linux-kernel - Re: [linux-pm] Re: Hibernation considerations

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Message-ID: <Pine.LNX.4.64.0707201314261.5166@asgard.lang.hm>
Date:	Fri, 20 Jul 2007 13:31:04 -0700 (PDT)
From:	david@...g.hm
To:	Alan Stern <stern@...land.harvard.edu>
cc:	Milton Miller <miltonm@....com>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Ying Huang <ying.huang@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-pm <linux-pm@...ts.linux-foundation.org>,
	Jeremy Maitin-Shepard <jbms@....edu>
Subject: Re: [linux-pm] Re: Hibernation considerations

On Fri, 20 Jul 2007, Alan Stern wrote:

> On Fri, 20 Jul 2007, Milton Miller wrote:
>
>>> We can't do this unless we have frozen tasks (this way, or another)
>>> before
>>> carrying out the entire operation.
>>
>> What can't we do?   We've already worked with the drivers to quesce the
>> hardware and put any information to resume the device in ram.  Now we
>> ask them to put their device in low power mode so we can go to sleep.
>> Even if we schedule, the only thing userspace could touch is memory.
>
> Userspace can submit I/O requests.  Someone will have to audit every
> driver to make sure that such I/O requests don't cause a quiesced
> device to become active.  If the device is active, it will make the
> memory snapshot inconsistent with the on-device data.

assuming this is the suspend-from-ram after a kexec back from the 
write-to-disk kernel I don't think you are correct.

when doing a suspend-to-ram you get to a point where you just don't use 
any userspace. from that point on you are just walking the device tree 
putting things into low-power mode. This is the point where we are talking 
about jumping to.

david Lang
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