linux/tools/memory-model/litmus-tests/ISA2+pooncerelease+poacquirerelease+poacquireonce.litmus
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   1C ISA2+pooncerelease+poacquirerelease+poacquireonce
   2
   3(*
   4 * Result: Never
   5 *
   6 * This litmus test demonstrates that a release-acquire chain suffices
   7 * to order P0()'s initial write against P2()'s final read.  The reason
   8 * that the release-acquire chain suffices is because in all but one
   9 * case (P2() to P0()), each process reads from the preceding process's
  10 * write.  In memory-model-speak, there is only one non-reads-from
  11 * (AKA non-rf) link, so release-acquire is all that is needed.
  12 *)
  13
  14{}
  15
  16P0(int *x, int *y)
  17{
  18        WRITE_ONCE(*x, 1);
  19        smp_store_release(y, 1);
  20}
  21
  22P1(int *y, int *z)
  23{
  24        int r0;
  25
  26        r0 = smp_load_acquire(y);
  27        smp_store_release(z, 1);
  28}
  29
  30P2(int *x, int *z)
  31{
  32        int r0;
  33        int r1;
  34
  35        r0 = smp_load_acquire(z);
  36        r1 = READ_ONCE(*x);
  37}
  38
  39exists (1:r0=1 /\ 2:r0=1 /\ 2:r1=0)
  40