0005188: double free corruption with bytecode system threads and stack reallocation

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0005188

OCaml

OCaml general

public

2010-12-04 13:11

2012-03-24 15:01

Reporter

herbelin

Assigned To

xleroy

Priority

normal

Severity

crash

Reproducibility

random

Status

closed

Resolution

fixed

Platform

OS Version

Product Version

3.11.2

Target Version

Fixed in Version

3.12.1+dev

Summary

0005188: double free corruption with bytecode system threads and stack reallocation

Description

Hi, the following code randomly but most often leads to a double free corruption.

let rec f x = if x = 0 then 0 else 1 + f (x-1)
let _ = Thread.join (Thread.create f 200)

(compiled with "ocamlc -thread unix.cma threads.cma bug.ml").

A valgrind analysis showed that the second illegal free is raised by the instruction "stat_free(th->stack_low);" at line 449 of posix.c: a reallocation of the stack happened but the th and th->stack_low did not get a chance to be updated yet (no entering in a blocking section). The attached patch seems to solve the problem in 3.11.

Apparently, thread implementation has been revised in 3.12 but the problem remains.

Incidentally, with a large system such as Coq, if we link it with the thread library, even though we might not make any use of the functions of the library, we randomly experiment out of memory errors at startup (in native code). Any ideas how to debug this?

Best regards. Hugo.

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Attached Files

patch.double-free-3.11 [^] (1,080 bytes) 2010-12-04 13:11

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Notes
(0005750) xleroy (administrator) 2010-12-22 14:42	Well spotted, thanks a lot. I adapted your fix to 3.12 and "committed" it in the 3.12 bugfix branch, for release in 3.12.1. I don't feel this bug warrants a new release of 3.11 but will let our esteemed release manager decide. As to the random out-of-memory errors at startup, I have no clue, but if you have a (semi-) repro case to suggest, I'll look into it.

Issue History
Date Modified	Username	Field	Change
2010-12-04 13:11	herbelin	New Issue
2010-12-04 13:11	herbelin	File Added: patch.double-free-3.11
2010-12-22 14:42	xleroy	Note Added: 0005750
2010-12-22 14:42	xleroy	Assigned To	=> xleroy
2010-12-22 14:42	xleroy	Status	new => resolved
2010-12-22 14:42	xleroy	Resolution	open => fixed
2010-12-22 14:42	xleroy	Fixed in Version	=> 3.12.1+dev
2012-03-24 15:01	xleroy	Status	resolved => closed