Commit Graph

148 Commits

Author SHA1 Message Date
Paul E. McKenney ad9fd20b6d tools/memory-model: Update README for addition of SRCU
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 <paulmck@linux.ibm.com>
Acked-by: Andrea Parri <andrea.parri@amarulasolutions.com>
2019-03-18 10:27:52 -07:00
Alan Stern a3f600d92d tools/memory-model: Add SRCU support
Add support for SRCU.  Herd creates srcu events and linux-kernel.def
associates them with three possible annotations (srcu-lock,
srcu-unlock, and sync-srcu) corresponding to the API routines
srcu_read_lock(), srcu_read_unlock(), and synchronize_srcu().

The linux-kernel.bell file now declares the annotations
and determines matching lock/unlock pairs delimiting SRCU read-side
critical sections, and it also checks for synchronize_srcu() calls
inside an RCU critical section (which would generate a "sleeping in
atomic context" error in real kernel code).  The linux-kernel.cat file
now adds SRCU-induced ordering, analogous to the existing RCU-induced
ordering, to the gp and rcu-fence relations.

Curiously enough, these small changes to the model's .cat code are all
that is needed to describe SRCU.

Portions of this patch (linux-kernel.def and the first hunk in
linux-kernel.bell) were written by Luc Maranget.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: Luc Maranget <luc.maranget@inria.fr>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Tested-by: Andrea Parri <andrea.parri@amarulasolutions.com>
2019-03-18 10:27:52 -07:00
Alan Stern 284749b0ae tools/memory-model: Refactor some RCU relations
In preparation for adding support for SRCU, refactor the definitions
of rcu-fence, rcu-rscsi, rcu-link, and rb by moving the po and po?
terms from the first two to the second two.  An rcu-gp relation is
added; it is equivalent to gp with the po and po? terms removed.

This is necessary because for SRCU, we will have to use the loc
relation to check that the terms at the start and end of each disjunct
in the definition of rcu-fence refer to the same srcu_struct
location.  If these terms are hidden behind po and po?, there's no way
to carry out this check.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Tested-by: Andrea Parri <andrea.parri@amarulasolutions.com>
2019-03-18 10:27:52 -07:00
Alan Stern 0172d9e322 tools/memory-model: Rename some RCU relations
In preparation for adding support for SRCU, rename "crit" to
"rcu-rscs", rename "rscs" to "rcu-rscsi", and remove the restriction
to only the outermost level of nesting.

The name change is needed for disambiguating RCU read-side critical
sections from SRCU read-side critical sections.  Adding the "i" at the
end of "rcu-rscsi" emphasizes that the relation is inverted; it links
rcu_read_unlock() events to their corresponding preceding
rcu_read_lock() events.

The restriction to outermost nesting levels was never essential; it
was included mostly to show that it could be done.  Rather than add
equivalent unnecessary code for SRCU lock nesting, it seemed better to
remove the existing code.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Tested-by: Andrea Parri <andrea.parri@amarulasolutions.com>
2019-03-18 10:23:22 -07:00
Paul E. McKenney 910cc9591d tools/memory-model: Make scripts take "-j" abbreviation for "--jobs"
The "--jobs" argument to the litmus-test scripts is similar to the "-jN"
argument to "make", so this commit allows the "-jN" form as well.  While
in the area, it also prohibits the various forms of "-j0".

Suggested-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/20181203230451.28921-3-paulmck@linux.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-01-21 11:07:04 +01:00
Paul E. McKenney b02eb5b096 tools/memory-model: Add scripts to check github litmus tests
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 <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: 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 <mingo@kernel.org>
2019-01-21 11:06:59 +01:00
Andrea Parri 5b735eb1ce tools/memory-model: Model smp_mb__after_unlock_lock()
The kernel documents smp_mb__after_unlock_lock() the following way:

  "Place this after a lock-acquisition primitive to guarantee that
   an UNLOCK+LOCK pair acts as a full barrier.  This guarantee applies
   if the UNLOCK and LOCK are executed by the same CPU or if the
   UNLOCK and LOCK operate on the same lock variable."

Formalize in LKMM the above guarantee by defining (new) mb-links according
to the law:

  ([M] ; po ; [UL] ; (co | po) ; [LKW] ;
	fencerel(After-unlock-lock) ; [M])

where the component ([UL] ; co ; [LKW]) identifies "UNLOCK+LOCK pairs on
the same lock variable" and the component ([UL] ; po ; [LKW]) identifies
"UNLOCK+LOCK pairs executed by the same CPU".

