Re: [PATCH 1/7] General notification queue with user mmap()'able ring buffer

On Wed, May 29, 2019 at 6:07 PM David Howells [off-list ref] wrote:

Greg KH [off-list ref] wrote:

quoted

everyone should use
it.  It saves us having to audit the same pattern over and over again.
And, even nicer, it uses a refcount now, and as you are trying to
reference count an object, it is exactly what this was written for.

So yes, I do think it should be used here, unless it is deemed to not
fit the pattern/usage model.

kref_put() enforces a very specific destructor signature.  I know of places
where that doesn't work because the destructor takes more than one argument
(granted that this is not the case here).  So why does kref_put() exist at
all?  Why not kref_dec_and_test()?

Why doesn't refcount_t get merged into kref, or vice versa?  Having both would
seem redundant.

Mind you, I've been gradually reverting atomic_t-to-refcount_t conversions
because it seems I'm not allowed refcount_inc/dec_return() and I want to get
at the point refcount for tracing purposes.

Yeeech, that's horrible, please don't do that.

Does this mean that refcount_read() isn't sufficient for what you want
to do with tracing (because for some reason you actually need to know
the values atomically at the time of increment/decrement)?