Re: Gem GTT mmaps..

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On Friday, February 6, 2009 1:35 pm Thomas Hellström wrote:
> Jesse Barnes wrote:
> > On Thursday, February 5, 2009 10:37 am Jesse Barnes wrote:
> >> So if we leave the lookup reference around from the GTT mapping ioctl,
> >> that would take care of new mappings.  And if we added/removed
> >> references at VM open/close time, we should be covered for fork.  But is
> >> it ok to add a new unref in the finish ioctl for GTT mapped objects?  I
> >> don't think so, because we don't know for sure if the caller was the one
> >> that created the new fake offset (which would be one way of detecting
> >> whether it was GTT mapped). Seems like we need a new unmap ioctl?  Or we
> >> could put the mapping ref/unref in libdrm, where it would be tracked on
> >> a per-process basis...
> >
> > Ah but maybe we should just tear down the fake offset at unmap time; then
> > we'd be able to use it as an existence test for the mapping and get the
> > refcounting right.  The last thing I thought of was whether we'd be ok in
> > a map_gtt -> crash case.  I *think* the vm_close code will deal with
> > that, if we do a deref there?
>
> Yes, an mmap() is always paired with a vm_close(), and the vm_close()
> also happens in a crash situation.

This one should cover the cases you found.
  - ref at map time will keep the object around so fault shouldn't fail
  - additional threads will take their refs in vm_open/close
  - unmap will unref and remove mmap_offset allowing object to be freed

-- 
Jesse Barnes, Intel Open Source Technology Center

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index 6915fb8..2752114 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -460,6 +460,23 @@ drm_gem_object_handle_free(struct kref *kref)
 }
 EXPORT_SYMBOL(drm_gem_object_handle_free);
 
+void drm_gem_vm_open(struct vm_area_struct *vma)
+{
+	struct drm_gem_object *obj = vma->vm_private_data;
+
+	drm_gem_object_reference(obj);
+}
+EXPORT_SYMBOL(drm_gem_vm_open);
+
+void drm_gem_vm_close(struct vm_area_struct *vma)
+{
+	struct drm_gem_object *obj = vma->vm_private_data;
+
+	drm_gem_object_unreference(obj);
+}
+EXPORT_SYMBOL(drm_gem_vm_close);
+
+
 /**
  * drm_gem_mmap - memory map routine for GEM objects
  * @filp: DRM file pointer
diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index aac12ee..a31cbdb 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -94,6 +94,8 @@ static int i915_resume(struct drm_device *dev)
 
 static struct vm_operations_struct i915_gem_vm_ops = {
 	.fault = i915_gem_fault,
+	.open = drm_gem_vm_open,
+	.close = drm_gem_vm_close,
 };
 
 static struct drm_driver driver = {
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 1441831..a476de0 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -52,6 +52,7 @@ static void i915_gem_object_free_page_list(struct drm_gem_object *obj);
 static int i915_gem_object_wait_rendering(struct drm_gem_object *obj);
 static int i915_gem_object_bind_to_gtt(struct drm_gem_object *obj,
 					   unsigned alignment);
+static void i915_gem_free_mmap_offset(struct drm_gem_object *obj);
 static int i915_gem_object_get_fence_reg(struct drm_gem_object *obj, bool write);
 static void i915_gem_clear_fence_reg(struct drm_gem_object *obj);
 static int i915_gem_evict_something(struct drm_device *dev);
@@ -497,6 +498,13 @@ i915_gem_sw_finish_ioctl(struct drm_device *dev, void *data,
 		i915_gem_object_flush_cpu_write_domain(obj);
 
 	drm_gem_object_unreference(obj);
+
+	/* If it's been GTT mapped, unref it again... */
+	if (obj_priv->mmap_offset) {
+		i915_gem_free_mmap_offset(obj);
+		drm_gem_object_unreference(obj);
+	}
+
 	mutex_unlock(&dev->struct_mutex);
 	return ret;
 }
@@ -607,8 +615,6 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 	case -EAGAIN:
 		return VM_FAULT_OOM;
 	case -EFAULT:
-	case -EBUSY:
-		DRM_ERROR("can't insert pfn??  fault or busy...\n");
 		return VM_FAULT_SIGBUS;
 	default:
 		return VM_FAULT_NOPAGE;
@@ -684,6 +690,32 @@ out_free_list:
 	return ret;
 }
 
+static void
+i915_gem_free_mmap_offset(struct drm_gem_object *obj)
+{
+	struct drm_device *dev = obj->dev;
+	struct drm_i915_gem_object *obj_priv = obj->driver_private;
+	struct drm_gem_mm *mm = dev->mm_private;
+	struct drm_map_list *list;
+	struct drm_map *map;
+
+	list = &obj->map_list;
+	drm_ht_remove_item(&mm->offset_hash, &list->hash);
+
+	if (list->file_offset_node) {
+		drm_mm_put_block(list->file_offset_node);
+		list->file_offset_node = NULL;
+	}
+
+	map = list->map;
+	if (map) {
+		drm_free(map, sizeof(*map), DRM_MEM_DRIVER);
+		list->map = NULL;
+	}
+
+	obj_priv->mmap_offset = 0;
+}
+
 /**
  * i915_gem_get_gtt_alignment - return required GTT alignment for an object
  * @obj: object to check
@@ -788,7 +820,7 @@ i915_gem_mmap_gtt_ioctl(struct drm_device *dev, void *data,
 		list_add(&obj_priv->list, &dev_priv->mm.inactive_list);
 	}
 
-	drm_gem_object_unreference(obj);
+	/* Leave lookup reference around until unmap time */
 	mutex_unlock(&dev->struct_mutex);
 
 	return 0;
@@ -2885,9 +2917,6 @@ int i915_gem_init_object(struct drm_gem_object *obj)
 void i915_gem_free_object(struct drm_gem_object *obj)
 {
 	struct drm_device *dev = obj->dev;
-	struct drm_gem_mm *mm = dev->mm_private;
-	struct drm_map_list *list;
-	struct drm_map *map;
 	struct drm_i915_gem_object *obj_priv = obj->driver_private;
 
 	while (obj_priv->pin_count > 0)
@@ -2898,20 +2927,6 @@ void i915_gem_free_object(struct drm_gem_object *obj)
 
 	i915_gem_object_unbind(obj);
 
-	list = &obj->map_list;
-	drm_ht_remove_item(&mm->offset_hash, &list->hash);
-
-	if (list->file_offset_node) {
-		drm_mm_put_block(list->file_offset_node);
-		list->file_offset_node = NULL;
-	}
-
-	map = list->map;
-	if (map) {
-		drm_free(map, sizeof(*map), DRM_MEM_DRIVER);
-		list->map = NULL;
-	}
-
 	drm_free(obj_priv->page_cpu_valid, 1, DRM_MEM_DRIVER);
 	drm_free(obj->driver_private, 1, DRM_MEM_DRIVER);
 }
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 8190b9b..e5f4ae9 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -1321,6 +1321,8 @@ void drm_gem_object_free(struct kref *kref);
 struct drm_gem_object *drm_gem_object_alloc(struct drm_device *dev,
 					    size_t size);
 void drm_gem_object_handle_free(struct kref *kref);
+void drm_gem_vm_open(struct vm_area_struct *vma);
+void drm_gem_vm_close(struct vm_area_struct *vma);
 int drm_gem_mmap(struct file *filp, struct vm_area_struct *vma);
 
 static inline void