linux/tools/memory-model/litmus-tests/ISA2+pooncelock+pooncelock+pombonce.litmus
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   1C ISA2+pooncelock+pooncelock+pombonce
   2
   3(*
   4 * Result: Never
   5 *
   6 * This test shows that write-write ordering provided by locks
   7 * (in P0() and P1()) is visible to external process P2().
   8 *)
   9
  10{}
  11
  12P0(int *x, int *y, spinlock_t *mylock)
  13{
  14        spin_lock(mylock);
  15        WRITE_ONCE(*x, 1);
  16        WRITE_ONCE(*y, 1);
  17        spin_unlock(mylock);
  18}
  19
  20P1(int *y, int *z, spinlock_t *mylock)
  21{
  22        int r0;
  23
  24        spin_lock(mylock);
  25        r0 = READ_ONCE(*y);
  26        WRITE_ONCE(*z, 1);
  27        spin_unlock(mylock);
  28}
  29
  30P2(int *x, int *z)
  31{
  32        int r1;
  33        int r2;
  34
  35        r2 = READ_ONCE(*z);
  36        smp_mb();
  37        r1 = READ_ONCE(*x);
  38}
  39
  40exists (1:r0=1 /\ 2:r2=1 /\ 2:r1=0)
  41