Re: [PATCHv2 2/4] tools/memory-model: Define applicable tags on operation in tools/...

[Jonas Oberhauser]

Am 6/5/2024 um 6:25 AM schrieb Boqun Feng:
> On Tue, Jun 04, 2024 at 06:04:09PM +0200, Jonas Oberhauser wrote:
> > Herd7 transforms reads, writes, and read-modify-writes by eliminating
> > 'acquire tags from writes, 'release tags from reads, and 'acquire,
> > 'release, and 'mb tags from failed read-modify-writes. We emulate this
> > behavior by redefining Acquire, Release, and Mb sets in linux-kernel.bell
> > to explicitly exclude those combinations.
> >
> > Herd7 furthermore adds 'noreturn tag to certain reads. Currently herd7
> > does not allow specifying the 'noreturn tag manually, but such manual
> > declaration (e.g., through a syntax __atomic_op{noreturn}) would add
> > invalid 'noreturn tags to writes; in preparation, we already also exclude
> > this combination.
> >
> > Signed-off-by: Jonas Oberhauser <jonas.oberhauser@xxxxxxxxxxxxxxx>
> > ---
> >   tools/memory-model/linux-kernel.bell | 7 +++++++
> >   1 file changed, 7 insertions(+)
> >
> > diff --git a/tools/memory-model/linux-kernel.bell b/tools/memory-model/linux-kernel.bell
> > index dba6b5b6dee0..2f49993644ed 100644
> > --- a/tools/memory-model/linux-kernel.bell
> > +++ b/tools/memory-model/linux-kernel.bell
> > @@ -36,6 +36,13 @@ enum Barriers = 'wmb (*smp_wmb*) ||
> >   		'after-srcu-read-unlock (*smp_mb__after_srcu_read_unlock*)
> >   instructions F[Barriers]
> >   
> > +(* Remove impossible tags, such as Acquire on a store or failed RMW *)
>
> This comment needs a bit help, "failed RMW"s still exist, they just
> don't provide ordering. How about:


Oh, I see how the comment can be misread. A smaller fix would be

"Acquire on a store or on a failed RMW"

but I actually like your longer explanation better, so I think I'll go 
with that.

> (*
>   * Filter out syntactic annotations that don't provide the corresponding
>   * semantic ordering, such as Acquire on a store or Mb on a failed RMW.
>   *)
>
> ?
>
> Regards,
> Boqun
>
> > +let FailedRMW = RMW \ (domain(rmw) | range(rmw))
> > +let Acquire = Acquire \ W \ FailedRMW
> > +let Release = Release \ R \ FailedRMW
> > +let Mb = Mb \ FailedRMW
> > +let Noreturn = Noreturn \ W
> > +
> >   (* SRCU *)
> >   enum SRCU = 'srcu-lock || 'srcu-unlock || 'sync-srcu
> >   instructions SRCU[SRCU]
> > --
> > 2.34.1