linux-ext4 - Re: EXT4-fs (dm-1): Couldn't remount RDWR because of unprocessed orphan inode list

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Date:	Thu, 8 Sep 2011 20:51:39 +0200
From:	Jan Kara <jack@...e.cz>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	Christian Kujau <lists@...dbynature.de>,
	linux-ext4@...r.kernel.org, mszeredi@...e.cz,
	Al Viro <viro@...IV.linux.org.uk>
Subject: Re: EXT4-fs (dm-1): Couldn't remount RDWR because of unprocessed
 orphan inode list

On Tue 06-09-11 11:44:45, Eric Sandeen wrote:
> On 9/6/11 11:37 AM, Christian Kujau wrote:
> > On Tue, 6 Sep 2011 at 11:17, Eric Sandeen wrote:
> >> It's probably not a bug or flaw; orphan inodes can occur for legitimate
> >> reasons (fs goes down while someone is holding open an unlinked file),
> > 
> > The filesystem is being constantly accessed by an application, holding at 
> > least one file open (readonly). And then there is this mechanism trying to 
> > remount the filesystem rw and then ro again every day. I guess this equals
> > the scenario of "fs goes down (remount!) while someone is holding open a 
> > file"?
> 
> well, no - "goes down" means "crashed or lost power"
> 
> >> Did you happen to also get a message like this on the original mount?
> >>                 ext4_msg(sb, KERN_ERR, "write access "
> >>                         "unavailable, skipping orphan cleanup");
> > 
> > I think I've seen this message before, but I'm nore sure where and it's 
> > not in the logs of this particular system.
> > 
> >> See also commit: 
> >>
> >> commit ead6596b9e776ac32d82f7d1931d7638e6d4a7bd
> >> Author: Eric Sandeen <sandeen@...hat.com>
> >> Date:   Sat Feb 10 01:46:08 2007 -0800
> >>
> >>     [PATCH] ext4: refuse ro to rw remount of fs with orphan inodes
> > 
> > Yes, I've seen this commit when I was searching where this message came
> > from. And I think I understand now why this is happening, but 
> > still...if I may ask: can't this be handled more elegantly? Do other 
> > filesystems have the same problem?
> 
> well, as the commit said, it'd be nice to handle it in remount, yes... :(
> 
> > Right now the procedure is to pause the application, stop the nfs exports,
> > unmount, fsck, mount, start nfs exports and resume the application. And
> > every few days/weeks this has to be repeated, "just because" these daily
> > remounts occur (which are the main reason for this, I suppose).
> 
> well, seems like you need to get to the root cause of the unprocessed
> orphan inodes.
> 
> I don't yet have my post-vacation thinking cap back on... does cycling
> rw/ro/rw/ro with open & unlinked files cause an orphan inode situation?
  There's race where VFS remount code can race with unlink and result will
be unlinked file in orphan list on read-only filesystem. Christian seems to
be hitting this race. Miklos Szeredi has patches
(http://lkml.indiana.edu/hypermail/linux/kernel/1108.3/00169.html) to
mostly close this hole but they're waiting for Al to find time to look at
them / merge them AFAIK.

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