inherit_event(struct perf_event *parent_event,
	      struct task_struct *parent,
	      struct perf_event_context *parent_ctx,
	      struct task_struct *child,
	      struct perf_event *group_leader,
	      struct perf_event_context *child_ctx)
{
	enum perf_event_active_state parent_state = parent_event->state;
	struct perf_event *child_event;
	unsigned long flags;

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

	child_event = perf_event_alloc(&parent_event->attr,
					   parent_event->cpu,
					   child,
					   group_leader, parent_event,
					   NULL, NULL, -1);
	if (IS_ERR(child_event))
		return child_event;

	/*
	 * is_orphaned_event() and list_add_tail(&parent_event->child_list)
	 * must be under the same lock in order to serialize against
	 * perf_event_release_kernel(), such that either we must observe
	 * is_orphaned_event() or they will observe us on the child_list.
	 */
	mutex_lock(&parent_event->child_mutex);
	if (is_orphaned_event(parent_event) ||
	    !atomic_long_inc_not_zero(&parent_event->refcount)) {
		mutex_unlock(&parent_event->child_mutex);
		free_event(child_event);
		return NULL;
	}

	get_ctx(child_ctx);

	/*
	 * Make the child state follow the state of the parent event,
	 * not its attr.disabled bit.  We hold the parent's mutex,
	 * so we won't race with perf_event_{en, dis}able_family.
	 */
	if (parent_state >= PERF_EVENT_STATE_INACTIVE)
		child_event->state = PERF_EVENT_STATE_INACTIVE;
	else
		child_event->state = PERF_EVENT_STATE_OFF;

	if (parent_event->attr.freq) {
		u64 sample_period = parent_event->hw.sample_period;
		struct hw_perf_event *hwc = &child_event->hw;

		hwc->sample_period = sample_period;
		hwc->last_period   = sample_period;

		local64_set(&hwc->period_left, sample_period);
	}

	child_event->ctx = child_ctx;
	child_event->overflow_handler = parent_event->overflow_handler;
	child_event->overflow_handler_context
		= parent_event->overflow_handler_context;

	/*
	 * Precalculate sample_data sizes
	 */
	perf_event__header_size(child_event);
	perf_event__id_header_size(child_event);

	/*
	 * Link it up in the child's context:
	 */
	raw_spin_lock_irqsave(&child_ctx->lock, flags);
	add_event_to_ctx(child_event, child_ctx);
	raw_spin_unlock_irqrestore(&child_ctx->lock, flags);

	/*
	 * Link this into the parent event's child list
	 */
	list_add_tail(&child_event->child_list, &parent_event->child_list);
	mutex_unlock(&parent_event->child_mutex);

	return child_event;
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.