Re: [PATCH 1/4] lockd: convert nlm_host.h_count from atomic_t to refcount_t

[J. Bruce Fields]

On Fri, Dec 22, 2017 at 09:29:15AM +0000, Reshetova, Elena wrote:
> 
> On Wed, Nov 29, 2017 at 01:15:43PM +0200, Elena Reshetova wrote:
> > atomic_t variables are currently used to implement reference
> > counters with the following properties:
> >  - counter is initialized to 1 using atomic_set()
> >  - a resource is freed upon counter reaching zero
> >  - once counter reaches zero, its further
> >    increments aren't allowed
> >  - counter schema uses basic atomic operations
> >    (set, inc, inc_not_zero, dec_and_test, etc.)
> 
> >Whoops, I forgot that this doesn't apply to h_count.
> 
> >Well, it's confusing, because h_count is actually used in two different
> >ways: depending on whether a nlm_host represents a client or server, it
> >may have the above properties or not.
> 
> 
> So, what happens when it is not having the above properties? Is the object 
> being reused or? 

The object isn't destroyed when the counter hits zero--zero is just
taken as a hint to some garbage collection algorithm that it would be OK
to destroy it.  So decrementing to or incrementing from zero is OK.

--b.