In particular, the LKMM forbids the following two behaviors (the second
litmus test below is based on:

  Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.html

c.f., Section "Tree RCU Grace Period Memory Ordering Building Blocks"):

C after-unlock-lock-same-cpu

(*
 * Result: Never
 *)

{}

P0(spinlock_t *s, spinlock_t *t, int *x, int *y)
{
	int r0;

	spin_lock(s);
	WRITE_ONCE(*x, 1);
	spin_unlock(s);
	spin_lock(t);
	smp_mb__after_unlock_lock();
	r0 = READ_ONCE(*y);
	spin_unlock(t);
}

P1(int *x, int *y)
{
	int r0;

	WRITE_ONCE(*y, 1);
	smp_mb();
	r0 = READ_ONCE(*x);
}

exists (0:r0=0 /\ 1:r0=0)

C after-unlock-lock-same-lock-variable

(*
 * Result: Never
 *)

{}

P0(spinlock_t *s, int *x, int *y)
{
	int r0;

	spin_lock(s);
	WRITE_ONCE(*x, 1);
	r0 = READ_ONCE(*y);
	spin_unlock(s);
}

P1(spinlock_t *s, int *y, int *z)
{
	int r0;

	spin_lock(s);
	smp_mb__after_unlock_lock();
	WRITE_ONCE(*y, 1);
	r0 = READ_ONCE(*z);
	spin_unlock(s);
}

P2(int *z, int *x)
{
	int r0;

	WRITE_ONCE(*z, 1);
	smp_mb();
	r0 = READ_ONCE(*x);
}

exists (0:r0=0 /\ 1:r0=0 /\ 2:r0=0)

Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Cc: Akira Yokosawa <akiyks@gmail.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Daniel Lustig <dlustig@nvidia.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luc Maranget <luc.maranget@inria.fr>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arch@vger.kernel.org
Cc: parri.andrea@gmail.com
Link: http://lkml.kernel.org/r/20181203230451.28921-1-paulmck@linux.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-01-21 11:06:55 +01:00
Paul E. McKenney d8fa25c4ef tools/memory-model: Add more LKMM limitations
This commit adds more detail about compiler optimizations and
not-yet-modeled Linux-kernel APIs.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
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 <mingo@kernel.org>
2018-10-02 10:28:04 +02:00
SeongJae Park 3d2046a6fa tools/memory-model: Fix a README typo
This commit fixes a duplicate-"the" typo in README.

Signed-off-by: SeongJae Park <sj38.park@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
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/20180926182920.27644-3-paulmck@linux.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-10-02 10:28:03 +02:00
Alan Stern 6e89e831a9 tools/memory-model: Add extra ordering for locks and remove it for ordinary release/acquire
More than one kernel developer has expressed the opinion that the LKMM
should enforce ordering of writes by locking.  In other words, given
the following code:

	WRITE_ONCE(x, 1);
	spin_unlock(&s):
	spin_lock(&s);
	WRITE_ONCE(y, 1);

the stores to x and y should be propagated in order to all other CPUs,
even though those other CPUs might not access the lock s.  In terms of
the memory model, this means expanding the cumul-fence relation.

Locks should also provide read-read (and read-write) ordering in a
similar way.  Given:

	READ_ONCE(x);
	spin_unlock(&s);
	spin_lock(&s);
	READ_ONCE(y);		// or WRITE_ONCE(y, 1);

the load of x should be executed before the load of (or store to) y.
The LKMM already provides this ordering, but it provides it even in
the case where the two accesses are separated by a release/acquire
pair of fences rather than unlock/lock.  This would prevent
architectures from using weakly ordered implementations of release and
acquire, which seems like an unnecessary restriction.  The patch
therefore removes the ordering requirement from the LKMM for that
case.

There are several arguments both for and against this change.  Let us
refer to these enhanced ordering properties by saying that the LKMM
would require locks to be RCtso (a bit of a misnomer, but analogous to
RCpc and RCsc) and it would require ordinary acquire/release only to
be RCpc.  (Note: In the following, the phrase "all supported
architectures" is meant not to include RISC-V.  Although RISC-V is
indeed supported by the kernel, the implementation is still somewhat
in a state of flux and therefore statements about it would be
premature.)

