Re: [linux-pm] Re: Hibernation considerations

david
2007-07-20T20:41:37Z

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