From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754673AbeBUPJC (ORCPT ); Wed, 21 Feb 2018 10:09:02 -0500 Received: from iolanthe.rowland.org ([192.131.102.54]:33012 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1754529AbeBUPJB (ORCPT ); Wed, 21 Feb 2018 10:09:01 -0500 Date: Wed, 21 Feb 2018 10:09:00 -0500 (EST) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: "Paul E. McKenney" cc: linux-kernel@vger.kernel.org, , , , , , , , , , , , Subject: Re: [PATCH RFC tools/lkmm 10/12] tools/memory-model: Add a S lock-based external-view litmus test In-Reply-To: <1519169112-20593-10-git-send-email-paulmck@linux.vnet.ibm.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 20 Feb 2018, Paul E. McKenney wrote: > From: Alan Stern > > This commit adds a litmus test in which P0() and P1() form a lock-based S > litmus test, with the addition of P2(), which observes P0()'s and P1()'s Why do you call this an "S" litmus test? Isn't ISA2 a better description? > accesses with a full memory barrier but without the lock. This litmus > test asks whether writes carried out by two different processes under the > same lock will be seen in order by a third process not holding that lock. > The answer to this question is "yes" for all architectures supporting > the Linux kernel, but is "no" according to the current version of LKMM. > > A patch to LKMM is under development. > > Signed-off-by: Alan Stern > Signed-off-by: Paul E. McKenney > --- > .../ISA2+pooncelock+pooncelock+pombonce.litmus | 41 ++++++++++++++++++++++ > 1 file changed, 41 insertions(+) > create mode 100644 tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus Aren't these tests supposed to be described in litmus-tests/README? > diff --git a/tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus b/tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus > new file mode 100644 > index 000000000000..7a39a0aaa976 > --- /dev/null > +++ b/tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus > @@ -0,0 +1,41 @@ > +C ISA2+pooncelock+pooncelock+pombonce.litmus > + > +(* > + * Result: Sometimes > + * > + * This test shows that the ordering provided by a lock-protected S > + * litmus test (P0() and P1()) are not visible to external process P2(). > + * This is likely to change soon. That last line may be premature. We haven't reached any consensus on how RISC-V will handle this. If RISC-V allows the test then the memory model can't forbid it. Alan > + *) > + > +{} > + > +P0(int *x, int *y, spinlock_t *mylock) > +{ > + spin_lock(mylock); > + WRITE_ONCE(*x, 1); > + WRITE_ONCE(*y, 1); > + spin_unlock(mylock); > +} > + > +P1(int *y, int *z, spinlock_t *mylock) > +{ > + int r0; > + > + spin_lock(mylock); > + r0 = READ_ONCE(*y); > + WRITE_ONCE(*z, 1); > + spin_unlock(mylock); > +} > + > +P2(int *x, int *z) > +{ > + int r1; > + int r2; > + > + r2 = READ_ONCE(*z); > + smp_mb(); > + r1 = READ_ONCE(*x); > +} > + > +exists (1:r0=1 /\ 2:r2=1 /\ 2:r1=0) > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from iolanthe.rowland.org ([192.131.102.54]:33016 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1754561AbeBUPJB (ORCPT ); Wed, 21 Feb 2018 10:09:01 -0500 Date: Wed, 21 Feb 2018 10:09:00 -0500 (EST) From: Alan Stern Subject: Re: [PATCH RFC tools/lkmm 10/12] tools/memory-model: Add a S lock-based external-view litmus test In-Reply-To: <1519169112-20593-10-git-send-email-paulmck@linux.vnet.ibm.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-arch-owner@vger.kernel.org List-ID: To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, mingo@kernel.org, parri.andrea@gmail.com, will.deacon@arm.com, peterz@infradead.org, boqun.feng@gmail.com, npiggin@gmail.com, dhowells@redhat.com, j.alglave@ucl.ac.uk, luc.maranget@inria.fr, akiyks@gmail.com, nborisov@suse.com On Tue, 20 Feb 2018, Paul E. McKenney wrote: > From: Alan Stern > > This commit adds a litmus test in which P0() and P1() form a lock-based S > litmus test, with the addition of P2(), which observes P0()'s and P1()'s Why do you call this an "S" litmus test? Isn't ISA2 a better description? > accesses with a full memory barrier but without the lock. This litmus > test asks whether writes carried out by two different processes under the > same lock will be seen in order by a third process not holding that lock. > The answer to this question is "yes" for all architectures supporting > the Linux kernel, but is "no" according to the current version of LKMM. > > A patch to LKMM is under development. > > Signed-off-by: Alan Stern > Signed-off-by: Paul E. McKenney > --- > .../ISA2+pooncelock+pooncelock+pombonce.litmus | 41 ++++++++++++++++++++++ > 1 file changed, 41 insertions(+) > create mode 100644 tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus Aren't these tests supposed to be described in litmus-tests/README? > diff --git a/tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus b/tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus > new file mode 100644 > index 000000000000..7a39a0aaa976 > --- /dev/null > +++ b/tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus > @@ -0,0 +1,41 @@ > +C ISA2+pooncelock+pooncelock+pombonce.litmus > + > +(* > + * Result: Sometimes > + * > + * This test shows that the ordering provided by a lock-protected S > + * litmus test (P0() and P1()) are not visible to external process P2(). > + * This is likely to change soon. That last line may be premature. We haven't reached any consensus on how RISC-V will handle this. If RISC-V allows the test then the memory model can't forbid it. Alan > + *) > + > +{} > + > +P0(int *x, int *y, spinlock_t *mylock) > +{ > + spin_lock(mylock); > + WRITE_ONCE(*x, 1); > + WRITE_ONCE(*y, 1); > + spin_unlock(mylock); > +} > + > +P1(int *y, int *z, spinlock_t *mylock) > +{ > + int r0; > + > + spin_lock(mylock); > + r0 = READ_ONCE(*y); > + WRITE_ONCE(*z, 1); > + spin_unlock(mylock); > +} > + > +P2(int *x, int *z) > +{ > + int r1; > + int r2; > + > + r2 = READ_ONCE(*z); > + smp_mb(); > + r1 = READ_ONCE(*x); > +} > + > +exists (1:r0=1 /\ 2:r2=1 /\ 2:r1=0) >