linux-kernel - Re: Prototype patch for Linux-kernel memory model

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Message-Id: <20171114171505.GS3624@linux.vnet.ibm.com>
Date:   Tue, 14 Nov 2017 09:15:05 -0800
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Peter Zijlstra <peterz@...radead.org>, parri.andrea@...il.com,
        will.deacon@....com, boqun.feng@...il.com, npiggin@...il.com,
        dhowells@...hat.com, j.alglave@....ac.uk, luc.maranget@...ia.fr,
        linux-kernel@...r.kernel.org, elena.reshetova@...el.com
Subject: Re: Prototype patch for Linux-kernel memory model

On Tue, Nov 14, 2017 at 10:19:21AM -0500, Alan Stern wrote:
> On Tue, 14 Nov 2017, Peter Zijlstra wrote:
> 
> > On Mon, Nov 13, 2017 at 10:40:31AM -0800, Paul E. McKenney wrote:
> > > commit 82a1431549b4eae531e83298fd72cd0acea08540
> > > Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > > Date:   Mon Nov 13 10:30:07 2017 -0800
> > > 
> > >     tools: Automate memory-barriers.txt; provide Linux-kernel memory model
> > >     
> > >     There is some reason to believe that Documentation/memory-barriers.txt
> > >     could use some help, and a major purpose of this patch is to provide
> > >     that help in the form of a design-time tool that can produce all valid
> > >     executions of a small fragment of concurrent Linux-kernel code, which is
> > >     called a "litmus test".  This tool's functionality is roughly similar to
> > >     a full state-space search.  Please note that this is a design-time tool,
> > >     not useful for regression testing.  However, we hope that the underlying
> > >     Linux-kernel memory model will be incorporated into other tools capable
> > >     of analyzing large bodies of code for regression-testing purposes.
> > >     
> > >     The main tool is herd7, together with the linux-kernel.bell,
> > >     linux-kernel.cat, linux-kernel.cfg, linux-kernel.def, and lock.cat files
> > >     added by this patch.  The herd7 executable takes the other files as input,
> > >     and all of these files collectively define the Linux-kernel memory memory
> > >     model.  A brief description of each of these other files is provided
> > >     in the README file.  Although this tool does have its limitations,
> > >     which are documented in the README file, it does improve on the version
> > >     reported on in the LWN series (https://lwn.net/Articles/718628/ and
> > >     https://lwn.net/Articles/720550/) by supporting locking and arithmetic,
> > >     including a much wider variety of read-modify-write atomic operations.
> > >     Please note that herd7 is not part of this submission, but is freely
> > >     available from http://diy.inria.fr/sources/index.html (and via "git"
> > >     at https://github.com/herd/herdtools7).
> > >     
> > >     A second tool is klitmus7, which converts litmus tests to loadable
> > >     kernel modules for direct testing.  As with herd7, the klitmus7
> > >     code is freely available from http://diy.inria.fr/sources/index.html
> > >     (and via "git" at https://github.com/herd/herdtools7).
> > >     
> > >     Of course, litmus tests are not always the best way to fully understand a
> > >     memory model, so this patch also includes Documentation/explanation.txt,
> > >     which describes the memory model in detail.  In addition,
> > >     Documentation/recipes.txt provides example known-good and known-bad use
> > >     cases for those who prefer working by example.
> > >     
> > >     This patch also includes a few sample litmus tests, and a great many
> > >     more litmus tests are available at https://github.com/paulmckrcu/litmus.
> > >     
> > >     Signed-off-by: Alan Stern <stern@...land.harvard.edu>
> > >     Signed-off-by: Andrea Parri <parri.andrea@...il.com>
> > >     Signed-off-by: Will Deacon <will.deacon@....com>
> > >     Signed-off-by: Peter Zijlstra <peterz@...radead.org>
> > >     Signed-off-by: Boqun Feng <boqun.feng@...il.com>
> > >     Signed-off-by: Nicholas Piggin <npiggin@...il.com>
> > >     Signed-off-by: David Howells <dhowells@...hat.com>
> > >     Signed-off-by: Jade Alglave <j.alglave@....ac.uk>
> > >     Signed-off-by: Luc Maranget <luc.maranget@...ia.fr>
> > >     Signed-off-by: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> > >     Cc: <linux-arch@...r.kernel.org>
> > 
> > So I think that SoB chains like that are utter crap. I think you meant
> > to have all but the one from you be an Ack or similar.
> 
> That's right.  Git doesn't understand the concept of multiple
> authorship.  Accepted practice is to have one Signed-off-by line and a
> bunch of Acked-by or Reviewed-by tags.
> 
> When there's a chain of Signed-off-by tags, it means the first person 
> was the author, who submitted it to the second person's tree, and it 
> went from there to the third person's tree, etc. (which would imply 
> multiple levels of maintainers and submaintainers).

I could add a paragraph just before the Signed-off-by/Acked-by/etc.
block describing the roles and contributions, convert the people who
were directly involved to Reviewed-by and everyone else to Acked-by
(unless they explicitly provided a Reviewed-by).

Would that work, or does someone have a better approach?

							Thanx, Paul