linux-kernel - Re: [patch 1/3] Create spin lock/spin unlock with distinct memory barrier

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Message-ID: <20100201072811.GG9085@laptop>
Date:	Mon, 1 Feb 2010 18:28:11 +1100
From:	Nick Piggin <npiggin@...e.de>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	akpm@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Nicholas Miell <nmiell@...cast.net>, laijs@...fujitsu.com,
	dipankar@...ibm.com, josh@...htriplett.org, dvhltc@...ibm.com,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com
Subject: Re: [patch 1/3] Create spin lock/spin unlock with distinct memory
 barrier

On Sun, Jan 31, 2010 at 03:52:55PM -0500, Mathieu Desnoyers wrote:
> +/*
> + * X86 spinlock-mb mappings. Use standard spinlocks with acquire/release
> + * semantics. Associated memory barriers are defined as no-ops, because the
> + * spinlock LOCK-prefixed atomic operations imply a full memory barrier.
> + */
> +
> +#define spin_lock__no_acquire			spin_lock
> +#define spin_unlock__no_release			spin_unlock
> +
> +#define spin_lock_irq__no_acquire		spin_lock_irq
> +#define spin_unlock_irq__no_release		spin_unlock_irq
> +
> +#define raw_spin_lock__no_acquire		raw_spin_lock
> +#define raw_spin_unlock__no_release		raw_spin_unlock
> +
> +#define raw_spin_lock_irq__no_acquire		raw_spin_lock_irq
> +#define raw_spin_unlock_irq__no_release		raw_spin_unlock_irq
> +
> +#define smp_acquire__after_spin_lock()		do { } while (0)
> +#define smp_release__before_spin_unlock()	do { } while (0)
> +
> +#define smp_mb__after_spin_lock()		do { } while (0)
> +#define smp_mb__before_spin_unlock()		do { } while (0)

Oh, and that one's wrong. loads can pass spin_unlock on x86 so it
needs to be smp_mb().

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