OpenCloudOS-Kernel/tools/memory-model/linux-kernel.cat

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Automate memory-barriers.txt; provide Linux-kernel memory model There is some reason to believe that Documentation/memory-barriers.txt could use some help, and a major purpose of this patch is to provide that help in the form of a design-time tool that can produce all valid executions of a small fragment of concurrent Linux-kernel code, which is called a "litmus test". This tool's functionality is roughly similar to a full state-space search. Please note that this is a design-time tool, not useful for regression testing. However, we hope that the underlying Linux-kernel memory model will be incorporated into other tools capable of analyzing large bodies of code for regression-testing purposes. The main tool is herd7, together with the linux-kernel.bell, linux-kernel.cat, linux-kernel.cfg, linux-kernel.def, and lock.cat files added by this patch. The herd7 executable takes the other files as input, and all of these files collectively define the Linux-kernel memory memory model. A brief description of each of these other files is provided in the README file. Although this tool does have its limitations, which are documented in the README file, it does improve on the version reported on in the LWN series (https://lwn.net/Articles/718628/ and https://lwn.net/Articles/720550/) by supporting locking and arithmetic, including a much wider variety of read-modify-write atomic operations. Please note that herd7 is not part of this submission, but is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). A second tool is klitmus7, which converts litmus tests to loadable kernel modules for direct testing. As with herd7, the klitmus7 code is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). Of course, litmus tests are not always the best way to fully understand a memory model, so this patch also includes Documentation/explanation.txt, which describes the memory model in detail. In addition, Documentation/recipes.txt provides example known-good and known-bad use cases for those who prefer working by example. This patch also includes a few sample litmus tests, and a great many more litmus tests are available at https://github.com/paulmckrcu/litmus. This patch was the result of a most excellent collaboration founded by Jade Alglave and also including Alan Stern, Andrea Parri, and Luc Maranget. For more details on the history of this collaboration, please refer to the Linux-kernel memory model presentations at 2016 LinuxCon EU, 2016 Kernel Summit, 2016 Linux Plumbers Conference, 2017 linux.conf.au, or 2017 Linux Plumbers Conference microconference. However, one aspect of the history does bear repeating due to weak copyright tracking earlier in this project, which extends back to early 2015. This weakness came to light in late 2017 after an LKMM presentation by Paul in which an audience member noted the similarity of some LKMM code to code in early published papers. This prompted a copyright review. From Alan Stern: To say that the model was mine is not entirely accurate. Pieces of it (especially the Scpv and Atomic axioms) were taken directly from Jade's models. And of course the Happens-before and Propagation relations and axioms were heavily based on Jade and Luc's work, even though they weren't identical to the earlier versions. Only the RCU portion was completely original. . . . One can make a much better case that I wrote the bulk of lock.cat. However, it was inspired by Luc's earlier version (and still shares some elements in common), and of course it benefited from feedback and testing from all members of our group. The model prior to Alan's was Luc Maranget's. From Luc: I totally agree on Alan Stern's account of the linux kernel model genesis. I thank him for his acknowledgments of my participation to previous model drafts. I'd like to complete Alan Stern's statement: any bell cat code I have written has its roots in discussions with Jade Alglave and Paul McKenney. Moreover I have borrowed cat and bell code written by Jade Alglave freely. This copyright review therefore resulted in late adds to the copyright statements of several files. Discussion of v1 has raised several issues, which we do not believe should block acceptance given that this level of change will be ongoing, just as it has been with memory-barriers.txt: o Under what conditions should ordering provided by pure locking be seen by CPUs not holding the relevant lock(s)? In particular, should the message-passing pattern be forbidden? o Should examples involving C11 release sequences be forbidden? Note that this C11 is still a moving target for this issue: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0735r0.html o Some details of the handling of internal dependencies for atomic read-modify-write atomic operations are still subject to debate. o Changes recently accepted into mainline greatly reduce the need to handle DEC Alpha as a special case. These changes add an smp_read_barrier_depends() to READ_ONCE(), thus causing Alpha to respect ordering of dependent reads. If these changes stick, the memory model can be simplified accordingly. o Will changes be required to accommodate RISC-V? Differences from v1: (http://lkml.kernel.org/r/20171113184031.GA26302@linux.vnet.ibm.com) o Add SPDX notations to .bell and .cat files, replacing textual license statements. o Add reference to upcoming ASPLOS paper to .bell and .cat files. o Updated identifier names in .bell and .cat files to match those used in the ASPLOS paper. o Updates to READMEs and other documentation based on review feedback. o Added a memory-ordering cheatsheet. o Update sigs to new Co-Developed-by and add acks and reviewed-bys. o Simplify rules detecting nested RCU read-side critical sections. o Update copyright statements as noted above. Co-Developed-by: Alan Stern <stern@rowland.harvard.edu> Co-Developed-by: Andrea Parri <parri.andrea@gmail.com> Co-Developed-by: Jade Alglave <j.alglave@ucl.ac.uk> Co-Developed-by: Luc Maranget <luc.maranget@inria.fr> Co-Developed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Jade Alglave <j.alglave@ucl.ac.uk> Signed-off-by: Luc Maranget <luc.maranget@inria.fr> Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: "Reshetova, Elena" <elena.reshetova@intel.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Akira Yokosawa <akiyks@gmail.com> Cc: <linux-arch@vger.kernel.org>
2018-01-19 11:58:55 +08:00
// SPDX-License-Identifier: GPL-2.0+
(*
* Copyright (C) 2015 Jade Alglave <j.alglave@ucl.ac.uk>,
* Copyright (C) 2016 Luc Maranget <luc.maranget@inria.fr> for Inria
* Copyright (C) 2017 Alan Stern <stern@rowland.harvard.edu>,
* Andrea Parri <parri.andrea@gmail.com>
*
* An earlier version of this file appeared in the companion webpage for
Automate memory-barriers.txt; provide Linux-kernel memory model There is some reason to believe that Documentation/memory-barriers.txt could use some help, and a major purpose of this patch is to provide that help in the form of a design-time tool that can produce all valid executions of a small fragment of concurrent Linux-kernel code, which is called a "litmus test". This tool's functionality is roughly similar to a full state-space search. Please note that this is a design-time tool, not useful for regression testing. However, we hope that the underlying Linux-kernel memory model will be incorporated into other tools capable of analyzing large bodies of code for regression-testing purposes. The main tool is herd7, together with the linux-kernel.bell, linux-kernel.cat, linux-kernel.cfg, linux-kernel.def, and lock.cat files added by this patch. The herd7 executable takes the other files as input, and all of these files collectively define the Linux-kernel memory memory model. A brief description of each of these other files is provided in the README file. Although this tool does have its limitations, which are documented in the README file, it does improve on the version reported on in the LWN series (https://lwn.net/Articles/718628/ and https://lwn.net/Articles/720550/) by supporting locking and arithmetic, including a much wider variety of read-modify-write atomic operations. Please note that herd7 is not part of this submission, but is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). A second tool is klitmus7, which converts litmus tests to loadable kernel modules for direct testing. As with herd7, the klitmus7 code is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). Of course, litmus tests are not always the best way to fully understand a memory model, so this patch also includes Documentation/explanation.txt, which describes the memory model in detail. In addition, Documentation/recipes.txt provides example known-good and known-bad use cases for those who prefer working by example. This patch also includes a few sample litmus tests, and a great many more litmus tests are available at https://github.com/paulmckrcu/litmus. This patch was the result of a most excellent collaboration founded by Jade Alglave and also including Alan Stern, Andrea Parri, and Luc Maranget. For more details on the history of this collaboration, please refer to the Linux-kernel memory model presentations at 2016 LinuxCon EU, 2016 Kernel Summit, 2016 Linux Plumbers Conference, 2017 linux.conf.au, or 2017 Linux Plumbers Conference microconference. However, one aspect of the history does bear repeating due to weak copyright tracking earlier in this project, which extends back to early 2015. This weakness came to light in late 2017 after an LKMM presentation by Paul in which an audience member noted the similarity of some LKMM code to code in early published papers. This prompted a copyright review. From Alan Stern: To say that the model was mine is not entirely accurate. Pieces of it (especially the Scpv and Atomic axioms) were taken directly from Jade's models. And of course the Happens-before and Propagation relations and axioms were heavily based on Jade and Luc's work, even though they weren't identical to the earlier versions. Only the RCU portion was completely original. . . . One can make a much better case that I wrote the bulk of lock.cat. However, it was inspired by Luc's earlier version (and still shares some elements in common), and of course it benefited from feedback and testing from all members of our group. The model prior to Alan's was Luc Maranget's. From Luc: I totally agree on Alan Stern's account of the linux kernel model genesis. I thank him for his acknowledgments of my participation to previous model drafts. I'd like to complete Alan Stern's statement: any bell cat code I have written has its roots in discussions with Jade Alglave and Paul McKenney. Moreover I have borrowed cat and bell code written by Jade Alglave freely. This copyright review therefore resulted in late adds to the copyright statements of several files. Discussion of v1 has raised several issues, which we do not believe should block acceptance given that this level of change will be ongoing, just as it has been with memory-barriers.txt: o Under what conditions should ordering provided by pure locking be seen by CPUs not holding the relevant lock(s)? In particular, should the message-passing pattern be forbidden? o Should examples involving C11 release sequences be forbidden? Note that this C11 is still a moving target for this issue: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0735r0.html o Some details of the handling of internal dependencies for atomic read-modify-write atomic operations are still subject to debate. o Changes recently accepted into mainline greatly reduce the need to handle DEC Alpha as a special case. These changes add an smp_read_barrier_depends() to READ_ONCE(), thus causing Alpha to respect ordering of dependent reads. If these changes stick, the memory model can be simplified accordingly. o Will changes be required to accommodate RISC-V? Differences from v1: (http://lkml.kernel.org/r/20171113184031.GA26302@linux.vnet.ibm.com) o Add SPDX notations to .bell and .cat files, replacing textual license statements. o Add reference to upcoming ASPLOS paper to .bell and .cat files. o Updated identifier names in .bell and .cat files to match those used in the ASPLOS paper. o Updates to READMEs and other documentation based on review feedback. o Added a memory-ordering cheatsheet. o Update sigs to new Co-Developed-by and add acks and reviewed-bys. o Simplify rules detecting nested RCU read-side critical sections. o Update copyright statements as noted above. Co-Developed-by: Alan Stern <stern@rowland.harvard.edu> Co-Developed-by: Andrea Parri <parri.andrea@gmail.com> Co-Developed-by: Jade Alglave <j.alglave@ucl.ac.uk> Co-Developed-by: Luc Maranget <luc.maranget@inria.fr> Co-Developed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Jade Alglave <j.alglave@ucl.ac.uk> Signed-off-by: Luc Maranget <luc.maranget@inria.fr> Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: "Reshetova, Elena" <elena.reshetova@intel.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Akira Yokosawa <akiyks@gmail.com> Cc: <linux-arch@vger.kernel.org>
2018-01-19 11:58:55 +08:00
* "Frightening small children and disconcerting grown-ups: Concurrency
* in the Linux kernel" by Alglave, Maranget, McKenney, Parri, and Stern,
* which appeared in ASPLOS 2018.
