linux-kernel - Re: [PATCH v7 5/6] MCS Lock: allow architectures to hook in to contended paths

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Message-ID: <20140120121948.GD31570@twins.programming.kicks-ass.net>
Date:	Mon, 20 Jan 2014 13:19:48 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E.McKenney" <paulmck@...ux.vnet.ibm.com>,
	Will Deacon <will.deacon@....com>,
	linux-kernel@...r.kernel.org, linux-mm <linux-mm@...ck.org>,
	linux-arch@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Waiman Long <waiman.long@...com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Alex Shi <alex.shi@...aro.org>,
	Andi Kleen <andi@...stfloor.org>,
	Michel Lespinasse <walken@...gle.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Matthew R Wilcox <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	George Spelvin <linux@...izon.com>,
	"H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
	Aswin Chandramouleeswaran <aswin@...com>,
	Scott J Norton <scott.norton@...com>,
	"Figo.zhang" <figo1802@...il.com>
Subject: Re: [PATCH v7 5/6] MCS Lock: allow architectures to hook in to
 contended paths

On Thu, Jan 16, 2014 at 04:08:31PM -0800, Tim Chen wrote:
> +#ifndef arch_mcs_spin_lock_contended
> +/*
> + * Using smp_load_acquire() provides a memory barrier that ensures
> + * subsequent operations happen after the lock is acquired.
> + */
> +#define arch_mcs_spin_lock_contended(l)					\
> +	while (!(smp_load_acquire(l))) {				\
> +		arch_mutex_cpu_relax();					\
> +	}
> +#endif

I think that wants to be:

#define arch_mcs_spin_lock_contended(l)				\
do {								\
	while (!smp_load_acquire(l))				\
		arch_mutex_cpu_relax();				\
} while (0)

So that we properly eat the ';' in: arch_mcs_spin_lock_contended(l);.

> +#ifndef arch_mcs_spin_unlock_contended
> +/*
> + * smp_store_release() provides a memory barrier to ensure all
> + * operations in the critical section has been completed before
> + * unlocking.
> + */
> +#define arch_mcs_spin_unlock_contended(l)				\
> +	smp_store_release((l), 1)
>  #endif
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