Re: [PATCH v2 2/2] arm: perf: Mark as non-removable

From: Russell King - ARM Linux
Date: Wed Jan 04 2017 - 06:41:25 EST


On Wed, Jan 04, 2017 at 11:30:25AM +0000, Mark Rutland wrote:
> On Wed, Jan 04, 2017 at 10:19:46AM +0100, Alexander Stein wrote:
> > I'm not sure if the change above works with remove functions set in struct
> > bus_type too.
> > But on the other hand this would hide errors in drivers which are actually
> > removable but do not cleanup properly which DEBUG_TEST_DRIVER_REMOVE tries to
> > detect.
> > By setting .suppress_bind_attrs = true explicitely you state "This
> > driver cannot be removed!", so the remove callback is not missing by accident.
>
> I'm not sure I follow. If the remove callback is accidentally missing,
> the driver is not "actually removable" today -- there's either no remove
> code, or it's not been wired up (the latter of which will likely result
> in a compiler warning about an unused function).
>
> Aborting the remove early in those cases is much safer than forcefully
> removing a driver without a remove callback.

Drivers without a remove function may be removable - there's more layers
than just the driver - there's the bus layer as well, which may or may
not direct to a private-bus pointer.

There's no real way for the core driver model code to know whether the
lack of the ->remove in the struct device_driver is something that
prevents a driver being removed, or whether it's handled via some other
method. Eg, platform drivers.

--
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.