Re: [PATCH v13 5/8] blk-mq: use hk cpus only when isolcpus=io_queue is enabled

[Daniel Wagner]

On Tue, May 12, 2026 at 08:55:06PM -0400, Aaron Tomlin wrote:
> +static void blk_mq_map_fallback(struct blk_mq_queue_map *qmap)
> +{
> +	unsigned int cpu;
> +
> +	/*
> +	 * Map all CPUs to the first hctx of this specific map to ensure
> +	 * at least one online CPU is serving it, respecting the map's
> +	 * boundaries so secondary maps do not route into the default map.
> +	 */
> +	for_each_possible_cpu(cpu)
> +		qmap->mq_map[cpu] = qmap->queue_offset;
> +}

I think this should also check if the CPU is online. The fallback should
ensure the system will boot.