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Message-ID: <b5df91f5-4b48-440b-9445-b8de0bd3260f@paulmck-laptop>
Date: Tue, 29 Oct 2024 16:42:00 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Jonas Oberhauser <jonas.oberhauser@...weicloud.com>,
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, lkmm@...ts.linux.dev,
hernan.poncedeleon@...weicloud.com
Subject: Re: [PATCH v4 4/5] tools/memory-model: Switch to softcoded herd7 tags
On Mon, Oct 28, 2024 at 05:04:38PM -0700, Boqun Feng wrote:
> 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@...weicloud.com>
> > Signed-off-by: Jonas Oberhauser <jonas.oberhauser@...weicloud.com>
>
> Reviewed-by: Boqun Feng <boqun.feng@...il.com>
>
> One bit below:
Jonas, if you agree, please feel free to send this as an updated patch
5/5 or as a separate patch. Either way, just let me know!
Thanx, Paul
> > ---
> > .../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
> >
> >
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