tools/memory-model: litmus: Add two tests for unlock(A)+lock(B) ordering

The memory model has been updated to provide a stronger ordering
guarantee for unlock(A)+lock(B) on the same CPU/thread. Ther

tools/memory-model: litmus: Add two tests for unlock(A)+lock(B) ordering

The memory model has been updated to provide a stronger ordering
guarantee for unlock(A)+lock(B) on the same CPU/thread. Therefore add
two litmus tests describing this new guarantee, these tests are simple
yet can clearly show the usage of the new guarantee, also they can serve
as the self tests for the modification in the model.

Co-developed-by: Alan Stern <[email protected]>
Signed-off-by: Alan Stern <[email protected]>
Signed-off-by: Boqun Feng <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>

show more ...

tools/memory-model: Do not use "herd" to refer to "herd7"

Use "herd7" in each such reference.

Signed-off-by: Andrea Parri <[email protected]>
Cc: Will Deacon <[email protected]>
C

tools/memory-model: Do not use "herd" to refer to "herd7"

Use "herd7" in each such reference.

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

show more ...

tools/memory-model: Add litmus-test naming scheme

This commit documents the scheme used to generate the names for the
litmus tests.

[ paulmck: Apply feedback from Andrea Parri and Will Deacon. ]
Si

tools/memory-model: Add litmus-test naming scheme

This commit documents the scheme used to generate the names for the
litmus tests.

[ paulmck: Apply feedback from Andrea Parri and Will Deacon. ]
Signed-off-by: Paul E. McKenney <[email protected]>
Acked-by: Will Deacon <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vince Weaver <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

show more ...

tools/memory-model: Rename litmus tests to comply to norm7

norm7 produces the 'normalized' name of a litmus test, when the test
can be generated from a single cycle that passes through each process

tools/memory-model: Rename litmus tests to comply to norm7

norm7 produces the 'normalized' name of a litmus test, when the test
can be generated from a single cycle that passes through each process
exactly once. The commit renames such tests in order to comply to the
naming scheme implemented by this tool.

Signed-off-by: Andrea Parri <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Acked-by: Alan Stern <[email protected]>
Cc: Akira Yokosawa <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: David Howells <[email protected]>
Cc: Jade Alglave <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Luc Maranget <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

show more ...

tools/memory-model: Add litmus test for full multicopy atomicity

This commit adds a litmus test suggested by Alan Stern that is forbidden
on fully multicopy atomic systems, but allowed on other-mult

tools/memory-model: Add litmus test for full multicopy atomicity

This commit adds a litmus test suggested by Alan Stern that is forbidden
on fully multicopy atomic systems, but allowed on other-multicopy and
on non-multicopy atomic systems. For reference, s390 is fully multicopy
atomic, x86 and ARMv8 are other-multicopy atomic, and ARMv7 and powerpc
are non-multicopy atomic.

Suggested-by: Alan Stern <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Acked-by: Alan Stern <[email protected]>
Acked-by: Andrea Parri <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

show more ...

tools/memory-model: Flag "cumulativity" and "propagation" tests

This commit flags WRC+pooncerelease+rmbonceonce+Once.litmus
as being forbidden by smp_store_release() A-cumulativity and
IRIW+mbonceon

tools/memory-model: Flag "cumulativity" and "propagation" tests

This commit flags WRC+pooncerelease+rmbonceonce+Once.litmus
as being forbidden by smp_store_release() A-cumulativity and
IRIW+mbonceonces+OnceOnce.litmus as being forbidden by the LKMM
propagation rule.

Suggested-by: Andrea Parri <[email protected]>
Reported-by: Paolo Bonzini <[email protected]>
[ paulmck: Updated wording as suggested by Alan Stern. ]
Signed-off-by: Paul E. McKenney <[email protected]>
Acked-by: Alan Stern <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

show more ...

tools/memory-model: Add model support for spin_is_locked()

This commit first adds a trivial macro for spin_is_locked() to
linux-kernel.def.

It also adds cat code for enumerating all possible matche

tools/memory-model: Add model support for spin_is_locked()

This commit first adds a trivial macro for spin_is_locked() to
linux-kernel.def.

It also adds cat code for enumerating all possible matches of lock
write events (set LKW) with islocked events returning true (set RL,
for Read from Lock), and unlock write events (set UL) with islocked
events returning false (set RU, for Read from Unlock). Note that this
intentionally does not model uniprocessor kernels (CONFIG_SMP=n) built
with CONFIG_DEBUG_SPINLOCK=n, in which spin_is_locked() unconditionally
returns zero.

It also adds a pair of litmus tests demonstrating the minimal ordering
provided by spin_is_locked() in conjunction with spin_lock(). Will Deacon
noted that this minimal ordering happens on ARMv8:
https://lkml.kernel.org/r/[email protected]

Notice that herd7 installations strictly older than version 7.49
do not handle the new constructs.

Signed-off-by: Luc Maranget <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Reviewed-by: Alan Stern <[email protected]>
Cc: Akira Yokosawa <[email protected]>
Cc: Andrea Parri <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: David Howells <[email protected]>
Cc: Jade Alglave <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Luc Maranget <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

show more ...

tools/memory-model: Add documentation of new litmus test

The litmus-tests/README file lacks any mention of the new litmus test
ISA2+pooncelock+pooncelock+pombonce.litmus. This commit therefore
adds

tools/memory-model: Add documentation of new litmus test

The litmus-tests/README file lacks any mention of the new litmus test
ISA2+pooncelock+pooncelock+pombonce.litmus. This commit therefore
adds a description of this test.

Reported-by: Alan Stern <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

show more ...

README: Fix a couple of punctuation errors

Signed-off-by: Paul E. McKenney <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Cc: Linus Torvalds <torvalds@linux-foundation.

README: Fix a couple of punctuation errors

Signed-off-by: Paul E. McKenney <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

show more ...

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 pr

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/[email protected])

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 <[email protected]>
Co-Developed-by: Andrea Parri <[email protected]>
Co-Developed-by: Jade Alglave <[email protected]>
Co-Developed-by: Luc Maranget <[email protected]>
Co-Developed-by: "Paul E. McKenney" <[email protected]>
Signed-off-by: Alan Stern <[email protected]>
Signed-off-by: Andrea Parri <[email protected]>
Signed-off-by: Jade Alglave <[email protected]>
Signed-off-by: Luc Maranget <[email protected]>
Signed-off-by: "Paul E. McKenney" <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
Acked-by: Will Deacon <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Acked-by: Nicholas Piggin <[email protected]>
Acked-by: David Howells <[email protected]>
Acked-by: "Reshetova, Elena" <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Acked-by: Akira Yokosawa <[email protected]>
Cc: <[email protected]>

show more ...