Automate memory-barriers.txt; provide Linux-kernel memory model There is some reason to believe that Documentation/memory-barriers.txt could use some help, and a major purpose of this patch is to provide that help in the form of a design-time tool that can produce all valid executions of a small fragment of concurrent Linux-kernel code, which is called a "litmus test". This tool's functionality is roughly similar to a full state-space search. Please note that this is a design-time tool, not useful for regression testing. However, we hope that the underlying Linux-kernel memory model will be incorporated into other tools capable of analyzing large bodies of code for regression-testing purposes. The main tool is herd7, together with the linux-kernel.bell, linux-kernel.cat, linux-kernel.cfg, linux-kernel.def, and lock.cat files added by this patch. The herd7 executable takes the other files as input, and all of these files collectively define the Linux-kernel memory memory model. A brief description of each of these other files is provided in the README file. Although this tool does have its limitations, which are documented in the README file, it does improve on the version reported on in the LWN series (https://lwn.net/Articles/718628/ and https://lwn.net/Articles/720550/) by supporting locking and arithmetic, including a much wider variety of read-modify-write atomic operations. Please note that herd7 is not part of this submission, but is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). A second tool is klitmus7, which converts litmus tests to loadable kernel modules for direct testing. As with herd7, the klitmus7 code is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). Of course, litmus tests are not always the best way to fully understand a memory model, so this patch also includes Documentation/explanation.txt, which describes the memory model in detail. In addition, Documentation/recipes.txt provides example known-good and known-bad use cases for those who prefer working by example. This patch also includes a few sample litmus tests, and a great many more litmus tests are available at https://github.com/paulmckrcu/litmus. This patch was the result of a most excellent collaboration founded by Jade Alglave and also including Alan Stern, Andrea Parri, and Luc Maranget. For more details on the history of this collaboration, please refer to the Linux-kernel memory model presentations at 2016 LinuxCon EU, 2016 Kernel Summit, 2016 Linux Plumbers Conference, 2017 linux.conf.au, or 2017 Linux Plumbers Conference microconference. However, one aspect of the history does bear repeating due to weak copyright tracking earlier in this project, which extends back to early 2015. This weakness came to light in late 2017 after an LKMM presentation by Paul in which an audience member noted the similarity of some LKMM code to code in early published papers. This prompted a copyright review. From Alan Stern: To say that the model was mine is not entirely accurate. Pieces of it (especially the Scpv and Atomic axioms) were taken directly from Jade's models. And of course the Happens-before and Propagation relations and axioms were heavily based on Jade and Luc's work, even though they weren't identical to the earlier versions. Only the RCU portion was completely original. . . . One can make a much better case that I wrote the bulk of lock.cat. However, it was inspired by Luc's earlier version (and still shares some elements in common), and of course it benefited from feedback and testing from all members of our group. The model prior to Alan's was Luc Maranget's. From Luc: I totally agree on Alan Stern's account of the linux kernel model genesis. I thank him for his acknowledgments of my participation to previous model drafts. I'd like to complete Alan Stern's statement: any bell cat code I have written has its roots in discussions with Jade Alglave and Paul McKenney. Moreover I have borrowed cat and bell code written by Jade Alglave freely. This copyright review therefore resulted in late adds to the copyright statements of several files. Discussion of v1 has raised several issues, which we do not believe should block acceptance given that this level of change will be ongoing, just as it has been with memory-barriers.txt: o Under what conditions should ordering provided by pure locking be seen by CPUs not holding the relevant lock(s)? In particular, should the message-passing pattern be forbidden? o Should examples involving C11 release sequences be forbidden? Note that this C11 is still a moving target for this issue: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0735r0.html o Some details of the handling of internal dependencies for atomic read-modify-write atomic operations are still subject to debate. o Changes recently accepted into mainline greatly reduce the need to handle DEC Alpha as a special case. These changes add an smp_read_barrier_depends() to READ_ONCE(), thus causing Alpha to respect ordering of dependent reads. If these changes stick, the memory model can be simplified accordingly. o Will changes be required to accommodate RISC-V? Differences from v1: (http://lkml.kernel.org/r/20171113184031.GA26302@linux.vnet.ibm.com) o Add SPDX notations to .bell and .cat files, replacing textual license statements. o Add reference to upcoming ASPLOS paper to .bell and .cat files. o Updated identifier names in .bell and .cat files to match those used in the ASPLOS paper. o Updates to READMEs and other documentation based on review feedback. o Added a memory-ordering cheatsheet. o Update sigs to new Co-Developed-by and add acks and reviewed-bys. o Simplify rules detecting nested RCU read-side critical sections. o Update copyright statements as noted above. Co-Developed-by: Alan Stern <stern@rowland.harvard.edu> Co-Developed-by: Andrea Parri <parri.andrea@gmail.com> Co-Developed-by: Jade Alglave <j.alglave@ucl.ac.uk> Co-Developed-by: Luc Maranget <luc.maranget@inria.fr> Co-Developed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Jade Alglave <j.alglave@ucl.ac.uk> Signed-off-by: Luc Maranget <luc.maranget@inria.fr> Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: "Reshetova, Elena" <elena.reshetova@intel.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Akira Yokosawa <akiyks@gmail.com> Cc: <linux-arch@vger.kernel.org>
2018-01-19 11:58:55 +08:00
*)
"Linux-kernel memory consistency model"
Automate memory-barriers.txt; provide Linux-kernel memory model There is some reason to believe that Documentation/memory-barriers.txt could use some help, and a major purpose of this patch is to provide that help in the form of a design-time tool that can produce all valid executions of a small fragment of concurrent Linux-kernel code, which is called a "litmus test". This tool's functionality is roughly similar to a full state-space search. Please note that this is a design-time tool, not useful for regression testing. However, we hope that the underlying Linux-kernel memory model will be incorporated into other tools capable of analyzing large bodies of code for regression-testing purposes. The main tool is herd7, together with the linux-kernel.bell, linux-kernel.cat, linux-kernel.cfg, linux-kernel.def, and lock.cat files added by this patch. The herd7 executable takes the other files as input, and all of these files collectively define the Linux-kernel memory memory model. A brief description of each of these other files is provided in the README file. Although this tool does have its limitations, which are documented in the README file, it does improve on the version reported on in the LWN series (https://lwn.net/Articles/718628/ and https://lwn.net/Articles/720550/) by supporting locking and arithmetic, including a much wider variety of read-modify-write atomic operations. Please note that herd7 is not part of this submission, but is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). A second tool is klitmus7, which converts litmus tests to loadable kernel modules for direct testing. As with herd7, the klitmus7 code is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). Of course, litmus tests are not always the best way to fully understand a memory model, so this patch also includes Documentation/explanation.txt, which describes the memory model in detail. In addition, Documentation/recipes.txt provides example known-good and known-bad use cases for those who prefer working by example. This patch also includes a few sample litmus tests, and a great many more litmus tests are available at https://github.com/paulmckrcu/litmus. This patch was the result of a most excellent collaboration founded by Jade Alglave and also including Alan Stern, Andrea Parri, and Luc Maranget. For more details on the history of this collaboration, please refer to the Linux-kernel memory model presentations at 2016 LinuxCon EU, 2016 Kernel Summit, 2016 Linux Plumbers Conference, 2017 linux.conf.au, or 2017 Linux Plumbers Conference microconference. However, one aspect of the history does bear repeating due to weak copyright tracking earlier in this project, which extends back to early 2015. This weakness came to light in late 2017 after an LKMM presentation by Paul in which an audience member noted the similarity of some LKMM code to code in early published papers. This prompted a copyright review. From Alan Stern: To say that the model was mine is not entirely accurate. Pieces of it (especially the Scpv and Atomic axioms) were taken directly from Jade's models. And of course the Happens-before and Propagation relations and axioms were heavily based on Jade and Luc's work, even though they weren't identical to the earlier versions. Only the RCU portion was completely original. . . . One can make a much better case that I wrote the bulk of lock.cat. However, it was inspired by Luc's earlier version (and still shares some elements in common), and of course it benefited from feedback and testing from all members of our group. The model prior to Alan's was Luc Maranget's. From Luc: I totally agree on Alan Stern's account of the linux kernel model genesis. I thank him for his acknowledgments of my participation to previous model drafts. I'd like to complete Alan Stern's statement: any bell cat code I have written has its roots in discussions with Jade Alglave and Paul McKenney. Moreover I have borrowed cat and bell code written by Jade Alglave freely. This copyright review therefore resulted in late adds to the copyright statements of several files. Discussion of v1 has raised several issues, which we do not believe should block acceptance given that this level of change will be ongoing, just as it has been with memory-barriers.txt: o Under what conditions should ordering provided by pure locking be seen by CPUs not holding the relevant lock(s)? In particular, should the message-passing pattern be forbidden? o Should examples involving C11 release sequences be forbidden? Note that this C11 is still a moving target for this issue: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0735r0.html o Some details of the handling of internal dependencies for atomic read-modify-write atomic operations are still subject to debate. o Changes recently accepted into mainline greatly reduce the need to handle DEC Alpha as a special case. These changes add an smp_read_barrier_depends() to READ_ONCE(), thus causing Alpha to respect ordering of dependent reads. If these changes stick, the memory model can be simplified accordingly. o Will changes be required to accommodate RISC-V? Differences from v1: (http://lkml.kernel.org/r/20171113184031.GA26302@linux.vnet.ibm.com) o Add SPDX notations to .bell and .cat files, replacing textual license statements. o Add reference to upcoming ASPLOS paper to .bell and .cat files. o Updated identifier names in .bell and .cat files to match those used in the ASPLOS paper. o Updates to READMEs and other documentation based on review feedback. o Added a memory-ordering cheatsheet. o Update sigs to new Co-Developed-by and add acks and reviewed-bys. o Simplify rules detecting nested RCU read-side critical sections. o Update copyright statements as noted above. Co-Developed-by: Alan Stern <stern@rowland.harvard.edu> Co-Developed-by: Andrea Parri <parri.andrea@gmail.com> Co-Developed-by: Jade Alglave <j.alglave@ucl.ac.uk> Co-Developed-by: Luc Maranget <luc.maranget@inria.fr> Co-Developed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Jade Alglave <j.alglave@ucl.ac.uk> Signed-off-by: Luc Maranget <luc.maranget@inria.fr> Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: "Reshetova, Elena" <elena.reshetova@intel.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Akira Yokosawa <akiyks@gmail.com> Cc: <linux-arch@vger.kernel.org>
2018-01-19 11:58:55 +08:00
(*
* File "lock.cat" handles locks and is experimental.
* It can be replaced by include "cos.cat" for tests that do not use locks.
*)
include "lock.cat"
(*******************)
(* Basic relations *)
(*******************)
(* Release Acquire *)
let acq-po = [Acquire] ; po ; [M]
let po-rel = [M] ; po ; [Release]
let po-unlock-lock-po = po ; [UL] ; (po|rf) ; [LKR] ; po
Automate memory-barriers.txt; provide Linux-kernel memory model There is some reason to believe that Documentation/memory-barriers.txt could use some help, and a major purpose of this patch is to provide that help in the form of a design-time tool that can produce all valid executions of a small fragment of concurrent Linux-kernel code, which is called a "litmus test". This tool's functionality is roughly similar to a full state-space search. Please note that this is a design-time tool, not useful for regression testing. However, we hope that the underlying Linux-kernel memory model will be incorporated into other tools capable of analyzing large bodies of code for regression-testing purposes. The main tool is herd7, together with the linux-kernel.bell, linux-kernel.cat, linux-kernel.cfg, linux-kernel.def, and lock.cat files added by this patch. The herd7 executable takes the other files as input, and all of these files collectively define the Linux-kernel memory memory model. A brief description of each of these other files is provided in the README file. Although this tool does have its limitations, which are documented in the README file, it does improve on the version reported on in the LWN series (https://lwn.net/Articles/718628/ and https://lwn.net/Articles/720550/) by supporting locking and arithmetic, including a much wider variety of read-modify-write atomic operations. Please note that herd7 is not part of this submission, but is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). A second tool is klitmus7, which converts litmus tests to loadable kernel modules for direct testing. As with herd7, the klitmus7 code is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). Of course, litmus tests are not always the best way to fully understand a memory model, so this patch also includes Documentation/explanation.txt, which describes the memory model in detail. In addition, Documentation/recipes.txt provides example known-good and known-bad use cases for those who prefer working by example. This patch also includes a few sample litmus tests, and a great many more litmus tests are available at https://github.com/paulmckrcu/litmus. This patch was the result of a most excellent collaboration founded by Jade Alglave and also including Alan Stern, Andrea Parri, and Luc Maranget. For more details on the history of this collaboration, please refer to the Linux-kernel memory model presentations at 2016 LinuxCon EU, 2016 Kernel Summit, 2016 Linux Plumbers Conference, 2017 linux.conf.au, or 2017 Linux Plumbers Conference microconference. However, one aspect of the history does bear repeating due to weak copyright tracking earlier in this project, which extends back to early 2015. This weakness came to light in late 2017 after an LKMM presentation by Paul in which an audience member noted the similarity of some LKMM code to code in early published papers. This prompted a copyright review. From Alan Stern: To say that the model was mine is not entirely accurate. Pieces of it (especially the Scpv and Atomic axioms) were taken directly from Jade's models. And of course the Happens-before and Propagation relations and axioms were heavily based on Jade and Luc's work, even though they weren't identical to the earlier versions. Only the RCU portion was completely original. . . . One can make a much better case that I wrote the bulk of lock.cat. However, it was inspired by Luc's earlier version (and still shares some elements in common), and of course it benefited