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

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Date:	Thu, 7 Jun 2007 15:04:55 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mark Lord <lkml@....ca>
Cc:	Chuck Ebbert <cebbert@...hat.com>,
	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

On Thu, 07 Jun 2007 17:38:54 -0400
Mark Lord <lkml@....ca> wrote:

> Andrew Morton wrote:
> > On Thu, 07 Jun 2007 12:11:58 -0400
> > Chuck Ebbert <cebbert@...hat.com> 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?
> > 
> > I can't think of anything in there at present which would cause that to
> > happen, and it's not immediately obvious how we _could_ make it happen - we
> > have an inode which potentially has no dirty pages and which is itself
> > clean.  The truncate can span multiple journal commits, so forcing a
> > journal commit in sync() won't necessarily block behind the truncate.
> > 
> > I guess we could ask sync to speculatively take and release every inode's
> > i_mutex or something.  But even that would involve quite some hoop-jumping
> > due to those infuriating spinlock-protected list_heads on the superblock.
> > 
> > hmm.
> 
> Yeah, I really don't know what to do with this either.
> We have to have a bounds on how long we wait at shutdown,
> but there doesn't seem to be an easy way to get notified
> once a filesystem becomes idle (?).
> 
> I suppose I could have the script loop on /proc/interrupts until
> it sees the disk activity has tapered off..
> 

I don't recall clarity on this question: did the umount fail?

Because it should have, in which case your script can poll that.

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