Re: [RFC] Implementation of SCSI dynamic power management

Alan Stern
2008-01-09T20:36:21Z

On Wed, 9 Jan 2008, Oliver Neukum wrote:

> 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.

For now, I think the best approach is "head-in-the-sand". There aren't
a lot of USB storage devices partnered with other functions at the
moment.

But it might be a good idea for all USB drivers to use GFP_NOIO in
their resume pathways.

Alan Stern