Re: [PATCH v4 0/4] Documentation/litmus-tests: Add litmus tests for atomic APIs

[Joel Fernandes]

On Thu, Mar 26, 2020 at 10:40:18AM +0800, Boqun Feng wrote:
> A recent discussion raises up the requirement for having test cases for
> atomic APIs:
> 
> 	https://lore.kernel.org/lkml/20200213085849.GL14897@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> 
> , and since we already have a way to generate a test module from a
> litmus test with klitmus[1]. It makes sense that we add more litmus
> tests for atomic APIs. And based on the previous discussion, I create a
> new directory Documentation/atomic-tests and put these litmus tests
> here.
> 
> This patchset starts the work by adding the litmus tests which are
> already used in atomic_t.txt, and also improve the atomic_t.txt to make
> it consistent with the litmus tests.
> 
> Previous version:
> v1: https://lore.kernel.org/linux-doc/20200214040132.91934-1-boqun.feng@xxxxxxxxx/
> v2: https://lore.kernel.org/lkml/20200219062627.104736-1-boqun.feng@xxxxxxxxx/
> v3: https://lore.kernel.org/linux-doc/20200227004049.6853-1-boqun.feng@xxxxxxxxx/

For full series:

Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>

One question I had was in the existing atomic_set() documentation, it talks
about atomic_add_unless() implementation based on locking could have issues.
It says the way to fix such cases is:

Quote:
    the typical solution is to then implement atomic_set{}() with
    atomic_xchg().

I didn't get how using atomic_xchg() fixes it. Is the assumption there that
atomic_xchg() would be implemented using locking to avoid atomic_set() having
issues? If so, we could clarify that in the document.

thanks,

 - Joel

> 
> Changes since v3:
> 
> *	Merge two patches on atomic-set litmus test into one as per
> 	Alan. (Alan, you have acked only one of the two patches, so I
> 	don't add you acked-by for the combined patch).
> 
> *	Move the atomic litmus tests into litmus-tests/atomic to align
> 	with Joel's recent patches on RCU litmus tests.
> 
> I think we still haven't reach to a conclusion for the difference of
> atomic_add_unless() in herdtools, and I'm currently reading the source
> code of herd to resovle this. This is just an updated version to resolve
> ealier comments and react on Joel's RCU litmus tests.
> 
> Regards,
> Boqun
> 
> [1]: http://diy.inria.fr/doc/litmus.html#klitmus
> 
> Boqun Feng (4):
>   tools/memory-model: Add an exception for limitations on _unless()
>     family
>   Documentation/litmus-tests: Introduce atomic directory
>   Documentation/litmus-tests/atomic: Add a test for atomic_set()
>   Documentation/litmus-tests/atomic: Add a test for
>     smp_mb__after_atomic()
> 
>  Documentation/atomic_t.txt                    | 24 +++++++-------
>  ...ter_atomic-is-stronger-than-acquire.litmus | 32 +++++++++++++++++++
>  ...c-RMW-ops-are-atomic-WRT-atomic_set.litmus | 24 ++++++++++++++
>  Documentation/litmus-tests/atomic/README      | 16 ++++++++++
>  tools/memory-model/README                     | 10 ++++--
>  5 files changed, 91 insertions(+), 15 deletions(-)
>  create mode 100644 Documentation/litmus-tests/atomic/Atomic-RMW+mb__after_atomic-is-stronger-than-acquire.litmus
>  create mode 100644 Documentation/litmus-tests/atomic/Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus
>  create mode 100644 Documentation/litmus-tests/atomic/README
> 
> -- 
> 2.25.1
>