Date: Sat, 12 Dec 2009 02:36:03 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Greg KH <gregkh@suse.de>, Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Thomas Gleixner <tglx@linutronix.de>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       linux-kernel@vger.kernel.org
Subject: Re: [GIT PATCH] TTY patches for 2.6.33-git
Message-Id: <20091212023603.93768833.akpm@linux-foundation.org>
In-Reply-To: <20091212101032.GB25286@elte.hu>
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	<20091212084611.GA28266@elte.hu>
	<20091212013927.58d386d1.akpm@linux-foundation.org>
	<20091212101032.GB25286@elte.hu>
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On Sat, 12 Dec 2009 11:10:32 +0100 Ingo Molnar <mingo@elte.hu> wrote:

> 
> * Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > Seems to be quite .config-dependent.
> 
> My theory is that it's a race and that it's thus timing dependent. TTY 
> SMP details get stressed most during a particular point during bootup, 
> when all the mingetty's are starting up all at once and race with each 
> other.
> 
> If you are lucky to not hit the bug then, then the likelyhood is much 
> lower later on.
> 
> It would be nice if Alan posted his TTY stress-testing code. It could 
> potentially make this bug bisectable.
> 

I'm surprised that lockdep didn't notice that ab/ba I thought I saw. 
Maybe the do_tty_hangup()->tty_fasync() never happens.

The machine I can reproduce this on is at work and I'm not, until
Monday.  I'd try removing the files_lock() calls from tty_io.c, see if
that helps.

I had

[   71.553228] Warning: dev (tty1) tty->count(7) != #fd's(6) in tty_release_dev

come out once, then it went away.

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