[PATCH 23/23] TEST: drm/i915: mutex-less reset engine

[Michel Thierry]

It can't be that simple.

Signed-off-by: Michel Thierry <michel.thierry at intel.com>
---
 drivers/gpu/drm/i915/i915_drv.c | 21 ++++++++++++++++++---
 drivers/gpu/drm/i915/i915_irq.c | 20 ++------------------
 2 files changed, 20 insertions(+), 21 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 032f08316835..7f222e2d8bea 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -1887,7 +1887,6 @@ int i915_reset_engine(struct intel_engine_cs *engine)
 	struct drm_i915_private *dev_priv = engine->i915;
 	struct i915_gpu_error *error = &dev_priv->gpu_error;
 
-	lockdep_assert_held(&dev_priv->drm.struct_mutex);
 	GEM_BUG_ON(!test_bit(I915_RESET_BACKOFF, &error->flags));
 
 	if (!test_and_clear_bit(I915_RESET_HANDOFF, &error->flags))
@@ -1990,7 +1989,7 @@ int i915_reset_engine(struct intel_engine_cs *engine)
  */
 void i915_reset(struct drm_i915_private *dev_priv, u32 engine_mask)
 {
-	/* try engine reset first */
+	/* try engine reset first; look mom, no mutex! */
 	if (intel_has_reset_engine(dev_priv) &&
 	    !(engine_mask & (engine_mask - 1))) {
 		struct intel_engine_cs *engine =
@@ -2003,7 +2002,23 @@ void i915_reset(struct drm_i915_private *dev_priv, u32 engine_mask)
 	}
 
 reset_chip:
-	i915_reset_chip(dev_priv);
+        do {
+                /*
+                 * All state reset _must_ be completed before we update the
+                 * reset counter, for otherwise waiters might miss the reset
+                 * pending state and not properly drop locks, resulting in
+                 * deadlocks with the reset work.
+                 */
+                if (mutex_trylock(&dev_priv->drm.struct_mutex)) {
+                        i915_reset_chip(dev_priv);
+                        mutex_unlock(&dev_priv->drm.struct_mutex);
+                }
+
+                /* We need to wait for anyone holding the lock to wakeup */
+        } while (wait_on_bit_timeout(&dev_priv->gpu_error.flags,
+                                     I915_RESET_HANDOFF,
+                                     TASK_UNINTERRUPTIBLE,
+                                     HZ));
 }
 
 static int i915_pm_suspend(struct device *kdev)
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 6543e77e0621..cee7cddff25f 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -2668,24 +2668,8 @@ static void i915_reset_and_wakeup(struct drm_i915_private *dev_priv)
 	set_bit(I915_RESET_HANDOFF, &dev_priv->gpu_error.flags);
 	wake_up_all(&dev_priv->gpu_error.wait_queue);
 
-	do {
-		/*
-		 * All state reset _must_ be completed before we update the
-		 * reset counter, for otherwise waiters might miss the reset
-		 * pending state and not properly drop locks, resulting in
-		 * deadlocks with the reset work.
-		 */
-		if (mutex_trylock(&dev_priv->drm.struct_mutex)) {
-			i915_reset(dev_priv,
-				   dev_priv->gpu_error.reset_engine_mask);
-			mutex_unlock(&dev_priv->drm.struct_mutex);
-		}
-
-		/* We need to wait for anyone holding the lock to wakeup */
-	} while (wait_on_bit_timeout(&dev_priv->gpu_error.flags,
-				     I915_RESET_HANDOFF,
-				     TASK_UNINTERRUPTIBLE,
-				     HZ));
+	i915_reset(dev_priv,
+		   dev_priv->gpu_error.reset_engine_mask);
 
 	intel_finish_reset(dev_priv);
 
-- 
2.11.0