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The current informal control dependency definition in explanation.txt is too broad and, as discussed, needs to be updated. Consider the following example: > if(READ_ONCE(x)) > return 42; > > WRITE_ONCE(y, 42); > > return 21; The read event determines whether the write event will be executed "at all" - as per the current definition - but the formal LKMM does not recognize this as a control dependency. Introduce a new definition which includes the requirement for the second memory access event to syntactically lie within the arm of a non-loop conditional. Link: https://lore.kernel.org/all/20220615114330.2573952-1-paul.heidekrueger@in.tum.de/ Cc: Marco Elver <elver@google.com> Cc: Charalampos Mainas <charalampos.mainas@gmail.com> Cc: Pramod Bhatotia <pramod.bhatotia@in.tum.de> Cc: Soham Chakraborty <s.s.chakraborty@tudelft.nl> Cc: Martin Fink <martin.fink@in.tum.de> Co-developed-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Paul Heidekrüger <paul.heidekrueger@in.tum.de> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> |
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| .. | ||
| access-marking.txt | ||
| cheatsheet.txt | ||
| control-dependencies.txt | ||
| explanation.txt | ||
| glossary.txt | ||
| litmus-tests.txt | ||
| ordering.txt | ||
| README | ||
| recipes.txt | ||
| references.txt | ||
| simple.txt | ||
It has been said that successful communication requires first identifying what your audience knows and then building a bridge from their current knowledge to what they need to know. Unfortunately, the expected Linux-kernel memory model (LKMM) audience might be anywhere from novice to expert both in kernel hacking and in understanding LKMM. This document therefore points out a number of places to start reading, depending on what you know and what you would like to learn. Please note that the documents later in this list assume that the reader understands the material provided by documents earlier in this list. o You are new to Linux-kernel concurrency: simple.txt o You have some background in Linux-kernel concurrency, and would like an overview of the types of low-level concurrency primitives that the Linux kernel provides: ordering.txt Here, "low level" means atomic operations to single variables. o You are familiar with the Linux-kernel concurrency primitives that you need, and just want to get started with LKMM litmus tests: litmus-tests.txt o You are familiar with Linux-kernel concurrency, and would like a detailed intuitive understanding of LKMM, including situations involving more than two threads: recipes.txt o You would like a detailed understanding of what your compiler can and cannot do to control dependencies: control-dependencies.txt o You are familiar with Linux-kernel concurrency and the use of LKMM, and would like a quick reference: cheatsheet.txt o You are familiar with Linux-kernel concurrency and the use of LKMM, and would like to learn about LKMM's requirements, rationale, and implementation: explanation.txt o You are interested in the publications related to LKMM, including hardware manuals, academic literature, standards-committee working papers, and LWN articles: references.txt ==================== DESCRIPTION OF FILES ==================== README This file. cheatsheet.txt Quick-reference guide to the Linux-kernel memory model. control-dependencies.txt Guide to preventing compiler optimizations from destroying your control dependencies. explanation.txt Detailed description of the memory model. litmus-tests.txt The format, features, capabilities, and limitations of the litmus tests that LKMM can evaluate. ordering.txt Overview of the Linux kernel's low-level memory-ordering primitives by category. recipes.txt Common memory-ordering patterns. references.txt Background information. simple.txt Starting point for someone new to Linux-kernel concurrency. And also a reminder of the simpler approaches to concurrency!