From: "Martin K. Petersen" <martin.petersen@oracle.com>
To: "jianchao.w.wang@oracle.com" <jianchao.w.wang@oracle.com>
Cc: Bart Van Assche <Bart.VanAssche@wdc.com>,
"jejb@linux.vnet.ibm.com" <jejb@linux.vnet.ibm.com>,
"martin.petersen@oracle.com" <martin.petersen@oracle.com>,
"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"hch@lst.de" <hch@lst.de>
Subject: Re: [PATCH V2] scsi: core: use blk_mq_requeue_request in __scsi_queue_insert
Date: Thu, 01 Mar 2018 20:43:08 -0500 [thread overview]
Message-ID: <yq17eqvz1zn.fsf@oracle.com> (raw)
In-Reply-To: <1519926225.2675.6.camel@wdc.com> (Bart Van Assche's message of "Thu, 1 Mar 2018 17:43:46 +0000")
Jianchao,
> Yes, the block layer core guarantees that scsi_mq_get_budget() will be
> called before scsi_queue_rq(). I think the full picture is as follows:
> * Before scsi_queue_rq() calls .queuecommand(), get_device() is called for the
> SCSI device and the device, target and host busy counters are incremented.
> * If the SCSI core decides to requeue a command, scsi_queue_insert() causes
> __scsi_queue_insert() to call scsi_device_unbusy(). That last function
> decreases the device, target and host busy counters but not put_device(sdev).
> Hence the need for a separate put_device() call after requeuing.
>
> It's unfortunate that the SCSI core became so asymmetric. Anyway,
> since I am now convinced that this patch is correct, feel free to add:
Please add something akin to Bart's explanation as a comment and repost.
Thanks!
--
Martin K. Petersen Oracle Linux Engineering
next prev parent reply other threads:[~2018-03-02 1:43 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-28 8:55 [PATCH V2] scsi: core: use blk_mq_requeue_request in __scsi_queue_insert Jianchao Wang
2018-02-28 17:52 ` Bart Van Assche
2018-03-01 1:57 ` jianchao.wang
2018-03-01 17:43 ` Bart Van Assche
2018-03-02 1:43 ` Martin K. Petersen [this message]
2018-03-02 2:17 ` jianchao.wang
2018-03-02 2:16 ` jianchao.wang
2018-03-02 1:44 ` Martin K. Petersen
2018-03-02 2:18 ` jianchao.wang
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