Re: atomic_dec_and_test for child dst needed in dst_destroy?

[Christoph Lameter <christoph@xxxxxxxxxxx>]

On Tue, 5 Apr 2005, David S. Miller wrote:

> On Tue, 5 Apr 2005 11:55:45 -0700 (PDT)
> Christoph Lameter <christoph@xxxxxxxxxxx> wrote:
>
> > Is the atomic_dec_and_test in dst_destroy just there to join two atomic
> > operations into one without being necessary for the correctness of freeing
> > dsts?
> atomic_dec() has no memory ordering guarentees, only the atomic
> routines returning values do the proper SMP memory barriers.
> So, based upon this alone I don't think your change is valid.

Correct that applies in general. But what could go wrong if the atomic_dec
is separated from the atomic_read in this specific location?

I fail to see what the point of having a single instance of
atomic_dec_and_test for __refcnt is. In particular since the upper layers
guarantee that dst_destroy is not called multiple times for the same dst
entry.