Pros:

	The kernel already provides RCtso ordering for locks on all
	supported architectures, even though this is not stated
	explicitly anywhere.  Therefore the LKMM should formalize it.

	In theory, guaranteeing RCtso ordering would reduce the need
	for additional barrier-like constructs meant to increase the
	ordering strength of locks.

	Will Deacon and Peter Zijlstra are strongly in favor of
	formalizing the RCtso requirement.  Linus Torvalds and Will
	would like to go even further, requiring locks to have RCsc
	behavior (ordering preceding writes against later reads), but
	they recognize that this would incur a noticeable performance
	degradation on the POWER architecture.  Linus also points out
	that people have made the mistake, in the past, of assuming
	that locking has stronger ordering properties than is
	currently guaranteed, and this change would reduce the
	likelihood of such mistakes.

	Not requiring ordinary acquire/release to be any stronger than
	RCpc may prove advantageous for future architectures, allowing
	them to implement smp_load_acquire() and smp_store_release()
	with more efficient machine instructions than would be
	possible if the operations had to be RCtso.  Will and Linus
	approve this rationale, hypothetical though it is at the
	moment (it may end up affecting the RISC-V implementation).
	The same argument may or may not apply to RMW-acquire/release;
	see also the second Con entry below.

	Linus feels that locks should be easy for people to use
	without worrying about memory consistency issues, since they
	are so pervasive in the kernel, whereas acquire/release is
	much more of an "experts only" tool.  Requiring locks to be
	RCtso is a step in this direction.

Cons:

	Andrea Parri and Luc Maranget think that locks should have the
	same ordering properties as ordinary acquire/release (indeed,
	Luc points out that the names "acquire" and "release" derive
	from the usage of locks).  Andrea points out that having
	different ordering properties for different forms of acquires
	and releases is not only unnecessary, it would also be
	confusing and unmaintainable.

	Locks are constructed from lower-level primitives, typically
	RMW-acquire (for locking) and ordinary release (for unlock).
	It is illogical to require stronger ordering properties from
	the high-level operations than from the low-level operations
	they comprise.  Thus, this change would make

		while (cmpxchg_acquire(&s, 0, 1) != 0)
			cpu_relax();

	an incorrect implementation of spin_lock(&s) as far as the
	LKMM is concerned.  In theory this weakness can be ameliorated
	by changing the LKMM even further, requiring
	RMW-acquire/release also to be RCtso (which it already is on
	all supported architectures).

	As far as I know, nobody has singled out any examples of code
	in the kernel that actually relies on locks being RCtso.
	(People mumble about RCU and the scheduler, but nobody has
	pointed to any actual code.  If there are any real cases,
	their number is likely quite small.)  If RCtso ordering is not
	needed, why require it?

	A handful of locking constructs (qspinlocks, qrwlocks, and
	mcs_spinlocks) are built on top of smp_cond_load_acquire()
	instead of an RMW-acquire instruction.  It currently provides
	only the ordinary acquire semantics, not the stronger ordering
	this patch would require of locks.  In theory this could be
	ameliorated by requiring smp_cond_load_acquire() in
	combination with ordinary release also to be RCtso (which is
	currently true on all supported architectures).

	On future weakly ordered architectures, people may be able to
	implement locks in a non-RCtso fashion with significant
	performance improvement.  Meeting the RCtso requirement would
	necessarily add run-time overhead.

Overall, the technical aspects of these arguments seem relatively
minor, and it appears mostly to boil down to a matter of opinion.
Since the opinions of senior kernel maintainers such as Linus,
Peter, and Will carry more weight than those of Luc and Andrea, this
patch changes the model in accordance with the maintainers' wishes.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Will Deacon <will.deacon@arm.com>
Reviewed-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
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
Link: http://lkml.kernel.org/r/20180926182920.27644-2-paulmck@linux.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-10-02 10:28:01 +02:00
Paul E. McKenney c4f790f244 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 <paulmck@linux.vnet.ibm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
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
Link: http://lkml.kernel.org/r/20180926182920.27644-1-paulmck@linux.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-10-02 10:28:00 +02:00
Andrea Parri 71b7ff5ebc 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 <andrea.parri@amarulasolutions.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Cc: Akira Yokosawa <akiyks@gmail.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luc Maranget <luc.maranget@inria.fr>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arch@vger.kernel.org
Cc: parri.andrea@gmail.com
Link: http://lkml.kernel.org/r/20180716180605.16115-14-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-07-17 09:30:36 +02:00
Yauheni Kaliuta 0fcff1715b tools/memory-model/Documentation: Fix typo, smb->smp
The tools/memory-model/Documentation/explanation.txt file says
"For each other CPU C', smb_wmb() forces all po-earlier stores"
This commit therefore replaces the "smb_wmb()" with "smp_wmb()".

