tools/memory-model: Add model support for spin_is_locked()

This commit first adds a trivial macro for spin_is_locked() to
linux-kernel.def.

It also adds cat code for enumerating all possible matches of lock
write events (set LKW) with islocked events returning true (set RL,
for Read from Lock), and unlock write events (set UL) with islocked
events returning false (set RU, for Read from Unlock).  Note that this
intentionally does not model uniprocessor kernels (CONFIG_SMP=n) built
with CONFIG_DEBUG_SPINLOCK=n, in which spin_is_locked() unconditionally
returns zero.

It also adds a pair of litmus tests demonstrating the minimal ordering
provided by spin_is_locked() in conjunction with spin_lock().  Will Deacon
noted that this minimal ordering happens on ARMv8:
https://lkml.kernel.org/r/20180226162426.GB17158@arm.com

Notice that herd7 installations strictly older than version 7.49
do not handle the new constructs.

Signed-off-by: Luc Maranget <luc.maranget@inria.fr>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Alan Stern <stern@rowland.harvard.edu>
Cc: Akira Yokosawa <akiyks@gmail.com>
Cc: Andrea Parri <parri.andrea@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luc Maranget <Luc.Maranget@inria.fr>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arch@vger.kernel.org
Link: http://lkml.kernel.org/r/1526340837-12222-10-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

3 files changed, 79 insertions, 0 deletions

diff --git a/tools/memory-model/litmus-tests/MP+polockmbonce+poacquiresilsil.litmus b/tools/memory-model/litmus-tests/MP+polockmbonce+poacquiresilsil.litmus
new file mode 100644
index 000000000000..50f4d62bbf0e
--- /dev/null
+++ b/tools/memory-model/litmus-tests/MP+polockmbonce+poacquiresilsil.litmus
@@ -0,0 +1,35 @@
+C MP+polockmbonce+poacquiresilsil
+
+(*
+ * Result: Never
+ *
+ * Do spinlocks combined with smp_mb__after_spinlock() provide order
+ * to outside observers using spin_is_locked() to sense the lock-held
+ * state, ordered by acquire?  Note that when the first spin_is_locked()
+ * returns false and the second true, we know that the smp_load_acquire()
+ * executed before the lock was acquired (loosely speaking).
+ *)
+
+{
+}
+
+P0(spinlock_t *lo, int *x)
+{
+	spin_lock(lo);
+	smp_mb__after_spinlock();
+	WRITE_ONCE(*x, 1);
+	spin_unlock(lo);
+}
+
+P1(spinlock_t *lo, int *x)
+{
+	int r1;
+	int r2;
+	int r3;
+
+	r1 = smp_load_acquire(x);
+	r2 = spin_is_locked(lo);
+	r3 = spin_is_locked(lo);
+}
+
+exists (1:r1=1 /\ 1:r2=0 /\ 1:r3=1)
diff --git a/tools/memory-model/litmus-tests/MP+polockonce+poacquiresilsil.litmus b/tools/memory-model/litmus-tests/MP+polockonce+poacquiresilsil.litmus
new file mode 100644
index 000000000000..abf81e7a0895
--- /dev/null
+++ b/tools/memory-model/litmus-tests/MP+polockonce+poacquiresilsil.litmus
@@ -0,0 +1,34 @@
+C MP+polockonce+poacquiresilsil
+
+(*
+ * Result: Sometimes
+ *
+ * Do spinlocks provide order to outside observers using spin_is_locked()
+ * to sense the lock-held state, ordered by acquire?  Note that when the
+ * first spin_is_locked() returns false and the second true, we know that
+ * the smp_load_acquire() executed before the lock was acquired (loosely
+ * speaking).
+ *)
+
+{
+}
+
+P0(spinlock_t *lo, int *x)
+{
+	spin_lock(lo);
+	WRITE_ONCE(*x, 1);
+	spin_unlock(lo);
+}
+
+P1(spinlock_t *lo, int *x)
+{
+	int r1;
+	int r2;
+	int r3;
+
+	r1 = smp_load_acquire(x);
+	r2 = spin_is_locked(lo);
+	r3 = spin_is_locked(lo);
+}
+
+exists (1:r1=1 /\ 1:r2=0 /\ 1:r3=1)
diff --git a/tools/memory-model/litmus-tests/README b/tools/memory-model/litmus-tests/README
index 04096fb8b8d9..6919909bbd0f 100644
--- a/tools/memory-model/litmus-tests/README
+++ b/tools/memory-model/litmus-tests/README
@@ -63,6 +63,16 @@ LB+poonceonces.litmus
 MP+onceassign+derefonce.litmus
 	As below, but with rcu_assign_pointer() and an rcu_dereference().
 
+MP+polockmbonce+poacquiresilsil.litmus
+	Protect the access with a lock and an smp_mb__after_spinlock()
+	in one process, and use an acquire load followed by a pair of
+	spin_is_locked() calls in the other process.
+
+MP+polockonce+poacquiresilsil.litmus
+	Protect the access with a lock in one process, and use an
+	acquire load followed by a pair of spin_is_locked() calls
+	in the other process.
+
 MP+polocks.litmus
 	As below, but with the second access of the writer process
 	and the first access of reader process protected by a lock.