On Thu, Oct 19, 2017 at 11:24:00PM +0000, Bart Van Assche wrote:

Are there any completion objects for which the cross-release checking is
useful? Are there any wait_for_completion() callers that hold a mutex or
other locking object?

Check /proc/lockdep, then you can find all dependencies wrt cross-lock.
I named a lock class of wait_for_completion(), a sting starting with
"(complete)".

For example, in my machine:

console_lock -> (complete)&req.done
cpu_hotplug_lock.rw_sem -> (complete)&st->done_up
cpuhp_state_mutex -> (complete)&st->done_up

and so on.