Re: [RFC][PATCH 2/7] kref: Add kref_read()

[Peter Zijlstra]

On Mon, Nov 21, 2016 at 03:39:19PM +0000, Reshetova, Elena wrote:
> > By the way, there are several sites where the use of
> > atomic_t/atomic_wrap_t as a counter ventures beyond the standard (inc,
> > dec, add, sub, read, set) operations we're planning on implementing
> > for both refcount_t and stats_t. 
> 
> Speaking of non-fitting patterns. This one is quite common in
> networking code for refcounters:
> 
> if (atomic_cmpxchg(&cur->refcnt, 1, 0) == 1) {} This is from
> net/netfilter/nfnetlink_acct.c, but there are similar ones in other
> places.

Cute, but weird it doesn't actually decrement if not 1.

> Also, simple atomic_dec() is used pretty much everywhere for counters,
> which we donât have a straight match in refcount_t API.

WARN_ON(refcount_dec_and_test(refs));

And seeing how I've implememented refcount_inc() in similar terms:

WARN_ON(!refcount_inc_not_zero(refs));

It might make sense to actually provide that.