Re: [PATCH] PM: Acquire device locks on suspend

Alan Stern
2008-01-06T04:04:35Z

On Sat, 5 Jan 2008, Rafael J. Wysocki wrote:

> On Saturday, 5 of January 2008, Alan Stern wrote:
> > On Sat, 5 Jan 2008, Rafael J. Wysocki wrote:

> > > Still, even doing that is not enough, since someone can call
> > > destroy_suspended_device() from a .suspend() routine and then the device
> > > will end up on a wrong list just as well.
> >
> > That should never happen. The whole idea of destroy_suspended_device()
> > is that the device couldn't be resumed and in fact should be
> > unregistered because it is no longer working or no longer present. A
> > suspend routine won't detect this sort of thing since it doesn't try to
> > resume the device.
> >
> > But it wouldn't hurt to mention in the kerneldoc that
> > destroy_suspended_device() is meant to be called only during a system
> > resume.
>
> Hmm. Please have a look at the appended patch.
>
> I have removed the warning from device_del() and used list_empty() to detect
> removed devices in the .suspend() routines. Is that viable?

It's not good.

The warning in device_del() is vital. It's what will tell people where
the problem is when a deadlock occurs during system resume because some
driver has mistakenly tried to unregister a device at the wrong time.
It would have pointed immediately to the msr driver in the case of the
bug Andrew found, for instance.

If you can figure out a way to disable the warning in device_del() for
just the one device being unregistered by
device_pm_destroy_suspended(), I suppose that would be okay.

Alan Stern