[Intel-gfx] [PATCH 3/5] drm/i915: Fix struct mutex vs. RPS lock inversion

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

RPS lock must be taken before the struct_mutex to avoid
locking inversion. So stop grabbing it for the whole
powersave initialization and instead only take it during
the sections which need it.

Also, struct_mutex is not needed any more since dedicated
RPS lock was added in:

   commit 4fc688ce79772496503d22263d61b071a8fb596e
   Author: Jesse Barnes <jbarnes at virtuousgeek.org>
   Date:   Fri Nov 2 11:14:01 2012 -0700

       drm/i915: protect RPS/RC6 related accesses (including PCU) with a new mutex

Based on prototype patch by Chris Wilson and a subsequent
mailing list discussion involving Ville, Imre, Chris and
Daniel.

v2: More details in the commit.

v3: Use drm_gem_object_unreference_unlocked. (Chris Wilson)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: Imre Deak <imre.deak at intel.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_display.c | 4 ----
 drivers/gpu/drm/i915/intel_pm.c      | 9 ++++-----
 2 files changed, 4 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 57e465ed088b..a0f3e399a2d9 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -15976,9 +15976,7 @@ void intel_modeset_gem_init(struct drm_device *dev)
 	struct drm_i915_gem_object *obj;
 	int ret;
 
-	mutex_lock(&dev->struct_mutex);
 	intel_init_gt_powersave(dev);
-	mutex_unlock(&dev->struct_mutex);
 
 	intel_modeset_init_hw(dev);
 
@@ -16058,9 +16056,7 @@ void intel_modeset_cleanup(struct drm_device *dev)
 
 	intel_cleanup_overlay(dev);
 
-	mutex_lock(&dev->struct_mutex);
 	intel_cleanup_gt_powersave(dev);
-	mutex_unlock(&dev->struct_mutex);
 
 	intel_teardown_gmbus(dev);
 }
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 379eabe093cb..8e869f183404 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -5229,8 +5229,6 @@ static void cherryview_setup_pctx(struct drm_device *dev)
 	u32 pcbr;
 	int pctx_size = 32*1024;
 
-	WARN_ON(!mutex_is_locked(&dev->struct_mutex));
-
 	pcbr = I915_READ(VLV_PCBR);
 	if ((pcbr >> VLV_PCBR_ADDR_SHIFT) == 0) {
 		DRM_DEBUG_DRIVER("BIOS didn't set up PCBR, fixing up\n");
@@ -5252,7 +5250,7 @@ static void valleyview_setup_pctx(struct drm_device *dev)
 	u32 pcbr;
 	int pctx_size = 24*1024;
 
-	WARN_ON(!mutex_is_locked(&dev->struct_mutex));
+	mutex_lock(&dev->struct_mutex);
 
 	pcbr = I915_READ(VLV_PCBR);
 	if (pcbr) {
@@ -5280,7 +5278,7 @@ static void valleyview_setup_pctx(struct drm_device *dev)
 	pctx = i915_gem_object_create_stolen(dev, pctx_size);
 	if (!pctx) {
 		DRM_DEBUG("not enough stolen space for PCTX, disabling\n");
-		return;
+		goto out;
 	}
 
 	pctx_paddr = dev_priv->mm.stolen_base + pctx->stolen->start;
@@ -5289,6 +5287,7 @@ static void valleyview_setup_pctx(struct drm_device *dev)
 out:
 	DRM_DEBUG_DRIVER("PCBR: 0x%08x\n", I915_READ(VLV_PCBR));
 	dev_priv->vlv_pctx = pctx;
+	mutex_unlock(&dev->struct_mutex);
 }
 
 static void valleyview_cleanup_pctx(struct drm_device *dev)
@@ -5298,7 +5297,7 @@ static void valleyview_cleanup_pctx(struct drm_device *dev)
 	if (WARN_ON(!dev_priv->vlv_pctx))
 		return;
 
-	drm_gem_object_unreference(&dev_priv->vlv_pctx->base);
+	drm_gem_object_unreference_unlocked(&dev_priv->vlv_pctx->base);
 	dev_priv->vlv_pctx = NULL;
 }
 
-- 
1.9.1