perf: Fix perf_pmu_migrate_context

 */

struct perf_event {

#ifdef CONFIG_PERF_EVENTS

	struct list_head		group_entry;

	/*

	 * entry onto perf_event_context::event_list;

	 *   modifications require ctx->lock

	 *   RCU safe iterations.

	 */

	struct list_head		event_entry;

	/*

	 * XXX: group_entry and sibling_list should be mutually exclusive;

	 * either you're a sibling on a group, or you're the group leader.

	 * Rework the code to always use the same list element.

	 *

	 * Locked for modification by both ctx->mutex and ctx->lock; holding

	 * either sufficies for read.

	 */

	struct list_head		group_entry;

	struct list_head		sibling_list;

	/*

	 * We need storage to track the entries in perf_pmu_migrate_context; we

	 * cannot use the event_entry because of RCU and we want to keep the

	 * group in tact which avoids us using the other two entries.

	 */

	struct list_head		migrate_entry;

	struct hlist_node		hlist_entry;

	int				nr_siblings;

	int				group_flags;

		perf_remove_from_context(event);

		unaccount_event_cpu(event, src_cpu);

		put_ctx(src_ctx);

		list_add(&event->event_entry, &events);

		list_add(&event->migrate_entry, &events);

	}

	mutex_unlock(&src_ctx->mutex);

	synchronize_rcu();

	mutex_lock(&dst_ctx->mutex);

	list_for_each_entry_safe(event, tmp, &events, event_entry) {

		list_del(&event->event_entry);

	list_for_each_entry_safe(event, tmp, &events, migrate_entry) {

		list_del(&event->migrate_entry);

		if (event->state >= PERF_EVENT_STATE_OFF)

			event->state = PERF_EVENT_STATE_INACTIVE;

		account_event_cpu(event, dst_cpu);