linux-kernel - Re: [PATCH 1/1] block: System crashes when cpu hotplug + bouncing port

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Message-ID: <20210628090703.apaowrsazl53lza4@beryllium.lan>
Date:   Mon, 28 Jun 2021 11:07:03 +0200
From:   Daniel Wagner <dwagner@...e.de>
To:     wenxiong@...ux.vnet.ibm.com
Cc:     ming.lei@...hat.com, linux-kernel@...r.kernel.org,
        james.smart@...adcom.com, wenxiong@...ibm.com
Subject: Re: [PATCH 1/1] block: System crashes when cpu hotplug + bouncing
 port

Hi Wen,

On Sun, Jun 27, 2021 at 10:14:32PM -0500, wenxiong@...ux.vnet.ibm.com wrote:
> @@ -468,8 +467,7 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
>  	data.hctx = q->queue_hw_ctx[hctx_idx];
>  	if (!blk_mq_hw_queue_mapped(data.hctx))
>  		goto out_queue_exit;
> -	cpu = cpumask_first_and(data.hctx->cpumask, cpu_online_mask);
> -	data.ctx = __blk_mq_get_ctx(q, cpu);
> +	data.ctx = __blk_mq_get_ctx(q, hctx_idx);

hctx_idx is just an index, not a CPU id. In this scenario, the hctx_idx
used to lookup the context happens to be valid. I am still a bit
confused why [1] doesn't work for this scenario.

As Ming pointed out in [2] we need to update cpumask for CPU hotplug
events.

Thanks,
Daniel

[1] https://lore.kernel.org/linux-block/20210608183339.70609-1-dwagner@suse.de/
[2] https://lore.kernel.org/linux-nvme/YNXTaUMAFCA84jfZ@T590/