linux/tools/memory-model/litmus-tests/MP+polockonce+poacquiresilsil.litmus
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   1C MP+polockonce+poacquiresilsil
   2
   3(*
   4 * Result: Sometimes
   5 *
   6 * Do spinlocks provide order to outside observers using spin_is_locked()
   7 * to sense the lock-held state, ordered by acquire?  Note that when the
   8 * first spin_is_locked() returns false and the second true, we know that
   9 * the smp_load_acquire() executed before the lock was acquired (loosely
  10 * speaking).
  11 *)
  12
  13{}
  14
  15P0(spinlock_t *lo, int *x) // Producer
  16{
  17        spin_lock(lo);
  18        WRITE_ONCE(*x, 1);
  19        spin_unlock(lo);
  20}
  21
  22P1(spinlock_t *lo, int *x) // Consumer
  23{
  24        int r1;
  25        int r2;
  26        int r3;
  27
  28        r1 = smp_load_acquire(x);
  29        r2 = spin_is_locked(lo);
  30        r3 = spin_is_locked(lo);
  31}
  32
  33exists (1:r1=1 /\ 1:r2=0 /\ 1:r3=1) (* Bad outcome. *)
  34