From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756329Ab2KVTFA (ORCPT ); Thu, 22 Nov 2012 14:05:00 -0500 Received: from cantor2.suse.de ([195.135.220.15]:38878 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756263Ab2KVTE5 (ORCPT ); Thu, 22 Nov 2012 14:04:57 -0500 Date: Thu, 22 Nov 2012 08:47:13 +1100 From: NeilBrown To: Jan Kara Cc: "Darrick J. Wong" , axboe@kernel.dk, lucho@ionkov.net, ericvh@gmail.com, tytso@mit.edu, rminnich@sandia.gov, viro@zeniv.linux.org.uk, martin.petersen@oracle.com, david@fromorbit.com, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, adilger.kernel@dilger.ca, bharrosh@panasas.com, jlayton@samba.org, v9fs-developer@lists.sourceforge.net, linux-ext4@vger.kernel.org Subject: Re: [PATCH 4/4] ext3: Warn if mounting rw on a disk requiring stable page writes Message-ID: <20121122084713.69e5b1fc@notabene.brown> In-Reply-To: <20121121213333.GF30250@quack.suse.cz> References: <20121121020027.10225.43206.stgit@blackbox.djwong.org> <20121121020056.10225.15220.stgit@blackbox.djwong.org> <20121121021543.GI10507@quack.suse.cz> <20121121211319.GA32202@blackbox.djwong.org> <20121121213333.GF30250@quack.suse.cz> X-Mailer: Claws Mail 3.8.1 (GTK+ 2.24.10; x86_64-suse-linux-gnu) Mime-Version: 1.0 Content-Type: multipart/signed; micalg=PGP-SHA1; boundary="Sig_/h.yWshvrZGapGhRWIvU.Aq/"; protocol="application/pgp-signature" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --Sig_/h.yWshvrZGapGhRWIvU.Aq/ Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Wed, 21 Nov 2012 22:33:33 +0100 Jan Kara wrote: > On Wed 21-11-12 13:13:19, Darrick J. Wong wrote: > > On Wed, Nov 21, 2012 at 03:15:43AM +0100, Jan Kara wrote: > > > On Tue 20-11-12 18:00:56, Darrick J. Wong wrote: > > > > ext3 doesn't properly isolate pages from changes during writeback. = Since the > > > > recommended fix is to use ext4, for now we'll just print a warning = if the user > > > > tries to mount in write mode. > > > >=20 > > > > Signed-off-by: Darrick J. Wong > > > > --- > > > > fs/ext3/super.c | 8 ++++++++ > > > > 1 file changed, 8 insertions(+) > > > >=20 > > > >=20 > > > > diff --git a/fs/ext3/super.c b/fs/ext3/super.c > > > > index 5366393..5b3725d 100644 > > > > --- a/fs/ext3/super.c > > > > +++ b/fs/ext3/super.c > > > > @@ -1325,6 +1325,14 @@ static int ext3_setup_super(struct super_blo= ck *sb, struct ext3_super_block *es, > > > > "forcing read-only mode"); > > > > res =3D MS_RDONLY; > > > > } > > > > + if (!read_only && > > > > + queue_requires_stable_pages(bdev_get_queue(sb->s_bdev))) { > > > > + ext3_msg(sb, KERN_ERR, > > > > + "error: ext3 cannot safely write data to a disk " > > > > + "requiring stable pages writes; forcing read-only " > > > > + "mode. Upgrading to ext4 is recommended."); > > > > + res =3D MS_RDONLY; > > > > + } > > > > if (read_only) > > > > return res; > > > > if (!(sbi->s_mount_state & EXT3_VALID_FS)) > > > Why this? ext3 should be fixed by your change to > > > filemap_page_mkwrite()... Or does testing show otherwise? > >=20 > > Yes, it's still broken even with this new set of changes. Now that I t= hink > > about it a little more, I recall that writeback mode was actually fine,= so this > > is a little harsh. > >=20 > > Hm... looking at the ordered code a little more, it looks like > > ext3_ordered_write_end is calling journal_dirty_data_fn, which (I guess= ?) tries > > to write mapped buffers back through the journal? Taking it out seems = to fix > > ordered mode, though I have a suspicion that it might very well break o= rdered > > mode too. > Oh, right. kjournald writing buffers directly (without setting > PageWriteback) will break things. So please, change warning to: >=20 > /* > * In data=3Dordered mode, kjournald writes buffers without setting > * PageWriteback bit thus generic code does not properly wait for > * writeback of those buffers to finish. > */ > if (!read_only && > test_opt(sb, DATA_FLAGS) =3D=3D EXT3_MOUNT_ORDERED_DATA && > queue_requires_stable_pages(bdev_get_queue(sb->s_bdev))) { > ext3_msg(sb, KERN_ERR, > "error: data=3Dordered mode does not support stable " > "page writes required by the disk; forcing read-only " > "mode. Upgrading to ext4 is recommended."); > res =3D MS_RDONLY; > } >=20 > then you need a similar check in ext3_remount() so that filesystem cannot > be remounted read-write. >=20 > Honza Given this restriction, there is no way that I can change md/raid5 to set t= he "stable pages" flag and stop copying pages into the stripe-cache. ext3 on raid5 will be much too common to allow this breakage. I would really like to be able to say "I prefer stable pages, but they aren= 't a requirement as long as I know which is which" .... 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