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Date:	Mon, 8 Aug 2011 14:48:19 +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 Mon 08-08-11 13:27:12, Toshiyuki Okajima wrote:
> >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:
> >>>>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
> 
> After I saw the following messages, I thought we must fix EXT3-fs error
> at first. So, I created the fix patch.
> 
> (1) kernel: EXT3-fs: <dev>: couldn't remount RDWR because of
>       unprocessed orphan inode list.  Please umount/remount instead.
> (2) kernel: EXT3-fs error (device <dev>) in start_transaction: Readonly filesystem
> 
> I wasn't aware that by fixing the race between "ro-remount" and "unlink",
> that EXT3-fs error can be also fixed then.
> 
> >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?
> OK.
> Now, I also think we need not modify ext3 to fix these problems.
> If we can prevent to add an inode into the orphan list (to start unlinking)
> while ro-remounting, we can also prevent (1) and (2).
> 
> However, new mechanism to confirm whether "no open-but-unlinked" files
> exist while ro-remounting is required, isn't it?
  Yes. Actually, VFS already tracks open-but-unlinked files but the check &
remount pair is not atomic so that needs to be fixed and it is not that
simple.

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