mirror of https://gitee.com/openkylin/linux.git
21 Commits
| Author | SHA1 | Message | Date |
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Alan Stern
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c58a801701 |
tools/memory-model/Documentation: Add plain accesses and data races to explanation.txt
This patch updates the Linux Kernel Memory Model's explanation.txt file by adding a section devoted to the model's handling of plain accesses and data-race detection. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Acked-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> |
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Alan Stern
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ddc82999f0 |
tools/memory-model/Documentation: Put redefinition of rcu-fence into explanation.txt
This patch updates the Linux Kernel Memory Model's explanation.txt
file to incorporate the introduction of the rcu-order relation and
the redefinition of rcu-fence made by commit
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Alan Stern
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3321ea1290 |
tools/memory-model/Documentation: Fix typos in explanation.txt
This patch fixes a few minor typos and improves word usage in a few places in the Linux Kernel Memory Model's explanation.txt file. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> Acked-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> |
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Andrea Parri
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6738ff85c3 |
tools/memory-model: Update the informal documentation
The formal memory consistency model has added support for plain accesses (and data races). While updating the informal documentation to describe this addition to the model is highly desirable and important future work, update the informal documentation to at least acknowledge such addition. Signed-off-by: Andrea Parri <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> Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com> Acked-by: Alan Stern <stern@rowland.harvard.edu> |
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Joel Fernandes (Google)
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6240973e56 |
tools/memory-model: Use cumul-fence instead of fence in ->prop example
To reduce ambiguity in the more exotic ->prop ordering example, this commit uses the term cumul-fence instead of the term fence for the two fences, so that the implict ->rfe on loads/stores to Y are covered by the description. Link: https://lore.kernel.org/lkml/20190729121745.GA140682@google.com Suggested-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Acked-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com> |
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Alan Stern
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648e717586 |
tools/memory-model: Update Documentation/explanation.txt to include SRCU support
The recent commit adding support for SRCU to the Linux Kernel Memory Model ended up changing the names and meanings of several relations. This patch updates the explanation.txt documentation file to reflect those changes. It also revises the statement of the RCU Guarantee to a more accurate form, and it adds a short paragraph mentioning the new support for SRCU. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Cc: Akira Yokosawa <akiyks@gmail.com> Cc: Andrea Parri <andrea.parri@amarulasolutions.com> 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: Luc Maranget <luc.maranget@inria.fr> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: "Paul E. McKenney" <paulmck@linux.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Will Deacon <will.deacon@arm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com> Acked-by: Andrea Parri <andrea.parri@amarulasolutions.com> |
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SeongJae Park
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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> |
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Alan Stern
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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> |
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Andrea Parri
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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> |
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Yauheni Kaliuta
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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> |
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Mark Rutland
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5bde06b63a |
tools/memory-model: Remove ACCESS_ONCE() from recipes
Since commit:
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Andrea Parri
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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> |
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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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Paul E. McKenney
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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> |
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Paul E. McKenney
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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> |
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Paolo Bonzini
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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> |
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Alan Stern
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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> |
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Alan Stern
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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> |
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Alan Stern
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bd5c0ba2cd |
tools/memory-model: Finish the removal of rb-dep, smp_read_barrier_depends(), and lockless_dereference()
Commit: |
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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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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> |