linux-kernel - Re: [regression] Re: 4.11-rc0, thinkpad x220: GPU hang

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Date:   Mon, 6 Mar 2017 11:47:58 +0000
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     Pavel Machek <pavel@....cz>,
        kernel list <linux-kernel@...r.kernel.org>,
        daniel.vetter@...el.com, jani.nikula@...ux.intel.com,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Subject: Re: [regression] Re: 4.11-rc0, thinkpad x220: GPU hang

On Mon, Mar 06, 2017 at 11:15:28AM +0000, Chris Wilson wrote:
> On Mon, Mar 06, 2017 at 12:01:51AM +0100, Pavel Machek wrote:
> > Hi!
> > 
> > > > mplayer stopped working after a while. Dmesg says:
> > > > 
> > > > [ 3000.266533] cdc_ether 2-1.2:1.0 usb0: register 'cdc_ether' at
> > 
> > Now I'm pretty sure it is a regression in v4.11-rc0. Any ideas what to
> > try? Bisect will be slow and nasty :-(.
> 
> I came the conclusion that #99671 is the ring HEAD overtaking the TAIL,
> and under the presumption that your bug matches (as the symptoms do):
> 
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 4ffa35faff49..62e31a7438ac 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -782,10 +782,10 @@ static void i9xx_submit_request(struct drm_i915_gem_request *request)
>  {
>         struct drm_i915_private *dev_priv = request->i915;
>  
> -       i915_gem_request_submit(request);
> -
>         GEM_BUG_ON(!IS_ALIGNED(request->tail, 8));
>         I915_WRITE_TAIL(request->engine, request->tail);
> +
> +       i915_gem_request_submit(request);

Hmm. request->tail is not set until i915_gem_request_submit() Uh oh.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre