Re: atomic_dec_and_test for child dst needed in dst_destroy?

[Christoph Lameter <christoph@xxxxxxxxxxx>]

On Wed, 6 Apr 2005, Herbert Xu wrote:

> > -               if (atomic_dec_and_test(&dst->__refcnt)) {
> > +               atomic_dec(&dst->__refcnt);
> > +               if (!atomic_read(&dst->__refcnt)) {
>
> This is racy (albeit very unlikely) because dst may be freed by
> dst_run_gc after the atomic_dec.

If that is so then it is also possible that the gc frees after
atomic_dec_and_test:

cpu0 dst_destroy        cpu1 dst_run_gc

atomic_dec_and_test(refcnt)
                        if (atomic_read(refcnt)) ...
                        ..
                        dst_destroy(dst)
                        kmem_cache_free(dst)
..
goto again
...
kmem_cache_free(dst)