From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756537Ab2INLSx (ORCPT ); Fri, 14 Sep 2012 07:18:53 -0400 Received: from mga01.intel.com ([192.55.52.88]:53290 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753744Ab2INLSu (ORCPT ); Fri, 14 Sep 2012 07:18:50 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.80,422,1344236400"; d="scan'208";a="222123135" Date: Fri, 14 Sep 2012 19:18:47 +0800 From: Fengguang Wu To: OGAWA Hirofumi Cc: viro@zeniv.linux.org.uk, jack@suse.cz, hch@lst.de, linux-kernel@vger.kernel.org Subject: Re: [PATCH] Fix queueing work if !bdi_cap_writeback_dirty() Message-ID: <20120914111847.GB19509@localhost> References: <87wr002z39.fsf@devron.myhome.or.jp> <20120913063906.GA24974@localhost> <871ui6e4tl.fsf@devron.myhome.or.jp> <87wqzwn9ha.fsf@devron.myhome.or.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87wqzwn9ha.fsf@devron.myhome.or.jp> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 14, 2012 at 08:13:05PM +0900, OGAWA Hirofumi wrote: > OGAWA Hirofumi writes: > > > Fengguang Wu writes: > > > >> On Wed, Sep 12, 2012 at 03:28:42AM +0900, OGAWA Hirofumi wrote: > >>> > >>> If bdi has BDI_CAP_NO_WRITEBACK, bdi_forker_thread() doesn't start > >>> writeback thread. This means there is no consumer of work item made > >>> by bdi_queue_work(). > >>> > >>> This adds to checking of !bdi_cap_writeback_dirty(sb->s_bdi) before > >>> calling bdi_queue_work(), otherwise queued work never be consumed. > >>> > >>> Signed-off-by: OGAWA Hirofumi > >>> --- > >>> > >>> fs/fs-writeback.c | 7 +++++-- > >>> 1 file changed, 5 insertions(+), 2 deletions(-) > >>> > >>> diff -puN fs/fs-writeback.c~noop_backing_dev_info-check-fix fs/fs-writeback.c > >>> --- linux/fs/fs-writeback.c~noop_backing_dev_info-check-fix 2012-09-11 06:12:30.000000000 +0900 > >>> +++ linux-hirofumi/fs/fs-writeback.c 2012-09-11 06:12:30.000000000 +0900 > >>> @@ -120,6 +120,9 @@ __bdi_start_writeback(struct backing_dev > >>> { > >>> struct wb_writeback_work *work; > >>> > >>> + if (!bdi_cap_writeback_dirty(bdi)) > >>> + return; > >> > >> Will someone in the current kernel actually call > >> __bdi_start_writeback() on a BDI_CAP_NO_WRITEBACK bdi? > >> > >> If the answer is no, VM_BUG_ON(!bdi_cap_writeback_dirty(bdi)) looks better. > > > > I guess nobody call it in current kernel though. Hmm.., but we also have > > check in __mark_inode_dirty(), nobody should be using it, right? > > > > If we defined it as the bug, I can't see what BDI_CAP_NO_WRITEBACK wants > > to do actually. We are not going to allow to disable the writeback task? > > ping. > > You are saying we should change bdi_cap_writeback_dirty(bdi) to > VM_BUG_ON() too in __mark_inode_dirty()? And probably, you are going to > remove the usage of BDI_CAP_NO_WRITEBACK for sb->s_bdi? No, I'm talking about this chunk only. My feeling is, adding the bdi_cap_writeback_dirty() detection in __bdi_start_writeback() sounds too late. If ever the test is false, it may well indicate a bug in the callers. Obviously the callers all assume success because __bdi_start_writeback() does not even return a value. Thanks, Fengguang