linux-toradex.git/tools/memory-model/README, branch v5.10-rc3

tools/memory-model: Add a simple entry point document

2020-09-03T16:51:01+00:00

Current LKMM documentation assumes that the reader already understands
concurrency in the Linux kernel, which won't necessarily always be the
case.  This commit supplies a simple.txt file that provides a starting
point for someone who is new to concurrency in the Linux kernel.
That said, this file might also useful as a reminder to experienced
developers of simpler approaches to dealing with concurrency.

Link: Link: https://lwn.net/Articles/827180/
[ paulmck: Apply feedback from Joel Fernandes. ]
Co-developed-by: Dave Chinner 
Signed-off-by: Dave Chinner 
Co-developed-by: Paul E. McKenney 
Signed-off-by: Paul E. McKenney

tools/memory-model: Improve litmus-test documentation

2020-09-03T16:51:01+00:00

The current LKMM documentation says very little about litmus tests, and
worse yet directs people to the herd7 documentation for more information.
Now, the herd7 documentation is quite voluminous and educational,
but it is intended for people creating and modifying memory models,
not those attempting to use them.

This commit therefore updates README and creates a litmus-tests.txt
file that gives an overview of litmus-test format and describes ways of
modeling various special cases, illustrated with numerous examples.

[ paulmck: Add Alan Stern feedback. ]
[ paulmck: Apply Dave Chinner feedback. ]
[ paulmck: Apply Andrii Nakryiko feedback. ]
[ paulmck: Apply Johannes Weiner feedback. ]
Link: https://lwn.net/Articles/827180/
Reported-by: Dave Chinner 
Acked-by: Peter Zijlstra (Intel) 
Signed-off-by: Paul E. McKenney

tools/memory-model/README: Mention herdtools7 7.56 in compatibility table

2020-06-29T19:05:18+00:00

herdtools7 7.56 is going to be released in the week of 22 Jun 2020.
This commit therefore adds the exact version in the compatibility table.

Acked-by: Andrea Parri 
Signed-off-by: Akira Yokosawa 
Signed-off-by: Paul E. McKenney

tools/memory-model/README: Expand dependency of klitmus7

2020-06-29T19:05:18+00:00

klitmus7 is independent of the memory model but depends on the
build-target kernel release.
It occasionally lost compatibility due to kernel API changes [1, 2, 3].
It was remedied in a backwards-compatible manner respectively [4, 5, 6].

Reflect this fact in README.

[1]: b899a850431e ("compiler.h: Remove ACCESS_ONCE()")
[2]: 0bb95f80a38f ("Makefile: Globally enable VLA warning")
[3]: d56c0d45f0e2 ("proc: decouple proc from VFS with "struct proc_ops"")
[4]: https://github.com/herd/herdtools7/commit/e87d7f9287d1
     ("klitmus: Use WRITE_ONCE and READ_ONCE in place of deprecated ACCESS_ONCE")
[5]: https://github.com/herd/herdtools7/commit/a0cbb10d02be
     ("klitmus: Avoid variable length array")
[6]: https://github.com/herd/herdtools7/commit/46b9412d3a58
     ("klitmus: Linux kernel v5.6.x compat")

NOTE: [5] was ahead of herdtools7 7.53, which did not make an
official release.  Code generated by klitmus7 without [5] can still be
built targeting Linux 4.20--5.5 if you don't care VLA warnings.

Acked-by: Andrea Parri 
Signed-off-by: Akira Yokosawa 
Signed-off-by: Paul E. McKenney

tools/memory-model: Add an exception for limitations on _unless() family

2020-06-29T19:05:18+00:00

According to Luc, atomic_add_unless() is directly provided by herd7,
therefore it can be used in litmus tests. So change the limitation
section in README to unlimit the use of atomic_add_unless().

Cc: Luc Maranget 
Acked-by: Andrea Parri 
Reviewed-by: Joel Fernandes (Google) 
Signed-off-by: Boqun Feng 
Signed-off-by: Paul E. McKenney

tools/memory-model: Update the informal documentation

2019-08-09T17:28:57+00:00

The formal memory consistency model has added support for plain accesses
(and data races).  While updating the informal documentation to describe
this addition to the model is highly desirable and important future work,
update the informal documentation to at least acknowledge such addition.

