From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751808Ab1AEOJe (ORCPT ); Wed, 5 Jan 2011 09:09:34 -0500 Received: from mx1.redhat.com ([209.132.183.28]:52253 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751309Ab1AEOJc (ORCPT ); Wed, 5 Jan 2011 09:09:32 -0500 Message-ID: <4D247B93.2010900@redhat.com> Date: Wed, 05 Jan 2011 15:09:23 +0100 From: Jerome Marchand User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.4pre) Gecko/20091014 Fedora/3.0-2.8.b4.fc11 Thunderbird/3.0b4 MIME-Version: 1.0 To: Jens Axboe 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> In-Reply-To: <4D247984.2030103@fusionio.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? > As per my last email, you > need a check in the rcu callback to ensure that the ref is 0. > >