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Date: Wed, 31 Mar 2010 00:50:40 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: LKML <linux-kernel@vger.kernel.org>, Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Greg KH <gregkh@suse.de>, Thomas Gleixner <tglx@linutronix.de>,
       Andrew Morton <akpm@linux-foundation.org>,
       John Kacur <jkacur@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>,
       Ingo Molnar <mingo@elte.hu>
Subject: Re: [RFC 9/9] tty: implement BTM as mutex instead of BKL
Message-ID: <20100330225038.GA5817@nowhere>
References: <1269982580-9361-1-git-send-email-arnd@arndb.de> <1269982580-9361-10-git-send-email-arnd@arndb.de>
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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.