On Sat, Dec 01, 2018 at 04:48:03PM +0900, Akira Yokosawa wrote:
> Hi Paul,
>
> As LKMM dropped lockless_dereference() when it was merged in v4.17,
> CodeSamples/formal/litmus/C-MP+o-wmb-o+ld-addr-o.litmus fails to
> be evaluated by "make run-herd7" under CodeSamples/formal/herd.
>
> lockless_dereference() is still covered by CodeSamples/formal/litmus/api.h
> and klitmus7, so the test can be evaluated by litmus7 and "klitmus7 at the
> moment.
>
> In commit 48ec12dac0c3 ("memorder: Update based on v4.15 Linux kernel
> de-Alpha-ication"), you added a footnote in Section 15.2.3 saying:
>
> Note that lockless_dereference() is not needed on v4.15 and later,
> and therefore is not available in these later Linux kernels.
>
> There remain several lockless_dereference()s in perfbook without any
> updates.
>
> In the Answer to Quick Quiz 15.15, lockless_dereference() is mentioned
> several times.
>
> Quick Quiz 15.17 says:
>
> Why doesn't line 18 of Listing 15.12 need a lockless_dereference()?
>
> Leading paragraph of Section 15.3.2.1 says:
>
> The load that heads your dependency chain must use proper ordering,
> for example, lockless_dereference(), rcu_dereference(), or a READ_ONCE()
> followed by smp_read_barrier_depends().
>
> In the middle of Section 15.5, there is a sentence:
>
> Note also that a dependency leading to a load must be headed by a
> lockless_dereference() or an rcu_dereference(): READ_ONCE() is not
> sufficient.
>
> Could you look into them?
>
> One problem in regard to litmus tests might be that there is no means
> to indicate plain accesses with no memory barrier in current LKMM.
> At the moment, C-MP+o-wmb-o+o-addr-o.litmus behaves identically as
> C-MP+o-wmb-o+ld-addr-o.litmus would do.
Good catches! How about the following?
1. I remove CodeSamples/formal/litmus/C-MP+o-wmb-o+ld-addr-o.litmus.
2. I add a comment to the lockless_dereference() call in
lst:memorder:Enforced Ordering of Message-Passing Address-Dependency Litmus Test
stating that this API member is obsolete.
3. I remove the (\path{C-MP+o-wmb-o+ld-addr-o.litmus}) from the
discussion. I also add a LaTeX comment stating which commit
removed this file for future reference.
4. I remove lockless_dereference() from CodeSamples/formal/litmus/api.h.
Does that sound reasonable?
Thanx, Paul
