xref: /linux/Documentation/litmus-tests/locking/RM-broken.litmus (revision ae22a94997b8a03dcb3c922857c203246711f9d4) 
1C RM-broken
2
3(*
4 * Result: DEADLOCK
5 *
6 * This litmus test demonstrates that the old "roach motel" approach
7 * to locking, where code can be freely moved into critical sections,
8 * cannot be used in the Linux kernel.
9 *)
10
11{
12	int x;
13	atomic_t y;
14}
15
16P0(int *x, atomic_t *y, spinlock_t *lck)
17{
18	int r2;
19
20	spin_lock(lck);
21	r2 = atomic_inc_return(y);
22	WRITE_ONCE(*x, 1);
23	spin_unlock(lck);
24}
25
26P1(int *x, atomic_t *y, spinlock_t *lck)
27{
28	int r0;
29	int r1;
30	int r2;
31
32	spin_lock(lck);
33	r0 = READ_ONCE(*x);
34	r1 = READ_ONCE(*x);
35	r2 = atomic_inc_return(y);
36	spin_unlock(lck);
37}
38
39locations [x;0:r2;1:r0;1:r1;1:r2]
40filter (1:r0=0 /\ 1:r1=1)
41exists (1:r2=1)
42