Subject: Re: ext3fs: umount+sync not enough to guarantee metadata-on-disk
From: "Stephen C. Tweedie" <sct@redhat.com>
To: Mark Lord <lkml@rtr.ca>
Cc: Andrew Morton <akpm@linux-foundation.org>, "Theodore Ts'o" <tytso@mit.edu>,
       linux-kernel <linux-kernel@vger.kernel.org>,
       Stephen Tweedie <sct@redhat.com>
In-Reply-To: <46682BE7.6080802@rtr.ca>
References: <46680BB8.50404@rtr.ca>
	 <20070607084142.42583639.akpm@linux-foundation.org>
	 <46682BE7.6080802@rtr.ca>
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Date: Thu, 07 Jun 2007 18:09:41 +0100
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Hi,

On Thu, 2007-06-07 at 12:01 -0400, Mark Lord wrote:

> >>    mount /var/lib/mythtv -oremount,ro
> >>    sync
> >>    umount /var/lib/mythtv
> > 
> > Did this succeed?  If the application is still truncating that file, the
> > umount should have failed.
> 
> Actually, what I expect to happen is for the remount,ro
> to block  until the file deletion completes.  But it doesn't.

No -- all that the remount,ro sees is that there's a fd still open for
write.  It has no idea if or when that fd is going to get closed, so it
should fail.  Returning -EBUSY is the only thing it _can_ do: waiting
for the fs to be remountable might wait forever.

So the fs is still writable after that point.

--Stephen


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