linux-kernel - Re: ext3fs: umount+sync not enough to guarantee metadata-on-disk

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Message-Id: <1181236181.10245.16.camel@sisko.scot.redhat.com>
Date:	Thu, 07 Jun 2007 18:09:41 +0100
From:	"Stephen C. Tweedie" <sct@...hat.com>
To:	Mark Lord <lkml@....ca>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Theodore Ts'o" <tytso@....edu>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Stephen Tweedie <sct@...hat.com>
Subject: Re: ext3fs: umount+sync not enough to guarantee metadata-on-disk

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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