linux/tools/memory-model/litmus-tests/MP+polocks.litmus
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   1C MP+polocks
   2
   3(*
   4 * Result: Never
   5 *
   6 * This litmus test demonstrates how lock acquisitions and releases can
   7 * stand in for smp_load_acquire() and smp_store_release(), respectively.
   8 * In other words, when holding a given lock (or indeed after releasing a
   9 * given lock), a CPU is not only guaranteed to see the accesses that other
  10 * CPUs made while previously holding that lock, it is also guaranteed
  11 * to see all prior accesses by those other CPUs.
  12 *)
  13
  14{}
  15
  16P0(int *buf, int *flag, spinlock_t *mylock) // Producer
  17{
  18        WRITE_ONCE(*buf, 1);
  19        spin_lock(mylock);
  20        WRITE_ONCE(*flag, 1);
  21        spin_unlock(mylock);
  22}
  23
  24P1(int *buf, int *flag, spinlock_t *mylock) // Consumer
  25{
  26        int r0;
  27        int r1;
  28
  29        spin_lock(mylock);
  30        r0 = READ_ONCE(*flag);
  31        spin_unlock(mylock);
  32        r1 = READ_ONCE(*buf);
  33}
  34
  35exists (1:r0=1 /\ 1:r1=0) (* Bad outcome. *)
  36