Signed-off-by: Andrea Parri 
Cc: Will Deacon 
Cc: Peter Zijlstra 
Cc: Boqun Feng 
Cc: Nicholas Piggin 
Cc: David Howells 
Cc: Jade Alglave 
Cc: Luc Maranget 
Cc: "Paul E. McKenney" 
Cc: Akira Yokosawa 
Cc: Daniel Lustig 
Signed-off-by: Paul E. McKenney 
Acked-by: Alan Stern

tools/memory-model: Avoid duplicating herdtools versions

2019-03-18T17:27:52+00:00

Currently, herdtools version information appears no fewer than three
times in the LKMM source, which is difficult to maintain.  This commit
therefore places the required version in one place, namely the
tools/memory-model/README file.

Signed-off-by: Andrea Parri 
Signed-off-by: Paul E. McKenney 
Acked-by: Alan Stern

tools/memory-model: Update README for addition of SRCU

2019-03-18T17:27:52+00:00

This commit updates the section on LKMM limitations to no longer say
that SRCU is not modeled, but instead describe how LKMM's modeling of
SRCU departs from the Linux-kernel implementation.

TL;DR:  There is no known valid use case that cares about the Linux
kernel's ability to have partially overlapping SRCU read-side critical
sections.

Signed-off-by: Paul E. McKenney 
Acked-by: Andrea Parri

tools/memory-model: Add scripts to check github litmus tests

2019-01-21T10:06:59+00:00

The https://github.com/paulmckrcu/litmus repository contains a large
number of C-language litmus tests that include "Result:" comments
predicting the verification result.  This commit adds a number of scripts
that run tests on these litmus tests:

checkghlitmus.sh:
	Runs all litmus tests in the https://github.com/paulmckrcu/litmus
        archive that are C-language and that have "Result:" comment lines
	documenting expected results, comparing the actual results to
	those expected.  Clones the repository if it has not already
	been cloned into the "tools/memory-model/litmus" directory.

initlitmushist.sh
	Run all litmus tests having no more than the specified number
	of processes given a specified timeout, recording the results in
	.litmus.out files.  Clones the repository if it has not already
	been cloned into the "tools/memory-model/litmus" directory.

newlitmushist.sh
	For all new or updated litmus tests having no more than the
	specified number of processes given a specified timeout, run
	and record the results in .litmus.out files.

checklitmushist.sh
	Run all litmus tests having .litmus.out files from previous
	initlitmushist.sh or newlitmushist.sh runs, comparing the
	herd output to that of the original runs.

The above scripts will run litmus tests concurrently, by default with
one job per available CPU.  Giving any of these scripts the --help
argument will cause them to print usage information.

This commit also adds a number of helper scripts that are not intended
to be invoked from the command line:

cmplitmushist.sh: Compare the output of two different runs of the same
	litmus test.

judgelitmus.sh: Compare the output of a litmus test to its "Result:"
	comment line.

parseargs.sh: Parse command-line arguments.

runlitmushist.sh: Run the litmus tests whose pathnames are provided one
	per line on standard input.

While in the area, this commit also makes the existing checklitmus.sh
and checkalllitmus.sh scripts use parseargs.sh in order to provide a
bit of uniformity.  In addition, per-litmus-test status output is directed
to stdout, while end-of-test summary information is directed to stderr.
Finally, the error flag standardizes on "!!!" to assist those familiar
with rcutorture output.

The defaults for the parseargs.sh arguments may be overridden by using
environment variables: LKMM_DESTDIR for --destdir, LKMM_HERD_OPTIONS
for --herdoptions, LKMM_JOBS for --jobs, LKMM_PROCS for --procs, and
LKMM_TIMEOUT for --timeout.

[ paulmck: History-check summary-line changes per Alan Stern feedback. ]
Signed-off-by: Paul E. McKenney 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
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: stern@rowland.harvard.edu
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/20181203230451.28921-2-paulmck@linux.ibm.com
Signed-off-by: Ingo Molnar

tools/memory-model: Add more LKMM limitations

2018-10-02T08:28:04+00:00

This commit adds more detail about compiler optimizations and
not-yet-modeled Linux-kernel APIs.

Signed-off-by: Paul E. McKenney 
Reviewed-by: Andrea Parri 
Cc: Alexander Shishkin 
Cc: Arnaldo Carvalho de Melo 
Cc: Jiri Olsa 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Stephane Eranian 
Cc: Thomas Gleixner 
Cc: Vince Weaver 
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: stern@rowland.harvard.edu
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/20180926182920.27644-4-paulmck@linux.ibm.com
Signed-off-by: Ingo Molnar