list_update_cgroup_event(struct perf_event *event,
			 struct perf_event_context *ctx, bool add)
{
	struct perf_cpu_context *cpuctx;
	struct list_head *cpuctx_entry;

	if (!is_cgroup_event(event))
		return;

	if (add && ctx->nr_cgroups++)
		return;
	else if (!add && --ctx->nr_cgroups)
		return;
	/*
	 * Because cgroup events are always per-cpu events,
	 * this will always be called from the right CPU.
	 */
	cpuctx = __get_cpu_context(ctx);
	cpuctx_entry = &cpuctx->cgrp_cpuctx_entry;
	/* cpuctx->cgrp is NULL unless a cgroup event is active in this CPU .*/
	if (add) {
		list_add(cpuctx_entry, this_cpu_ptr(&cgrp_cpuctx_list));
		if (perf_cgroup_from_task(current, ctx) == event->cgrp)
			cpuctx->cgrp = event->cgrp;
	} else {
		list_del(cpuctx_entry);
		cpuctx->cgrp = NULL;
	}
}

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.