C MP-unlock-lock {} P0(int *x, int *y, spinlock_t *s) { spin_lock(s); WRITE_ONCE(*x, 1); spin_unlock(s); spin_lock(s); WRITE_ONCE(*y, 1); spin_unlock(s); } P1(int *x, int *y) { int r0; int r1; r0 = READ_ONCE(*y); smp_rmb(); r1 = READ_ONCE(*x); } Observed 1:r1=0; 1:r0=1;