From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756093AbbJGUYT (ORCPT ); Wed, 7 Oct 2015 16:24:19 -0400 Received: from smtp.nue.novell.com ([195.135.221.5]:52542 "EHLO smtp.nue.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753553AbbJGUYE (ORCPT ); Wed, 7 Oct 2015 16:24:04 -0400 Subject: Re: [PATCHv2 1/1] SCSI: update hosts module to use idr index management To: James Bottomley , Lee Duncan References: <1a69690d615610c1dee725db7e6d81cf2db28266.1444085255.git.lduncan@suse.com> <20151006094040.GA24624@infradead.org> <56140188.6070107@suse.com> <1444151854.2245.18.camel@HansenPartnership.com> Cc: Christoph Hellwig , linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, Tejun Heo , Johannes Thumshirn From: Hannes Reinecke Message-ID: <56157F49.5030101@suse.com> Date: Wed, 7 Oct 2015 22:23:37 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: <1444151854.2245.18.camel@HansenPartnership.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/06/2015 07:17 PM, James Bottomley wrote: > On Tue, 2015-10-06 at 10:14 -0700, Lee Duncan wrote: >> On 10/06/2015 02:40 AM, Christoph Hellwig wrote: >>>> struct Scsi_Host *scsi_host_lookup(unsigned short hostnum) >>>> { >>>> - struct device *cdev; >>>> - struct Scsi_Host *shost = NULL; >>>> - >>>> - cdev = class_find_device(&shost_class, NULL, &hostnum, >>>> - __scsi_host_match); >>>> - if (cdev) { >>>> - shost = scsi_host_get(class_to_shost(cdev)); >>>> - put_device(cdev); >>>> - } >>>> + struct Scsi_Host *shost; >>>> + >>>> + spin_lock(&host_index_lock); >>>> + shost = idr_find(&host_index_idr, hostnum); >>>> + spin_unlock(&host_index_lock); >>>> + >>>> return shost; >>> >>> How does this actually grab a reference to the host? >> >> Good catch -- I should have noticed that. >> >> I will resubmit the patch. > > I'll wait to see what you produce, but I don't think, using a separate > idr array, you can close the race window between lookup and get. One of > the nice things about using the cdev iterator is that the get is part of > the lookup process. > Hmm. Should be possible if you free up the IDR in scsi_remove_host(), just after setting the state to SHOST_DEL. Cheers, Hannes