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Message-ID: <63236ee7-916a-ef6e-bc6e-051acb3caf95@huaweicloud.com>
Date: Wed, 2 Oct 2024 19:34:29 +0200
From: Hernan Ponce de Leon <hernan.poncedeleon@...weicloud.com>
To: Jonas Oberhauser <jonas.oberhauser@...weicloud.com>, paulmck@...nel.org
Cc: stern@...land.harvard.edu, 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, lkmm@...ts.linux.dev
Subject: Re: [PATCH v4 4/5] tools/memory-model: Switch to softcoded herd7 tags
On 9/30/2024 12:57 PM, 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.
The changes required for this patch were already merged to herd7.
>
> 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@...weicloud.com>
Signed-off-by: Hernan Ponce de Leon <hernan.poncedeleon@...weicloud.com>
> Signed-off-by: Jonas Oberhauser <jonas.oberhauser@...weicloud.com>
> ---
> .../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] |
> | 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)
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