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

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Date:	Thu, 07 Sep 2006 12:40:46 -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 15:57, Eric W. Biederman wrote:
>> Jean Delvare <jdelvare@...e.de> writes:
>> > I'll now apply Oleg's fix and see if things get better.
>
> After 8 hours of stress testing on two machines, no crash and no freeze. 
> So Oleg's fix seems to do the trick. Thanks Oleg :)
>
> I'll keep the patches applied on both machines, even without stress tests 
> it is still better to make sure nothing bad happens in the long run.
>
>> > "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.
>
> There's nothing really special running on this laptop. Slackware 10.2 with 
> xterm, firefox, sylpheed, xchat, and that's about it. At least one of the 
> crashes I had yesterday happened when I was actively using firefox, I 
> can't tell for the other one.

Well firefox is threaded so that may be enough.  It takes a threaded
program to be able to trigger it.

> The difference with the system where no problem was observed may be that 
> the laptop has a preemptive kernel, and the desktop hasn't.

I suspect that just has the potential to make the window bigger.

Eric

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