Signed-off-by: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
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/20180716180605.16115-13-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-07-17 09:30:35 +02:00
Paul E. McKenney 24675bb554 tools/memory-model: Make scripts executable
This commit makes the scripts executable to avoid the need for everyone
to do so manually in their archive.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Akira Yokosawa <akiyks@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.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: npiggin@gmail.com
Cc: parri.andrea@gmail.com
Cc: stern@rowland.harvard.edu
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/20180716180605.16115-7-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-07-17 09:30:17 +02:00
Mark Rutland af41db5ef7 tools/memory-model: Remove ACCESS_ONCE() from model
Since commit:

  b899a85043 ("compiler.h: Remove ACCESS_ONCE()")

... there has been no definition of ACCESS_ONCE() in the kernel tree,
and it has been necessary to use READ_ONCE() or WRITE_ONCE() instead.

Correspondingly, let's remove ACCESS_ONCE() from the kernel memory
model.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: Akira Yokosawa <akiyks@gmail.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luc Maranget <luc.maranget@inria.fr>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arch@vger.kernel.org
Cc: parri.andrea@gmail.com
Link: http://lkml.kernel.org/r/20180716180605.16115-6-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-07-17 09:29:35 +02:00
Mark Rutland 5bde06b63a tools/memory-model: Remove ACCESS_ONCE() from recipes
Since commit:

  b899a85043 ("compiler.h: Remove ACCESS_ONCE()")

... there has been no definition of ACCESS_ONCE() in the kernel tree,
and it has been necessary to use READ_ONCE() or WRITE_ONCE() instead.

Let's update the exmaples in recipes.txt likewise for consistency, using
READ_ONCE() for reads.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: Akira Yokosawa <akiyks@gmail.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luc Maranget <luc.maranget@inria.fr>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arch@vger.kernel.org
Cc: parri.andrea@gmail.com
Link: http://lkml.kernel.org/r/20180716180605.16115-5-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-07-17 09:29:34 +02:00
Paul E. McKenney acb6c96c52 tools/memory-model: Fix ISA2+pooncelock+pooncelock+pombonce name
The names on the first line of the litmus tests are arbitrary,
but the convention is that they be the filename without the trailing
".litmus".  This commit therefore removes the stray trailing ".litmus"
from ISA2+pooncelock+pooncelock+pombonce.litmus's name.

Reported-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
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/20180716180605.16115-2-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-07-17 09:29:31 +02:00
Paul E. McKenney b464818978 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 <stern@rowland.harvard.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Andrea Parri <andrea.parri@amarulasolutions.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/20180716180605.16115-1-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-07-17 09:29:29 +02:00
Andrea Parri 99c12749b1 tools/memory-model: Add reference for 'Simplifying ARM concurrency'
The paper discusses the revised ARMv8 memory model; such revision
had an important impact on the design of the LKMM.

Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Akira Yokosawa <akiyks@gmail.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luc Maranget <luc.maranget@inria.fr>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arch@vger.kernel.org
Cc: parri.andrea@gmail.com
Link: http://lkml.kernel.org/r/1526340837-12222-19-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 08:11:19 +02:00
Andrea Parri 1a00b4554d tools/memory-model: Update ASPLOS information
ASPLOS 2018 was held in March: make sure this is reflected in
header comments and references.

Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Akira Yokosawa <akiyks@gmail.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luc Maranget <luc.maranget@inria.fr>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arch@vger.kernel.org
Cc: parri.andrea@gmail.com
Link: http://lkml.kernel.org/r/1526340837-12222-18-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 08:11:18 +02:00
Andrea Parri 05604e7e3a tools/memory-model: Fix coding style in 'lock.cat'
This commit uses tabs for indentation and adds spaces around binary
operator.

Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
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
Link: http://lkml.kernel.org/r/1526340837-12222-16-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 08:11:18 +02:00
Alan Stern cee0321a40 tools/memory-model: Remove out-of-date comments and code from lock.cat
lock.cat contains old comments and code referring to the possibility
of LKR events that are not part of an RMW pair.  This is a holdover
from when I though we might end up using LKR events to implement
spin_is_locked().  Reword the comments to remove this assumption and
replace domain(lk-rmw) in the code with LKR.

Tested-by: Andrea Parri <andrea.parri@amarulasolutions.com>
[ paulmck: Pulled as lock-nest into previous line as discussed. ]
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Akira Yokosawa <akiyks@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luc Maranget <luc.maranget@inria.fr>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arch@vger.kernel.org
Cc: parri.andrea@gmail.com
Link: http://lkml.kernel.org/r/1526340837-12222-15-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 08:11:18 +02:00
Alan Stern 30b795df11 tools/memory-model: Improve mixed-access checking in lock.cat
The code in lock.cat which checks for normal read/write accesses to
spinlock variables doesn't take into account the newly added RL and RU
events.  Add them into the test, and move the resulting code up near
the start of the file, since a violation would indicate a pretty
severe conceptual error in a litmus test.

Tested-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Akira Yokosawa <akiyks@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luc Maranget <luc.maranget@inria.fr>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arch@vger.kernel.org
Cc: parri.andrea@gmail.com
Link: http://lkml.kernel.org/r/1526340837-12222-14-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 08:11:18 +02:00
Alan Stern fd0359dbac tools/memory-model: Improve comments in lock.cat
This patch improves the comments in tools/memory-model/lock.cat.  In
addition to making the text more uniform and removing redundant
comments, it adds a description of all the possible locking events
that herd can generate.

Tested-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Akira Yokosawa <akiyks@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luc Maranget <luc.maranget@inria.fr>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arch@vger.kernel.org
Cc: parri.andrea@gmail.com
Link: http://lkml.kernel.org/r/1526340837-12222-13-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 08:11:18 +02:00
Alan Stern 8559183cca tools/memory-model: Remove duplicated code from lock.cat
This patch simplifies the implementation of spin_is_locked in the
LKMM.  It capitalizes on the fact that a failed spin_trylock() and a
spin_is_locked() which returns True have exactly the same semantics
(those of READ_ONCE) and ordering properties (none).  Therefore the
two kinds of events can be combined and handled by the same code,
instead of treated separately as they are currently.

Tested-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Akira Yokosawa <akiyks@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luc Maranget <luc.maranget@inria.fr>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arch@vger.kernel.org
Cc: parri.andrea@gmail.com
Link: http://lkml.kernel.org/r/1526340837-12222-12-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 08:11:17 +02:00
Paul E. McKenney 1bd3742043 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 <andrea.parri@amarulasolutions.com>
Reported-by: Paolo Bonzini <pbonzini@redhat.com>
[ paulmck: Updated wording as suggested by Alan Stern. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
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
Link: http://lkml.kernel.org/r/1526340837-12222-11-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 08:11:17 +02:00
Luc Maranget 15553dcbca 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/20180226162426.GB17158@arm.com

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

Signed-off-by: Luc Maranget <luc.maranget@inria.fr>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Alan Stern <stern@rowland.harvard.edu>
Cc: Akira Yokosawa <akiyks@gmail.com>
Cc: Andrea Parri <parri.andrea@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luc Maranget <Luc.Maranget@inria.fr>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arch@vger.kernel.org
Link: http://lkml.kernel.org/r/1526340837-12222-10-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 08:11:17 +02:00
Paul E. McKenney 2fb6ae162f tools/memory-model: Add scripts to test memory model
This commit adds a pair of scripts that run the memory model on litmus
tests, checking that the verification result of each litmus test matches
the result flagged in the litmus test itself.  These scripts permit easier
checking of changes to the memory model against preconceived notions.

To run the scripts, go to the tools/memory-model directory and type
"scripts/checkalllitmus.sh".  If all is well, the last line printed will
be "All litmus tests verified as was expected."

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
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
Link: http://lkml.kernel.org/r/1526340837-12222-9-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 08:11:17 +02:00
Andrea Parri d17013e0ba tools/memory-model: Fix coding style in 'linux-kernel.def'
This commit fixes white spaces around semicolons.

Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
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
Link: http://lkml.kernel.org/r/1526340837-12222-8-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 08:11:17 +02:00
Andrea Parri bf8c6d963d tools/memory-model: Model 'smp_store_mb()'
This commit models 'smp_store_mb(x, val);' to be semantically equivalent
to 'WRITE_ONCE(x, val); smp_mb();'.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
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
Link: http://lkml.kernel.org/r/1526340837-12222-7-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 08:11:16 +02:00
Paul E. McKenney bfd403bb36 tools/memory-order: Update the cheat-sheet to show that smp_mb__after_atomic() orders later RMW operations
The current cheat sheet does not claim that smp_mb__after_atomic()
orders later RMW atomic operations, which it must, at least against
earlier RMW atomic operations and whatever precedes them.

This commit therefore adds the needed "Y".

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
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
Link: http://lkml.kernel.org/r/1526340837-12222-6-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 08:11:16 +02:00
Paul E. McKenney 35bb6ee679 tools/memory-order: Improve key for SELF and SV
The key for "SELF" was missing completely and the key for "SV" was
a bit obtuse.  This commit therefore adds a key for "SELF" and improves
the one for "SV".

Reported-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
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
Link: http://lkml.kernel.org/r/1526340837-12222-5-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 08:11:16 +02:00
Paolo Bonzini a839195186 tools/memory-model: Fix cheat sheet typo
"RWM" should be "RMW".

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
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
Link: http://lkml.kernel.org/r/1526340837-12222-4-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 08:11:16 +02:00
Akira Yokosawa 5b62832c1e tools/memory-model: Update required version of herdtools7
Code generated by klitmus7 version 7.48 doesn't compile with kernel
header of 4.15 and later due to the absence of ACCESS_ONCE().
As the issue has been resolved in herdtools7 7.49, bump the required
version number in README.

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Andrea Parri <parri.andrea@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luc Maranget <luc.maranget@inria.fr>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arch@vger.kernel.org
Link: http://lkml.kernel.org/r/1526340837-12222-3-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 08:11:16 +02:00
Alan Stern 9d036883a1 tools/memory-model: Redefine rb in terms of rcu-fence
This patch reorganizes the definition of rb in the Linux Kernel Memory
Consistency Model.  The relation is now expressed in terms of
rcu-fence, which consists of a sequence of gp and rscs links separated
by rcu-link links, in which the number of occurrences of gp is >= the
number of occurrences of rscs.

Arguments similar to those published in
http://diy.inria.fr/linux/long.pdf show that rcu-fence behaves like an
inter-CPU strong fence.  Furthermore, the definition of rb in terms of
rcu-fence is highly analogous to the definition of pb in terms of
strong-fence, which can help explain why rcu-path expresses a form of
temporal ordering.

This change should not affect the semantics of the memory model, just
its internal organization.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Andrea Parri <parri.andrea@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: akiyks@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
Link: http://lkml.kernel.org/r/1526340837-12222-2-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 08:11:16 +02:00
Alan Stern 1ee2da5f9b tools/memory-model: Rename link and rcu-path to rcu-link and rb
This patch makes a simple non-functional change to the RCU portion of
the Linux Kernel Memory Consistency Model by renaming the "link" and
"rcu-path" relations to "rcu-link" and "rb", respectively.

The name "link" was an unfortunate choice, because it was too generic
and subject to confusion with other meanings of the same word, which
occur quite often in LKMM documentation.  The name "rcu-path" is not
very appropriate, because the relation is analogous to the
happens-before (hb) and propagates-before (pb) relations -- although
that fact won't become apparent until the second patch in this series.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Andrea Parri <parri.andrea@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
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
Link: http://lkml.kernel.org/r/1526340837-12222-1-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 08:11:15 +02:00
Alan Stern bd5c0ba2cd tools/memory-model: Finish the removal of rb-dep, smp_read_barrier_depends(), and lockless_dereference()
Commit:

  bf28ae5627 ("tools/memory-model: Remove rb-dep, smp_read_barrier_depends, and lockless_dereference")

was merged too early, while it was still in RFC form.  This patch adds in
the missing pieces.

Akira pointed out some typos in the original patch, and he noted that
cheatsheet.txt should indicate that READ_ONCE() now implies an address
dependency.  Andrea suggested documenting the relationship betwwen
unsuccessful RMW operations and address dependencies.

