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SubjectRe: Prototype patch for Linux-kernel memory model
On Wed, Nov 15, 2017 at 08:37:49AM -0800, Paul E. McKenney wrote:
> On Tue, Nov 14, 2017 at 09:15:05AM -0800, Paul E. McKenney wrote:
> > 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@linux.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@rowland.harvard.edu>
> > > > > Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
> > > > > Signed-off-by: Will Deacon <will.deacon@arm.com>
> > > > > Signed-off-by: Peter Zijlstra <peterz@infradead.org>
> > > > > Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> > > > > Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> > > > > Signed-off-by: David Howells <dhowells@redhat.com>
> > > > > Signed-off-by: Jade Alglave <j.alglave@ucl.ac.uk>
> > > > > Signed-off-by: Luc Maranget <luc.maranget@inria.fr>
> > > > > Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> > > > > Cc: <linux-arch@vger.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?
>

How about using the shiny new "Co-Developed-by"?

https://marc.info/?l=linux-kernel&m=151083859723653&w=2

Besides, as you know, I've been following and learning a lot from this
model from maybe very beginning, and I have read throught the documents
and cat files, and even got a chance to verify some RCU-involved code
with Andrea using this model ;-) So feel free to add:

Reviewed-by: Boqun Feng <boqun.feng@gmail.com>

Regards,
Boqun

> Hearing no objections, here is an updated prototype patch. Thank you
> all for the review, comments, and updates!
>
> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> commit 869b3c396eb908e3dfafbd75ed33421b3bcd50bf
> Author: Paul E. McKenney <paulmck@linux.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.
>
> This patch was the result of a most excellent collaboration founded
> by Jade Alglave and also including Alan Stern, Andrea Parri, and Luc
> Maranget. For more details on the history of this collaboration, please
> refer to the Linux-kernel memory model presentations at 2016 LinuxCon EU,
> 2016 Kernel Summit, 2016 Linux Plumbers Conference, 2017 linux.conf.au,
> or 2017 Linux Plumbers Conference microconference.
>
> Reviewed-by: Alan Stern <stern@rowland.harvard.edu>
> Reviewed-by: Andrea Parri <parri.andrea@gmail.com>
> Reviewed-by: Jade Alglave <j.alglave@ucl.ac.uk>
> Reviewed-by: Luc Maranget <luc.maranget@inria.fr>
> Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> Acked-by: Will Deacon <will.deacon@arm.com>
> Acked-by: Peter Zijlstra <peterz@infradead.org>
> Acked-by: Boqun Feng <boqun.feng@gmail.com>
> Acked-by: Nicholas Piggin <npiggin@gmail.com>
> Acked-by: David Howells <dhowells@redhat.com>
> Acked-by: "Reshetova, Elena" <elena.reshetova@intel.com>
> Cc: <linux-arch@vger.kernel.org>
>
[...]
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