[PATCH v2] drm/i915: Remove struct_mutex for destroying framebuffers

[Chris Wilson <chris@chris-wilson.co.uk>]

We do not need to hold struct_mutex for destroying drm_i915_gem_objects
any longer, and with a little care taken over tracking
obj->framebuffer_references, we can relinquish BKL locking around the
destroy of intel_framebuffer.

v2: Use atomic check for WARN_ON framebuffer miscounting

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
---
 drivers/gpu/drm/i915/i915_gem_object.h   | 2 +-
 drivers/gpu/drm/i915/i915_gem_shrinker.c | 2 +-
 drivers/gpu/drm/i915/i915_gem_tiling.c   | 2 +-
 drivers/gpu/drm/i915/intel_display.c     | 9 ++++-----
 4 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_object.h b/drivers/gpu/drm/i915/i915_gem_object.h
index 02365a5f7c80..ef4893a4f08c 100644
--- a/drivers/gpu/drm/i915/i915_gem_object.h
+++ b/drivers/gpu/drm/i915/i915_gem_object.h
@@ -165,7 +165,7 @@ struct drm_i915_gem_object {
 	struct reservation_object *resv;
 
 	/** References from framebuffers, locks out tiling changes. */
-	unsigned long framebuffer_references;
+	atomic_t framebuffer_references;
 
 	/** Record of address bit 17 of each page at last unbind. */
 	unsigned long *bit_17;
diff --git a/drivers/gpu/drm/i915/i915_gem_shrinker.c b/drivers/gpu/drm/i915/i915_gem_shrinker.c
index f249a1eb46ac..8bc515e8b2a2 100644
--- a/drivers/gpu/drm/i915/i915_gem_shrinker.c
+++ b/drivers/gpu/drm/i915/i915_gem_shrinker.c
@@ -207,7 +207,7 @@ i915_gem_shrink(struct drm_i915_private *dev_priv,
 
 			if (!(flags & I915_SHRINK_ACTIVE) &&
 			    (i915_gem_object_is_active(obj) ||
-			     obj->framebuffer_references))
+			     atomic_read(&obj->framebuffer_references)))
 				continue;
 
 			if (!can_release_pages(obj))
diff --git a/drivers/gpu/drm/i915/i915_gem_tiling.c b/drivers/gpu/drm/i915/i915_gem_tiling.c
index 8b2b507bdf7e..46ade36dcee6 100644
--- a/drivers/gpu/drm/i915/i915_gem_tiling.c
+++ b/drivers/gpu/drm/i915/i915_gem_tiling.c
@@ -238,7 +238,7 @@ i915_gem_object_set_tiling(struct drm_i915_gem_object *obj,
 	if ((tiling | stride) == obj->tiling_and_stride)
 		return 0;
 
-	if (obj->framebuffer_references)
+	if (atomic_read(&obj->framebuffer_references))
 		return -EBUSY;
 
 	/* We need to rebind the object if its current allocation
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 0d46a8db5c6f..3b0ef752cd8b 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -14266,14 +14266,13 @@ static void intel_setup_outputs(struct drm_i915_private *dev_priv)
 
 static void intel_user_framebuffer_destroy(struct drm_framebuffer *fb)
 {
-	struct drm_device *dev = fb->dev;
 	struct intel_framebuffer *intel_fb = to_intel_framebuffer(fb);
 
 	drm_framebuffer_cleanup(fb);
-	mutex_lock(&dev->struct_mutex);
-	WARN_ON(!intel_fb->obj->framebuffer_references--);
+
+	WARN_ON(atomic_dec_return(&intel_fb->obj->framebuffer_references) < 0);
 	i915_gem_object_put(intel_fb->obj);
-	mutex_unlock(&dev->struct_mutex);
+
 	kfree(intel_fb);
 }
 
@@ -14510,7 +14509,7 @@ static int intel_framebuffer_init(struct drm_device *dev,
 		return ret;
 	}
 
-	intel_fb->obj->framebuffer_references++;
+	atomic_inc(&intel_fb->obj->framebuffer_references);
 
 	return 0;
 }
-- 
2.11.0

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