From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751774Ab1AEORw (ORCPT ); Wed, 5 Jan 2011 09:17:52 -0500 Received: from mx2.fusionio.com ([64.244.102.31]:48354 "EHLO mx2.fusionio.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751146Ab1AEORv (ORCPT ); Wed, 5 Jan 2011 09:17:51 -0500 X-ASG-Debug-ID: 1294237070-71f7602d0001-xx1T2L X-Barracuda-Envelope-From: JAxboe@fusionio.com Message-ID: <4D247D89.3090700@fusionio.com> Date: Wed, 5 Jan 2011 15:17:45 +0100 From: Jens Axboe MIME-Version: 1.0 To: Jerome Marchand CC: Vivek Goyal , Satoru Takeuchi , Linus Torvalds , Yasuaki Ishimatsu , "linux-kernel@vger.kernel.org" , Greg Kroah-Hartman Subject: Re: [PATCH 2/2] block: fix accounting bug on cross partition merges References: <4CFF3DA4.5060705@jp.fujitsu.com> <4CFF9A2C.1070401@fusionio.com> <4D025154.8030400@redhat.com> <20101210165553.GE31737@redhat.com> <4D07D2AC.6000500@fusionio.com> <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> <4D247984.2030103@fusionio.com> <4D247B93.2010900@redhat.com> X-ASG-Orig-Subj: Re: [PATCH 2/2] block: fix accounting bug on cross partition merges In-Reply-To: <4D247B93.2010900@redhat.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: 1294237070 X-Barracuda-URL: http://10.101.1.181:8000/cgi-mod/mark.cgi 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 3.2.2.51502 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 15:09, Jerome Marchand wrote: > On 01/05/2011 03:00 PM, Jens Axboe wrote: >> On 2011-01-04 16:55, Jerome Marchand wrote: >>> + } else { >>> + part = disk_map_sector_rcu(rq->rq_disk, blk_rq_pos(rq)); >>> + if (!kref_test_and_get(&part->ref)) { >>> + /* >>> + * The partition is already being removed, >>> + * the request will be accounted on the disk only >>> + * >>> + * We take a reference on disk->part0 although that >>> + * partition will never be deleted, so we can treat >>> + * it as any other partition. >>> + */ >>> + part = &rq->rq_disk->part0; >>> + kref_get(&part->ref); >>> + } >> >> This still doesn't work. So you are inside the if {} block, you know >> what someone has dropped the last reference and the call_rcu() is being >> scheduled. Adding a reference now will not prevent 'part' from going >> away as soon as you do part_stat_unlock(). > > And what is the problem with that since we don't use 'part' (as returned > by disk_map_sector_rcu()), but disk->part0 instead? Ugh, I'm the one who's blind now. part0 is indeed fine, I didn't read that carefully enough. So I think your patch looks safe now, I don't see any holes in it. Whether we move the kref to inside the lookup or not, that doesn't change anything wrt using an atomic_inc_not_zero(). Can you resend 1/2 with the manual barriers removed? -- Jens Axboe