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

From: Chen Yu
Date: Thu Jul 14 2016 - 06:37:14 EST


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:

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.
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
Please see the new version of this patch:
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)
+ if (snapshot_test)
+ software_resume();
return error;

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


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
OK, I've used this solution and sent a v3 out.