linux-kernel - Re: Regression due to d29f3ef "tty

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Message-ID: <20120508103512.42db1c4b@pyramind.ukuu.org.uk>
Date:	Tue, 8 May 2012 10:35:12 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Alan Cox <alan@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: Regression due to d29f3ef "tty_lock: Localise the lock"

On Mon, 07 May 2012 17:06:38 -0600
Stephen Warren <swarren@...dotorg.org> wrote:

> Alan,
> 
> Commit d29f3ef "tty_lock: Localise the lock" appears to cause a problem
> for me.
> 
> With this commit (as in next-20120507), I can no longer log into my
> system (NVIDIA Tegra device with ARM CPU) over the serial console, since
> the login prompt no longer appears. If I wait a few minutes, I see the
> following console spew:

Eep. If it's reproducable can you test whether adding the unlock/relock
in drivers/tty/pty.c does the trick ?


ie:
	tty_unlock(tty);
	tty_vhangup(tty);
	tty_lock(tty);

or if changing it for tty_hangup(tty) does it.


There's some kind of lurking circular locking deadlock that I've not
managed to trigger here but a couple of reports point towards.
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