C SB+locked-diff+mb {} P0(int* y,spinlock_t* lock_y,int* x,spinlock_t* lock_x) { spin_lock(lock_x); WRITE_ONCE(*x,1); spin_unlock(lock_x); spin_lock(lock_y); int r0 = READ_ONCE(*y); spin_unlock(lock_y); } P1(int* y,int* x) { WRITE_ONCE(*y,1); smp_mb(); int r0 = READ_ONCE(*x); } Observed 1:r0=0; 0:r0=0;