linux-kernel - Re: 2.6.25.3: su gets stuck for root

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Date:	Sat, 14 Jun 2008 23:26:58 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Joe Peterson" <joe@...rush.com>
Cc:	"Alan Cox" <alan@...hat.com>,
	"Alan Cox" <alan@...rguk.ukuu.org.uk>,
	"David Newall" <davidn@...idnewall.com>,
	"Willy Tarreau" <w@....eu>,
	"Harald Dunkel" <harald.dunkel@...nline.de>,
	linux-kernel@...r.kernel.org
Subject: Re: 2.6.25.3: su gets stuck for root

On Sat, Jun 14, 2008 at 10:52 PM, Joe Peterson <joe@...rush.com> wrote:
> Vegard Nossum wrote:
>> Yeah, a user-space process can do this, and it's the right behaviour
>> for the kernel. I did post a program that would "reproduce" what
>> you're seeing. I do now believe that it's something timing-related, as
>> Alan suggested initially. (But timing-related with your scripts, that
>> is. I must say, that "sleep 2" does look a bit suspicious; I have no
>> idea what that is supposed to do :-))
>
> Ah, that is something I put in there to artificially make it more
> reproducible.  Here's the reason: when I first encountered the problem,
> it was happening if the home dir of the user was on the "btrfs"
> filesystem (the new checksumming one from Oracle).  This made me suspect
> btrfs initially.  But I reproduced the problem [more sporadically] when
> the home was on ext3 as well.  Since btrfs has a different performance
> profile, especially when first accessed after a mount (and it is a
> filesystem still under development, so some optimizations are yet to
> come), I figured it might be timing-related, and sure enough, adding the
> "sleep 2" proved that.

I'm not sure it is. Try adding sleep 3 instead. Because I have the
"sleep 2" when I run "su foo" as well, and I _didn't_ put it there:

[pid  6298] execve("/bin/sleep", ["sleep", "2"], [/* 47 vars */]
<unfinished ...>


Vegard

-- 
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
	-- E. W. Dijkstra, EWD1036
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