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Date:	Sat, 22 Sep 2012 21:59:13 +0200
From:	Pavel Machek <pavel@....cz>
To:	Theodore Ts'o <tytso@....edu>, Matt Sealey <matt@...esi-usa.com>,
	Mike Thompson <mpthompson@...il.com>,
	Shawn Guo <shawn.guo@...aro.org>,
	Linux-Arm-Kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-ext4@...r.kernel.org, linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org, "Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: Tracking down suspend/resume ext3/mmc issues on imx233

Hi!

On Wed 2012-09-19 20:01:10, Theodore Ts'o wrote:
> On Thu, Sep 20, 2012 at 01:23:49AM +0200, Pavel Machek wrote:
> > 
> > I'm not sure I agree.
> > 
> > If you treat root fs as removable, you'll get "crash". You'll need to
> > replay the journal, but data is safe.
> > 
> > If you treat it as non-removable, and someone manages to remove it,
> > mount, and reinsert, you'll get silent data corruption.
> 
> We could detect this case; if the file system gets mounted, the last
> mount time will change.  So one of the things we could do is have the
> file system code freeze the file system at suspend time, so the file
> system is consistent (which will reduce the probability of data loss
> if the system never comes back up after the suspend), and save the
> last mount time and last write time in memory.  When the system comes
> back from resume, have the file system code check the last mount and
> last write time, and if they have changed, it can refuse the resume
> and abort the system to avoid data corruption.  It would require
> making ext3/ext4 suspend-aware, but it would be doable, if we really
> wanted to support this.

Yes please; I'd love to see this done.

We used to do sync() to get filesystem in consistent state, and I
believe that these days we are doing filesystem freeze; but code
validating the last mount time is certainly missing.

Looking forward,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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