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

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Date:	Thu, 14 Jul 2016 18:44:49 +0800
From:	Chen Yu <yu.c.chen@...el.com>
To:	"Rafael J. Wysocki" <rafael@...nel.org>,
	Pavel Machek <pavel@....cz>
Cc:	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

Hi,

On 2016年07月14日 06:18, Rafael J. Wysocki wrote:
> On Thu, Jul 14, 2016 at 12:00 AM, Rafael J. Wysocki <rafael@...nel.org> wrote:
>> On Wed, Jul 13, 2016 at 11:45 PM, Pavel Machek <pavel@....cz> 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@....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?
>> 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