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* tools/memory-model: Add more LKMM limitationsPaul E. McKenney2018-10-021-0/+39
| | | | | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Fix a README typoSeongJae Park2018-10-021-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Add extra ordering for locks and remove it for ordinary ↵Alan Stern2018-10-023-51/+150
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Add litmus-test naming schemePaul E. McKenney2018-10-021-2/+102
| | | | | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Rename litmus tests to comply to norm7Andrea Parri2018-07-1711-30/+30
| | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model/Documentation: Fix typo, smb->smpYauheni Kaliuta2018-07-171-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Make scripts executablePaul E. McKenney2018-07-172-2/+2
| | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Remove ACCESS_ONCE() from modelMark Rutland2018-07-171-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Since commit: b899a850431e2dd0 ("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>
* tools/memory-model: Remove ACCESS_ONCE() from recipesMark Rutland2018-07-171-2/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Since commit: b899a850431e2dd0 ("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>
* tools/memory-model: Fix ISA2+pooncelock+pooncelock+pombonce namePaul E. McKenney2018-07-171-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Add litmus test for full multicopy atomicityPaul E. McKenney2018-07-172-0/+41
| | | | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Add reference for 'Simplifying ARM concurrency'Andrea Parri2018-05-151-0/+6
| | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Update ASPLOS informationAndrea Parri2018-05-154-11/+12
| | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Fix coding style in 'lock.cat'Andrea Parri2018-05-151-14/+14
| | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Remove out-of-date comments and code from lock.catAlan Stern2018-05-151-9/+6
| | | | | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Improve mixed-access checking in lock.catAlan Stern2018-05-151-11/+11
| | | | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Improve comments in lock.catAlan Stern2018-05-151-15/+36
| | | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Remove duplicated code from lock.catAlan Stern2018-05-151-22/+6
| | | | | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Flag "cumulativity" and "propagation" testsPaul E. McKenney2018-05-153-5/+10
| | | | | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Add model support for spin_is_locked()Luc Maranget2018-05-155-4/+129
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Add scripts to test memory modelPaul E. McKenney2018-05-153-0/+160
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Fix coding style in 'linux-kernel.def'Andrea Parri2018-05-151-14/+14
| | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Model 'smp_store_mb()'Andrea Parri2018-05-151-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-order: Update the cheat-sheet to show that ↵Paul E. McKenney2018-05-151-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-order: Improve key for SELF and SVPaul E. McKenney2018-05-151-1/+2
| | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Fix cheat sheet typoPaolo Bonzini2018-05-151-1/+1
| | | | | | | | | | | | | | | | | | | | | | | "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>
* tools/memory-model: Update required version of herdtools7Akira Yokosawa2018-05-151-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Redefine rb in terms of rcu-fenceAlan Stern2018-05-152-72/+129
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Rename link and rcu-path to rcu-link and rbAlan Stern2018-05-152-54/+55
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Finish the removal of rb-dep, ↵Alan Stern2018-03-103-6/+6
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | smp_read_barrier_depends(), and lockless_dereference() Commit: bf28ae562744 ("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: 5a8897cc7631 ("locking/atomics/alpha: Add smp_read_barrier_depends() to _release()/_relaxed() atomics") ... as an important precursor, and he contributed commit: cb13b424e986 ("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: bf28ae562744 ("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>
* tools/memory-model: Add documentation of new litmus testPaul E. McKenney2018-03-101-0/+6
| | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Remove mention of docker/gentoo imagePaul E. McKenney2018-03-101-15/+0
| | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Remove rb-dep, smp_read_barrier_depends, and ↵Alan Stern2018-02-215-48/+46
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | lockless_dereference Since commit 76ebbe78f739 ("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 59ecbbe7b31c ("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>
* tools/memory-model: Convert underscores to hyphensPaul E. McKenney2018-02-213-9/+9
| | | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Add a S lock-based external-view litmus testAlan Stern2018-02-211-0/+41
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Add required herd7 version to README filePaul E. McKenney2018-02-211-1/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | 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>
* README: Fix a couple of punctuation errorsPaul E. McKenney2018-02-211-2/+2
| | | | | | | | | | | | | | | | | | | | 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>
* EXP litmus_tests: Add comments explaining tests' purposesPaul E. McKenney2018-02-2128-1/+246
| | | | | | | | | | | | | | | | | | | | | | | | | 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>
* MAINTAINERS: Add the Memory Consistency Model subsystemAndrea Parri2018-02-211-15/+0
| | | | | | | | | | | | | | | | | | | | | | | | | | 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>
* tools/memory-model: Clarify the origin/scope of the tool nameAndrea Parri2018-02-214-10/+10
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 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>
* Automate memory-barriers.txt; provide Linux-kernel memory modelPaul E. McKenney2018-01-2440-0/+3973
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>