linux-kernel - Re: [PATCH] proc: readdir race fix (take 3)

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Message-ID: <m1wt8frd7j.fsf@ebiederm.dsl.xmission.com>
Date:	Thu, 07 Sep 2006 07:57:52 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Jean Delvare <jdelvare@...e.de>
Cc:	Andrew Morton <akpm@...l.org>, Oleg Nesterov <oleg@...sign.ru>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org, ak@...e.de
Subject: Re: [PATCH] proc: readdir race fix (take 3)

Jean Delvare <jdelvare@...e.de> writes:

> On Thursday 7 September 2006 00:43, Eric W. Biederman wrote:
>> Have you tested 2.6.18-rc6 without my patch?
>
> Yes I did, it didn't crash after a couple hours. Of course it doesn't 
> prove anything as the crash appears to be the result of a race.
>
> I'll now apply Oleg's fix and see if things get better.
>
>> I guess the practical question is what was your test methodology to
>> reproduce this problem?  A couple of more people running the same
>> test on a few more machines might at least give us confidence in what
>> is going on.
>
> "My" test program forks 1000 children who sleep for 1 second then look for 
> themselves in /proc, warn if they can't find themselves, and exit. So 
> basically the idea is that the process list will shrink very rapidly at 
> the same moment every child does readdir(/proc).
>
> I attached the test program, I take no credit (nor shame) for it, it was 
> provided to me by IBM (possibly on behalf of one of their own customers) 
> as a way to demonstrate and reproduce the original readdir(/proc) race 
> bug.

Ok.  So whatever is creating lots of child threads that tripped you
up is probably peculiar to the environment on your laptop.

Eric
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