From: Greg KH <gregkh@linuxfoundation.org>
Date: Wed, 12 Feb 2014 17:39:02 -0800

Yes, that's horrible as well, but as was already pointed out in this
thread, you can't rely on that value to really be "1" after reading it
due to the way krefs work, what happened if someone else just grabbed
it?

If all they want is a "count" for when to start polling, then use a
separate atomic count, but don't abuse the kref interface for this, I
don't think that will work properly at all.

They want to know which thread of control decrements the count to "1"
as buffers are released.

That seems entirely reasonable to me.

They could add another atomic counter for this, but that's rather
silly since the kref already has an atomic they can use for this
purpose.