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

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Date:   Mon, 6 Mar 2017 11:15:28 +0000
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     Pavel Machek <pavel@....cz>
Cc:     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 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);
 }
 
 static void i9xx_emit_breadcrumb(struct drm_i915_gem_request *req, u32 *cs)


-- 
Chris Wilson, Intel Open Source Technology Centre