From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754722Ab0JNXap (ORCPT ); Thu, 14 Oct 2010 19:30:45 -0400 Received: from e7.ny.us.ibm.com ([32.97.182.137]:58486 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753183Ab0JNXao (ORCPT ); Thu, 14 Oct 2010 19:30:44 -0400 Date: Thu, 14 Oct 2010 16:30:41 -0700 From: "Paul E. McKenney" To: Jens Axboe Cc: KOSAKI Motohiro , Yasuaki Ishimatsu , linux-kernel@vger.kernel.org Subject: Re: [PATCH] blk: fix a wrong accounting of hd_struct->in_flight Message-ID: <20101014233041.GJ2447@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <4CB40281.1020403@jp.fujitsu.com> <20101014150742.F9EC.A69D9226@jp.fujitsu.com> <4CB6FB30.1000502@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4CB6FB30.1000502@kernel.dk> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 14, 2010 at 02:44:32PM +0200, Jens Axboe wrote: > On 2010-10-14 08:07, KOSAKI Motohiro wrote: > >> @@ -1268,7 +1270,17 @@ static int __make_request(struct request > >> * not touch req->buffer either... > >> */ > >> req->buffer = bio_data(bio); > >> + src_part = disk_map_sector_rcu(req->rq_disk, blk_rq_pos(req)); > >> req->__sector = bio->bi_sector; > >> + dst_part = disk_map_sector_rcu(req->rq_disk, blk_rq_pos(req)); > > > > I think this is wrong. disk_map_sector_rcu() require > > rcu read lock held (see function comment). all other call site take > > part_stat_lock() before disk_map_sector_rcu() call. > > It's called under the queue lock with irqs disabled, which implies a > rcu critical section. Having irqs disabled does imply an rcu_read_lock_sched() or an rcu_read_lock_bh(), but not an rcu_read_lock(), especially if CONFIG_PREEMPT_RCU. So an explicit rcu_read_lock() does seem to be needed here. Thanx, Paul