AVIO class present

AVIO: Detecting Atomicity Violations via AccessInterleaving Invariants

Dacong (Tony) Yan

January 25, 2011

Motivation

CSE 788.07, Dacong (Tony) Yan AVIO: Detecting Atomicity Violations via Access Interleaving Invariants 2/21

Motivation


Agenda

Motivation

AVIO Idea

AVIO Algorithms

AVIO Implementations

Discussion


AVIO Idea

Idea: access interleaving invariants!


AVIO Idea

Idea: access interleaving invariants!


Eight Cases of Access Interleavings


AVIO Idea

Two Phases

Training: extracts access interleaving invariants from a large set ofcorrect runs;Detection: monitors the program execution, and checks whether thefour buggy cases occur.

Discussion

Correctness: are correct runs indeed correct?Sufficiency: is the number of correct runs large enough?


AVIO Idea

Two Phases

Training: extracts access interleaving invariants from a large set ofcorrect runs;

Detection: monitors the program execution, and checks whether thefour buggy cases occur.

Discussion



AVIO Idea

Two Phases


Discussion



AVIO Idea

Two Phases


Discussion



AVIO Algorithms

Detection Algorithm

What is an access inverleaving invariant?

A pair of accesses (P-Instruction, I-Instruction).

Detection procedure:


Detection Algorithm





Detection Algorithm





Extraction Algorithm

Idea: eliminate non-invariants from the whole set of pairs ofaccesses.

1. Suppose ai is an invariant: ai ∈ AISet;2. If ai is violated in correct runs, remove ai from AISet.

Pseudocode





Pseudocode





Pseudocode


AVIO Implementations

AVIO-H

L1 cache line extension

Hardware-based decision procedure


AVIO-H

L1 cache line extension

Hardware-based decision procedure


AVIO-S

Two access tables

Local access table: latest access information per threadGlobal access table: thread id of latest write among all threads

Detection at I-instruction

P-instruction: extracts from local access tableRemote access: extracts from global access table


AVIO-S

Two access tables

Local access table: latest access information per threadGlobal access table: thread id of latest write among all threads

Detection at I-instruction

P-instruction: extracts from local access tableRemote access: extracts from global access table


Discussion

Q1: How can we fix this bug?


Solution: busy-waiting


Q2: Will AVIO report this violation?

Q2.1: Will < (shared == null)rd , (shared = newObj)wr > beincluded in AISet? Yes!

Q2.2: Will the buggy interleaving be detected? Yes!



Q2.1: Will < (shared == null)rd , (shared = newObj)wr > beincluded in AISet?

Yes!









Q2.2: Will the buggy interleaving be detected?

Yes!






Q3: Why does AVIO-H have much lower overhead?

Answer: extra bits needed by the algorithm can be piggybacked in thecache coherence protocol, inducing very little extra cost.


Q3: Why does AVIO-H have much lower overhead?

Answer: extra bits needed by the algorithm can be piggybacked in thecache coherence protocol, inducing very little extra cost.


Q4: Why does AVIO-H report more false positives?



Will an atomicity violation warning be raised by AVIO-H?

False sharing



Will an atomicity violation warning be raised by AVIO-H?

False sharing


Thank you!

AVIO class present

Technology