From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752469Ab1AESqj (ORCPT ); Wed, 5 Jan 2011 13:46:39 -0500 Received: from mx1.fusionio.com ([64.244.102.30]:43574 "EHLO mx1.fusionio.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752368Ab1AESqi (ORCPT ); Wed, 5 Jan 2011 13:46:38 -0500 X-ASG-Debug-ID: 1294253196-178954e30001-xx1T2L X-Barracuda-Envelope-From: JAxboe@fusionio.com Message-ID: <4D24BC88.4090804@fusionio.com> Date: Wed, 5 Jan 2011 19:46:32 +0100 From: Jens Axboe MIME-Version: 1.0 To: Greg KH CC: Jerome Marchand , Vivek Goyal , Satoru Takeuchi , Linus Torvalds , Yasuaki Ishimatsu , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 2/2] block: fix accounting bug on cross partition merges References: <4D0B68AF.80804@redhat.com> <4D0BB4A1.8080305@fusionio.com> <4D13664C.3020500@redhat.com> <20101223153915.GE9502@redhat.com> <4D13810B.8000304@redhat.com> <20101224192916.GB2082@redhat.com> <4D23423A.60707@redhat.com> <4D2342E1.8010405@redhat.com> <20110104210011.GB4180@kroah.com> <4D247867.9040502@fusionio.com> <20110105155816.GD2072@kroah.com> X-ASG-Orig-Subj: Re: [PATCH 2/2] block: fix accounting bug on cross partition merges In-Reply-To: <20110105155816.GD2072@kroah.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Barracuda-Connect: mail1.int.fusionio.com[10.101.1.21] X-Barracuda-Start-Time: 1294253196 X-Barracuda-URL: http://10.101.1.180:8000/cgi-mod/mark.cgi X-Barracuda-Bayes: INNOCENT GLOBAL 0.5000 1.0000 0.0000 X-Barracuda-Spam-Score: 0.41 X-Barracuda-Spam-Status: No, SCORE=0.41 using global scores of TAG_LEVEL=1000.0 QUARANTINE_LEVEL=1000.0 KILL_LEVEL=9.0 tests=SUBJECT_FUZZY_TION X-Barracuda-Spam-Report: Code version 3.2, rules version 3.2.2.51520 Rule breakdown below pts rule name description ---- ---------------------- -------------------------------------------------- 0.41 SUBJECT_FUZZY_TION Attempt to obfuscate words in Subject: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2011-01-05 16:58, Greg KH wrote: > On Wed, Jan 05, 2011 at 02:55:51PM +0100, Jens Axboe wrote: >> On 2011-01-04 22:00, Greg KH wrote: >>> On Tue, Jan 04, 2011 at 04:55:13PM +0100, Jerome Marchand wrote: >>>> Also add a refcount to struct hd_struct to keep the partition in >>>> memory as long as users exist. We use kref_test_and_get() to ensure >>>> we don't add a reference to a partition which is going away. >>> >>> No, don't do this, use a kref correctly and no such function should be >>> needed. >>> >>>> + } else { >>>> + part = disk_map_sector_rcu(rq->rq_disk, blk_rq_pos(rq)); >>> >>> That is the function that should properly increment the reference count >>> on the object. If the object is "being removed", then it will return >>> NULL and you need to check that. Do that and you do not need to add: >> >> It doesn't matter if you do it in there of after the fact, since the >> "lock" (RCU) is being held across the call. See my original suggestion >> here: >> >> https://lkml.org/lkml/2010/12/17/275 > > Ok, that's fine, just do it without adding that kref function and I have > no objection :) Why? The code is perfectly fine. I originally objected to making an API like this for simple reference counting - seems I was right. Please actually look at the code and use. Alexey asked whether this was a toy API or a real one, I'd like to know that as well. If this is meant just for very basic get/put references, fine, then document that. But then what's the point of having this API in the first place? -- Jens Axboe