On Fri, 16 Feb 2018, Akira Yokosawa wrote:
> So, I attempted to rebase the patch to current (somewhat old) master of
> https://github.com/aparri/memory-model. Why? Because the lkmm branch
> in Paul's -rcu tree doesn't have linux-kernel-hardware.cat.
>
> However, after this change, Z6.0+pooncelock+pooncelock+pombonce still
> has the result "Sometimes". I must have done something wrong in the
> conflict resolution.
>
> Note: I have almost no idea what this patch is doing. I'm just hoping
> to give a starting point of a discussion.
Yes, that litmus test gives "Sometimes" both with and without the
patch. But consider instead this slightly changed version of that
test, in which P2 reads Z instead of writing it:
C Z6.0-variant
{}
P0(int *x, int *y, spinlock_t *mylock)
{
spin_lock(mylock);
WRITE_ONCE(*x, 1);
WRITE_ONCE(*y, 1);
spin_unlock(mylock);
}
P1(int *y, int *z, spinlock_t *mylock)
{
int r0;
spin_lock(mylock);
r0 = READ_ONCE(*y);
WRITE_ONCE(*z, 1);
spin_unlock(mylock);
}
P2(int *x, int *z)
{
int r1;
int r2;
r2 = READ_ONCE(*z);
smp_mb();
r1 = READ_ONCE(*x);
}
exists (1:r0=1 /\ 2:r2=1 /\ 2:r1=0)
Without the patch, this test gives "Sometimes"; with the patch it gives
"Never". That is what I thought Paul was talking about originally.
Sorry if my misunderstanding caused too much confusion for other
people.
Alan
