linux-kernel - Re: [PATCHv2 0/4] tools/memory-model: Define more of LKMM in tools/memory-model

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Date: Mon, 10 Jun 2024 10:38:11 +0200
From: Hernan Ponce de Leon <hernan.poncedeleon@...weicloud.com>
To: Alan Stern <stern@...land.harvard.edu>,
 Jonas Oberhauser <jonas.oberhauser@...weicloud.com>
Cc: paulmck@...nel.org, parri.andrea@...il.com, will@...nel.org,
 peterz@...radead.org, boqun.feng@...il.com, npiggin@...il.com,
 dhowells@...hat.com, j.alglave@....ac.uk, luc.maranget@...ia.fr,
 akiyks@...il.com, dlustig@...dia.com, joel@...lfernandes.org,
 urezki@...il.com, quic_neeraju@...cinc.com, frederic@...nel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 0/4] tools/memory-model: Define more of LKMM in
 tools/memory-model

On 6/8/2024 3:00 AM, Alan Stern wrote:
> On Wed, Jun 05, 2024 at 09:58:42PM +0200, Jonas Oberhauser wrote:
>>
>>
>> Am 6/4/2024 um 7:56 PM schrieb Alan Stern:
>>> Just to clarify: Your first step encompasses patches 1 - 3, and the
>>> second step is patch 4.  The first three patches can be applied now, but
>>> the last one needs to wait until herd7 has been updated.  Is this all
>>> correct?
>>
>> Exactly.
> 
> With regard to patch 4, how much thought have you and Hernan given to
> backward compatibility?  Once herd7 is changed, old memory model files
> will no longer work correctly.
> 

Honestly, I did not think much about this (at least until Akira 
mentioned in my PR). My hope was that changes to the model could be 
back-ported to previous kernel versions. However that would not work for 
existing out-of-tree files.

My question is: is compatibility with out-of-tree files really a 
requirement? I would argue that if people are using outdated models, 
they may get wrong results anyway. This is because some of the changes 
done to lkmm during the last few years change the expected result for 
some litmus tests.

Hernan