[PATCH 20/21] drm/i915: Use a slab for object allocation

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

The primary purpose of this was to debug some use-after-free memory
corruption that was causing an OOPS inside drm/i915. As it turned out
the corruption was being caused elsewhere and i915.ko as a major user of
many objects was being hit hardest.

Indeed as we do frequent the generic kmalloc caches, dedicating one to
ourselves (or at least naming one for us depending upon the core) aids
debugging our own slab usage.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_dma.c |    3 +++
 drivers/gpu/drm/i915/i915_drv.h |    2 ++
 drivers/gpu/drm/i915/i915_gem.c |   12 +++++++++---
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index 3b69f38..d8269f3 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -2167,6 +2167,9 @@ int i915_driver_unload(struct drm_device *dev)
 
 	destroy_workqueue(dev_priv->wq);
 
+	if (dev_priv->slab)
+		kmem_cache_destroy(dev_priv->slab);
+
 	pci_dev_put(dev_priv->bridge_dev);
 	kfree(dev->dev_private);
 
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 30fbf3b..a8733ac 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -265,6 +265,8 @@ typedef struct drm_i915_private {
 
 	const struct intel_device_info *info;
 
+	struct kmem_cache *slab;
+
 	int has_gem;
 	int relative_constants_mode;
 
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index fe45f4e..f554273 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -3785,7 +3785,7 @@ struct drm_i915_gem_object *i915_gem_alloc_object(struct drm_device *dev,
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct drm_i915_gem_object *obj;
 
-	obj = kzalloc(sizeof(*obj), GFP_KERNEL);
+	obj = kmem_cache_alloc(dev_priv->slab, GFP_KERNEL | __GFP_ZERO);
 	if (obj == NULL)
 		return NULL;
 
@@ -3860,7 +3860,7 @@ static void i915_gem_free_object_tail(struct drm_i915_gem_object *obj)
 
 	kfree(obj->page_cpu_valid);
 	kfree(obj->bit_17);
-	kfree(obj);
+	kmem_cache_free(dev_priv->slab, obj);
 }
 
 void i915_gem_free_object(struct drm_gem_object *gem_obj)
@@ -4051,8 +4051,14 @@ init_ring_lists(struct intel_ring_buffer *ring)
 void
 i915_gem_load(struct drm_device *dev)
 {
-	int i;
 	drm_i915_private_t *dev_priv = dev->dev_private;
+	int i;
+
+	dev_priv->slab =
+		kmem_cache_create("i915_gem_object",
+				  sizeof(struct drm_i915_gem_object), 0,
+				  SLAB_HWCACHE_ALIGN,
+				  NULL);
 
 	INIT_LIST_HEAD(&dev_priv->mm.active_list);
 	INIT_LIST_HEAD(&dev_priv->mm.flushing_list);
-- 
1.7.4.1