linux-kernel - Re: [GIT PATCH] TTY patches for 2.6.33-git

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Date:	Sat, 12 Dec 2009 02:36:03 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Greg KH <gregkh@...e.de>, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [GIT PATCH] TTY patches for 2.6.33-git

On Sat, 12 Dec 2009 11:10:32 +0100 Ingo Molnar <mingo@...e.hu> wrote:

> 
> * Andrew Morton <akpm@...ux-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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