From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1164014AbeCBBsU (ORCPT ); Thu, 1 Mar 2018 20:48:20 -0500 Received: from userp2120.oracle.com ([156.151.31.85]:59596 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1163120AbeCBBsR (ORCPT ); Thu, 1 Mar 2018 20:48:17 -0500 To: "jianchao.w.wang\@oracle.com" Cc: Bart Van Assche , "jejb\@linux.vnet.ibm.com" , "martin.petersen\@oracle.com" , "linux-scsi\@vger.kernel.org" , "linux-kernel\@vger.kernel.org" , "hch\@lst.de" Subject: Re: [PATCH V2] scsi: core: use blk_mq_requeue_request in __scsi_queue_insert From: "Martin K. Petersen" Organization: Oracle Corporation References: <1519808113-2863-1-git-send-email-jianchao.w.wang@oracle.com> <1519840355.2777.8.camel@wdc.com> <624cedc6-9658-7b76-9c63-61c30fdfe6be@oracle.com> <1519926225.2675.6.camel@wdc.com> Date: Thu, 01 Mar 2018 20:43:08 -0500 In-Reply-To: <1519926225.2675.6.camel@wdc.com> (Bart Van Assche's message of "Thu, 1 Mar 2018 17:43:46 +0000") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8819 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=873 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1711220000 definitions=main-1803020015 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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