linux-kernel - Re: [patch] timer/hrtimer: take per cpu locks in sane order

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Date:	Fri, 2 Mar 2007 14:04:33 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	john stultz <johnstul@...ibm.com>,
	Roman Zippel <zippel@...ux-m68k.org>,
	Christian Borntraeger <cborntra@...ibm.com>,
	linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch] timer/hrtimer: take per cpu locks in sane order


* Heiko Carstens <heiko.carstens@...ibm.com> wrote:

> -	spin_lock(&new_base->lock);
> -	spin_lock(&old_base->lock);
> +	/*
> +	 * If we take a lock from a different cpu, make sure we have always
> +	 * the same locking order. That is the lock that belongs to the cpu
> +	 * with the lowest number is taken first.
> +	 */
> +	lock1 = smp_processor_id() < cpu ? &new_base->lock : &old_base->lock;
> +	lock2 = smp_processor_id() < cpu ? &old_base->lock : &new_base->lock;
> +	spin_lock(lock1);
> +	spin_lock(lock2);

looks good to me. Wouldnt this be cleaner via double_lock_timer() - 
similar to how double_rq_lock() works in kernel/sched.c - instead of 
open-coding it?

	Ingo
-
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