linux-kernel - Re: tty related lockdep trace during bootup on 3.2-rc2

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Date:	Tue, 22 Nov 2011 23:28:31 -0800
From:	Havard Skinnemoen <hskinnemoen@...gle.com>
To:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Havard Skinnemoen <hskinnemoen@...gle.com>
Subject: Re: tty related lockdep trace during bootup on 3.2-rc2

On Tue, Nov 22, 2011 at 7:38 PM, Dave Jones <davej@...hat.com> wrote:
> From Linus' current tree...
>
> related to 5dc2470c602da8851907ec18942cd876c3b4ecc1 maybe ?

Yes, probably. I did have a bad feeling about the locking, but it
seemed to behave well during testing. Wonder why I didn't see this.

So what's happening is that tty_open() holds big_tty_mutex while
calling acm_tty_open which takes open_lock, and acm_tty_close holds
open_lock while calling tty_port_close_start which takes
big_tty_mutex?

Not sure how to solve this. Not taking the lock before calling
tty_port_close_start means the tty_port may get freed before it
returns.

Havard
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