Re: [PATCH] driver core: reject devices with unregistered buses

[Johan Hovold <johan@kernel.org>]

On Tue, Apr 28, 2026 at 09:09:04PM +0200, Danilo Krummrich wrote:
> On Mon Apr 27, 2026 at 12:28 PM CEST, Johan Hovold wrote:
> > Trying to register a device on a bus which has not yet been registered
> > used to trigger a NULL-pointer dereference, but since the const bus
> > structure rework registration instead succeeds without the device being
> > added to the bus.
> >
> > Reject devices with unregistered buses to catch any callers that get
> > the ordering wrong and to handle bus registration failures more
> > gracefully.
> >
> > Fixes: 5221b82d46f2 ("driver core: bus: bus_add/probe/remove_device() cleanups")
> > Cc: stable@vger.kernel.org	# 6.3
> 
> Hm...this sounds like hardening and not like a "real" bug fix. Do you have a
> specific reason why you added Cc: stable?

It's certainly a bug fix and this change in behaviour was clearly
unintended.

Any caller getting the ordering wrong would now succeed in registering
devices, but no driver would ever be bound which is harder to detect
than the earlier crashes. 

Whether any offenders have snuck in since 6.3 I don't know, but I still
think this warrants a backport.

Johan