from feedback and testing from all members of our group. The model prior to Alan's was Luc Maranget's. From Luc: I totally agree on Alan Stern's account of the linux kernel model genesis. I thank him for his acknowledgments of my participation to previous model drafts. I'd like to complete Alan Stern's statement: any bell cat code I have written has its roots in discussions with Jade Alglave and Paul McKenney. Moreover I have borrowed cat and bell code written by Jade Alglave freely. This copyright review therefore resulted in late adds to the copyright statements of several files. Discussion of v1 has raised several issues, which we do not believe should block acceptance given that this level of change will be ongoing, just as it has been with memory-barriers.txt: o Under what conditions should ordering provided by pure locking be seen by CPUs not holding the relevant lock(s)? In particular, should the message-passing pattern be forbidden? o Should examples involving C11 release sequences be forbidden? Note that this C11 is still a moving target for this issue: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0735r0.html o Some details of the handling of internal dependencies for atomic read-modify-write atomic operations are still subject to debate. o Changes recently accepted into mainline greatly reduce the need to handle DEC Alpha as a special case. These changes add an smp_read_barrier_depends() to READ_ONCE(), thus causing Alpha to respect ordering of dependent reads. If these changes stick, the memory model can be simplified accordingly. o Will changes be required to accommodate RISC-V? Differences from v1: (http://lkml.kernel.org/r/20171113184031.GA26302@linux.vnet.ibm.com) o Add SPDX notations to .bell and .cat files, replacing textual license statements. o Add reference to upcoming ASPLOS paper to .bell and .cat files. o Updated identifier names in .bell and .cat files to match those used in the ASPLOS paper. o Updates to READMEs and other documentation based on review feedback. o Added a memory-ordering cheatsheet. o Update sigs to new Co-Developed-by and add acks and reviewed-bys. o Simplify rules detecting nested RCU read-side critical sections. o Update copyright statements as noted above. Co-Developed-by: Alan Stern <stern@rowland.harvard.edu> Co-Developed-by: Andrea Parri <parri.andrea@gmail.com> Co-Developed-by: Jade Alglave <j.alglave@ucl.ac.uk> Co-Developed-by: Luc Maranget <luc.maranget@inria.fr> Co-Developed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Jade Alglave <j.alglave@ucl.ac.uk> Signed-off-by: Luc Maranget <luc.maranget@inria.fr> Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: "Reshetova, Elena" <elena.reshetova@intel.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Akira Yokosawa <akiyks@gmail.com> Cc: <linux-arch@vger.kernel.org>
2018-01-19 11:58:55 +08:00
(* Fences *)
let R4rmb = R \ Noreturn (* Reads for which rmb works *)
let rmb = [R4rmb] ; fencerel(Rmb) ; [R4rmb]
Automate memory-barriers.txt; provide Linux-kernel memory model There is some reason to believe that Documentation/memory-barriers.txt could use some help, and a major purpose of this patch is to provide that help in the form of a design-time tool that can produce all valid executions of a small fragment of concurrent Linux-kernel code, which is called a "litmus test". This tool's functionality is roughly similar to a full state-space search. Please note that this is a design-time tool, not useful for regression testing. However, we hope that the underlying Linux-kernel memory model will be incorporated into other tools capable of analyzing large bodies of code for regression-testing purposes. The main tool is herd7, together with the linux-kernel.bell, linux-kernel.cat, linux-kernel.cfg, linux-kernel.def, and lock.cat files added by this patch. The herd7 executable takes the other files as input, and all of these files collectively define the Linux-kernel memory memory model. A brief description of each of these other files is provided in the README file. Although this tool does have its limitations, which are documented in the README file, it does improve on the version reported on in the LWN series (https://lwn.net/Articles/718628/ and https://lwn.net/Articles/720550/) by supporting locking and arithmetic, including a much wider variety of read-modify-write atomic operations. Please note that herd7 is not part of this submission, but is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). A second tool is klitmus7, which converts litmus tests to loadable kernel modules for direct testing. As with herd7, the klitmus7 code is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). Of course, litmus tests are not always the best way to fully understand a memory model, so this patch also includes Documentation/explanation.txt, which describes the memory model in detail. In addition, Documentation/recipes.txt provides example known-good and known-bad use cases for those who prefer working by example. This patch also includes a few sample litmus tests, and a great many more litmus tests are available at https://github.com/paulmckrcu/litmus. This patch was the result of a most excellent collaboration founded by Jade Alglave and also including Alan Stern, Andrea Parri, and Luc Maranget. For more details on the history of this collaboration, please refer to the Linux-kernel memory model presentations at 2016 LinuxCon EU, 2016 Kernel Summit, 2016 Linux Plumbers Conference, 2017 linux.conf.au, or 2017 Linux Plumbers Conference microconference. However, one aspect of the history does bear repeating due to weak copyright tracking earlier in this project, which extends back to early 2015. This weakness came to light in late 2017 after an LKMM presentation by Paul in which an audience member noted the similarity of some LKMM code to code in early published papers. This prompted a copyright review. From Alan Stern: To say that the model was mine is not entirely accurate. Pieces of it (especially the Scpv and Atomic axioms) were taken directly from Jade's models. And of course the Happens-before and Propagation relations and axioms were heavily based on Jade and Luc's work, even though they weren't identical to the earlier versions. Only the RCU portion was completely original. . . . One can make a much better case that I wrote the bulk of lock.cat. However, it was inspired by Luc's earlier version (and still shares some elements in common), and of course it benefited from feedback and testing from all members of our group. The model prior to Alan's was Luc Maranget's. From Luc: I totally agree on Alan Stern's account of the linux kernel model genesis. I thank him for his acknowledgments of my participation to previous model drafts. I'd like to complete Alan Stern's statement: any bell cat code I have written has its roots in discussions with Jade Alglave and Paul McKenney. Moreover I have borrowed cat and bell code written by Jade Alglave freely. This copyright review therefore resulted in late adds to the copyright statements of several files. Discussion of v1 has raised several issues, which we do not believe should block acceptance given that this level of change will be ongoing, just as it has been with memory-barriers.txt: o Under what conditions should ordering provided by pure locking be seen by CPUs not holding the relevant lock(s)? In particular, should the message-passing pattern be forbidden? o Should examples involving C11 release sequences be forbidden? Note that this C11 is still a moving target for this issue: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0735r0.html o Some details of the handling of internal dependencies for atomic read-modify-write atomic operations are still subject to debate. o Changes recently accepted into mainline greatly reduce the need to handle DEC Alpha as a special case. These changes add an smp_read_barrier_depends() to READ_ONCE(), thus causing Alpha to respect ordering of dependent reads. If these changes stick, the memory model can be simplified accordingly. o Will changes be required to accommodate RISC-V? Differences from v1: (http://lkml.kernel.org/r/20171113184031.GA26302@linux.vnet.ibm.com) o Add SPDX notations to .bell and .cat files, replacing textual license statements. o Add reference to upcoming ASPLOS paper to .bell and .cat files. o Updated identifier names in .bell and .cat files to match those used in the ASPLOS paper. o Updates to READMEs and other documentation based on review feedback. o Added a memory-ordering cheatsheet. o Update sigs to new Co-Developed-by and add acks and reviewed-bys. o Simplify rules detecting nested RCU read-side critical sections. o Update copyright statements as noted above. Co-Developed-by: Alan Stern <stern@rowland.harvard.edu> Co-Developed-by: Andrea Parri <parri.andrea@gmail.com> Co-Developed-by: Jade Alglave <j.alglave@ucl.ac.uk> Co-Developed-by: Luc Maranget <luc.maranget@inria.fr> Co-Developed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Jade Alglave <j.alglave@ucl.ac.uk> Signed-off-by: Luc Maranget <luc.maranget@inria.fr> Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: "Reshetova, Elena" <elena.reshetova@intel.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Akira Yokosawa <akiyks@gmail.com> Cc: <linux-arch@vger.kernel.org>
2018-01-19 11:58:55 +08:00
let wmb = [W] ; fencerel(Wmb) ; [W]
let mb = ([M] ; fencerel(Mb) ; [M]) |
([M] ; fencerel(Before-atomic) ; [RMW] ; po? ; [M]) |
([M] ; po? ; [RMW] ; fencerel(After-atomic) ; [M]) |
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>
2018-12-04 07:04:49 +08:00
([M] ; po? ; [LKW] ; fencerel(After-spinlock) ; [M]) |
([M] ; po ; [UL] ; (co | po) ; [LKW] ;
fencerel(After-unlock-lock) ; [M])
let gp = po ; [Sync-rcu | Sync-srcu] ; po?
Automate memory-barriers.txt; provide Linux-kernel memory model There is some reason to believe that Documentation/memory-barriers.txt could use some help, and a major purpose of this patch is to provide that help in the form of a design-time tool that can produce all valid executions of a small fragment of concurrent Linux-kernel code, which is called a "litmus test". This tool's functionality is roughly similar to a full state-space search. Please note that this is a design-time tool, not useful for regression testing. However, we hope that the underlying Linux-kernel memory model will be incorporated into other tools capable of analyzing large bodies of code for regression-testing purposes. The main tool is herd7, together with the linux-kernel.bell, linux-kernel.cat, linux-kernel.cfg, linux-kernel.def, and lock.cat files added by this patch. The herd7 executable takes the other files as input, and all of these files collectively define the Linux-kernel memory memory model. A brief description of each of these other files is provided in the README file. Although this tool does have its limitations, which are documented in the README file, it does improve on the version reported on in the LWN series (https://lwn.net/Articles/718628/ and https://lwn.net/Articles/720550/) by supporting locking and arithmetic, including a much wider variety of read-modify-write atomic operations. Please note that herd7 is not part of this submission, but is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). A second tool is klitmus7, which converts litmus tests to loadable kernel modules for direct testing. As with herd7, the klitmus7 code is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). Of course, litmus tests are not always the best way to fully understand a memory model, so this patch also includes Documentation/explanation.txt, which describes the memory model in detail. In addition, Documentation/recipes.txt provides example known-good and known-bad use cases for those who prefer working by example. This patch also includes a few sample litmus tests, and a great many more litmus tests are available at https://github.com/paulmckrcu/litmus. This patch was the result of a most excellent collaboration founded by Jade Alglave and also including Alan Stern, Andrea Parri, and Luc Maranget. For more details on the history of this collaboration, please refer to the Linux-kernel memory model presentations at 2016 LinuxCon EU, 2016 Kernel Summit, 2016 Linux Plumbers Conference, 2017 linux.conf.au, or 2017 Linux Plumbers Conference microconference. However, one aspect of the history does bear repeating due to weak copyright tracking earlier in this project, which extends back to early 2015. This weakness came to light in late 2017 after an LKMM presentation by Paul in which an audience member noted the similarity of some LKMM code to code in early published papers. This prompted a copyright review. From Alan Stern: To say that the model was mine is not entirely accurate. Pieces of it (especially the Scpv and Atomic axioms) were taken directly from Jade's models. And of course the Happens-before and Propagation relations and axioms were heavily based on Jade and Luc's work, even though they weren't identical to the earlier versions. Only the RCU portion was completely original. . . . One can make a much better case that I wrote the bulk of lock.cat. However, it was inspired by Luc's earlier version (and still shares some elements in common), and of course it benefited from feedback and testing from all members of our group. The model prior to Alan's was Luc Maranget's. From Luc: I totally agree on Alan Stern's account of the linux kernel model genesis. I thank him for his acknowledgments of my participation to previous model drafts. I'd like to complete Alan Stern's statement: any bell cat code I have written has its roots in discussions with Jade Alglave and Paul McKenney. Moreover I have borrowed cat and bell code written by Jade Alglave freely. This copyright review therefore resulted in late adds to the copyright statements of several files. Discussion of v1 has raised several issues, which we do not believe should block acceptance given that this level of change will be ongoing, just as it has been with memory-barriers.txt: o Under what conditions should ordering provided by pure locking be seen by CPUs not holding the relevant lock(s)? In particular, should the message-passing pattern be forbidden? o Should examples involving C11 release sequences be forbidden? Note that this C11 is still a moving target for this issue: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0735r0.html o Some details of the handling of internal dependencies for atomic read-modify-write atomic operations are still subject to debate. o Changes recently accepted into mainline greatly reduce the need to handle DEC Alpha as a special case. These changes add an smp_read_barrier_depends() to READ_ONCE(), thus causing Alpha to respect ordering of dependent reads. If these changes stick, the memory model can be simplified accordingly. o Will changes be required to accommodate RISC-V? Differences from v1: (http://lkml.kernel.org/r/20171113184031.GA26302@linux.vnet.ibm.com) o Add SPDX notations to .bell and .cat files, replacing textual license statements. o Add reference to upcoming ASPLOS paper to .bell and .cat files. o Updated identifier names in .bell and .cat files to match those used in the ASPLOS paper. o Updates to READMEs and other documentation based on review feedback. o Added a memory-ordering cheatsheet. o Update sigs to new Co-Developed-by and add acks and reviewed-bys. o Simplify rules detecting nested RCU read-side critical sections. o Update copyright statements as noted above. Co-Developed-by: Alan Stern <stern@rowland.harvard.edu> Co-Developed-by: Andrea Parri <parri.andrea@gmail.com> Co-Developed-by: Jade Alglave <j.alglave@ucl.ac.uk> Co-Developed-by: Luc Maranget <luc.maranget@inria.fr> Co-Developed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Jade Alglave <j.alglave@ucl.ac.uk> Signed-off-by: Luc Maranget <luc.maranget@inria.fr> Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: "Reshetova, Elena" <elena.reshetova@intel.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Akira Yokosawa <akiyks@gmail.com> Cc: <linux-arch@vger.kernel.org>
2018-01-19 11:58:55 +08:00
let strong-fence = mb | gp
let nonrw-fence = strong-fence | po-rel | acq-po
let fence = nonrw-fence | wmb | rmb
let barrier = fencerel(Barrier | Rmb | Wmb | Mb | Sync-rcu | Sync-srcu |
Before-atomic | After-atomic | Acquire | Release |
Rcu-lock | Rcu-unlock | Srcu-lock | Srcu-unlock) |
(po ; [Release]) | ([Acquire] ; po)
