linux-kernel - Re: patch "TTY: remove tty

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Date:	Wed, 24 Aug 2011 13:47:37 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	Arnd Bergmann <arnd@...db.de>
CC:	gregkh@...e.de, alan@...ux.intel.com,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: patch "TTY: remove tty_locked" added to tty tree

On 08/24/2011 01:20 PM, Arnd Bergmann wrote:
> It's not clear to me what state->mutex protects in the serial_core, but
> it has been around forever (used to be called state->sem)

It was actually moved in uart_close back in 2003. Formerly (when there
was only a coarse grained port_sem) it was right before uart_shutdown.
But there were some flags to handle some races. I'm not sure whether the
flags protected any race here though.

> and is held in
> all uart functions, which is at least consistent. IIRC what Alan's plan
> for this was, uart_close should eventually get changed to use
> tty_port_close_start or even tty_port_close. Maybe the time for that has
> come now, lacking better alternatives?

Yes, I have such a patch in my queue. But it's not easy to get there.
You may take a look at:
http://decibel.fi.muni.cz/gitweb/?p=linux.git;a=shortlog;h=refs/heads/devel

But it's still far from ready. And yet, in the queue, I still have
port->mutex locked before tty_port_close_start like it is now.

> A lot of other drivers call tty_port_close_start() before taking port->mutex.

Yes, that's true. That's why I wrote that before. But most of the
drivers doesn't have so complex locking dependencies like uart.

thanks,
-- 
js
suse labs
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