0001 C MP+polocks
0002
0003 (*
0004 * Result: Never
0005 *
0006 * This litmus test demonstrates how lock acquisitions and releases can
0007 * stand in for smp_load_acquire() and smp_store_release(), respectively.
0008 * In other words, when holding a given lock (or indeed after releasing a
0009 * given lock), a CPU is not only guaranteed to see the accesses that other
0010 * CPUs made while previously holding that lock, it is also guaranteed
0011 * to see all prior accesses by those other CPUs.
0012 *)
0013
0014 {}
0015
0016 P0(int *buf, int *flag, spinlock_t *mylock) // Producer
0017 {
0018 WRITE_ONCE(*buf, 1);
0019 spin_lock(mylock);
0020 WRITE_ONCE(*flag, 1);
0021 spin_unlock(mylock);
0022 }
0023
0024 P1(int *buf, int *flag, spinlock_t *mylock) // Consumer
0025 {
0026 int r0;
0027 int r1;
0028
0029 spin_lock(mylock);
0030 r0 = READ_ONCE(*flag);
0031 spin_unlock(mylock);
0032 r1 = READ_ONCE(*buf);
0033 }
0034
0035 exists (1:r0=1 /\ 1:r1=0) (* Bad outcome. *)