Automate memory-barriers.txt; provide Linux-kernel memory model There is some reason to believe that Documentation/memory-barriers.txt could use some help, and a major purpose of this patch is to provide that help in the form of a design-time tool that can produce all valid executions of a small fragment of concurrent Linux-kernel code, which is called a "litmus test". This tool's functionality is roughly similar to a full state-space search. Please note that this is a design-time tool, not useful for regression testing. However, we hope that the underlying Linux-kernel memory model will be incorporated into other tools capable of analyzing large bodies of code for regression-testing purposes. The main tool is herd7, together with the linux-kernel.bell, linux-kernel.cat, linux-kernel.cfg, linux-kernel.def, and lock.cat files added by this patch. The herd7 executable takes the other files as input, and all of these files collectively define the Linux-kernel memory memory model. A brief description of each of these other files is provided in the README file. Although this tool does have its limitations, which are documented in the README file, it does improve on the version reported on in the LWN series (https://lwn.net/Articles/718628/ and https://lwn.net/Articles/720550/) by supporting locking and arithmetic, including a much wider variety of read-modify-write atomic operations. Please note that herd7 is not part of this submission, but is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). A second tool is klitmus7, which converts litmus tests to loadable kernel modules for direct testing. As with herd7, the klitmus7 code is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). Of course, litmus tests are not always the best way to fully understand a memory model, so this patch also includes Documentation/explanation.txt, which describes the memory model in detail. In addition, Documentation/recipes.txt provides example known-good and known-bad use cases for those who prefer working by example. This patch also includes a few sample litmus tests, and a great many more litmus tests are available at https://github.com/paulmckrcu/litmus. This patch was the result of a most excellent collaboration founded by Jade Alglave and also including Alan Stern, Andrea Parri, and Luc Maranget. For more details on the history of this collaboration, please refer to the Linux-kernel memory model presentations at 2016 LinuxCon EU, 2016 Kernel Summit, 2016 Linux Plumbers Conference, 2017 linux.conf.au, or 2017 Linux Plumbers Conference microconference. However, one aspect of the history does bear repeating due to weak copyright tracking earlier in this project, which extends back to early 2015. This weakness came to light in late 2017 after an LKMM presentation by Paul in which an audience member noted the similarity of some LKMM code to code in early published papers. This prompted a copyright review. From Alan Stern: To say that the model was mine is not entirely accurate. Pieces of it (especially the Scpv and Atomic axioms) were taken directly from Jade's models. And of course the Happens-before and Propagation relations and axioms were heavily based on Jade and Luc's work, even though they weren't identical to the earlier versions. Only the RCU portion was completely original. . . . One can make a much better case that I wrote the bulk of lock.cat. However, it was inspired by Luc's earlier version (and still shares some elements in common), and of course it benefited from feedback and testing from all members of our group. The model prior to Alan's was Luc Maranget's. From Luc: I totally agree on Alan Stern's account of the linux kernel model genesis. I thank him for his acknowledgments of my participation to previous model drafts. I'd like to complete Alan Stern's statement: any bell cat code I have written has its roots in discussions with Jade Alglave and Paul McKenney. Moreover I have borrowed cat and bell code written by Jade Alglave freely. This copyright review therefore resulted in late adds to the copyright statements of several files. Discussion of v1 has raised several issues, which we do not believe should block acceptance given that this level of change will be ongoing, just as it has been with memory-barriers.txt: o Under what conditions should ordering provided by pure locking be seen by CPUs not holding the relevant lock(s)? In particular, should the message-passing pattern be forbidden? o Should examples involving C11 release sequences be forbidden? Note that this C11 is still a moving target for this issue: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0735r0.html o Some details of the handling of internal dependencies for atomic read-modify-write atomic operations are still subject to debate. o Changes recently accepted into mainline greatly reduce the need to handle DEC Alpha as a special case. These changes add an smp_read_barrier_depends() to READ_ONCE(), thus causing Alpha to respect ordering of dependent reads. If these changes stick, the memory model can be simplified accordingly. o Will changes be required to accommodate RISC-V? Differences from v1: (http://lkml.kernel.org/r/20171113184031.GA26302@linux.vnet.ibm.com) o Add SPDX notations to .bell and .cat files, replacing textual license statements. o Add reference to upcoming ASPLOS paper to .bell and .cat files. o Updated identifier names in .bell and .cat files to match those used in the ASPLOS paper. o Updates to READMEs and other documentation based on review feedback. o Added a memory-ordering cheatsheet. o Update sigs to new Co-Developed-by and add acks and reviewed-bys. o Simplify rules detecting nested RCU read-side critical sections. o Update copyright statements as noted above. Co-Developed-by: Alan Stern <stern@rowland.harvard.edu> Co-Developed-by: Andrea Parri <parri.andrea@gmail.com> Co-Developed-by: Jade Alglave <j.alglave@ucl.ac.uk> Co-Developed-by: Luc Maranget <luc.maranget@inria.fr> Co-Developed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Jade Alglave <j.alglave@ucl.ac.uk> Signed-off-by: Luc Maranget <luc.maranget@inria.fr> Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: "Reshetova, Elena" <elena.reshetova@intel.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Akira Yokosawa <akiyks@gmail.com> Cc: <linux-arch@vger.kernel.org>
2018-01-19 11:58:55 +08:00
(**********************************)
(* Fundamental coherence ordering *)
(**********************************)
(* Sequential Consistency Per Variable *)
let com = rf | co | fr
acyclic po-loc | com as coherence
(* Atomic Read-Modify-Write *)
empty rmw & (fre ; coe) as atomic
(**********************************)
(* Instruction execution ordering *)
(**********************************)
(* Preserved Program Order *)
let dep = addr | data
let rwdep = (dep | ctrl) ; [W]
let overwrite = co | fr
let to-w = rwdep | (overwrite & int) | (addr ; [Plain] ; wmb)
let to-r = addr | (dep ; [Marked] ; rfi)
let ppo = to-r | to-w | fence | (po-unlock-lock-po & int)
Automate memory-barriers.txt; provide Linux-kernel memory model There is some reason to believe that Documentation/memory-barriers.txt could use some help, and a major purpose of this patch is to provide that help in the form of a design-time tool that can produce all valid executions of a small fragment of concurrent Linux-kernel code, which is called a "litmus test". This tool's functionality is roughly similar to a full state-space search. Please note that this is a design-time tool, not useful for regression testing. However, we hope that the underlying Linux-kernel memory model will be incorporated into other tools capable of analyzing large bodies of code for regression-testing purposes. The main tool is herd7, together with the linux-kernel.bell, linux-kernel.cat, linux-kernel.cfg, linux-kernel.def, and lock.cat files added by this patch. The herd7 executable takes the other files as input, and all of these files collectively define the Linux-kernel memory memory model. A brief description of each of these other files is provided in the README file. Although this tool does have its limitations, which are documented in the README file, it does improve on the version reported on in the LWN series (https://lwn.net/Articles/718628/ and https://lwn.net/Articles/720550/) by supporting locking and arithmetic, including a much wider variety of read-modify-write atomic operations. Please note that herd7 is not part of this submission, but is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). A second tool is klitmus7, which converts litmus tests to loadable kernel modules for direct testing. As with herd7, the klitmus7 code is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). Of course, litmus tests are not always the best way to fully understand a memory model, so this patch also includes Documentation/explanation.txt, which describes the memory model in detail. In addition, Documentation/recipes.txt provides example known-good and known-bad use cases for those who prefer working by example. This patch also includes a few sample litmus tests, and a great many more litmus tests are available at https://github.com/paulmckrcu/litmus. This patch was the result of a most excellent collaboration founded by Jade Alglave and also including Alan Stern, Andrea Parri, and Luc Maranget. For more details on the history of this collaboration, please refer to the Linux-kernel memory model presentations at 2016 LinuxCon EU, 2016 Kernel Summit, 2016 Linux Plumbers Conference, 2017 linux.conf.au, or 2017 Linux Plumbers Conference microconference. However, one aspect of the history does bear repeating due to weak copyright tracking earlier in this project, which extends back to early 2015. This weakness came to light in late 2017 after an LKMM presentation by Paul in which an audience member noted the similarity of some LKMM code to code in early published papers. This prompted a copyright review. From Alan Stern: To say that the model was mine is not entirely accurate. Pieces of it (especially the Scpv and Atomic axioms) were taken directly from Jade's models. And of course the Happens-before and Propagation relations and axioms were heavily based on Jade and Luc's work, even though they weren't identical to the earlier versions. Only the RCU portion was completely original. . . . One can make a much better case that I wrote the bulk of lock.cat. However, it was inspired by Luc's earlier version (and still shares some elements in common), and of course it benefited from feedback and testing from all members of our group. The model prior to Alan's was Luc Maranget's. From Luc: I totally agree on Alan Stern's account of the linux kernel model genesis. I thank him for his acknowledgments of my participation to previous model drafts. I'd like to complete Alan Stern's statement: any bell cat code I have written has its roots in discussions with Jade Alglave and Paul McKenney. Moreover I have borrowed cat and bell code written by Jade Alglave freely. This copyright review therefore resulted in late adds to the copyright statements of several files. Discussion of v1 has raised several issues, which we do not believe should block acceptance given that this level of change will be ongoing, just as it has been with memory-barriers.txt: o Under what conditions should ordering provided by pure locking be seen by CPUs not holding the relevant lock(s)? In particular, should the message-passing pattern be forbidden? o Should examples involving C11 release sequences be forbidden? Note that this C11 is still a moving target for this issue: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0735r0.html o Some details of the handling of internal dependencies for atomic read-modify-write atomic operations are still subject to debate. o Changes recently accepted into mainline greatly reduce the need to handle DEC Alpha as a special case. These changes add an smp_read_barrier_depends() to READ_ONCE(), thus causing Alpha to respect ordering of dependent reads. If these changes stick, the memory model can be simplified accordingly. o Will changes be required to accommodate RISC-V? Differences from v1: (http://lkml.kernel.org/r/20171113184031.GA26302@linux.vnet.ibm.com) o Add SPDX notations to .bell and .cat files, replacing textual license statements. o Add reference to upcoming ASPLOS paper to .bell and .cat files. o Updated identifier names in .bell and .cat files to match those used in the ASPLOS paper. o Updates to READMEs and other documentation based on review feedback. o Added a memory-ordering cheatsheet. o Update sigs to new Co-Developed-by and add acks and reviewed-bys. o Simplify rules detecting nested RCU read-side critical sections. o Update copyright statements as noted above. Co-Developed-by: Alan Stern <stern@rowland.harvard.edu> Co-Developed-by: Andrea Parri <parri.andrea@gmail.com> Co-Developed-by: Jade Alglave <j.alglave@ucl.ac.uk> Co-Developed-by: Luc Maranget <luc.maranget@inria.fr> Co-Developed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Jade Alglave <j.alglave@ucl.ac.uk> Signed-off-by: Luc Maranget <luc.maranget@inria.fr> Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: "Reshetova, Elena" <elena.reshetova@intel.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Akira Yokosawa <akiyks@gmail.com> Cc: <linux-arch@vger.kernel.org>
2018-01-19 11:58:55 +08:00
(* Propagation: Ordering from release operations and strong fences. *)
let A-cumul(r) = (rfe ; [Marked])? ; r
let cumul-fence = [Marked] ; (A-cumul(strong-fence | po-rel) | wmb |
po-unlock-lock-po) ; [Marked]
let prop = [Marked] ; (overwrite & ext)? ; cumul-fence* ;
[Marked] ; rfe? ; [Marked]
Automate memory-barriers.txt; provide Linux-kernel memory model There is some reason to believe that Documentation/memory-barriers.txt could use some help, and a major purpose of this patch is to provide that help in the form of a design-time tool that can produce all valid executions of a small fragment of concurrent Linux-kernel code, which is called a "litmus test". This tool's functionality is roughly similar to a full state-space search. Please note that this is a design-time tool, not useful for regression testing. However, we hope that the underlying Linux-kernel memory model will be incorporated into other tools capable of analyzing large bodies of code for regression-testing purposes. The main tool is herd7, together with the linux-kernel.bell, linux-kernel.cat, linux-kernel.cfg, linux-kernel.def, and lock.cat files added by this patch. The herd7 executable takes the other files as input, and all of these files collectively define the Linux-kernel memory memory model. A brief description of each of these other files is provided in the README file. Although this tool does have its limitations, which are documented in the README file, it does improve on the version reported on in the LWN series (https://lwn.net/Articles/718628/ and https://lwn.net/Articles/720550/) by supporting locking and arithmetic, including a much wider variety of read-modify-write atomic operations. Please note that herd7 is not part of this submission, but is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). A second tool is klitmus7, which converts litmus tests to loadable kernel modules for direct testing. As with herd7, the klitmus7 code is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). Of course, litmus tests are not always the best way to fully understand a memory model, so this patch also includes Documentation/explanation.txt, which describes the memory model in detail. In addition, Documentation/recipes.txt provides example known-good and known-bad use cases for those who prefer working by example. This patch also includes a few sample litmus tests, and a great many more litmus tests are available at https://github.com/paulmckrcu/litmus. This patch was the result of a most excellent collaboration founded by Jade Alglave and also including Alan Stern, Andrea Parri, and Luc Maranget. For more details on the history of this collaboration, please refer to the Linux-kernel memory model presentations at 2016 LinuxCon EU, 2016 Kernel Summit, 2016 Linux Plumbers Conference, 2017 linux.conf.au, or 2017 Linux Plumbers Conference microconference. However, one aspect of the history does bear repeating due to weak copyright tracking earlier in this project, which extends back to early 2015. This weakness came to light in late 2017 after an LKMM presentation by Paul in which an audience member noted the similarity of some LKMM code to code in early published papers. This prompted a copyright review. From Alan Stern: To say that the model was mine is not entirely accurate. Pieces of it (especially the Scpv and Atomic axioms) were taken directly from Jade's models. And of course the Happens-before and Propagation relations and axioms