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

[Chen Yu]

Hi,

On 2016å07æ14æ 06:18, Rafael J. Wysocki wrote:
> On Thu, Jul 14, 2016 at 12:00 AM, Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
> > On Wed, Jul 13, 2016 at 11:45 PM, Pavel Machek <pavel@xxxxxx> wrote:
> > > On Wed 2016-07-13 22:44:24, Rafael J. Wysocki wrote:
> > > > On Wed, Jul 13, 2016 at 10:26 PM, Pavel Machek <pavel@xxxxxx> 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@xxxxxx> 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?
> > OK, there is a bug.
> >
> > The thawing of user space is potentially dangerous, so in the
> > "snapshot" test mode hibernate() should just call
> > free_basic_memory_bitmaps() and from there invoke the code below the
> > Check_image label in software_resume(), roughly.
> Or rather call free_basic_memory_bitmaps() and
> unlock_device_hotplug(), then do swsusp_check() and invoke the code
> starting with the "PM: Loading hibernation image.\n" message in
> software_resume().
OK, I've used this solution and sent a v3 out.
thanks!
> Thanks,
> Rafael