Messages in this thread | | | Date | Thu, 15 Feb 2018 12:51:56 -0500 (EST) | From | Alan Stern <> | Subject | Re: Trial of conflict resolution of Alan's patch |
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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
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