[Intel-gfx] [PATCH] drm/i915: Protect gen7 irq_seqno_barrier with uncore lock

[Chris Wilson]

Faced with sporadic machine hangs on gen7, that mimic the issue of
concurrent writes to the same cacheline and seem to start with
commit 9b9ed309 (drm/i915: Remove forcewake dance from seqno/irq
barrier on legacy gen6+), let us restore the spinlock around the mmio
read.

Fixes: 9b9ed3093613288247a27a55a6dd07f1222150f1
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala at intel.com>
---
 drivers/gpu/drm/i915/intel_ringbuffer.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 66f69cdd1d36..ad5bd3808d8b 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -1590,7 +1590,10 @@ gen6_seqno_barrier(struct intel_engine_cs *engine)
 	 * interrupt (with the same net latency).
 	 */
 	struct drm_i915_private *dev_priv = engine->dev->dev_private;
+
+	spin_lock_irq(&dev_priv->uncore.lock);
 	POSTING_READ_FW(RING_ACTHD(engine->mmio_base));
+	spin_unlock_irq(&dev_priv->uncore.lock);
 }
 
 static u32
-- 
2.8.1