tools/memory-model: Add a S lock-based external-view litmus test

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
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 <stern@rowland.harvard.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: akiyks@gmail.com
Cc: boqun.feng@gmail.com
Cc: dhowells@redhat.com
Cc: j.alglave@ucl.ac.uk
Cc: linux-arch@vger.kernel.org
Cc: luc.maranget@inria.fr
Cc: nborisov@suse.com
Cc: npiggin@gmail.com
Cc: parri.andrea@gmail.com
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1519169112-20593-10-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

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 (file)
index 0000000..7a39a0a
--- /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.
+ *)
+
+{}
+
+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)