Andrea pointed out that the macro for rcu_dereference() in linux.def
should now use the "once" annotation instead of "deref".  He also
suggested that the comments should mention commit:

  5a8897cc76 ("locking/atomics/alpha: Add smp_read_barrier_depends() to _release()/_relaxed() atomics")

... as an important precursor, and he contributed commit:

  cb13b424e9 ("locking/xchg/alpha: Add unconditional memory barrier to cmpxchg()")

which is another prerequisite.

Suggested-by: Akira Yokosawa <akiyks@gmail.com>
Suggested-by: Andrea Parri <parri.andrea@gmail.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
[ Fixed read_read_lock() typo reported by Akira. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Andrea Parri <parri.andrea@gmail.com>
Acked-by: Akira Yokosawa <akiyks@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.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: npiggin@gmail.com
Cc: will.deacon@arm.com
Fixes: bf28ae5627 ("tools/memory-model: Remove rb-dep, smp_read_barrier_depends, and lockless_dereference")
Link: http://lkml.kernel.org/r/1520443660-16858-4-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 ff1fe5e079 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 <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/1520443660-16858-3-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 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
Alan Stern bf28ae5627 tools/memory-model: Remove rb-dep, smp_read_barrier_depends, and lockless_dereference
Since commit 76ebbe78f7 ("locking/barriers: Add implicit
smp_read_barrier_depends() to READ_ONCE()") was merged for the 4.15
kernel, it has not been necessary to use smp_read_barrier_depends().
Similarly, commit 59ecbbe7b3 ("locking/barriers: Kill
lockless_dereference()") removed lockless_dereference() from the
kernel.

Since these primitives are no longer part of the kernel, they do not
belong in the Linux Kernel Memory Consistency Model.  This patch
removes them, along with the internal rb-dep relation, and updates the
revelant documentation.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
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: 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
Cc: parri.andrea@gmail.com
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1519169112-20593-12-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-02-21 09:58:16 +01:00
Paul E. McKenney cac79a39f2 tools/memory-model: Convert underscores to hyphens
Typical cat-language code uses hyphens for word separators in
identifiers, but several LKMM identifiers use underscores instead.
This commit therefore converts underscores to hyphens in the .bell-
and .cat-file identifiers corresponding to smp_mb__before_atomic(),
smp_mb__after_atomic(), and smp_mb__after_spinlock().

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: 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
Cc: parri.andrea@gmail.com
Cc: stern@rowland.harvard.edu
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1519169112-20593-11-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-02-21 09:58:15 +01:00
Alan Stern 556bb7d252 tools/memory-model: Add a S lock-based external-view litmus test
This commit adds a litmus test in which P0() and P1() form a lock-based S
litmus test, with the addition of P2(), which observes P0()'s and P1()'s
accesses with a full memory barrier but without the lock.  This litmus
test asks whether writes carried out by two different processes under the
same lock will be seen in order by a third process not holding that lock.
The answer to this question is "yes" for all architectures supporting
the Linux kernel, but is "no" according to the current version of LKMM.

A patch to LKMM is under development.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
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: 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
Cc: parri.andrea@gmail.com
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1519169112-20593-10-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-02-21 09:58:15 +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
Paul E. McKenney 6215514704 README: Fix a couple of punctuation errors
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: 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
Cc: parri.andrea@gmail.com
Cc: stern@rowland.harvard.edu
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1519169112-20593-5-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-02-21 09:58:14 +01:00
Paul E. McKenney 8f32543b61 EXP litmus_tests: Add comments explaining tests' purposes
This commit adds comments to the litmus tests summarizing what these
tests are intended to demonstrate.

[ paulmck: Apply Andrea's and Alan's feedback. ]
Suggested-by: Ingo Molnar <mingo@kernel.org>
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: 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
Cc: parri.andrea@gmail.com
Cc: stern@rowland.harvard.edu
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1519169112-20593-4-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-02-21 09:58:13 +01:00
Andrea Parri e7d74c9f90 MAINTAINERS: Add the Memory Consistency Model subsystem
Move the contents of tools/memory-model/MAINTAINERS into the main
MAINTAINERS file, removing tools/memory-model/MAINTAINERS. This
allows get_maintainer.pl to correctly identify the maintainers of
tools/memory-model/.

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/1519169112-20593-2-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-02-21 09:58:12 +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