linux-kernel - Re: [PATCH] scsi: core: use blk_mq_requeue_request in __scsi_queue

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Date:   Tue, 27 Feb 2018 03:41:15 +0000
From:   Bart Van Assche <Bart.VanAssche@....com>
To:     "jejb@...ux.vnet.ibm.com" <jejb@...ux.vnet.ibm.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "jianchao.w.wang@...cle.com" <jianchao.w.wang@...cle.com>
CC:     "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "hch@....de" <hch@....de>
Subject: Re: [PATCH] scsi: core: use blk_mq_requeue_request in
 __scsi_queue_insert

On Tue, 2018-02-27 at 11:28 +0800, jianchao.wang wrote:
> If that is true, what if aacraid driver uses block legacy instead of blk-mq ?
> w/ blk-mq disabled, __scsi_queue_insert just requeue the request with blk_requeue_request.
> 
> __scsi_queue_insert
> ...
> 	if (q->mq_ops) {
> 		scsi_mq_requeue_cmd(cmd);
> 		return;
> 	}
> 	spin_lock_irqsave(q->queue_lock, flags);
> 	blk_requeue_request(q, cmd->request);
> 	kblockd_schedule_work(&device->requeue_work);
> 	spin_unlock_irqrestore(q->queue_lock, flags);
> ...
> 
> no prep/unprep code there for block legacy code.

Hello Jianchao,

For the legacy block layer preparing and unpreparing a request happens from
inside the block layer core. Please have a look at block/blk-core.c and the
code in that file that handles the request flag RQF_DONTPREP.

Thanks,

Bart.