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10 Commits
| Author | SHA1 | Message | Date | |
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Luc Maranget
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9393998e9e |
tools/memory-model: Dynamically check SRCU lock-to-unlock matching
This commit checks that the return value of srcu_read_lock() is passed
to the matching srcu_read_unlock(), where "matching" is determined by
nesting. This check operates as follows:
1. srcu_read_lock() creates an integer token, which is stored into
the generated events.
2. srcu_read_unlock() records its second (token) argument into the
generated event.
3. A new herd primitive 'different-values' filters out pairs of events
with identical values from the relation passed as its argument.
4. The bell file applies the above primitive to the (srcu)
read-side-critical-section relation 'srcu-rscs' and flags non-empty
results.
BEWARE: Works only with herd version 7.51+6 and onwards.
Signed-off-by: Luc Maranget <Luc.Maranget@inria.fr>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
[ paulmck: Apply Andrea Parri's off-list feedback. ]
Acked-by: Alan Stern <stern@rowland.harvard.edu>
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Alan Stern
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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> |
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Alan Stern
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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> |
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Andrea Parri
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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>
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Mark Rutland
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af41db5ef7 |
tools/memory-model: Remove ACCESS_ONCE() from model
Since commit:
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Andrea Parri
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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> |
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Alan Stern
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bf28ae5627 |
tools/memory-model: Remove rb-dep, smp_read_barrier_depends, and lockless_dereference
Since commit |
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Paul E. McKenney
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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> |
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Andrea Parri
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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> |
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Paul E. McKenney
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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> |