linux-kernel - Re: linux-next: build failure after merge of the tip tree (from the drm-intel tree)

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Date:	Tue, 5 Jul 2016 10:59:59 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	Chris Wilson <chris@...is-wilson.co.uk>
Subject: Re: linux-next: build failure after merge of the tip tree (from the
 drm-intel tree)

On Tue, Jul 05, 2016 at 10:25:12AM +0200, Peter Zijlstra wrote:
> 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.

Agreed!  At first glance, this code wants READ_ONCE() rather than
lockless_dereference().

							Thanx, Paul