Re: [PATCH v4 4/5] tools/memory-model: Switch to softcoded herd7 tags

[Boqun Feng <boqun.feng@gmail.com>]

On Mon, Sep 30, 2024 at 12:57:09PM +0200, Jonas Oberhauser wrote:
> A new version of herd7 provides a -lkmmv2 switch which overrides the old herd7
> behavior of simply ignoring any softcoded tags in the .def and .bell files. We
> port LKMM to this version of herd7 by providing the switch in linux-kernel.cfg
> and reporting an error if the LKMM is used without this switch.
> 
> To preserve the semantics of LKMM, we also softcode the Noreturn tag on atomic
> RMW which do not return a value and define atomic_add_unless with an Mb tag in
> linux-kernel.def.
> 
> We update the herd-representation.txt accordingly and clarify some of the
> resulting combinations.
> 
> (To be) Signed-off-by: Hernan Ponce de Leon <hernan.poncedeleon@huaweicloud.com>
> Signed-off-by: Jonas Oberhauser <jonas.oberhauser@huaweicloud.com>

Reviewed-by: Boqun Feng <boqun.feng@gmail.com>

One bit below:

> ---
>  .../Documentation/herd-representation.txt     | 27 ++++++++++---------
>  tools/memory-model/README                     |  2 +-
>  tools/memory-model/linux-kernel.bell          |  3 +++
>  tools/memory-model/linux-kernel.cfg           |  1 +
>  tools/memory-model/linux-kernel.def           | 18 +++++++------
>  5 files changed, 30 insertions(+), 21 deletions(-)
> 
> diff --git a/tools/memory-model/Documentation/herd-representation.txt b/tools/memory-model/Documentation/herd-representation.txt
> index ed988906f2b7..7ae1ff3d3769 100644
> --- a/tools/memory-model/Documentation/herd-representation.txt
> +++ b/tools/memory-model/Documentation/herd-representation.txt
> @@ -18,6 +18,11 @@
>  #
>  # By convention, a blank line in a cell means "same as the preceding line".
>  #
> +# Note that the syntactic representation does not always match the sets and
> +# relations in linux-kernel.cat, due to redefinitions in linux-kernel.bell and
> +# lock.cat. For example, the po link between LKR and LKW is upgraded to an rmw
> +# link, and W[acquire] are not included in the Acquire set.
> +#
>  # Disclaimer.  The table includes representations of "add" and "and" operations;
>  # corresponding/identical representations of "sub", "inc", "dec" and "or", "xor",
>  # "andnot" operations are omitted.
> @@ -60,14 +65,13 @@
>      ------------------------------------------------------------------------------
>      |       RMW ops w/o return value |                                           |
>      ------------------------------------------------------------------------------
> -    |                     atomic_add | R*[noreturn] ->rmw W*[once]               |
> +    |                     atomic_add | R*[noreturn] ->rmw W*[noreturn]           |

Not in this patch, but don't you need to update this again to all cap
to match your changes in patch #5? ;-)

