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

Alan Stern
2008-01-06T22:21:51Z

On Sun, 6 Jan 2008, Rafael J. Wysocki wrote:

> > Still, shouldn't we fail the removal of the device apart from giving the
> > warning?
>
> Actually, having thought about it a bit more, I don't see the point in
> preventing the removal of the device from the list in device_pm_remove() if
> we allow all of the operations in device_del() preceding it to be performed.

That's not the issue. We _don't_ allow all of the operations in
device_del() preceding the call to device_pm_remove(). In particular,
the call to the device's driver's remove method will deadlock because
device_release_driver() always has to acquire dev->sem.

> Shouldn't we just take pm_sleep_rwsem in device_del() upfront and block on that
> if locked?

No -- the whole idea here is to print an error message in the system
log if a driver's resume method tries to call device_del(). Deadlock
is unavoidable in this case, but at least we'll know which driver is
guilty.

Alan Stern