[PATCH v2] drm/i915: Prevent machine hang from Broxton's vtd w/a and error capture

[Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>]

Since capturing the error state requires fiddling around with the GGTT
to read arbitrary buffers and is itself run under stop_machine(), it
deadlocks the machine (effectively a hard hang) when run in conjunction
with Broxton's VTd workaround to serialize GGTT access.

v2: Store the ERR_PTR in first_error so that the error can be reported
to the user via sysfs.

Fixes: 0ef34ad6222a ("drm/i915: Serialize GTT/Aperture accesses on BXT")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Jon Bloomfield <jon.bloomfield@xxxxxxxxx>
Cc: John Harrison <john.C.Harrison@xxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
---
 drivers/gpu/drm/i915/i915_drv.h       |  8 +++++++-
 drivers/gpu/drm/i915/i915_gem_gtt.c   |  3 +++
 drivers/gpu/drm/i915/i915_gpu_error.c | 15 ++++++++++++++-
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 594fd14e66c5..1eca4f954050 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3990,6 +3990,7 @@ static inline void i915_gpu_state_put(struct i915_gpu_state *gpu)
 
 struct i915_gpu_state *i915_first_error_state(struct drm_i915_private *i915);
 void i915_reset_error_state(struct drm_i915_private *i915);
+void i915_disable_error_state(struct drm_i915_private *i915, int err);
 
 #else
 
@@ -4002,13 +4003,18 @@ static inline void i915_capture_error_state(struct drm_i915_private *dev_priv,
 static inline struct i915_gpu_state *
 i915_first_error_state(struct drm_i915_private *i915)
 {
-	return NULL;
+	return ERR_PTR(-ENODEV);
 }
 
 static inline void i915_reset_error_state(struct drm_i915_private *i915)
 {
 }
 
+static inline void i915_disable_error_state(struct drm_i915_private *i915,
+					    int err)
+{
+}
+
 #endif
 
 const char *i915_cache_level_str(struct drm_i915_private *i915, int type);
diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index f3c35e826321..0264d88b4cff 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -3373,6 +3373,9 @@ static int gen8_gmch_probe(struct i915_ggtt *ggtt)
 		ggtt->base.insert_page    = bxt_vtd_ggtt_insert_page__BKL;
 		if (ggtt->base.clear_range != nop_clear_range)
 			ggtt->base.clear_range = bxt_vtd_ggtt_clear_range__BKL;
+
+		/* Prevent recursively calling stop_machine() and deadlocks. */
+		i915_disable_error_state(dev_priv, -ENODEV);
 	}
 
 	ggtt->invalidate = gen6_ggtt_invalidate;
diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
index 48418fb81066..0b45d28624b7 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/drivers/gpu/drm/i915/i915_gpu_error.c
@@ -633,6 +633,9 @@ int i915_error_state_to_str(struct drm_i915_error_state_buf *m,
 		return 0;
 	}
 
+	if (IS_ERR(error))
+		return PTR_ERR(error);
+
 	if (*error->error_msg)
 		err_printf(m, "%s\n", error->error_msg);
 	err_printf(m, "Kernel: " UTS_RELEASE "\n");
@@ -1819,6 +1822,7 @@ void i915_capture_error_state(struct drm_i915_private *dev_priv,
 	error = i915_capture_gpu_state(dev_priv);
 	if (!error) {
 		DRM_DEBUG_DRIVER("out of memory, not capturing error state\n");
+		i915_disable_error_state(dev_priv, -ENOMEM);
 		return;
 	}
 
@@ -1874,5 +1878,14 @@ void i915_reset_error_state(struct drm_i915_private *i915)
 	i915->gpu_error.first_error = NULL;
 	spin_unlock_irq(&i915->gpu_error.lock);
 
-	i915_gpu_state_put(error);
+	if (!IS_ERR(error))
+		i915_gpu_state_put(error);
+}
+
+void i915_disable_error_state(struct drm_i915_private *i915, int err)
+{
+	spin_lock_irq(&i915->gpu_error.lock);
+	if (!i915->gpu_error.first_error)
+		i915->gpu_error.first_error = ERR_PTR(err);
+	spin_unlock_irq(&i915->gpu_error.lock);
 }
-- 
2.15.1

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