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C MP+porevlocks {} P0(int *x, int *y, spinlock_t *mylock) { int r0; int r1; r0 = READ_ONCE(*y); spin_lock(mylock); r1 = READ_ONCE(*x); spin_unlock(mylock); } P1(int *x, int *y, spinlock_t *mylock) { spin_lock(mylock); WRITE_ONCE(*x, 1); spin_unlock(mylock); WRITE_ONCE(*y, 1); } exists (0:r0=1 /\ 0:r1=0)