linux-kernel - Re: [RFC 9/9] tty: implement BTM as mutex instead of BKL

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Date:	Wed, 31 Mar 2010 00:50:40 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, Greg KH <gregkh@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	John Kacur <jkacur@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC 9/9] tty: implement BTM as mutex instead of BKL

On Tue, Mar 30, 2010 at 10:56:20PM +0200, Arnd Bergmann wrote:
> +config TTY_MUTEX
> +	bool "Use a mutex instead of BKL for TTY locking"
> +	depends on EXPERIMENTAL && SMP


You still need it on UP-PREEMPT.

The bkl disables preemption so you need to "reproduce"
this atomicity by locking your path.

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