linux-kernel - Re: [RFC][PATCH] PM / Sleep: Freeze filesystems during system suspend/hibernation

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Date:	Thu, 19 Dec 2013 11:22:16 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Josh Boyer <jwboyer@...oraproject.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Linux PM list <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, Jan Kara <jack@...e.cz>,
	linux-fsdevel@...r.kernel.org,
	Nigel Cunningham <nigel@...onice.net>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Subject: Re: [RFC][PATCH] PM / Sleep: Freeze filesystems during system
 suspend/hibernation

On Wed, Dec 18, 2013 at 03:08:42PM +0100, Pavel Machek wrote:
> > > > I disagree - given the problem it is resolving leads to silent
> > > > filesystem corruption, this patch should be considered somewhat of a
> > > > priority to push...
> > > 
> > > Umm. Ok, I forgot what it does, really.
> > 
> > It ensures that the filesystem is in an quiescent state both in
> > memory and on disk, and it cannot be modified in memory or on disk
> > whilst the suspend image is being generated, or by log recovery
> > after a resume before the suspended image has been restored.
> 
> If someone attempts to run log recovery before resume, that's a bug
> and yes, it will corrupt filesystems. (Including ext3). Don't do that.

Freezing the filesystem prevents that accidental mount of the
filesystem from being an issue. It fixes a bug that:

> Documentation/power/swsusp.txt:
> 
>  * BIG FAT WARNING
>    *********************************************************
>  *
>  * If you touch anything on disk between suspend and resume...
>  *                              ...kiss your data goodbye.

Makes this a whole lot less dangerous.

> > > So... for few years now suspend corrupts data on XFS? And Fedora has
> > > the fix but it is not in mainline? That does not sound right...
> > 
> > The issues freezing the filesystem before the suspend image is
> > created affect every journalled filesystem linux supports, be
> > it XFS, ext4, reiser, btrfs, etc.
> 
> Did not it have some problems with ext3?

Please read more carefully: "affect every journalled filesystem
linux supports". So, ext3 is affected because it's a journalling
filesystem.  I didn't list every journalled filesystem Linux
supports - "etc" means there are more examples that aren't
explicitly listed.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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