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

From: Hernan Ponce de Leon
Date: Wed Oct 02 2024 - 13:35:19 EST

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@xxxxxxxxxxxxxxx>

Signed-off-by: Hernan Ponce de Leon <hernan.poncedeleon@xxxxxxxxxxxxxxx>

Signed-off-by: Jonas Oberhauser <jonas.oberhauser@xxxxxxxxxxxxxxx>
---
.../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)