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

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Message-Id: <201201302205.34159.rjw@sisk.pl>
Date:	Mon, 30 Jan 2012 22:05:33 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Jan Kara <jack@...e.cz>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org, Dave Chinner <david@...morbit.com>,
	Nigel Cunningham <nigel@...onice.net>,
	Pavel Machek <pavel@....cz>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [RFC][PATCH] PM / Sleep: Freeze filesystems during system suspend/hibernation

On Monday, January 30, 2012, Jan Kara wrote:
> On Sat 28-01-12 14:45:49, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rjw@...k.pl>
> > 
> > Freeze all filesystems during system suspend and (kernel-driven)
> > hibernation by calling freeze_supers() for all superblocks and thaw
> > them during the subsequent resume with the help of thaw_supers().
> > 
> > This makes filesystems stay in a consistent state in case something
> > goes wrong between system suspend (or hibernation) and the subsequent
> > resume (e.g. journal replays won't be necessary in those cases).  In
> > particular, this should help to solve a long-standing issue that, in
> > some cases, during resume from hibernation the boot loader causes the
> > journal to be replied for the filesystem containing the kernel image
> > and/or initrd causing it to become inconsistent with the information
> > stored in the hibernation image.
> > 
> > The user-space-driven hibernation (s2disk) is not covered by this
> > change, because the freezing of filesystems prevents s2disk from
> > accessing device special files it needs to do its job.
> > 
> > This change is based on earlier work by Nigel Cunningham.
> > 
> > Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
> > ---
> >  fs/super.c               |   73 +++++++++++++++++++++++++++++++++++++++++++++++
> >  include/linux/fs.h       |    3 +
> >  kernel/power/hibernate.c |   11 +++++--
> >  kernel/power/power.h     |   23 --------------
> >  kernel/power/suspend.c   |   42 +++++++++++++++++++++++++++
> >  5 files changed, 128 insertions(+), 24 deletions(-)
> > 
> > Index: linux/fs/super.c
> > ===================================================================
> > --- linux.orig/fs/super.c
> > +++ linux/fs/super.c
> > @@ -594,6 +594,79 @@ void iterate_supers_type(struct file_sys
> >  EXPORT_SYMBOL(iterate_supers_type);
> >  
> >  /**
> > + *	thaw_supers - call thaw_super() for all superblocks
> > + */
> > +void thaw_supers(void)
> > +{
> > +	struct super_block *sb, *p = NULL;
> > +
> > +	spin_lock(&sb_lock);
> > +	list_for_each_entry(sb, &super_blocks, s_list) {
> > +		if (list_empty(&sb->s_instances))
> > +			continue;
> > +		sb->s_count++;
> > +		spin_unlock(&sb_lock);
> > +
> > +		if (sb->s_flags & MS_FROZEN) {
> > +			thaw_super(sb);
> > +			sb->s_flags &= ~MS_FROZEN;
> > +		}
> > +
> > +		spin_lock(&sb_lock);
> > +		if (p)
> > +			__put_super(p);
> > +		p = sb;
> > +	}
> > +	if (p)
> > +		__put_super(p);
> > +	spin_unlock(&sb_lock);
> > +}
>   At least for thawing you can use iterate_supers() helper.

OK

> > +/**
> > + *	freeze_supers - call freeze_super() for all superblocks
> > + */
> > +int freeze_supers(void)
> > +{
> > +	struct super_block *sb, *p = NULL;
> > +	int error = 0;
> > +
> > +	spin_lock(&sb_lock);
> > +	/*
> > +	 * Freeze in reverse order so filesystems depending on others are
> > +	 * frozen in the right order (eg. loopback on ext3).
> > +	 */
>   Ho, hum, are you sure the order in super_blocks list is the one you need?
> Maybe it is but I'm not sure you are guaranteed it is.

Well, is there any way I can get the right order?

> I've added Al to CC,
> he'll likely have opinion on this...
> 
> > +	list_for_each_entry_reverse(sb, &super_blocks, s_list) {
> > +		if (list_empty(&sb->s_instances))
> > +			continue;
> > +		sb->s_count++;
> > +		spin_unlock(&sb_lock);
> > +
> > +		if (sb->s_root && sb->s_frozen != SB_FREEZE_TRANS
> > +		    && !(sb->s_flags & MS_RDONLY)) {
> > +			error = freeze_super(sb);
> > +			if (!error)
> > +				sb->s_flags |= MS_FROZEN;
> > +		}
> > +
> > +		spin_lock(&sb_lock);
> > +		if (error)
> > +			break;
> > +		if (p)
> > +			__put_super(p);
> > +		p = sb;
> > +	}
> > +	if (p)
> > +		__put_super(p);
> > +	spin_unlock(&sb_lock);
> > +
> > +	if (error)
> > +		thaw_supers();
> > +
> > +	return error;
> > +}
> > +
> > +
> > +/**
> >   *	get_super - get the superblock of a device
> >   *	@bdev: device to get the superblock for
> >   *	

Thanks,
Rafael
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