Date: Mon, 1 Feb 2010 18:28:11 +1100
From: Nick Piggin <npiggin@suse.de>
To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, akpm@linux-foundation.org,
       Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Steven Rostedt <rostedt@goodmis.org>,
       "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
       Nicholas Miell <nmiell@comcast.net>, laijs@cn.fujitsu.com,
       dipankar@in.ibm.com, josh@joshtriplett.org, dvhltc@us.ibm.com,
       niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org,
       Valdis.Kletnieks@vt.edu, dhowells@redhat.com
Subject: Re: [patch 1/3] Create spin lock/spin unlock with distinct memory
 barrier
Message-ID: <20100201072811.GG9085@laptop>
References: <20100131205254.407214951@polymtl.ca>
 <20100131210013.265317204@polymtl.ca>
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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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