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    Subject[PATCH RFC tools/lkmm 10/12] tools/memory-model: Add a S lock-based external-view litmus test
    Date
    From: Alan Stern <stern@rowland.harvard.edu>

    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>
    ---
    .../ISA2+pooncelock+pooncelock+pombonce.litmus | 41 ++++++++++++++++++++++
    1 file changed, 41 insertions(+)
    create mode 100644 tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus

    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.
    + *)
    +
    +{}
    +
    +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)
    --
    2.5.2
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