Re: [RFC] Implementation of SCSI dynamic power management

Oliver Neukum
2008-01-09T17:31:29Z

Am Mittwoch, 9. Januar 2008 18:22:51 schrieb Alan Stern:
> On Wed, 9 Jan 2008, Oliver Neukum wrote:
>
> > This has an interesting implication. As the storage driver can share
> > a device with in principle any other usb driver, we must audit all usb
> > drivers if we wish to adopt this patch.
> > All a device's interfaces must be resumed when the storage interface
> > is resumed. To resume a storage device no memory must be allocated
> > because that could deadlock.
>
> Maybe people shouldn't enable autosuspend for their swap device...

Good advice, but not sufficient to avoid this problem. The vm may write
out normal dirty cached pages to scsi devices, which affects storage.

> What happens during normal system resume if a driver (not just USB!)
> needs to allocate memory before the swap device has been resumed?

I have no idea. I guess these code paths have a sync in the suspend path,
so a lot of clean pages will be available.

Regards
Oliver