From: "Paul E. McKenney" <paulmck@linux.ibm.com>
To: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
mingo@kernel.org
Cc: stern@rowland.harvard.edu, 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,
Andrea Parri <andrea.parri@amarulasolutions.com>,
"Paul E. McKenney" <paulmck@linux.ibm.com>,
Daniel Lustig <dlustig@nvidia.com>
Subject: [PATCH memory-model 1/3] tools/memory-model: Model smp_mb__after_unlock_lock()
Date: Mon, 3 Dec 2018 15:04:49 -0800 [thread overview]
Message-ID: <20181203230451.28921-1-paulmck@linux.ibm.com> (raw)
In-Reply-To: <20181203230411.GA27476@linux.ibm.com>
From: Andrea Parri <andrea.parri@amarulasolutions.com>
>From the header comment for smp_mb__after_unlock_lock():
"Place this after a lock-acquisition primitive to guarantee that
an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies
if the UNLOCK and LOCK are executed by the same CPU or if the
UNLOCK and LOCK operate on the same lock variable."
This formalizes the above guarantee by defining (new) mb-links according
to the law:
([M] ; po ; [UL] ; (co | po) ; [LKW] ;
fencerel(After-unlock-lock) ; [M])
where the component ([UL] ; co ; [LKW]) identifies "UNLOCK+LOCK pairs on
the same lock variable" and the component ([UL] ; po ; [LKW]) identifies
"UNLOCK+LOCK pairs executed by the same CPU".
In particular, the LKMM forbids the following two behaviors (the second
litmus test below is based on
Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.html
c.f., Section "Tree RCU Grace Period Memory Ordering Building Blocks"):
C after-unlock-lock-same-cpu
(*
* Result: Never
*)
{}
P0(spinlock_t *s, spinlock_t *t, int *x, int *y)
{
int r0;
spin_lock(s);
WRITE_ONCE(*x, 1);
spin_unlock(s);
spin_lock(t);
smp_mb__after_unlock_lock();
r0 = READ_ONCE(*y);
spin_unlock(t);
}
P1(int *x, int *y)
{
int r0;
WRITE_ONCE(*y, 1);
smp_mb();
r0 = READ_ONCE(*x);
}
exists (0:r0=0 /\ 1:r0=0)
C after-unlock-lock-same-lock-variable
(*
* Result: Never
*)
{}
P0(spinlock_t *s, int *x, int *y)
{
int r0;
spin_lock(s);
WRITE_ONCE(*x, 1);
r0 = READ_ONCE(*y);
spin_unlock(s);
}
P1(spinlock_t *s, int *y, int *z)
{
int r0;
spin_lock(s);
smp_mb__after_unlock_lock();
WRITE_ONCE(*y, 1);
r0 = READ_ONCE(*z);
spin_unlock(s);
}
P2(int *z, int *x)
{
int r0;
WRITE_ONCE(*z, 1);
smp_mb();
r0 = READ_ONCE(*x);
}
exists (0:r0=0 /\ 1:r0=0 /\ 2:r0=0)
Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Luc Maranget <luc.maranget@inria.fr>
Cc: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: Akira Yokosawa <akiyks@gmail.com>
Cc: Daniel Lustig <dlustig@nvidia.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
---
tools/memory-model/linux-kernel.bell | 3 ++-
tools/memory-model/linux-kernel.cat | 4 +++-
tools/memory-model/linux-kernel.def | 1 +
3 files changed, 6 insertions(+), 2 deletions(-)
diff --git a/tools/memory-model/linux-kernel.bell b/tools/memory-model/linux-kernel.bell
index b84fb2f67109..796513362c05 100644
--- a/tools/memory-model/linux-kernel.bell
+++ b/tools/memory-model/linux-kernel.bell
@@ -29,7 +29,8 @@ enum Barriers = 'wmb (*smp_wmb*) ||
'sync-rcu (*synchronize_rcu*) ||
'before-atomic (*smp_mb__before_atomic*) ||
'after-atomic (*smp_mb__after_atomic*) ||
- 'after-spinlock (*smp_mb__after_spinlock*)
+ 'after-spinlock (*smp_mb__after_spinlock*) ||
+ 'after-unlock-lock (*smp_mb__after_unlock_lock*)
instructions F[Barriers]
(* Compute matching pairs of nested Rcu-lock and Rcu-unlock *)
diff --git a/tools/memory-model/linux-kernel.cat b/tools/memory-model/linux-kernel.cat
index 882fc33274ac..8f23c74a96fd 100644
--- a/tools/memory-model/linux-kernel.cat
+++ b/tools/memory-model/linux-kernel.cat
@@ -30,7 +30,9 @@ let wmb = [W] ; fencerel(Wmb) ; [W]
let mb = ([M] ; fencerel(Mb) ; [M]) |
([M] ; fencerel(Before-atomic) ; [RMW] ; po? ; [M]) |
([M] ; po? ; [RMW] ; fencerel(After-atomic) ; [M]) |
- ([M] ; po? ; [LKW] ; fencerel(After-spinlock) ; [M])
+ ([M] ; po? ; [LKW] ; fencerel(After-spinlock) ; [M]) |
+ ([M] ; po ; [UL] ; (co | po) ; [LKW] ;
+ fencerel(After-unlock-lock) ; [M])
let gp = po ; [Sync-rcu] ; po?
let strong-fence = mb | gp
diff --git a/tools/memory-model/linux-kernel.def b/tools/memory-model/linux-kernel.def
index 6fa3eb28d40b..b27911cc087d 100644
--- a/tools/memory-model/linux-kernel.def
+++ b/tools/memory-model/linux-kernel.def
@@ -23,6 +23,7 @@ smp_wmb() { __fence{wmb}; }
smp_mb__before_atomic() { __fence{before-atomic}; }
smp_mb__after_atomic() { __fence{after-atomic}; }
smp_mb__after_spinlock() { __fence{after-spinlock}; }
+smp_mb__after_unlock_lock() { __fence{after-unlock-lock}; }
// Exchange
xchg(X,V) __xchg{mb}(X,V)
--
2.17.1
next prev parent reply other threads:[~2018-12-03 23:08 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-03 23:04 [PATCH memory-model 0/3] Updates to the formal memory model Paul E. McKenney
2018-12-03 23:04 ` Paul E. McKenney [this message]
2018-12-04 6:33 ` [tip:locking/core] tools/memory-model: Model smp_mb__after_unlock_lock() tip-bot for Andrea Parri
2019-01-21 11:23 ` tip-bot for Andrea Parri
2018-12-03 23:04 ` [PATCH memory-model 2/3] EXP tools/memory-model: Add scripts to check github litmus tests Paul E. McKenney
2018-12-04 6:34 ` [tip:locking/core] " tip-bot for Paul E. McKenney
2019-01-21 11:24 ` tip-bot for Paul E. McKenney
2018-12-03 23:04 ` [PATCH memory-model 3/3] EXP tools/memory-model: Make scripts take "-j" abbreviation for "--jobs" Paul E. McKenney
2018-12-04 6:35 ` [tip:locking/core] " tip-bot for Paul E. McKenney
2019-01-21 11:25 ` tip-bot for Paul E. McKenney
2018-12-03 23:28 ` [PATCH memory-model 0/3] Updates to the formal memory model Akira Yokosawa
2018-12-03 23:51 ` Paul E. McKenney
2018-12-04 15:40 ` Akira Yokosawa
2018-12-04 16:36 ` Paul E. McKenney
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