Message-ID: <20080916125345.GA13388@mit.edu>
Date:	Tue, 16 Sep 2008 08:53:46 -0400
From:	Theodore Tso <tytso@....edu>
To:	Amit Chaudhary <amitch@...gad.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: ext3 mount infinite loop over orphan list issue, please
	release 2.6.27

On Mon, Sep 15, 2008 at 03:09:22PM -0700, Amit Chaudhary wrote:
> Over the weekend, due to a crash, I ran into the ext3 mount infinite  
> loop over orphan list issue. This was on Ubuntu 8.04. I tried many  
> things, including using 18 month old distributions, nothing works. Only  
> solution is to boot off a alpha version of next Ubunuty which has the  
> 2.6.27 kernel (rc1 has the fix), more details are below:
>
> Can you please release 2.6.27 so that it can make it to stable  
> distributions.

As you point out, this problem has been fixed in 2.6.27-rc1.
Unfortunately, it is a problem which has been around for a very long
time --- perhaps since ext3 was first written.  No one had noticed the
problem for a very long time; in fact the first time someone reported
it as far I know was June 6, 2008, when Sami Liedes found it via a
synthetic testing program, fsfuzzer, which creates filesystems, then
corrupts them randomly and then sees whether or not they cause the
kernel to panic or hang when they are mounted.

You seem to have had the bad luck of running into the problem in a
real world situation relatively recently, but this has been a
long-standing problem.

As far as releasing 2.6.27, there still is a fairly large set of
regressions (i.e., bugs introduced in 2.6.27-rc1 or later) which need
to be fixed before we can release it; otherwise more users will have
bad experiences when older kernels that had worked fine for them will
break for them.  So while it might have helped you to have released
2.6.27, it could make things worse for many other users.  So that's
not a realistic option.  If I had to guess, given currently the
projected regression bug fix rates, there still is at least 2 or so of
bug fixing that still needs to be done before 2.6.27 is ready for
release.

We could take this bug fix and nominate it for release in the next
2.6.26-stable series, which distributions could then pick up --- maybe
we should have, but when the patch went in, it was seen was a fix for
largely theoretical problems, and not something that needed
accelerated handling.  This is still something we could do, but
realistically I'm not sure it's going to help the Ubuntu Intrepid
release, since it's pretty late in their schedule.  You might be
better off asking the Ubuntu kernel team if they are willing to cherry
pick the commit in question (ae76dd9a) and include it in their
release; they do have the ability to do that without waiting for an
upstream release, you know.

You also should have been able to work around the problem if you had
booted a rescue CD and checked your filesystem from the rescue CD.
That is the normal way these sorts of problems are fixed, and I'm a
bit surprised you didn't try this first.  It could be that Ubuntu
Rescue CD's could be made better by automating the ability of (upon
request) detecting the root filesystem on Ubuntu systems and then
running e2fsck on the filesystem before trying to mount them.

If you are willing to help out, we can always use more testers to test
the development kernels.  We can't do this alone, you know.  We've
wanted to shorten the release window, but in order to do that we need
more people helping to find and fix bugs during the development cycle.
Remember, this is open source.  If you see a problem you don't like,
you can help fix it.  And in fact, that's the most likely way that it
will get fixed.

Best regards,

						- Ted
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