| C DCL-broken | |
| (* | |
| * Result: Sometimes | |
| * | |
| * This litmus test demonstrates more than just locking is required to | |
| * correctly implement double-checked locking. | |
| *) | |
| { | |
| int flag; | |
| int data; | |
| } | |
| P0(int *flag, int *data, spinlock_t *lck) | |
| { | |
| int r0; | |
| int r1; | |
| int r2; | |
| r0 = READ_ONCE(*flag); | |
| if (r0 == 0) { | |
| spin_lock(lck); | |
| r1 = READ_ONCE(*flag); | |
| if (r1 == 0) { | |
| WRITE_ONCE(*data, 1); | |
| WRITE_ONCE(*flag, 1); | |
| } | |
| spin_unlock(lck); | |
| } | |
| r2 = READ_ONCE(*data); | |
| } | |
| P1(int *flag, int *data, spinlock_t *lck) | |
| { | |
| int r0; | |
| int r1; | |
| int r2; | |
| r0 = READ_ONCE(*flag); | |
| if (r0 == 0) { | |
| spin_lock(lck); | |
| r1 = READ_ONCE(*flag); | |
| if (r1 == 0) { | |
| WRITE_ONCE(*data, 1); | |
| WRITE_ONCE(*flag, 1); | |
| } | |
| spin_unlock(lck); | |
| } | |
| r2 = READ_ONCE(*data); | |
| } | |
| locations [flag;data;0:r0;0:r1;1:r0;1:r1] | |
| exists (0:r2=0 \/ 1:r2=0) |