linux-kernel - Re: [PATCH] PM / hibernate: Introduce snapshot test mode for hibernation

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Message-ID: <20160713214546.GA26692@amd>
Date:	Wed, 13 Jul 2016 23:45:46 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	Chen Yu <yu.c.chen@...el.com>, Linux PM <linux-pm@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PM / hibernate: Introduce snapshot test mode for
 hibernation

On Wed 2016-07-13 22:44:24, Rafael J. Wysocki wrote:
> On Wed, Jul 13, 2016 at 10:26 PM, Pavel Machek <pavel@....cz> wrote:
> > On Wed 2016-07-13 22:04:27, Rafael J. Wysocki wrote:
> >> On Wed, Jul 13, 2016 at 7:01 PM, Pavel Machek <pavel@....cz> wrote:
> >> > Hi!
> >> >
> >> >> >>and then swapon the swap device, and do a testing. This should be safer?
> >> >> >Yeah, that's the way. Read-only root is other option.
> >> >> >
> >> >> >>>I guess updating documentation would be welcome from my side,
> >> >> >>>otherwise it should be ok.
> >> >> >>OK, I'll  update the documents.
> >> >> >Just add fat warning into the documentation.
> >> >> OK.
> >> >
> >> > Actually... If you could add
> >> >
> >> > printk(KERN_ALERT "Hibernation image written. If you have any
> >> > filesystems mounted read-write and attempt to resume, you'll corrupt
> >> > your data. To prevent that, remove the hibernation image.\n")
> >> >
> >> > ...I guess that would save someone's filesystem. (Yes, very high
> >> > loglevel. If you attempt to do this from anything else then singleuser
> >> > or initrd, you are asking for problems, so... lets make sure user sees
> >> > it.)
> >>
> >> Please see the new version of this patch:
> >> https://patchwork.kernel.org/patch/9226837/
> >
> > New version changes nothing, right? You still need to be sure
> > filesystems are not mounted r/w. So I would still like to see printk()
> > with warning.
> 
> It shouldn't matter how they are mounted, because the contents of
> persistent storage don't change.

@@ -721,6 +724,9 @@  int hibernate(void)
   atomic_inc(&snapshot_device_available);
     Unlock:
	unlock_system_sleep();
	+	if (snapshot_test)
	+	   software_resume();
	+
		return error;
		 }

Aha, I see, immediate wakeup here. Makes sense. ... ...

No.

AFAICT, freezer is used in hibernation_snapshot, which means at
Unlock:, kernel threads are running; software_resume() freezes them
again, but they had chance to run and potentially corrupt the
persistent storage... right?

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