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commit 4c830eef806679dc243e191f962c488dd9d00708 upstream.
Andrea reported that the following innocuous litmus test:
C T
{}
P0(spinlock_t *x)
{
int r0;
spin_lock(x);
spin_unlock(x);
r0 = spin_is_locked(x);
}
gives rise to a nonsensical empty result with no executions:
$ herd7 -conf linux-kernel.cfg T.litmus
Test T Required
States 0
Ok
Witnesses
Positive: 0 Negative: 0
Condition forall (true)
Observation T Never 0 0
Time T 0.00
Hash=6fa204e139ddddf2cb6fa963bad117c0
The problem is caused by a bug in the lock.cat part of the LKMM. Its
computation of the rf relation for RU (read-unlocked) events is
faulty; it implicitly assumes that every RU event must read from
either a UL (unlock) event in another thread or from the lock's
initial state. Neither is true in the litmus test above, so the
computation yields no possible executions.
The lock.cat code tries to make up for this deficiency by allowing RU
events outside of critical sections to read from the last po-previous
UL event. But it does this incorrectly, trying to keep these rfi links
separate from the rfe links that might also be needed, and passing only
the latter to herd7's cross() macro.
The problem is fixed by merging the two sets of possible rf links for
RU events and using them all in the call to cross().
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Andrea Parri <parri.andrea@gmail.com>
Closes: https://lore.kernel.org/linux-arch/ZlC0IkzpQdeGj+a3@andrea/
Tested-by: Andrea Parri <parri.andrea@gmail.com>
Acked-by: Andrea Parri <parri.andrea@gmail.com>
Fixes: 15553dcbca06 ("tools/memory-model: Add model support for spin_is_locked()")
CC: <stable@vger.kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Use "herd7" in each such reference.
Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Luc Maranget <luc.maranget@inria.fr>
Cc: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: Akira Yokosawa <akiyks@gmail.com>
Cc: Daniel Lustig <dlustig@nvidia.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
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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 <andrea.parri@amarulasolutions.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
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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>
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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>
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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>
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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>
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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>
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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>
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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>
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