Re: [PATCH 0/6] Rework REFCOUNT_FULL using atomic_fetch_* operations

[Peter Zijlstra]

On Fri, Aug 02, 2019 at 11:09:54AM +0100, Will Deacon wrote:

> Although the revised implementation passes all of the lkdtm REFCOUNT
> tests, there is a race condition introduced by the deferred saturation
> whereby if INT_MIN + 2 tasks take a reference on a refcount at
> REFCOUNT_MAX and are each preempted between detecting overflow and
> writing the saturated value without being rescheduled, then another task
> may end up erroneously freeing the object when it drops the refcount and
> sees zero. It doesn't feel like a particularly realistic case to me, but
> I thought I should mention it in case somebody else knows better.

So my OCD has always found that hole objectionable. Also I suppose the
cmpxchg ones are simpler to understand.

Maybe make this fancy stuff depend on !FULL ?