Messages in this thread | | | Date | Tue, 24 Jan 2023 11:03:49 -0500 | From | Alan Stern <> | Subject | Re: [PATCH] tools/memory-model: Make ppo a subrelation of po |
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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 superseded by pb as well, but it seems odd not to have it in hb.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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