From: Guillaume Marcais <guslist@...>
Date: 2005-09-11T11:23:01+09:00
Subject: Re: Mmap crash when appending

Le 10 sept. 05, � 15:01, Ara.T.Howard a �crit :

> works fine for me:
>
>   harp:~ > irb -r mmap -r fileutils
>   irb(main):001:0> FileUtils::touch 'mmap'
>   => ["mmap"]
>   irb(main):002:0> mm = Mmap.new("mmap", "rw")

Yes, as suggested by Guy, using "rw" instead of "w" fixes the problem, 
however weird that may seem. His patch in ruby-talk:155557 fixed the 
problem too.
>
> thoughts:
>
>   - redhat has had many bugs with there mmap code.  a short while ago i
>     reported a simple c program that would hang the kernel
>
>       https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=124626
>
>     perhaps your linux version is buggy.  if so bug the developers - 
> mmap is
>     such a fundemental operation (programs are always mmap'd when run 
> by the
>     kernel) that it's astounding that bugs like this get released.

I am not using RedHat but Mandrake (note that I am not claiming 
anything about the quality of one over the other).

>   - did you install ruby via some package manager but compile the mmap 
> dist?
>     if you i'd (always) compile ruby vs. trusting the binary dists and 
> compile
>     mmap using this ruby, then see if the problem persists.

Correct, it is the distro binary of ruby and a self compile mmap.

> other than that i can tell you i'm abusing mmap in the most sinister 
> ways with
> no crashes or data corruption on a variety of linux dists.

Well, your recent posts on the subject have been inspirational... I 
have crashed ruby using mmap after forking (haven't nailed down the bug 
yet). I'll recompile ruby to see if that's the problem.

Guillaume.