regulator: dummy: force synchronous probing

In the Linux kernel, the following vulnerability has been resolved:

regulator: dummy: force synchronous probing

Sometimes I get a NULL pointer dereference at boot time in kobject_get()

with the following call stack:

anatop_regulator_probe()

devm_regulator_register()

regulator_register()

regulator_resolve_supply()

kobject_get()

By placing some extra BUG_ON() statements I could verify that this is

raised because probing of the 'dummy' regulator driver is not completed

('dummy_regulator_rdev' is still NULL).

In the JTAG debugger I can see that dummy_regulator_probe() and

anatop_regulator_probe() can be run by different kernel threads

(kworker/u4:*). I haven't further investigated whether this can be

changed or if there are other possibilities to force synchronization

between these two probe routines. On the other hand I don't expect much

boot time penalty by probing the 'dummy' regulator synchronously.