were heavily based on Jade and Luc's work, even though they weren't identical to the earlier versions. Only the RCU portion was completely original. . . . One can make a much better case that I wrote the bulk of lock.cat. However, it was inspired by Luc's earlier version (and still shares some elements in common), and of course it benefited from feedback and testing from all members of our group. The model prior to Alan's was Luc Maranget's. From Luc: I totally agree on Alan Stern's account of the linux kernel model genesis. I thank him for his acknowledgments of my participation to previous model drafts. I'd like to complete Alan Stern's statement: any bell cat code I have written has its roots in discussions with Jade Alglave and Paul McKenney. Moreover I have borrowed cat and bell code written by Jade Alglave freely. This copyright review therefore resulted in late adds to the copyright statements of several files. Discussion of v1 has raised several issues, which we do not believe should block acceptance given that this level of change will be ongoing, just as it has been with memory-barriers.txt: o Under what conditions should ordering provided by pure locking be seen by CPUs not holding the relevant lock(s)? In particular, should the message-passing pattern be forbidden? o Should examples involving C11 release sequences be forbidden? Note that this C11 is still a moving target for this issue: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0735r0.html o Some details of the handling of internal dependencies for atomic read-modify-write atomic operations are still subject to debate. o Changes recently accepted into mainline greatly reduce the need to handle DEC Alpha as a special case. These changes add an smp_read_barrier_depends() to READ_ONCE(), thus causing Alpha to respect ordering of dependent reads. If these changes stick, the memory model can be simplified accordingly. o Will changes be required to accommodate RISC-V? Differences from v1: (http://lkml.kernel.org/r/20171113184031.GA26302@linux.vnet.ibm.com) o Add SPDX notations to .bell and .cat files, replacing textual license statements. o Add reference to upcoming ASPLOS paper to .bell and .cat files. o Updated identifier names in .bell and .cat files to match those used in the ASPLOS paper. o Updates to READMEs and other documentation based on review feedback. o Added a memory-ordering cheatsheet. o Update sigs to new Co-Developed-by and add acks and reviewed-bys. o Simplify rules detecting nested RCU read-side critical sections. o Update copyright statements as noted above. Co-Developed-by: Alan Stern <stern@rowland.harvard.edu> Co-Developed-by: Andrea Parri <parri.andrea@gmail.com> Co-Developed-by: Jade Alglave <j.alglave@ucl.ac.uk> Co-Developed-by: Luc Maranget <luc.maranget@inria.fr> Co-Developed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Jade Alglave <j.alglave@ucl.ac.uk> Signed-off-by: Luc Maranget <luc.maranget@inria.fr> Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: "Reshetova, Elena" <elena.reshetova@intel.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Akira Yokosawa <akiyks@gmail.com> Cc: <linux-arch@vger.kernel.org>
2018-01-19 11:58:55 +08:00
(*
* Happens Before: Ordering from the passage of time.
* No fences needed here for prop because relation confined to one process.
*)
let hb = [Marked] ; (ppo | rfe | ((prop \ id) & int)) ; [Marked]
Automate memory-barriers.txt; provide Linux-kernel memory model There is some reason to believe that Documentation/memory-barriers.txt could use some help, and a major purpose of this patch is to provide that help in the form of a design-time tool that can produce all valid executions of a small fragment of concurrent Linux-kernel code, which is called a "litmus test". This tool's functionality is roughly similar to a full state-space search. Please note that this is a design-time tool, not useful for regression testing. However, we hope that the underlying Linux-kernel memory model will be incorporated into other tools capable of analyzing large bodies of code for regression-testing purposes. The main tool is herd7, together with the linux-kernel.bell, linux-kernel.cat, linux-kernel.cfg, linux-kernel.def, and lock.cat files added by this patch. The herd7 executable takes the other files as input, and all of these files collectively define the Linux-kernel memory memory model. A brief description of each of these other files is provided in the README file. Although this tool does have its limitations, which are documented in the README file, it does improve on the version reported on in the LWN series (https://lwn.net/Articles/718628/ and https://lwn.net/Articles/720550/) by supporting locking and arithmetic, including a much wider variety of read-modify-write atomic operations. Please note that herd7 is not part of this submission, but is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). A second tool is klitmus7, which converts litmus tests to loadable kernel modules for direct testing. As with herd7, the klitmus7 code is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). Of course, litmus tests are not always the best way to fully understand a memory model, so this patch also includes Documentation/explanation.txt, which describes the memory model in detail. In addition, Documentation/recipes.txt provides example known-good and known-bad use cases for those who prefer working by example. This patch also includes a few sample litmus tests, and a great many more litmus tests are available at https://github.com/paulmckrcu/litmus. This patch was the result of a most excellent collaboration founded by Jade Alglave and also including Alan Stern, Andrea Parri, and Luc Maranget. For more details on the history of this collaboration, please refer to the Linux-kernel memory model presentations at 2016 LinuxCon EU, 2016 Kernel Summit, 2016 Linux Plumbers Conference, 2017 linux.conf.au, or 2017 Linux Plumbers Conference microconference. However, one aspect of the history does bear repeating due to weak copyright tracking earlier in this project, which extends back to early 2015. This weakness came to light in late 2017 after an LKMM presentation by Paul in which an audience member noted the similarity of some LKMM code to code in early published papers. This prompted a copyright review. From Alan Stern: To say that the model was mine is not entirely accurate. Pieces of it (especially the Scpv and Atomic axioms) were taken directly from Jade's models. And of course the Happens-before and Propagation relations and axioms were heavily based on Jade and Luc's work, even though they weren't identical to the earlier versions. Only the RCU portion was completely original. . . . One can make a much better case that I wrote the bulk of lock.cat. However, it was inspired by Luc's earlier version (and still shares some elements in common), and of course it benefited from feedback and testing from all members of our group. The model prior to Alan's was Luc Maranget's. From Luc: I totally agree on Alan Stern's account of the linux kernel model genesis. I thank him for his acknowledgments of my participation to previous model drafts. I'd like to complete Alan Stern's statement: any bell cat code I have written has its roots in discussions with Jade Alglave and Paul McKenney. Moreover I have borrowed cat and bell code written by Jade Alglave freely. This copyright review therefore resulted in late adds to the copyright statements of several files. Discussion of v1 has raised several issues, which we do not believe should block acceptance given that this level of change will be ongoing, just as it has been with memory-barriers.txt: o Under what conditions should ordering provided by pure locking be seen by CPUs not holding the relevant lock(s)? In particular, should the message-passing pattern be forbidden? o Should examples involving C11 release sequences be forbidden? Note that this C11 is still a moving target for this issue: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0735r0.html o Some details of the handling of internal dependencies for atomic read-modify-write atomic operations are still subject to debate. o Changes recently accepted into mainline greatly reduce the need to handle DEC Alpha as a special case. These changes add an smp_read_barrier_depends() to READ_ONCE(), thus causing Alpha to respect ordering of dependent reads. If these changes stick, the memory model can be simplified accordingly. o Will changes be required to accommodate RISC-V? Differences from v1: (http://lkml.kernel.org/r/20171113184031.GA26302@linux.vnet.ibm.com) o Add SPDX notations to .bell and .cat files, replacing textual license statements. o Add reference to upcoming ASPLOS paper to .bell and .cat files. o Updated identifier names in .bell and .cat files to match those used in the ASPLOS paper. o Updates to READMEs and other documentation based on review feedback. o Added a memory-ordering cheatsheet. o Update sigs to new Co-Developed-by and add acks and reviewed-bys. o Simplify rules detecting nested RCU read-side critical sections. o Update copyright statements as noted above. Co-Developed-by: Alan Stern <stern@rowland.harvard.edu> Co-Developed-by: Andrea Parri <parri.andrea@gmail.com> Co-Developed-by: Jade Alglave <j.alglave@ucl.ac.uk> Co-Developed-by: Luc Maranget <luc.maranget@inria.fr> Co-Developed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Jade Alglave <j.alglave@ucl.ac.uk> Signed-off-by: Luc Maranget <luc.maranget@inria.fr> Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: "Reshetova, Elena" <elena.reshetova@intel.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Akira Yokosawa <akiyks@gmail.com> Cc: <linux-arch@vger.kernel.org>
2018-01-19 11:58:55 +08:00
acyclic hb as happens-before
(****************************************)
(* Write and fence propagation ordering *)
(****************************************)
(* Propagation: Each non-rf link needs a strong fence. *)
let pb = prop ; strong-fence ; hb* ; [Marked]
Automate memory-barriers.txt; provide Linux-kernel memory model There is some reason to believe that Documentation/memory-barriers.txt could use some help, and a major purpose of this patch is to provide that help in the form of a design-time tool that can produce all valid executions of a small fragment of concurrent Linux-kernel code, which is called a "litmus test". This tool's functionality is roughly similar to a full state-space search. Please note that this is a design-time tool, not useful for regression testing. However, we hope that the underlying Linux-kernel memory model will be incorporated into other tools capable of analyzing large bodies of code for regression-testing purposes. The main tool is herd7, together with the linux-kernel.bell, linux-kernel.cat, linux-kernel.cfg, linux-kernel.def, and lock.cat files added by this patch. The herd7 executable takes the other files as input, and all of these files collectively define the Linux-kernel memory memory model. A brief description of each of these other files is provided in the README file. Although this tool does have its limitations, which are documented in the README file, it does improve on the version reported on in the LWN series (https://lwn.net/Articles/718628/ and https://lwn.net/Articles/720550/) by supporting locking and arithmetic, including a much wider variety of read-modify-write atomic operations. Please note that herd7 is not part of this submission, but is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). A second tool is klitmus7, which converts litmus tests to loadable kernel modules for direct testing. As with herd7, the klitmus7 code is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). Of course, litmus tests are not always the best way to fully understand a memory model, so this patch also includes Documentation/explanation.txt, which describes the memory model in detail. In addition, Documentation/recipes.txt provides example known-good and known-bad use cases for those who prefer working by example. This patch also includes a few sample litmus tests, and a great many more litmus tests are available at https://github.com/paulmckrcu/litmus. This patch was the result of a most excellent collaboration founded by Jade Alglave and also including Alan Stern, Andrea Parri, and Luc Maranget. For more details on the history of this collaboration, please refer to the Linux-kernel memory model presentations at 2016 LinuxCon EU, 2016 Kernel Summit, 2016 Linux Plumbers Conference, 2017 linux.conf.au, or 2017 Linux Plumbers Conference microconference. However, one aspect of the history does bear repeating due to weak copyright tracking earlier in this project, which extends back to early 2015. This weakness came to light in late 2017 after an LKMM presentation by Paul in which an audience member noted the similarity of some LKMM code to code in early published papers. This prompted a copyright review. From Alan Stern: To say that the model was mine is not entirely accurate. Pieces of it (especially the Scpv and Atomic axioms) were taken directly from Jade's models. And of course the Happens-before and Propagation relations and axioms were heavily based on Jade and Luc's work, even though they weren't identical to the earlier versions. Only the RCU portion was completely original. . . . One can make a much better case that I wrote the bulk of lock.cat. However, it was inspired by Luc's earlier version (and still shares some elements in common), and of course it benefited from feedback and testing from all members of our group. The model prior to Alan's was Luc Maranget's. From Luc: I totally agree on Alan Stern's account of the linux kernel model genesis. I thank him for his acknowledgments of my participation to previous model drafts. I'd like to complete Alan Stern's statement: any bell cat code I have written has its roots in discussions with Jade Alglave and Paul McKenney. Moreover I have borrowed cat and bell code written by Jade Alglave freely. This copyright review therefore resulted in late adds to the copyright statements of several files. Discussion of v1 has raised several issues, which we do not believe should block acceptance given that this level of change will be ongoing, just as it has been with memory-barriers.txt: o Under what conditions should ordering provided by pure locking be seen by CPUs not holding the relevant lock(s)? In particular, should the message-passing pattern be forbidden? o Should examples involving C11 release sequences be forbidden? Note that this C11 is still a moving target for this issue: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0735r0.html o Some details of the handling of internal dependencies for atomic read-modify-write atomic operations are still subject to debate. o Changes recently accepted into mainline greatly reduce the need to handle DEC Alpha as a special case. These changes add an smp_read_barrier_depends() to READ_ONCE(), thus causing Alpha to respect ordering of dependent reads. If these changes stick, the memory model can be simplified accordingly. o Will changes be required to accommodate RISC-V? Differences from v1: (http://lkml.kernel.org/r/20171113184031.GA26302@linux.vnet.ibm.com) o Add SPDX notations to .bell and .cat files, replacing textual license statements. o Add reference to upcoming ASPLOS paper to .bell and .cat files. o Updated identifier names in .bell and .cat files to match those used in the ASPLOS paper. o Updates to READMEs and other documentation based on review feedback. o Added a memory-ordering cheatsheet. o Update sigs to new Co-Developed-by and add acks and reviewed-bys. o Simplify rules detecting nested RCU read-side critical sections. o Update copyright statements as noted above. Co-Developed-by: Alan Stern <stern@rowland.harvard.edu> Co-Developed-by: Andrea Parri <parri.andrea@gmail.com> Co-Developed-by: Jade Alglave <j.alglave@ucl.ac.uk> Co-Developed-by: Luc Maranget <luc.maranget@inria.fr> Co-Developed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Jade Alglave <j.alglave@ucl.ac.uk> Signed-off-by: Luc Maranget <luc.maranget@inria.fr> Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: "Reshetova, Elena" <elena.reshetova@intel.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Akira Yokosawa <akiyks@gmail.com> Cc: <linux-arch@vger.kernel.org>
2018-01-19 11:58:55 +08:00
acyclic pb as propagation
(*******)
(* RCU *)
(*******)
(*
* Effects of read-side critical sections proceed from the rcu_read_unlock()
* or srcu_read_unlock() backwards on the one hand, and from the
* rcu_read_lock() or srcu_read_lock() forwards on the other hand.
