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Date:	Wed, 3 Aug 2011 18:25:25 +0200
From:	Jan Kara <jack@...e.cz>
To:	Toshiyuki Okajima <toshi.okajima@...fujitsu.com>
Cc:	Jan Kara <jack@...e.cz>, akpm@...ux-foundation.org,
	adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext3: fix message in ext3_remount for rw-remount case

  Hello,

On Wed 03-08-11 22:25:48, Toshiyuki Okajima wrote:
> On Wed, 3 Aug 2011 11:57:54 +0200
> Jan Kara <jack@...e.cz> wrote:
> > On Wed 03-08-11 11:42:03, Toshiyuki Okajima wrote:
> > > >(2011/08/01 18:57), Jan Kara wrote:
> > > >>On Mon 01-08-11 18:45:58, Toshiyuki Okajima wrote:
> > > >>>(2011/08/01 17:45), Jan Kara wrote:
> > > >>>>On Mon 01-08-11 13:54:51, Toshiyuki Okajima wrote:
> > > >>>>>If there are some inodes in orphan list while a filesystem is being
> > > >>>>>read-only mounted, we should recommend that pepole umount and then
> > > >>>>>mount it when they try to remount with read-write. But the current
> > > >>>>>message/comment recommends that they umount and then remount it.
> > > <SNIP>
> > > >>>>the most... BTW, I guess you didn't really see this message in practice, did
> > > >>>>you?
> > > >>>No.
> > > >>>I have seen this message in practice while quotacheck command was repeatedly
> > > >>>executed per an hour.
> > > >>Interesting. Are you able to reproduce this? Quotacheck does remount
> > > >>read-only + remount read-write but you cannot really remount the filesystem
> > > >>read-only when it has orphan inodes and so you should not see those when
> > > >>you remount read-write again. Possibly there's race between remounting and
> > > >>unlinking...
> > > >Yes. I can reproduce it. However, it is not frequently reproduced
> > > >by using the original procedure (qutacheck per an hour). So, I made a
> > > >reproducer.
> > > To tell the truth, I think the race creates the message:
> > > -----------------------------------------------------------------------
> > >  EXT3-fs: <dev>: couldn't remount RDWR because of
> > >       unprocessed orphan inode list.  Please umount/remount instead.
> > > -----------------------------------------------------------------------
> > > which hides a serious problem.
> >   I've inquired about this at linux-fsdevel (I think you were in CC unless
> > I forgot). It's a race in VFS remount code as you properly analyzed below.
> > People are working on fixing it but it's not trivial. Filesystem is really
> > a wrong place to fix such problem. If there is a trivial fix for ext3 to
> > workaround the issue, I can take it but I'm not willing to push anything
> > complex - effort should better be spent working on a generic fix.
> I also think read-only remount race in VFS layer should be fixed.
> However, I think this race depends on ext3/ext4 filesystem 
> implementation. (Orphan inode list)
> So, we should modify ext3/ext4(jbd/jbd2) to fix it.
  Umm, I don't understand here. If VFS makes sure that there are no
files open for writing, no unfinished operations changing the filesystem (e.g.
unlink), and no open-but-unlinked files, what remains for ext3 to check?

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