linux-ext4 - Re: [PATCH 4/4] ext3: Warn if mounting rw on a disk requiring stable page writes

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Message-ID: <20121121211319.GA32202@blackbox.djwong.org>
Date:	Wed, 21 Nov 2012 13:13:19 -0800
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	Jan Kara <jack@...e.cz>
Cc:	axboe@...nel.dk, lucho@...kov.net, ericvh@...il.com, tytso@....edu,
	rminnich@...dia.gov, viro@...iv.linux.org.uk,
	martin.petersen@...cle.com, neilb@...e.de, david@...morbit.com,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	adilger.kernel@...ger.ca, bharrosh@...asas.com, jlayton@...ba.org,
	v9fs-developer@...ts.sourceforge.net, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 4/4] ext3: Warn if mounting rw on a disk requiring stable
 page writes

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.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> > ---
> >  fs/ext3/super.c |    8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > 
> > 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_block *sb, struct ext3_super_block *es,
> >  			"forcing read-only mode");
> >  		res = 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 = 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?

Yes, it's still broken even with this new set of changes.  Now that I think
about it a little more, I recall that writeback mode was actually fine, so this
is a little harsh.

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 ordered
mode too.

--D
> 
> 								Honza
> -- 
> Jan Kara <jack@...e.cz>
> SUSE Labs, CR
> --
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