linux-kernel - Re: [PATCH] nvme: replace meaningless judgement by checking whether req is null

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Message-ID: <20200921150824.GA4034182@dhcp-10-100-145-180.wdl.wdc.com>
Date:   Mon, 21 Sep 2020 08:08:24 -0700
From:   Keith Busch <kbusch@...nel.org>
To:     Xianting Tian <tian.xianting@....com>
Cc:     axboe@...com, hch@....de, sagi@...mberg.me,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nvme: replace meaningless judgement by checking whether
 req is null

On Mon, Sep 21, 2020 at 10:10:52AM +0800, Xianting Tian wrote:
> @@ -940,13 +940,6 @@ static inline void nvme_handle_cqe(struct nvme_queue *nvmeq, u16 idx)
>  	struct nvme_completion *cqe = &nvmeq->cqes[idx];
>  	struct request *req;
>  
> -	if (unlikely(cqe->command_id >= nvmeq->q_depth)) {
> -		dev_warn(nvmeq->dev->ctrl.device,
> -			"invalid id %d completed on queue %d\n",
> -			cqe->command_id, le16_to_cpu(cqe->sq_id));
> -		return;
> -	}
> -
>  	/*
>  	 * AEN requests are special as they don't time out and can
>  	 * survive any kind of queue freeze and often don't respond to
> @@ -960,6 +953,13 @@ static inline void nvme_handle_cqe(struct nvme_queue *nvmeq, u16 idx)
>  	}
>  
>  	req = blk_mq_tag_to_rq(nvme_queue_tagset(nvmeq), cqe->command_id);
> +	if (unlikely(!req)) {
> +		dev_warn(nvmeq->dev->ctrl.device,
> +			"req is null for tag %d completed on queue %d\n",
> +			cqe->command_id, le16_to_cpu(cqe->sq_id));
> +		return;
> +	}

This is making sense now, though I think we should retain the existing
dev_warn() since it's still accurate and provides continuity for people
who are used to looking for these sorts of messages.

Your changelog is a bit much though. I think we can say it a bit more
succinctly. This is what I'm thinking:

  The driver registers interrupts for queues before initializing the
  tagset because it uses the number of successful request_irq() calls
  to configure the tagset parameters. This allows a race condition with
  the current tag validity check if the controller happens to produce
  an interrupt with a corrupted CQE before the tagset is initialized.

  Replace the driver's indirect tag check with the one already provided
  by the block layer.