linux-kernel - Re: [PATCH v2 06/17] ibmvfc: add handlers to drain and complete Sub-CRQ responses

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Message-ID: <8a3c6a0b-ebf5-581a-e3e9-748c09373d92@linux.vnet.ibm.com>
Date:   Wed, 2 Dec 2020 09:56:26 -0600
From:   Brian King <brking@...ux.vnet.ibm.com>
To:     Tyrel Datwyler <tyreld@...ux.ibm.com>,
        james.bottomley@...senpartnership.com
Cc:     martin.petersen@...cle.com, linux-scsi@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        brking@...ux.ibm.com
Subject: Re: [PATCH v2 06/17] ibmvfc: add handlers to drain and complete
 Sub-CRQ responses

On 12/1/20 6:53 PM, Tyrel Datwyler wrote:
> +static void ibmvfc_handle_scrq(struct ibmvfc_crq *crq, struct ibmvfc_host *vhost)
> +{
> +	struct ibmvfc_event *evt = (struct ibmvfc_event *)be64_to_cpu(crq->ioba);
> +	unsigned long flags;
> +
> +	switch (crq->valid) {
> +	case IBMVFC_CRQ_CMD_RSP:
> +		break;
> +	case IBMVFC_CRQ_XPORT_EVENT:
> +		return;
> +	default:
> +		dev_err(vhost->dev, "Got and invalid message type 0x%02x\n", crq->valid);
> +		return;
> +	}
> +
> +	/* The only kind of payload CRQs we should get are responses to
> +	 * things we send. Make sure this response is to something we
> +	 * actually sent
> +	 */
> +	if (unlikely(!ibmvfc_valid_event(&vhost->pool, evt))) {
> +		dev_err(vhost->dev, "Returned correlation_token 0x%08llx is invalid!\n",
> +			crq->ioba);
> +		return;
> +	}
> +
> +	if (unlikely(atomic_read(&evt->free))) {
> +		dev_err(vhost->dev, "Received duplicate correlation_token 0x%08llx!\n",
> +			crq->ioba);
> +		return;
> +	}
> +
> +	spin_lock_irqsave(vhost->host->host_lock, flags);
> +	del_timer(&evt->timer);
> +	list_del(&evt->queue);
> +	ibmvfc_trc_end(evt);

Another thought here... If you are going through ibmvfc_purge_requests at the same time
as this code, you could check the free bit above, then have ibmvfc_purge_requests
put the event on the free queue and call scsi_done, then you come down and get the host
lock here, remove the command from the free list, and call the done function again,
which could result in a double completion to the scsi layer.

I think you need to grab the host lock before you check the free bit to avoid this race.

> +	spin_unlock_irqrestore(vhost->host->host_lock, flags);
> +	evt->done(evt);
> +}
> +


-- 
Brian King
Power Linux I/O
IBM Linux Technology Center