user_lock_limit = sysctl_perf_event_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) && perf_paranoid_tracepoint_raw() &&
		!capable(CAP_IPC_LOCK)) {
		ret = -EPERM;
		goto unlock;
	}

	WARN_ON(event->data);

	data = perf_mmap_data_alloc(event, nr_pages);
	ret = -ENOMEM;
	if (!data)
		goto unlock;

	ret = 0;
	perf_mmap_data_init(event, data);

	atomic_set(&event->mmap_count, 1);
	atomic_long_add(user_extra, &user->locked_vm);
	vma->vm_mm->locked_vm += extra;
	event->data->nr_locked = extra;
	if (vma->vm_flags & VM_WRITE)
		event->data->writable = 1;

unlock:
	mutex_unlock(&event->mmap_mutex);

	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_event *event = filp->private_data;
	int retval;

	mutex_lock(&inode->i_mutex);
	retval = fasync_helper(fd, filp, on, &event->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 event wakeup
 *
 * If there's data, ensure we set the poll() state and publish everything
 * to user-space before waking everybody up.
 */

void perf_event_wakeup(struct perf_event *event)
{
	wake_up_all(&event->waitq);

	if (event->pending_kill) {
		kill_fasync(&event->fasync, SIGIO, event->pending_kill);
		event->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_event(struct perf_pending_entry *entry)
{
	struct perf_event *event = container_of(entry,
			struct perf_event, pending);

	if (event->pending_disable) {
		event->pending_disable = 0;
		__perf_event_disable(event);
	}

	if (event->pending_wakeup) {
		event->pending_wakeup = 0;
		perf_event_wakeup(event);
	}
}

#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_event_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_event *event)
{
	/*
	 * 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 event->pending.next == NULL;
}

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

void perf_event_do_pending(void)
{
	__perf_pending_run();
}

/*
 * Callchain support -- arch specific
 */

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

/*
 * Output
 */
static bool perf_output_space(struct perf_mmap_data *data, unsigned long tail,
			      unsigned long offset, unsigned long head)
{
	unsigned long mask;

	if (!data->writable)
		return true;

	mask = perf_data_size(data) - 1;

	offset = (offset - tail) & mask;
	head   = (head   - tail) & mask;

	if ((int)(head - offset) < 0)
		return false;

	return true;
}

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

	if (handle->nmi) {
		handle->event->pending_wakeup = 1;
		perf_pending_queue(&handle->event->pending,
				   perf_pending_event);
	} else
		perf_event_wakeup(handle->event);
}

/*
 * Curious locking construct.
 *
 * We need to ensure a later event_id doesn't publish a head when a former
 * event_id 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_id completes.
 */
static void perf_output_lock(struct perf_output_handle *handle)
{
	struct perf_mmap_data *data = handle->data;
	int cur, cpu = get_cpu();

	handle->locked = 0;

	for (;;) {
		cur = atomic_cmpxchg(&data->lock, -1, cpu);
		if (cur == -1) {
			handle->locked = 1;
			break;
		}
		if (cur == cpu)
			break;

		cpu_relax();
	}
}

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_i