linux-kernel - Re: [RFC][PATCH 2/4] tools/memory-model: Define applicable tags on operation in tools/...

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Date: Mon, 27 May 2024 11:59:55 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Jonas Oberhauser <jonas.oberhauser@...weicloud.com>
Cc: paulmck@...nel.org, parri.andrea@...il.com, will@...nel.org,
  peterz@...radead.org, boqun.feng@...il.com, npiggin@...il.com,
  dhowells@...hat.com, j.alglave@....ac.uk, luc.maranget@...ia.fr,
  akiyks@...il.com, dlustig@...dia.com, joel@...lfernandes.org,
  urezki@...il.com, quic_neeraju@...cinc.com, frederic@...nel.org,
  linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 2/4] tools/memory-model: Define applicable tags on
 operation in tools/...

On Mon, May 27, 2024 at 05:22:51PM +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@...weicloud.com>
> ---
>  tools/memory-model/linux-kernel.bell | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/memory-model/linux-kernel.bell b/tools/memory-model/linux-kernel.bell
> index 1b2444cdf8d1..08fa1ccb1328 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 *)
> +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]
> @@ -82,4 +89,4 @@ let Plain = M \ Marked
>  let carry-dep = (data ; [~ Srcu-unlock] ; rfi)*
>  let addr = carry-dep ; addr
>  let ctrl = carry-dep ; ctrl
> -let data = carry-dep ; data
> +let data = carry-dep ; data
> \ No newline at end of file

It looks like the final newline was accidentally deleted.

Alan