linux/tools/memory-model/litmus-tests/IRIW+fencembonceonces+OnceOnce.litmus
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   1C IRIW+fencembonceonces+OnceOnce
   2
   3(*
   4 * Result: Never
   5 *
   6 * Test of independent reads from independent writes with smp_mb()
   7 * between each pairs of reads.  In other words, is smp_mb() sufficient to
   8 * cause two different reading processes to agree on the order of a pair
   9 * of writes, where each write is to a different variable by a different
  10 * process?  This litmus test exercises LKMM's "propagation" rule.
  11 *)
  12
  13{}
  14
  15P0(int *x)
  16{
  17        WRITE_ONCE(*x, 1);
  18}
  19
  20P1(int *x, int *y)
  21{
  22        int r0;
  23        int r1;
  24
  25        r0 = READ_ONCE(*x);
  26        smp_mb();
  27        r1 = READ_ONCE(*y);
  28}
  29
  30P2(int *y)
  31{
  32        WRITE_ONCE(*y, 1);
  33}
  34
  35P3(int *x, int *y)
  36{
  37        int r0;
  38        int r1;
  39
  40        r0 = READ_ONCE(*y);
  41        smp_mb();
  42        r1 = READ_ONCE(*x);
  43}
  44
  45exists (1:r0=1 /\ 1:r1=0 /\ 3:r0=1 /\ 3:r1=0)
  46