Regards,
Boqun

>      |                     atomic_and |                                           |
>      |                      spin_lock | LKR ->po LKW                              |
>      ------------------------------------------------------------------------------
>      |        RMW ops w/ return value |                                           |
>      ------------------------------------------------------------------------------
> -    |              atomic_add_return | F[mb] ->po R*[once]                       |
> -    |                                |     ->rmw W*[once] ->po F[mb]             |
> +    |              atomic_add_return | R*[mb] ->rmw W*[mb]                       |
>      |               atomic_fetch_add |                                           |
>      |               atomic_fetch_and |                                           |
>      |                    atomic_xchg |                                           |
> @@ -79,13 +83,13 @@
>      |            atomic_xchg_relaxed |                                           |
>      |                   xchg_relaxed |                                           |
>      |    atomic_add_negative_relaxed |                                           |
> -    |      atomic_add_return_acquire | R*[acquire] ->rmw W*[once]                |
> +    |      atomic_add_return_acquire | R*[acquire] ->rmw W*[acquire]             |
>      |       atomic_fetch_add_acquire |                                           |
>      |       atomic_fetch_and_acquire |                                           |
>      |            atomic_xchg_acquire |                                           |
>      |                   xchg_acquire |                                           |
>      |    atomic_add_negative_acquire |                                           |
> -    |      atomic_add_return_release | R*[once] ->rmw W*[release]                |
> +    |      atomic_add_return_release | R*[release] ->rmw W*[release]             |
>      |       atomic_fetch_add_release |                                           |
>      |       atomic_fetch_and_release |                                           |
>      |            atomic_xchg_release |                                           |
> @@ -94,17 +98,16 @@
>      ------------------------------------------------------------------------------
>      |            Conditional RMW ops |                                           |
>      ------------------------------------------------------------------------------
> -    |                 atomic_cmpxchg | On success: F[mb] ->po R*[once]           |
> -    |                                |                 ->rmw W*[once] ->po F[mb] |
> -    |                                | On failure: R*[once]                      |
> +    |                 atomic_cmpxchg | On success: R*[mb] ->rmw W*[mb]           |
> +    |                                | On failure: R*[mb]                        |
>      |                        cmpxchg |                                           |
>      |              atomic_add_unless |                                           |
>      |         atomic_cmpxchg_relaxed | On success: R*[once] ->rmw W*[once]       |
>      |                                | On failure: R*[once]                      |
> -    |         atomic_cmpxchg_acquire | On success: R*[acquire] ->rmw W*[once]    |
> -    |                                | On failure: R*[once]                      |
> -    |         atomic_cmpxchg_release | On success: R*[once] ->rmw W*[release]    |
> -    |                                | On failure: R*[once]                      |
> +    |         atomic_cmpxchg_acquire | On success: R*[acquire] ->rmw W*[acquire] |
> +    |                                | On failure: R*[acquire]                   |
> +    |         atomic_cmpxchg_release | On success: R*[release] ->rmw W*[release] |
> +    |                                | On failure: R*[release]                   |
>      |                   spin_trylock | On success: LKR ->po LKW                  |
>      |                                | On failure: LF                            |
>      ------------------------------------------------------------------------------
> diff --git a/tools/memory-model/README b/tools/memory-model/README
> index dab38904206a..59bc15edeb8a 100644
> --- a/tools/memory-model/README
> +++ b/tools/memory-model/README
> @@ -20,7 +20,7 @@ that litmus test to be exercised within the Linux kernel.
>  REQUIREMENTS
>  ============
>  
> -Version 7.52 or higher of the "herd7" and "klitmus7" tools must be
> +Version 7.58 or higher of the "herd7" and "klitmus7" tools must be
>  downloaded separately:
>  
>    https://github.com/herd/herdtools7
> diff --git a/tools/memory-model/linux-kernel.bell b/tools/memory-model/linux-kernel.bell
> index 7c9ae48b9437..8ae47545df97 100644
> --- a/tools/memory-model/linux-kernel.bell
> +++ b/tools/memory-model/linux-kernel.bell
> @@ -94,3 +94,6 @@ let carry-dep = (data ; [~ Srcu-unlock] ; rfi)*
>  let addr = carry-dep ; addr
>  let ctrl = carry-dep ; ctrl
>  let data = carry-dep ; data
> +
> +flag ~empty (if "lkmmv2" then 0 else _)
> +  as this-model-requires-variant-higher-than-lkmmv1
> diff --git a/tools/memory-model/linux-kernel.cfg b/tools/memory-model/linux-kernel.cfg
> index 3c8098e99f41..69b04f3aad73 100644
> --- a/tools/memory-model/linux-kernel.cfg
> +++ b/tools/memory-model/linux-kernel.cfg
> @@ -1,6 +1,7 @@
>  macros linux-kernel.def
>  bell linux-kernel.bell
>  model linux-kernel.cat
> +variant lkmmv2
>  graph columns
>  squished true
>  showevents noregs
> diff --git a/tools/memory-model/linux-kernel.def b/tools/memory-model/linux-kernel.def
> index a12b96c547b7..d7279a357cba 100644
> --- a/tools/memory-model/linux-kernel.def
> +++ b/tools/memory-model/linux-kernel.def
> @@ -63,14 +63,14 @@ atomic_set(X,V) { WRITE_ONCE(*X,V); }
>  atomic_read_acquire(X) smp_load_acquire(X)
>  atomic_set_release(X,V) { smp_store_release(X,V); }
>  
> -atomic_add(V,X) { __atomic_op(X,+,V); }
> -atomic_sub(V,X) { __atomic_op(X,-,V); }
> -atomic_and(V,X) { __atomic_op(X,&,V); }
> -atomic_or(V,X)  { __atomic_op(X,|,V); }
> -atomic_xor(V,X) { __atomic_op(X,^,V); }
> -atomic_inc(X)   { __atomic_op(X,+,1); }
> -atomic_dec(X)   { __atomic_op(X,-,1); }
> -atomic_andnot(V,X) { __atomic_op(X,&~,V); }
> +atomic_add(V,X) { __atomic_op{noreturn}(X,+,V); }
> +atomic_sub(V,X) { __atomic_op{noreturn}(X,-,V); }
> +atomic_and(V,X) { __atomic_op{noreturn}(X,&,V); }
> +atomic_or(V,X)  { __atomic_op{noreturn}(X,|,V); }
> +atomic_xor(V,X) { __atomic_op{noreturn}(X,^,V); }
> +atomic_inc(X)   { __atomic_op{noreturn}(X,+,1); }
> +atomic_dec(X)   { __atomic_op{noreturn}(X,-,1); }
> +atomic_andnot(V,X) { __atomic_op{noreturn}(X,&~,V); }
>  
>  atomic_add_return(V,X) __atomic_op_return{mb}(X,+,V)
>  atomic_add_return_relaxed(V,X) __atomic_op_return{once}(X,+,V)
> @@ -144,3 +144,5 @@ atomic_fetch_andnot(V,X) __atomic_fetch_op{mb}(X,&~,V)
>  atomic_fetch_andnot_acquire(V,X) __atomic_fetch_op{acquire}(X,&~,V)
>  atomic_fetch_andnot_release(V,X) __atomic_fetch_op{release}(X,&~,V)
>  atomic_fetch_andnot_relaxed(V,X) __atomic_fetch_op{once}(X,&~,V)
> +
> +atomic_add_unless(X,V,W) __atomic_add_unless{mb}(X,V,W)
> -- 
> 2.34.1
> 
>