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[106.167.171.201]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-207946fc352sm100946035ad.206.2024.09.20.19.44.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 20 Sep 2024 19:44:40 -0700 (PDT) Message-ID: <8cb4e810-da6c-4d8f-b608-5bdba56da2bd@gmail.com> Date: Sat, 21 Sep 2024 11:44:32 +0900 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 4/5] tools/memory-model: Switch to softcoded herd7 tags To: Jonas Oberhauser , paulmck@kernel.org Cc: stern@rowland.harvard.edu, parri.andrea@gmail.com, will@kernel.org, peterz@infradead.org, boqun.feng@gmail.com, npiggin@gmail.com, dhowells@redhat.com, j.alglave@ucl.ac.uk, luc.maranget@inria.fr, dlustig@nvidia.com, joel@joelfernandes.org, urezki@gmail.com, quic_neeraju@quicinc.com, frederic@kernel.org, linux-kernel@vger.kernel.org, lkmm@lists.linux.dev, hernan.poncedeleon@huaweicloud.com, Akira Yokosawa References: <20240919130634.298181-1-jonas.oberhauser@huaweicloud.com> <20240919130634.298181-5-jonas.oberhauser@huaweicloud.com> Content-Language: en-US From: Akira Yokosawa In-Reply-To: <20240919130634.298181-5-jonas.oberhauser@huaweicloud.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On Thu, 19 Sep 2024 15:06:33 +0200, Jonas Oberhauser wrote: > A new version of Herd7 provides a -lkmmv1 switch which overrides the old herd7 Why -lkmmv1? You mean current (unversioned) LKMM has to be called v0 ??? My preference is to call current one as v1 and your new version as v2. Either way, Reviewed-by: Akira Yokosawa Please find a few more comments inline below. > 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. > > We also add a litmus test for atomic_add_unless which uncovered a bug in early > iterations of the Herd7 patch that implements the new switch. > > (To be) Signed-off-by: Hernan Ponce de Leon > Signed-off by: Jonas Oberhauser > --- > .../Documentation/herd-representation.txt | 27 ++++++++++--------- > tools/memory-model/linux-kernel.bell | 3 +++ > tools/memory-model/linux-kernel.cfg | 1 + > tools/memory-model/linux-kernel.def | 18 +++++++------ > .../litmus-tests/add-unless-mb.litmus | 27 +++++++++++++++++++ > 5 files changed, 56 insertions(+), 20 deletions(-) > create mode 100644 tools/memory-model/litmus-tests/add-unless-mb.litmus > [...] > diff --git a/tools/memory-model/linux-kernel.def b/tools/memory-model/linux-kernel.def > index a12b96c547b7..4281572732bd 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) > \ No newline at end of file Please fix this warning. > diff --git a/tools/memory-model/litmus-tests/add-unless-mb.litmus b/tools/memory-model/litmus-tests/add-unless-mb.litmus > new file mode 100644 > index 000000000000..72f76ff3f59d > --- /dev/null > +++ b/tools/memory-model/litmus-tests/add-unless-mb.litmus > @@ -0,0 +1,27 @@ > +C add_unless_mb > + > +(* > + * Result: Never > + * > + * This litmus test demonstrates that a successful atomic_add_unless > + * acts as a full memory barrier, ensuring that *x=1 propagates to P1 > + * before P1 executes *x=2. > + *) > + > +{} > + > +P0(atomic_t *x, atomic_t *y, atomic_t *z) > +{ > + WRITE_ONCE(*x, 1); > + int r0 = atomic_add_unless(z,1,5); > + WRITE_ONCE(*y, 1); > +} > + > +P1(atomic_t *x, atomic_t *y) > +{ > + int r0 = READ_ONCE(*y); > + if (r0 == 1) > + WRITE_ONCE(*x, 2); > +} > + > +exists (1:r0=1 /\ x=1) This litmus test is not compatible with klitmus7, which is much stricter than herd7's C parser. You can have only int or int* variables in the exists clause. Register variables need their declarations at the top of each Pn() (classic C). See below for klitmus7 ready code. And tools/memory-model/litmus-tests/README need to mention this litmus test. Thanks, Akira --------------------------------------------- P0(int *x, int *y, atomic_t *z) { int r0; WRITE_ONCE(*x, 1); r0 = atomic_add_unless(z,1,5); WRITE_ONCE(*y, 1); } P1(int *x, int *y) { int r0; r0 = READ_ONCE(*y); if (r0 == 1) WRITE_ONCE(*x, 2); } exists (1:r0=1 /\ x=1) ---------------------------------------------