linux-kernel - Re: [RFC][PATCH] spinlock: Kill spin_unlock

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Message-ID: <20110105192634.GA30361@redhat.com>
Date:	Wed, 5 Jan 2011 20:26:34 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Nick Piggin <npiggin@...nel.dk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Chris Mason <chris.mason@...cle.com>,
	Frank Rowand <frank.rowand@...sony.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Galbraith <efault@....de>, Paul Turner <pjt@...gle.com>,
	Jens Axboe <axboe@...nel.dk>,
	Yong Zhang <yong.zhang0@...il.com>,
	linux-kernel@...r.kernel.org,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Linux-Arch <linux-arch@...r.kernel.org>,
	Jeff Garzik <jeff@...zik.org>, Tejun Heo <tj@...nel.org>
Subject: Re: [RFC][PATCH] spinlock: Kill spin_unlock_wait()

On 01/05, Peter Zijlstra wrote:
>
> On Tue, 2011-01-04 at 17:45 +1100, Nick Piggin wrote:
> > So I agree, taking it out the back and shooting it in the head would make
> > the world a better place.
>
> There appear to be only two callsites of said horror,

Not sure I understand why spin_unlock_wait() is really awful, but OK.

> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -956,7 +956,8 @@ NORET_TYPE void do_exit(long code)
>  	 * an exiting task cleaning up the robust pi futexes.
>  	 */
>  	smp_mb();
> -	raw_spin_unlock_wait(&tsk->pi_lock);
> +	raw_spin_lock_irq(&tsk->pi_lock);
> +	raw_spin_unlock_irq(&tsk->pi_lock);

then you can kill smp_mb() above.

Oleg.

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