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Author SHA1 Message Date
Paul E. McKenney
d095c12c53 tools/memory-model: Remove mention of docker/gentoo image 
Because the docker and gentoo images haven't been updated in quite some
time, they are likely to provide more confusion than help.  This commit
therefore removes mention of them from the README file.

Reported-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: akiyks@gmail.com
Cc: boqun.feng@gmail.com
Cc: dhowells@redhat.com
Cc: j.alglave@ucl.ac.uk
Cc: linux-arch@vger.kernel.org
Cc: luc.maranget@inria.fr
Cc: npiggin@gmail.com
Cc: parri.andrea@gmail.com
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1520443660-16858-2-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
 2018-03-10 10:22:23 +01:00
Paul E. McKenney
8f7f2fbd00 tools/memory-model: Add required herd7 version to README file 
LKMM and the herd7 tool are co-evolving, and out-of-date herd7 tools
produce inaccurate results, often with no obvious error messages.  This
commit therefore adds the required herd7 version to the LKMM README file.

Longer term, it would be good if .cat files could specify the required
version in a manner allowing herd7 to produce clear diagnostics.

Suggested-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boqun.feng@gmail.com
Cc: dhowells@redhat.com
Cc: j.alglave@ucl.ac.uk
Cc: linux-arch@vger.kernel.org
Cc: luc.maranget@inria.fr
Cc: nborisov@suse.com
Cc: npiggin@gmail.com
Cc: parri.andrea@gmail.com
Cc: stern@rowland.harvard.edu
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1519169112-20593-9-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
 2018-02-21 09:58:15 +01:00
Andrea Parri
48d44d4e8a tools/memory-model: Clarify the origin/scope of the tool name 
Ingo pointed out that:

  "The "memory model" name is overly generic, ambiguous and somewhat
   misleading, as we usually mean the virtual memory layout/model
   when we say "memory model". GCC too uses it in that sense [...]"

Make it clear that tools/memory-model/ uses the term "memory model" as
shorthand for "memory consistency model" by calling out this convention
in tools/memory-model/README.

Stick to the original "memory model" term in sources' headers and for
the subsystem name.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: akiyks@gmail.com
Cc: boqun.feng@gmail.com
Cc: dhowells@redhat.com
Cc: j.alglave@ucl.ac.uk
Cc: linux-arch@vger.kernel.org
Cc: luc.maranget@inria.fr
Cc: nborisov@suse.com
Cc: npiggin@gmail.com
Link: http://lkml.kernel.org/r/1519169112-20593-1-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
 2018-02-21 09:58:12 +01:00
Paul E. McKenney
1c27b644c0 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.  However, one aspect
of the history does bear repeating due to weak copyright tracking earlier
in this project, which extends back to early 2015.  This weakness came
to light in late 2017 after an LKMM presentation by Paul in which an
audience member noted the similarity of some LKMM code to code in early
published papers.  This prompted a copyright review.

From Alan Stern:

	To say that the model was mine is not entirely accurate.
	Pieces of it (especially the Scpv and Atomic axioms) were taken
	directly from Jade's models.  And of course the Happens-before
	and Propagation relations and axioms were heavily based on
	Jade and Luc's work, even though they weren't identical to the
	earlier versions.  Only the RCU portion was completely original.

	. . .

	One can make a much better case that I wrote the bulk of lock.cat.
	However, it was inspired by Luc's earlier version (and still
	shares some elements in common), and of course it benefited from
	feedback and testing from all members of our group.

The model prior to Alan's was Luc Maranget's.  From Luc:

	 I totally agree on Alan Stern's account of the linux kernel model
	 genesis.  I thank him for his acknowledgments of my participation
	 to previous model drafts.  I'd like to complete Alan Stern's
	 statement: any bell cat code I have written has its roots in
	 discussions with Jade Alglave and Paul McKenney. Moreover I
	 have borrowed cat and bell code written by Jade Alglave freely.

This copyright review therefore resulted in late adds to the copyright
statements of several files.

Discussion of v1 has raised several issues, which we do not believe should
block acceptance given that this level of change will be ongoing, just
as it has been with memory-barriers.txt:

o	Under what conditions should ordering provided by pure locking
	be seen by CPUs not holding the relevant lock(s)?  In particular,
	should the message-passing pattern be forbidden?

o	Should examples involving C11 release sequences be forbidden?
	Note that this C11 is still a moving target for this issue:
	http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0735r0.html

o	Some details of the handling of internal dependencies for atomic
	read-modify-write atomic operations are still subject to debate.

o	Changes recently accepted into mainline greatly reduce the need
	to handle DEC Alpha as a special case.  These changes add an
	smp_read_barrier_depends() to READ_ONCE(), thus causing Alpha
	to respect ordering of dependent reads.  If these changes stick,
	the memory model can be simplified accordingly.

o	Will changes be required to accommodate RISC-V?

Differences from v1:
	(http://lkml.kernel.org/r/20171113184031.GA26302@linux.vnet.ibm.com)

o	Add SPDX notations to .bell and .cat files, replacing
	textual license statements.

o	Add reference to upcoming ASPLOS paper to .bell and .cat files.

o	Updated identifier names in .bell and .cat files to match those
	used in the ASPLOS paper.

o	Updates to READMEs and other documentation based on review
	feedback.

o	Added a memory-ordering cheatsheet.

o	Update sigs to new Co-Developed-by and add acks and
	reviewed-bys.

o	Simplify rules detecting nested RCU read-side critical sections.

o	Update copyright statements as noted above.

Co-Developed-by: Alan Stern <stern@rowland.harvard.edu>
Co-Developed-by: Andrea Parri <parri.andrea@gmail.com>
Co-Developed-by: Jade Alglave <j.alglave@ucl.ac.uk>
Co-Developed-by: Luc Maranget <luc.maranget@inria.fr>
Co-Developed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Andrea Parri <parri.andrea@gmail.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>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Nicholas Piggin <npiggin@gmail.com>
Acked-by: David Howells <dhowells@redhat.com>
Acked-by: "Reshetova, Elena" <elena.reshetova@intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Akira Yokosawa <akiyks@gmail.com>
Cc: <linux-arch@vger.kernel.org>
 2018-01-24 20:53:49 -08:00