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Scalable Multi-core Model Checking Fairness Enhanced Systems. Yang Liu, Jun Sun and Jin Song Dong School of Computing National University of Singapore. Outline. General Introduction to PAT http://pat.comp.nus.edu.sg Motivation: Parallel Model Checking Model Checking with Fairness

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scalable multi core model checking fairness enhanced systems

Scalable Multi-core Model Checking Fairness Enhanced Systems

Yang Liu, Jun Sun and Jin Song Dong

School of Computing

National University of Singapore

outline
Outline
  • General Introduction to PAT
    • http://pat.comp.nus.edu.sg
  • Motivation: Parallel Model Checking
  • Model Checking with Fairness
  • Experiment Results
  • Conclusion
model checking
Model Checking
  • Determining whether a model satisfies a property by the means of exhaustive searching.

Model

Model Checker

Counterexample!

Property

model checking works
Model Checking Works!
  • Three researchers won Turing Award 2007 for their pioneer work on model checking!
  • Intel Core i7 processor is verified by symbolic model checking completely without executing a single test case!
  • The Slam project from Microsoft successfully detected many bugs in many driver software!
pat motivation
PAT: Motivation
  • We aim to develop a self-contained framework for formal specification and verification of compositional systems which involves,
    • concurrency,
    • real-time,
    • complex data structures and operations,
    • complicated control flows,
    • and etc.
motivation
Motivation
  • Model checking is limited by state space explosion.
  • We do have multiple cores nowadays!
safety
Safety
  • “Something bad never happens”
  • Reachability analysis
    • Depth-first search
    • Breadth-first search
liveness
Liveness
  • “Something good eventually happens”
  • Liveness checking = bad loop searching
    • Nested depth-first-search
    • SCC-based algorithms
fairness
Fairness
  • Liveness often requires fairness!
    • Process level weak/strong fairness
    • Event level weak/strong fairness
    • Strong global fairness
verification under fairness
Verification under Fairness
  • Automata-based LTL model checking
    • weak fairness: SCC search
    • strong fairness: strongly connected sub-graph search
    • strong global fairness = terminal SCC search
verification under fairness1
Verification under Fairness
  • A lasso is counterexample if and only if the loop is fair and it fails the liveness property.
    • It is (process-level) weak fair iff there is NO process which is always enabled during the loop and never made any progress.
    • It is (process-level) strong fair iff there is NO process which is enabled during the loop and never made any progress.
    • It is strong global fairness iff …
sequential algorithm
Sequential Algorithm

A: Find SCC-0

True

Is Not Fair

B: Check if SCC-0 is fair

Is Fair

C: Generate Counterexample

parallel algorithm
Parallel Algorithm

A0

B0

A1

B1

A2

B2

Thread 1

Thread 2

Thread 3

Thread 4

parallel algorithm1
Parallel Algorithm

A0

A1

A2

Thread 1

B0

B1

Thread 2

B2

Thread 3

Thread 4

effectiveness
Effectiveness
  • Overhead – negligible
    • Based on shared-memory architecture.
  • Depends on how expensive checking whether a SCC satisfies the fairness constraint
    • Weak fairness: linear in the number of transitions
    • Strong fairness: bounded by #states * #transitions
    • Global fairness: linear in the number of transitions
conclusion
Conclusion
  • A simple way of making use of multi-cores for model checking with fairness.
  • The technique is available in PAT.
    • http://pat.comp.nus.edu.sg
  • Related work
    • Spin’s liveness checking algorithm for dual-core systems
    • Barnat et al. multi-core LTL model checking
    • MAP, OWCTY, NEGC, OBF