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Date: Thu, 4 Feb 2016 10:06:11 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Davidlohr Bueso <dave@stgolabs.net>
cc: Mel Gorman <mgorman@techsingularity.net>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Chris Mason <clm@fb.com>, Darren Hart <dvhart@linux.intel.com>,
        Hugh Dickins <hughd@google.com>, linux-kernel@vger.kernel.org,
        Davidlohr Bueso <dbueso@suse.de>, Mel Gorman <mgorman@suse.de>
Subject: Re: [PATCH v5] futex: Remove requirement for lock_page in
 get_futex_key
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On Wed, 3 Feb 2016, Davidlohr Bueso wrote:
> +		 * We are not calling into get_futex_key_refs() in file-backed
> +		 * cases, therefore a successful atomic_inc return below will
> +		 * guarantee that get_futex_key() will continue to imply MB (B).

Can you please make that "MB (B)" part a bit more outstanding. I really had to
search for it.

> +		 */
> +		if (WARN_ON_ONCE(!atomic_inc_not_zero(&inode->i_count))) {
> +			rcu_read_unlock();
> +			put_page(page);
> +
> +			goto again;
> +		}

Don't we need 

		smp_mb__after_atomic();

here to make it a full barrier on all architectures?

Thanks,

	tglx