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Date: Tue, 5 Jul 2016 10:25:12 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-next@vger.kernel.org, linux-kernel@vger.kernel.org,
        Chris Wilson <chris@chris-wilson.co.uk>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>
Subject: Re: linux-next: build failure after merge of the tip tree (from the
 drm-intel tree)
Message-ID: <20160705082512.GX30921@twins.programming.kicks-ass.net>
References: <20160705135303.6a1bc80a@canb.auug.org.au>
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On Tue, Jul 05, 2016 at 01:53:03PM +1000, Stephen Rothwell wrote:
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index d3502c0603e5..1f91f187b2a8 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -3290,7 +3290,7 @@ i915_gem_retire_work_handler(struct work_struct *work)
>  	 * We do not need to do this test under locking as in the worst-case
>  	 * we queue the retire worker once too often.
>  	 */
> -	if (lockless_dereference(dev_priv->gt.awake))
> +	if (/*lockless_dereference*/(dev_priv->gt.awake))
>  		queue_delayed_work(dev_priv->wq,
>  				   &dev_priv->gt.retire_work,
>  				   round_jiffies_up_relative(HZ));
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index f6de8dd567a2..2c1926418691 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -3095,7 +3095,7 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
>  	if (!i915.enable_hangcheck)
>  		return;
>  
> -	if (!lockless_dereference(dev_priv->gt.awake))
> +	if (!/*lockless_dereference*/(dev_priv->gt.awake))
>  		return;
>  
>  	/* As enabling the GPU requires fairly extensive mmio access,

Right, neither case appears to include a data dependency and thus
lockless_dereference() seems misguided.