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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)
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