*
* In the definition of rcu-fence below, the po term at the left-hand side
* of each disjunct and the po? term at the right-hand end have been factored
* out. They have been moved into the definitions of rcu-link and rb.
* This was necessary in order to apply the "& loc" tests correctly.
Automate memory-barriers.txt; provide Linux-kernel memory model There is some reason to believe that Documentation/memory-barriers.txt could use some help, and a major purpose of this patch is to provide that help in the form of a design-time tool that can produce all valid executions of a small fragment of concurrent Linux-kernel code, which is called a "litmus test". This tool's functionality is roughly similar to a full state-space search. Please note that this is a design-time tool, not useful for regression testing. However, we hope that the underlying Linux-kernel memory model will be incorporated into other tools capable of analyzing large bodies of code for regression-testing purposes. The main tool is herd7, together with the linux-kernel.bell, linux-kernel.cat, linux-kernel.cfg, linux-kernel.def, and lock.cat files added by this patch. The herd7 executable takes the other files as input, and all of these files collectively define the Linux-kernel memory memory model. A brief description of each of these other files is provided in the README file. Although this tool does have its limitations, which are documented in the README file, it does improve on the version reported on in the LWN series (https://lwn.net/Articles/718628/ and https://lwn.net/Articles/720550/) by supporting locking and arithmetic, including a much wider variety of read-modify-write atomic operations. Please note that herd7 is not part of this submission, but is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). A second tool is klitmus7, which converts litmus tests to loadable kernel modules for direct testing. As with herd7, the klitmus7 code is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). Of course, litmus tests are not always the best way to fully understand a memory model, so this patch also includes Documentation/explanation.txt, which describes the memory model in detail. In addition, Documentation/recipes.txt provides example known-good and known-bad use cases for those who prefer working by example. This patch also includes a few sample litmus tests, and a great many more litmus tests are available at https://github.com/paulmckrcu/litmus. This patch was the result of a most excellent collaboration founded by Jade Alglave and also including Alan Stern, Andrea Parri, and Luc Maranget. For more details on the history of this collaboration, please refer to the Linux-kernel memory model presentations at 2016 LinuxCon EU, 2016 Kernel Summit, 2016 Linux Plumbers Conference, 2017 linux.conf.au, or 2017 Linux Plumbers Conference microconference. However, one aspect of the history does bear repeating due to weak copyright tracking earlier in this project, which extends back to early 2015. This weakness came to light in late 2017 after an LKMM presentation by Paul in which an audience member noted the similarity of some LKMM code to code in early published papers. This prompted a copyright review. From Alan Stern: To say that the model was mine is not entirely accurate. Pieces of it (especially the Scpv and Atomic axioms) were taken directly from Jade's models. And of course the Happens-before and Propagation relations and axioms were heavily based on Jade and Luc's work, even though they weren't identical to the earlier versions. Only the RCU portion was completely original. . . . One can make a much better case that I wrote the bulk of lock.cat. However, it was inspired by Luc's earlier version (and still shares some elements in common), and of course it benefited from feedback and testing from all members of our group. The model prior to Alan's was Luc Maranget's. From Luc: I totally agree on Alan Stern's account of the linux kernel model genesis. I thank him for his acknowledgments of my participation to previous model drafts. I'd like to complete Alan Stern's statement: any bell cat code I have written has its roots in discussions with Jade Alglave and Paul McKenney. Moreover I have borrowed cat and bell code written by Jade Alglave freely. This copyright review therefore resulted in late adds to the copyright statements of several files. Discussion of v1 has raised several issues, which we do not believe should block acceptance given that this level of change will be ongoing, just as it has been with memory-barriers.txt: o Under what conditions should ordering provided by pure locking be seen by CPUs not holding the relevant lock(s)? In particular, should the message-passing pattern be forbidden? o Should examples involving C11 release sequences be forbidden? Note that this C11 is still a moving target for this issue: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0735r0.html o Some details of the handling of internal dependencies for atomic read-modify-write atomic operations are still subject to debate. o Changes recently accepted into mainline greatly reduce the need to handle DEC Alpha as a special case. These changes add an smp_read_barrier_depends() to READ_ONCE(), thus causing Alpha to respect ordering of dependent reads. If these changes stick, the memory model can be simplified accordingly. o Will changes be required to accommodate RISC-V? Differences from v1: (http://lkml.kernel.org/r/20171113184031.GA26302@linux.vnet.ibm.com) o Add SPDX notations to .bell and .cat files, replacing textual license statements. o Add reference to upcoming ASPLOS paper to .bell and .cat files. o Updated identifier names in .bell and .cat files to match those used in the ASPLOS paper. o Updates to READMEs and other documentation based on review feedback. o Added a memory-ordering cheatsheet. o Update sigs to new Co-Developed-by and add acks and reviewed-bys. o Simplify rules detecting nested RCU read-side critical sections. o Update copyright statements as noted above. Co-Developed-by: Alan Stern <stern@rowland.harvard.edu> Co-Developed-by: Andrea Parri <parri.andrea@gmail.com> Co-Developed-by: Jade Alglave <j.alglave@ucl.ac.uk> Co-Developed-by: Luc Maranget <luc.maranget@inria.fr> Co-Developed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Jade Alglave <j.alglave@ucl.ac.uk> Signed-off-by: Luc Maranget <luc.maranget@inria.fr> Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: "Reshetova, Elena" <elena.reshetova@intel.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Akira Yokosawa <akiyks@gmail.com> Cc: <linux-arch@vger.kernel.org>
2018-01-19 11:58:55 +08:00
*)
let rcu-gp = [Sync-rcu] (* Compare with gp *)
let srcu-gp = [Sync-srcu]
let rcu-rscsi = rcu-rscs^-1
let srcu-rscsi = srcu-rscs^-1
Automate memory-barriers.txt; provide Linux-kernel memory model There is some reason to believe that Documentation/memory-barriers.txt could use some help, and a major purpose of this patch is to provide that help in the form of a design-time tool that can produce all valid executions of a small fragment of concurrent Linux-kernel code, which is called a "litmus test". This tool's functionality is roughly similar to a full state-space search. Please note that this is a design-time tool, not useful for regression testing. However, we hope that the underlying Linux-kernel memory model will be incorporated into other tools capable of analyzing large bodies of code for regression-testing purposes. The main tool is herd7, together with the linux-kernel.bell, linux-kernel.cat, linux-kernel.cfg, linux-kernel.def, and lock.cat files added by this patch. The herd7 executable takes the other files as input, and all of these files collectively define the Linux-kernel memory memory model. A brief description of each of these other files is provided in the README file. Although this tool does have its limitations, which are documented in the README file, it does improve on the version reported on in the LWN series (https://lwn.net/Articles/718628/ and https://lwn.net/Articles/720550/) by supporting locking and arithmetic, including a much wider variety of read-modify-write atomic operations. Please note that herd7 is not part of this submission, but is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). A second tool is klitmus7, which converts litmus tests to loadable kernel modules for direct testing. As with herd7, the klitmus7 code is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). Of course, litmus tests are not always the best way to fully understand a memory model, so this patch also includes Documentation/explanation.txt, which describes the memory model in detail. In addition, Documentation/recipes.txt provides example known-good and known-bad use cases for those who prefer working by example. This patch also includes a few sample litmus tests, and a great many more litmus tests are available at https://github.com/paulmckrcu/litmus. This patch was the result of a most excellent collaboration founded by Jade Alglave and also including Alan Stern, Andrea Parri, and Luc Maranget. For more details on the history of this collaboration, please refer to the Linux-kernel memory model presentations at 2016 LinuxCon EU, 2016 Kernel Summit, 2016 Linux Plumbers Conference, 2017 linux.conf.au, or 2017 Linux Plumbers Conference microconference. However, one aspect of the history does bear repeating due to weak copyright tracking earlier in this project, which extends back to early 2015. This weakness came to light in late 2017 after an LKMM presentation by Paul in which an audience member noted the similarity of some LKMM code to code in early published papers. This prompted a copyright review. From Alan Stern: To say that the model was mine is not entirely accurate. Pieces of it (especially the Scpv and Atomic axioms) were taken directly from Jade's models. And of course the Happens-before and Propagation relations and axioms were heavily based on Jade and Luc's work, even though they weren't identical to the earlier versions. Only the RCU portion was completely original. . . . One can make a much better case that I wrote the bulk of lock.cat. However, it was inspired by Luc's earlier version (and still shares some elements in common), and of course it benefited from feedback and testing from all members of our group. The model prior to Alan's was Luc Maranget's. From Luc: I totally agree on Alan Stern's account of the linux kernel model genesis. I thank him for his acknowledgments of my participation to previous model drafts. I'd like to complete Alan Stern's statement: any bell cat code I have written has its roots in discussions with Jade Alglave and Paul McKenney. Moreover I have borrowed cat and bell code written by Jade Alglave freely. This copyright review therefore resulted in late adds to the copyright statements of several files. Discussion of v1 has raised several issues, which we do not believe should block acceptance given that this level of change will be ongoing, just as it has been with memory-barriers.txt: o Under what conditions should ordering provided by pure locking be seen by CPUs not holding the relevant lock(s)? In particular, should the message-passing pattern be forbidden? o Should examples involving C11 release sequences be forbidden? Note that this C11 is still a moving target for this issue: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0735r0.html o Some details of the handling of internal dependencies for atomic read-modify-write atomic operations are still subject to debate. o Changes recently accepted into mainline greatly reduce the need to handle DEC Alpha as a special case. These changes add an smp_read_barrier_depends() to READ_ONCE(), thus causing Alpha to respect ordering of dependent reads. If these changes stick, the memory model can be simplified accordingly. o Will changes be required to accommodate RISC-V? Differences from v1: (http://lkml.kernel.org/r/20171113184031.GA26302@linux.vnet.ibm.com) o Add SPDX notations to .bell and .cat files, replacing textual license statements. o Add reference to upcoming ASPLOS paper to .bell and .cat files. o Updated identifier names in .bell and .cat files to match those used in the ASPLOS paper. o Updates to READMEs and other documentation based on review feedback. o Added a memory-ordering cheatsheet. o Update sigs to new Co-Developed-by and add acks and reviewed-bys. o Simplify rules detecting nested RCU read-side critical sections. o Update copyright statements as noted above. Co-Developed-by: Alan Stern <stern@rowland.harvard.edu> Co-Developed-by: Andrea Parri <parri.andrea@gmail.com> Co-Developed-by: Jade Alglave <j.alglave@ucl.ac.uk> Co-Developed-by: Luc Maranget <luc.maranget@inria.fr> Co-Developed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Jade Alglave <j.alglave@ucl.ac.uk> Signed-off-by: Luc Maranget <luc.maranget@inria.fr> Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: "Reshetova, Elena" <elena.reshetova@intel.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Akira Yokosawa <akiyks@gmail.com> Cc: <linux-arch@vger.kernel.org>
2018-01-19 11:58:55 +08:00
(*
* The synchronize_rcu() strong fence is special in that it can order not
* one but two non-rf relations, but only in conjunction with an RCU
* read-side critical section.
