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

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Message-ID: <20070611110547.GA26561@atrey.karlin.mff.cuni.cz>
Date:	Mon, 11 Jun 2007 13:05:47 +0200
From:	Jan Kara <jack@...e.cz>
To:	Mark Lord <lkml@....ca>
Cc:	Chuck Ebbert <cebbert@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Stephen Tweedie <sct@...hat.com>,
	Theodore Ts'o <tytso@....edu>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: ext3fs: umount+sync not enough to guarantee metadata-on-disk

> Chuck Ebbert wrote:
> >On 06/07/2007 11:41 AM, Andrew Morton 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.
> >
> >Shouldn't sync should wait for truncate to finish?
> 
> The part that gets me here, and that others might be missing,
> is that we are not waiting for ftruncate at this point.
> 
> We're waiting for unlink.  The application that was doing ftruncate
> in tiny little doses has been sent a kill-9 signal, so what should
> be happening now (confirmed by disk activity LEDs) is the file should
> just be getting deleted the same as if we did "rm bigfile" on it.
  But if that app has been waiting in D state, kill -9 does nothing to it
until it wakes up, doesn't it? So fd's are still open and umount fails.

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