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

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Message-ID: <Zl_oxj9-ypX0U2HZ@Boquns-Mac-mini.home>
Date: Tue, 4 Jun 2024 21:25:42 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Jonas Oberhauser <jonas.oberhauser@...weicloud.com>
Cc: paulmck@...nel.org, stern@...land.harvard.edu, parri.andrea@...il.com,
	will@...nel.org, peterz@...radead.org, 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: [PATCHv2 2/4] tools/memory-model: Define applicable tags on
 operation in tools/...

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@...weicloud.com>
> ---
>  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:

(*
 * 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
>