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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <73013289.R6WJLciOm2@wuerfel>
Date:	Wed, 24 Aug 2011 10:46:30 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Jiri Slaby <jslaby@...e.cz>
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 Tuesday 23 August 2011 20:54:08 Jiri Slaby wrote:
> On 08/23/2011 08:46 PM, Arnd Bergmann wrote:
> > According to http://kernelnewbies.org/BigKernelLock, I concluded back then
> > that tty_wait_until_sent would always be called without BTM held. Has that
> > changed recently, or did I miss a caller that holds the BTM?
> 
> Every tty_operations->close and ->hangup :).

Ah, right, I remember. The chart I did was only to prove that locking was
consistent (i.e. no deadlocks), it ignored that the function needs to be
called without BTM because I had incorrectly convinced myself that the
wait_event_interruptible_timeout() didn't need to release it.

I think I just saw another problem: uart_close takes port->mutex while
holding the BTM, then calls tty_wait_until_sent(). If this releases
and reaquires the BTM, you get an AB-BA deadlock with port->mutex.

	Arnd
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/