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SubjectRe: [PATCH] tools/memory-model: Make ppo a subrelation of po
On Tue, Jan 24, 2023 at 01:54:14PM +0100, Jonas Oberhauser wrote:
>
>
> On 1/23/2023 9:25 PM, Alan Stern wrote:
> > On Mon, Jan 23, 2023 at 07:25:48PM +0100, Jonas Oberhauser wrote:
> > > Alright, after some synchronization in the other parts of this thread I am
> > > beginning to prepare the next iteration of the patch.
> > >
> > > On 1/19/2023 4:13 AM, Alan Stern wrote:
> > > > On Wed, Jan 18, 2023 at 10:38:11PM +0100, Jonas Oberhauser wrote:
> > > > > On 1/18/2023 8:52 PM, Alan Stern wrote:
> > > > > > On Tue, Jan 17, 2023 at 08:31:59PM +0100, Jonas Oberhauser wrote:
> > > > > > > - ([M] ; po? ; [LKW] ; fencerel(After-spinlock) ; [M]) |
> > > > > > > - ([M] ; po ; [UL] ; (co | po) ; [LKW] ;
> > > > > > > - fencerel(After-unlock-lock) ; [M])
> > > > > > > + ([M] ; po? ; [LKW] ; fencerel(After-spinlock) ; [M])
> > > > > > Shouldn't the po case of (co | po) remain intact here?
> > > > > You can leave it here, but it is already covered by two other parts: the
> > > > > ordering given through ppo/hb is covered by the po-unlock-lock-po & int in
> > > > > ppo, and the ordering given through pb is covered by its inclusion in
> > > > > strong-order.
> > > > What about the ordering given through
> > > > A-cumul(strong-fence)/cumul-fence/prop/hb? I suppose that might be
> > > > superseded by pb as well, but it seems odd not to have it in hb.
> > > How should we resolve this?
> > > My current favorite (compromise :D) solution would be to
> > > 1. still eliminate both po and co cases from first definition of
> > > strong-fence which is used in ppo,
> > > 2. define a relation equal to the strong-order in this patch (with po|rf)
> > Wouldn't it need to have po|co? Consider:
> >
> > Wx=1 Rx=1 Ry=1 Rz=1
> > lock(s) lock(s) lock(s)
> > unlock(s) unlock(s) unlock(s)
> > Wy=1 Wz=1 smp_mb__after_unlock_lock
> > Rx=0
> >
> > With the co term this is forbidden. With only the rf term it is
> > allowed, because po-unlock-lock-po isn't A-cumulative.
> No, but unlock() is ( https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/tree/tools/memory-model/lock.cat?h=dev.2023.01.19a#n67
> ). So you get

So it is. I had forgotten about that. The model is getting too
complicated to fit entirely in my mind...

>   Rx=0 ->overwrite Wx=1  ->rfe Rx1 ->po-rel  T1:unlock(s) ->rfe T2:lock(s)
> ->po-unlock-lock-po;after ... fence;po Rx=0
> which is
>   Rx=0          ->prop ;                           po-unlock-lock-po;after
> ... fence;po Rx=0
>
> Are you ok going forward like this then?

I guess so, provided we mention somewhere in the code or documentation
that this relation extends beyond a single rf.

Alan

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