*)
let rcu-link = po? ; hb* ; pb* ; prop ; po
Automate memory-barriers.txt; provide Linux-kernel memory model There is some reason to believe that Documentation/memory-barriers.txt could use some help, and a major purpose of this patch is to provide that help in the form of a design-time tool that can produce all valid executions of a small fragment of concurrent Linux-kernel code, which is called a "litmus test". This tool's functionality is roughly similar to a full state-space search. Please note that this is a design-time tool, not useful for regression testing. However, we hope that the underlying Linux-kernel memory model will be incorporated into other tools capable of analyzing large bodies of code for regression-testing purposes. The main tool is herd7, together with the linux-kernel.bell, linux-kernel.cat, linux-kernel.cfg, linux-kernel.def, and lock.cat files added by this patch. The herd7 executable takes the other files as input, and all of these files collectively define the Linux-kernel memory memory model. A brief description of each of these other files is provided in the README file. Although this tool does have its limitations, which are documented in the README file, it does improve on the version reported on in the LWN series (https://lwn.net/Articles/718628/ and https://lwn.net/Articles/720550/) by supporting locking and arithmetic, including a much wider variety of read-modify-write atomic operations. Please note that herd7 is not part of this submission, but is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). A second tool is klitmus7, which converts litmus tests to loadable kernel modules for direct testing. As with herd7, the klitmus7 code is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). Of course, litmus tests are not always the best way to fully understand a memory model, so this patch also includes Documentation/explanation.txt, which describes the memory model in detail. In addition, Documentation/recipes.txt provides example known-good and known-bad use cases for those who prefer working by example. This patch also includes a few sample litmus tests, and a great many more litmus tests are available at https://github.com/paulmckrcu/litmus. This patch was the result of a most excellent collaboration founded by Jade Alglave and also including Alan Stern, Andrea Parri, and Luc Maranget. For more details on the history of this collaboration, please refer to the Linux-kernel memory model presentations at 2016 LinuxCon EU, 2016 Kernel Summit, 2016 Linux Plumbers Conference, 2017 linux.conf.au, or 2017 Linux Plumbers Conference microconference. However, one aspect of the history does bear repeating due to weak copyright tracking earlier in this project, which extends back to early 2015. This weakness came to light in late 2017 after an LKMM presentation by Paul in which an audience member noted the similarity of some LKMM code to code in early published papers. This prompted a copyright review. From Alan Stern: To say that the model was mine is not entirely accurate. Pieces of it (especially the Scpv and Atomic axioms) were taken directly from Jade's models. And of course the Happens-before and Propagation relations and axioms were heavily based on Jade and Luc's work, even though they weren't identical to the earlier versions. Only the RCU portion was completely original. . . . One can make a much better case that I wrote the bulk of lock.cat. However, it was inspired by Luc's earlier version (and still shares some elements in common), and of course it benefited from feedback and testing from all members of our group. The model prior to Alan's was Luc Maranget's. From Luc: I totally agree on Alan Stern's account of the linux kernel model genesis. I thank him for his acknowledgments of my participation to previous model drafts. I'd like to complete Alan Stern's statement: any bell cat code I have written has its roots in discussions with Jade Alglave and Paul McKenney. Moreover I have borrowed cat and bell code written by Jade Alglave freely. This copyright review therefore resulted in late adds to the copyright statements of several files. Discussion of v1 has raised several issues, which we do not believe should block acceptance given that this level of change will be ongoing, just as it has been with memory-barriers.txt: o Under what conditions should ordering provided by pure locking be seen by CPUs not holding the relevant lock(s)? In particular, should the message-passing pattern be forbidden? o Should examples involving C11 release sequences be forbidden? Note that this C11 is still a moving target for this issue: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0735r0.html o Some details of the handling of internal dependencies for atomic read-modify-write atomic operations are still subject to debate. o Changes recently accepted into mainline greatly reduce the need to handle DEC Alpha as a special case. These changes add an smp_read_barrier_depends() to READ_ONCE(), thus causing Alpha to respect ordering of dependent reads. If these changes stick, the memory model can be simplified accordingly. o Will changes be required to accommodate RISC-V? Differences from v1: (http://lkml.kernel.org/r/20171113184031.GA26302@linux.vnet.ibm.com) o Add SPDX notations to .bell and .cat files, replacing textual license statements. o Add reference to upcoming ASPLOS paper to .bell and .cat files. o Updated identifier names in .bell and .cat files to match those used in the ASPLOS paper. o Updates to READMEs and other documentation based on review feedback. o Added a memory-ordering cheatsheet. o Update sigs to new Co-Developed-by and add acks and reviewed-bys. o Simplify rules detecting nested RCU read-side critical sections. o Update copyright statements as noted above. Co-Developed-by: Alan Stern <stern@rowland.harvard.edu> Co-Developed-by: Andrea Parri <parri.andrea@gmail.com> Co-Developed-by: Jade Alglave <j.alglave@ucl.ac.uk> Co-Developed-by: Luc Maranget <luc.maranget@inria.fr> Co-Developed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Jade Alglave <j.alglave@ucl.ac.uk> Signed-off-by: Luc Maranget <luc.maranget@inria.fr> Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: "Reshetova, Elena" <elena.reshetova@intel.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Akira Yokosawa <akiyks@gmail.com> Cc: <linux-arch@vger.kernel.org>
2018-01-19 11:58:55 +08:00
(*
tools/memory-model: Redefine rb in terms of rcu-fence This patch reorganizes the definition of rb in the Linux Kernel Memory Consistency Model. The relation is now expressed in terms of rcu-fence, which consists of a sequence of gp and rscs links separated by rcu-link links, in which the number of occurrences of gp is >= the number of occurrences of rscs. Arguments similar to those published in http://diy.inria.fr/linux/long.pdf show that rcu-fence behaves like an inter-CPU strong fence. Furthermore, the definition of rb in terms of rcu-fence is highly analogous to the definition of pb in terms of strong-fence, which can help explain why rcu-path expresses a form of temporal ordering. This change should not affect the semantics of the memory model, just its internal organization. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Reviewed-by: Andrea Parri <parri.andrea@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will.deacon@arm.com> Cc: akiyks@gmail.com Cc: dhowells@redhat.com Cc: j.alglave@ucl.ac.uk Cc: linux-arch@vger.kernel.org Cc: luc.maranget@inria.fr Cc: npiggin@gmail.com Link: http://lkml.kernel.org/r/1526340837-12222-2-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 07:33:40 +08:00
* Any sequence containing at least as many grace periods as RCU read-side
* critical sections (joined by rcu-link) induces order like a generalized
* inter-CPU strong fence.
* Likewise for SRCU grace periods and read-side critical sections, provided
* the synchronize_srcu() and srcu_read_[un]lock() calls refer to the same
* struct srcu_struct location.
Automate memory-barriers.txt; provide Linux-kernel memory model There is some reason to believe that Documentation/memory-barriers.txt could use some help, and a major purpose of this patch is to provide that help in the form of a design-time tool that can produce all valid executions of a small fragment of concurrent Linux-kernel code, which is called a "litmus test". This tool's functionality is roughly similar to a full state-space search. Please note that this is a design-time tool, not useful for regression testing. However, we hope that the underlying Linux-kernel memory model will be incorporated into other tools capable of analyzing large bodies of code for regression-testing purposes. The main tool is herd7, together with the linux-kernel.bell, linux-kernel.cat, linux-kernel.cfg, linux-kernel.def, and lock.cat files added by this patch. The herd7 executable takes the other files as input, and all of these files collectively define the Linux-kernel memory memory model. A brief description of each of these other files is provided in the README file. Although this tool does have its limitations, which are documented in the README file, it does improve on the version reported on in the LWN series (https://lwn.net/Articles/718628/ and https://lwn.net/Articles/720550/) by supporting locking and arithmetic, including a much wider variety of read-modify-write atomic operations. Please note that herd7 is not part of this submission, but is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). A second tool is klitmus7, which converts litmus tests to loadable kernel modules for direct testing. As with herd7, the klitmus7 code is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). Of course, litmus tests are not always the best way to fully understand a memory model, so this patch also includes Documentation/explanation.txt, which describes the memory model in detail. In addition, Documentation/recipes.txt provides example known-good and known-bad use cases for those who prefer working by example. This patch also includes a few sample litmus tests, and a great many more litmus tests are available at https://github.com/paulmckrcu/litmus. This patch was the result of a most excellent collaboration founded by Jade Alglave and also including Alan Stern, Andrea Parri, and Luc Maranget. For more details on the history of this collaboration, please refer to the Linux-kernel memory model presentations at 2016 LinuxCon EU, 2016 Kernel Summit, 2016 Linux Plumbers Conference, 2017 linux.conf.au, or 2017 Linux Plumbers Conference microconference. However, one aspect of the history does bear repeating due to weak copyright tracking earlier in this project, which extends back to early 2015. This weakness came to light in late 2017 after an LKMM presentation by Paul in which an audience member noted the similarity of some LKMM code to code in early published papers. This prompted a copyright review. From Alan Stern: To say that the model was mine is not entirely accurate. Pieces of it (especially the Scpv and Atomic axioms) were taken directly from Jade's models. And of course the Happens-before and Propagation relations and axioms were heavily based on Jade and Luc's work, even though they weren't identical to the earlier versions. Only the RCU portion was completely original. . . . One can make a much better case that I wrote the bulk of lock.cat. However, it was inspired by Luc's earlier version (and still shares some elements in common), and of course it benefited from feedback and testing from all members of our group. The model prior to Alan's was Luc Maranget's. From Luc: I totally agree on Alan Stern's account of the linux kernel model genesis. I thank him for his acknowledgments of my participation to previous model drafts. I'd like to complete Alan Stern's statement: any bell cat code I have written has its roots in discussions with Jade Alglave and Paul McKenney. Moreover I have borrowed cat and bell code written by Jade Alglave freely. This copyright review therefore resulted in late adds to the copyright statements of several files. Discussion of v1 has raised several issues, which we do not believe should block acceptance given that this level of change will be ongoing, just as it has been with memory-barriers.txt: o Under what conditions should ordering provided by pure locking be seen by CPUs not holding the relevant lock(s)? In particular, should the message-passing pattern be forbidden? o Should examples involving C11 release sequences be forbidden? Note that this C11 is still a moving target for this issue: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0735r0.html o Some details of the handling of internal dependencies for atomic read-modify-write atomic operations are still subject to debate. o Changes recently accepted into mainline greatly reduce the need to handle DEC Alpha as a special case. These changes add an smp_read_barrier_depends() to READ_ONCE(), thus causing Alpha to respect ordering of dependent reads. If these changes stick, the memory model can be simplified accordingly. o Will changes be required to accommodate RISC-V? Differences from v1: (http://lkml.kernel.org/r/20171113184031.GA26302@linux.vnet.ibm.com) o Add SPDX notations to .bell and .cat files, replacing textual license statements. o Add reference to upcoming ASPLOS paper to .bell and .cat files. o Updated identifier names in .bell and .cat files to match those used in the ASPLOS paper. o Updates to READMEs and other documentation based on review feedback. o Added a memory-ordering cheatsheet. o Update sigs to new Co-Developed-by and add acks and reviewed-bys. o Simplify rules detecting nested RCU read-side critical sections. o Update copyright statements as noted above. Co-Developed-by: Alan Stern <stern@rowland.harvard.edu> Co-Developed-by: Andrea Parri <parri.andrea@gmail.com> Co-Developed-by: Jade Alglave <j.alglave@ucl.ac.uk> Co-Developed-by: Luc Maranget <luc.maranget@inria.fr> Co-Developed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Jade Alglave <j.alglave@ucl.ac.uk> Signed-off-by: Luc Maranget <luc.maranget@inria.fr> Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: "Reshetova, Elena" <elena.reshetova@intel.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Akira Yokosawa <akiyks@gmail.com> Cc: <linux-arch@vger.kernel.org>
2018-01-19 11:58:55 +08:00
*)
let rec rcu-order = rcu-gp | srcu-gp |
(rcu-gp ; rcu-link ; rcu-rscsi) |
((srcu-gp ; rcu-link ; srcu-rscsi) & loc) |
(rcu-rscsi ; rcu-link ; rcu-gp) |
((srcu-rscsi ; rcu-link ; srcu-gp) & loc) |
(rcu-gp ; rcu-link ; rcu-order ; rcu-link ; rcu-rscsi) |
((srcu-gp ; rcu-link ; rcu-order ; rcu-link ; srcu-rscsi) & loc) |
(rcu-rscsi ; rcu-link ; rcu-order ; rcu-link ; rcu-gp) |
((srcu-rscsi ; rcu-link ; rcu-order ; rcu-link ; srcu-gp) & loc) |
(rcu-order ; rcu-link ; rcu-order)
let rcu-fence = po ; rcu-order ; po?
