tools/memory-model/litmus-tests/IRIW+fencembonceonces+OnceOnce.litmus

   1 C 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
  15 P0(int *x)
  16 {
  17         WRITE_ONCE(*x, 1);
  18 }
  19
  20 P1(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
  30 P2(int *y)
  31 {
  32         WRITE_ONCE(*y, 1);
  33 }
  34
  35 P3(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
  45 exists (1:r0=1 /\ 1:r1=0 /\ 3:r0=1 /\ 3:r1=0)