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Date: Wed, 30 Oct 2013 20:11:41 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Victor Kaplansky <VICTORK@il.ibm.com>
Subject: Re: perf events ring buffer memory barrier on powerpc
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Cc: Michael Neuling <mikey@neuling.org>,
 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
 LKML <linux-kernel@vger.kernel.org>, Oleg Nesterov <oleg@redhat.com>,
 Linux PPC dev <linuxppc-dev@ozlabs.org>, Anton Blanchard <anton@samba.org>,
 Frederic Weisbecker <fweisbec@gmail.com>, paulmck@linux.vnet.ibm.com
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On Wed, Oct 30, 2013 at 07:29:30PM +0100, Peter Zijlstra wrote:
> +	page_shift = PAGE_SHIFT + page_order(rb);
> +
> +	handle->page = (offset >> page_shift) & (rb->nr_pages - 1);
> +
> +	offset &= page_shift - 1;

offset &= (1UL << page_shift) - 1;

Weird that it even appeared to work.. /me wonders if he even booted the
right kernel.

> +
> +	handle->addr = rb->data_pages[handle->page] + offset;
> +	handle->size = (1 << page_shift) - offset;