let fence = fence | rcu-fence
let strong-fence = strong-fence | rcu-fence
tools/memory-model: Redefine rb in terms of rcu-fence This patch reorganizes the definition of rb in the Linux Kernel Memory Consistency Model. The relation is now expressed in terms of rcu-fence, which consists of a sequence of gp and rscs links separated by rcu-link links, in which the number of occurrences of gp is >= the number of occurrences of rscs. Arguments similar to those published in http://diy.inria.fr/linux/long.pdf show that rcu-fence behaves like an inter-CPU strong fence. Furthermore, the definition of rb in terms of rcu-fence is highly analogous to the definition of pb in terms of strong-fence, which can help explain why rcu-path expresses a form of temporal ordering. This change should not affect the semantics of the memory model, just its internal organization. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Reviewed-by: Andrea Parri <parri.andrea@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will.deacon@arm.com> Cc: akiyks@gmail.com Cc: dhowells@redhat.com Cc: j.alglave@ucl.ac.uk Cc: linux-arch@vger.kernel.org Cc: luc.maranget@inria.fr Cc: npiggin@gmail.com Link: http://lkml.kernel.org/r/1526340837-12222-2-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 07:33:40 +08:00
(* rb orders instructions just as pb does *)
let rb = prop ; rcu-fence ; hb* ; pb* ; [Marked]
Automate memory-barriers.txt; provide Linux-kernel memory model There is some reason to believe that Documentation/memory-barriers.txt could use some help, and a major purpose of this patch is to provide that help in the form of a design-time tool that can produce all valid executions of a small fragment of concurrent Linux-kernel code, which is called a "litmus test". This tool's functionality is roughly similar to a full state-space search. Please note that this is a design-time tool, not useful for regression testing. However, we hope that the underlying Linux-kernel memory model will be incorporated into other tools capable of analyzing large bodies of code for regression-testing purposes. The main tool is herd7, together with the linux-kernel.bell, linux-kernel.cat, linux-kernel.cfg, linux-kernel.def, and lock.cat files added by this patch. The herd7 executable takes the other files as input, and all of these files collectively define the Linux-kernel memory memory model. A brief description of each of these other files is provided in the README file. Although this tool does have its limitations, which are documented in the README file, it does improve on the version reported on in the LWN series (https://lwn.net/Articles/718628/ and https://lwn.net/Articles/720550/) by supporting locking and arithmetic, including a much wider variety of read-modify-write atomic operations. Please note that herd7 is not part of this submission, but is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). A second tool is klitmus7, which converts litmus tests to loadable kernel modules for direct testing. As with herd7, the klitmus7 code is freely available from http://diy.inria.fr/sources/index.html (and via "git" at https://github.com/herd/herdtools7). Of course, litmus tests are not always the best way to fully understand a memory model, so this patch also includes Documentation/explanation.txt, which describes the memory model in detail. In addition, Documentation/recipes.txt provides example known-good and known-bad use cases for those who prefer working by example. This patch also includes a few sample litmus tests, and a great many more litmus tests are available at https://github.com/paulmckrcu/litmus. This patch was the result of a most excellent collaboration founded by Jade Alglave and also including Alan Stern, Andrea Parri, and Luc Maranget. For more details on the history of this collaboration, please refer to the Linux-kernel memory model presentations at 2016 LinuxCon EU, 2016 Kernel Summit, 2016 Linux Plumbers Conference, 2017 linux.conf.au, or 2017 Linux Plumbers Conference microconference. However, one aspect of the history does bear repeating due to weak copyright tracking earlier in this project, which extends back to early 2015. This weakness came to light in late 2017 after an LKMM presentation by Paul in which an audience member noted the similarity of some LKMM code to code in early published papers. This prompted a copyright review. From Alan Stern: To say that the model was mine is not entirely accurate. Pieces of it (especially the Scpv and Atomic axioms) were taken directly from Jade's models. And of course the Happens-before and Propagation relations and axioms were heavily based on Jade and Luc's work, even though they weren't identical to the earlier versions. Only the RCU portion was completely original. . . . One can make a much better case that I wrote the bulk of lock.cat. However, it was inspired by Luc's earlier version (and still shares some elements in common), and of course it benefited from feedback and testing from all members of our group. The model prior to Alan's was Luc Maranget's. From Luc: I totally agree on Alan Stern's account of the linux kernel model genesis. I thank him for his acknowledgments of my participation to previous model drafts. I'd like to complete Alan Stern's statement: any bell cat code I have written has its roots in discussions with Jade Alglave and Paul McKenney. Moreover I have borrowed cat and bell code written by Jade Alglave freely. This copyright review therefore resulted in late adds to the copyright statements of several files. Discussion of v1 has raised several issues, which we do not believe should block acceptance given that this level of change will be ongoing, just as it has been with memory-barriers.txt: o Under what conditions should ordering provided by pure locking be seen by CPUs not holding the relevant lock(s)? In particular, should the message-passing pattern be forbidden? o Should examples involving C11 release sequences be forbidden? Note that this C11 is still a moving target for this issue: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0735r0.html o Some details of the handling of internal dependencies for atomic read-modify-write atomic operations are still subject to debate. o Changes recently accepted into mainline greatly reduce the need to handle DEC Alpha as a special case. These changes add an smp_read_barrier_depends() to READ_ONCE(), thus causing Alpha to respect ordering of dependent reads. If these changes stick, the memory model can be simplified accordingly. o Will changes be required to accommodate RISC-V? Differences from v1: (http://lkml.kernel.org/r/20171113184031.GA26302@linux.vnet.ibm.com) o Add SPDX notations to .bell and .cat files, replacing textual license statements. o Add reference to upcoming ASPLOS paper to .bell and .cat files. o Updated identifier names in .bell and .cat files to match those used in the ASPLOS paper. o Updates to READMEs and other documentation based on review feedback. o Added a memory-ordering cheatsheet. o Update sigs to new Co-Developed-by and add acks and reviewed-bys. o Simplify rules detecting nested RCU read-side critical sections. o Update copyright statements as noted above. Co-Developed-by: Alan Stern <stern@rowland.harvard.edu> Co-Developed-by: Andrea Parri <parri.andrea@gmail.com> Co-Developed-by: Jade Alglave <j.alglave@ucl.ac.uk> Co-Developed-by: Luc Maranget <luc.maranget@inria.fr> Co-Developed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Andrea Parri <parri.andrea@gmail.com> Signed-off-by: Jade Alglave <j.alglave@ucl.ac.uk> Signed-off-by: Luc Maranget <luc.maranget@inria.fr> Signed-off-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: David Howells <dhowells@redhat.com> Acked-by: "Reshetova, Elena" <elena.reshetova@intel.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Akira Yokosawa <akiyks@gmail.com> Cc: <linux-arch@vger.kernel.org>
2018-01-19 11:58:55 +08:00
irreflexive rb as rcu
tools/memory-model: Redefine rb in terms of rcu-fence This patch reorganizes the definition of rb in the Linux Kernel Memory Consistency Model. The relation is now expressed in terms of rcu-fence, which consists of a sequence of gp and rscs links separated by rcu-link links, in which the number of occurrences of gp is >= the number of occurrences of rscs. Arguments similar to those published in http://diy.inria.fr/linux/long.pdf show that rcu-fence behaves like an inter-CPU strong fence. Furthermore, the definition of rb in terms of rcu-fence is highly analogous to the definition of pb in terms of strong-fence, which can help explain why rcu-path expresses a form of temporal ordering. This change should not affect the semantics of the memory model, just its internal organization. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Boqun Feng <boqun.feng@gmail.com> Reviewed-by: Andrea Parri <parri.andrea@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will.deacon@arm.com> Cc: akiyks@gmail.com Cc: dhowells@redhat.com Cc: j.alglave@ucl.ac.uk Cc: linux-arch@vger.kernel.org Cc: luc.maranget@inria.fr Cc: npiggin@gmail.com Link: http://lkml.kernel.org/r/1526340837-12222-2-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-05-15 07:33:40 +08:00
(*
* The happens-before, propagation, and rcu constraints are all
* expressions of temporal ordering. They could be replaced by
* a single constraint on an "executes-before" relation, xb:
*
* let xb = hb | pb | rb
* acyclic xb as executes-before
*)
(*********************************)
(* Plain accesses and data races *)
(*********************************)
(* Warn about plain writes and marked accesses in the same region *)
let mixed-accesses = ([Plain & W] ; (po-loc \ barrier) ; [Marked]) |
([Marked] ; (po-loc \ barrier) ; [Plain & W])
flag ~empty mixed-accesses as mixed-accesses
(* Executes-before and visibility *)
let xbstar = (hb | pb | rb)*
let vis = cumul-fence* ; rfe? ; [Marked] ;
((strong-fence ; [Marked] ; xbstar) | (xbstar & int))
(* Boundaries for lifetimes of plain accesses *)
let w-pre-bounded = [Marked] ; (addr | fence)?
let r-pre-bounded = [Marked] ; (addr | nonrw-fence |
([R4rmb] ; fencerel(Rmb) ; [~Noreturn]))?
let w-post-bounded = fence? ; [Marked]
let r-post-bounded = (nonrw-fence | ([~Noreturn] ; fencerel(Rmb) ; [R4rmb]))? ;
[Marked]
(* Visibility and executes-before for plain accesses *)
tools/memory-model: Improve data-race detection Herbert Xu recently reported a problem concerning RCU and compiler barriers. In the course of discussing the problem, he put forth a litmus test which illustrated a serious defect in the Linux Kernel Memory Model's data-race-detection code [1]. The defect was that the LKMM assumed visibility and executes-before ordering of plain accesses had to be mediated by marked accesses. In Herbert's litmus test this wasn't so, and the LKMM claimed the litmus test was allowed and contained a data race although neither is true. In fact, plain accesses can be ordered by fences even in the absence of marked accesses. In most cases this doesn't matter, because most fences only order accesses within a single thread. But the rcu-fence relation is different; it can order (and induce visibility between) accesses in different threads -- events which otherwise might be concurrent. This makes it relevant to data-race detection. This patch makes two changes to the memory model to incorporate the new insight: If a store is separated by a fence from another access, the store is necessarily visible to the other access (as reflected in the ww-vis and wr-vis relations). Similarly, if a load is separated by a fence from another access then the load necessarily executes before the other access (as reflected in the rw-xbstar relation). If a store is separated by a strong fence from a marked access then it is necessarily visible to any access that executes after the marked access (as reflected in the ww-vis and wr-vis relations). With these changes, the LKMM gives the desired result for Herbert's litmus test and other related ones [2]. [1] https://lore.kernel.org/lkml/Pine.LNX.4.44L0.1906041026570.1731-100000@iolanthe.rowland.org/ [2] https://github.com/paulmckrcu/litmus/blob/master/manual/plain/C-S-rcunoderef-1.litmus https://github.com/paulmckrcu/litmus/blob/master/manual/plain/C-S-rcunoderef-2.litmus https://github.com/paulmckrcu/litmus/blob/master/manual/plain/C-S-rcunoderef-3.litmus https://github.com/paulmckrcu/litmus/blob/master/manual/plain/C-S-rcunoderef-4.litmus https://github.com/paulmckrcu/litmus/blob/master/manual/plain/strong-vis.litmus Reported-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Acked-by: Andrea Parri <andrea.parri@amarulasolutions.com> Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com> Tested-by: Akira Yokosawa <akiyks@gmail.com>
2019-06-20 23:55:58 +08:00
let ww-vis = fence | (strong-fence ; xbstar ; w-pre-bounded) |
(w-post-bounded ; vis ; w-pre-bounded)
let wr-vis = fence | (strong-fence ; xbstar ; r-pre-bounded) |
(w-post-bounded ; vis ; r-pre-bounded)
let rw-xbstar = fence | (r-post-bounded ; xbstar ; w-pre-bounded)
(* Potential races *)
let pre-race = ext & ((Plain * M) | ((M \ IW) * Plain))
(* Coherence requirements for plain accesses *)
let wr-incoh = pre-race & rf & rw-xbstar^-1
let rw-incoh = pre-race & fr & wr-vis^-1
let ww-incoh = pre-race & co & ww-vis^-1
empty (wr-incoh | rw-incoh | ww-incoh) as plain-coherence
(* Actual races *)
let ww-nonrace = ww-vis & ((Marked * W) | rw-xbstar) & ((W * Marked) | wr-vis)
let ww-race = (pre-race & co) \ ww-nonrace
let wr-race = (pre-race & (co? ; rf)) \ wr-vis \ rw-xbstar^-1
let rw-race = (pre-race & fr) \ rw-xbstar
flag ~empty (ww-race | wr-race | rw-race) as data-race