drm/i915/ttm: Drop region reference counting

There is an interesting refcounting loop:
struct intel_memory_region has a struct ttm_resource_manager,
ttm_resource_manager->move may hold a reference to i915_request,
i915_request may hold a reference to intel_context,
intel_context may hold a reference to drm_i915_gem_object,
drm_i915_gem_object may hold a reference to intel_memory_region.

Break this loop by dropping region reference counting.

In addition, Have regions with a manager moving fence make sure
that all region objects are released before freeing the region.

v6:
- Fix a code comment.
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211122214554.371864-4-thomas.hellstrom@linux.intel.com

drivers/gpu/drm/i915/gem/i915_gem_region.c

@@ -11,7 +11,7 @@
 void i915_gem_object_init_memory_region(struct drm_i915_gem_object *obj,
 					struct intel_memory_region *mem)
 {
-	obj->mm.region = intel_memory_region_get(mem);
+	obj->mm.region = mem;
 
 	mutex_lock(&mem->objects.lock);
 	list_add(&obj->mm.region_link, &mem->objects.list);
@@ -25,8 +25,6 @@ void i915_gem_object_release_memory_region(struct drm_i915_gem_object *obj)
 	mutex_lock(&mem->objects.lock);
 	list_del(&obj->mm.region_link);
 	mutex_unlock(&mem->objects.lock);
-
-	intel_memory_region_put(mem);
 }
 
 struct drm_i915_gem_object *

drivers/gpu/drm/i915/gem/i915_gem_shmem.c

@@ -664,9 +664,10 @@ static int init_shmem(struct intel_memory_region *mem)
 	return 0; /* Don't error, we can simply fallback to the kernel mnt */
 }
 
-static void release_shmem(struct intel_memory_region *mem)
+static int release_shmem(struct intel_memory_region *mem)
 {
 	i915_gemfs_fini(mem->i915);
+	return 0;
 }
 
 static const struct intel_memory_region_ops shmem_region_ops = {

drivers/gpu/drm/i915/gem/i915_gem_stolen.c

@@ -720,9 +720,10 @@ static int init_stolen_smem(struct intel_memory_region *mem)
 	return i915_gem_init_stolen(mem);
 }
 
-static void release_stolen_smem(struct intel_memory_region *mem)
+static int release_stolen_smem(struct intel_memory_region *mem)
 {
 	i915_gem_cleanup_stolen(mem->i915);
+	return 0;
 }
 
 static const struct intel_memory_region_ops i915_region_stolen_smem_ops = {
@@ -759,10 +760,11 @@ static int init_stolen_lmem(struct intel_memory_region *mem)
 	return err;
 }
 
-static void release_stolen_lmem(struct intel_memory_region *mem)
+static int release_stolen_lmem(struct intel_memory_region *mem)
 {
 	io_mapping_fini(&mem->iomap);
 	i915_gem_cleanup_stolen(mem->i915);
+	return 0;
 }
 
 static const struct intel_memory_region_ops i915_region_stolen_lmem_ops = {

drivers/gpu/drm/i915/gem/i915_gem_ttm.c

@@ -997,7 +997,7 @@ int __i915_gem_ttm_object_init(struct intel_memory_region *mem,
 	i915_gem_object_init(obj, &i915_gem_ttm_obj_ops, &lock_class, flags);
 
 	/* Don't put on a region list until we're either locked or fully initialized. */
-	obj->mm.region = intel_memory_region_get(mem);
+	obj->mm.region = mem;
 	INIT_LIST_HEAD(&obj->mm.region_link);
 
 	INIT_RADIX_TREE(&obj->ttm.get_io_page.radix, GFP_KERNEL | __GFP_NOWARN);
@@ -1044,6 +1044,7 @@ int __i915_gem_ttm_object_init(struct intel_memory_region *mem,
 
 static const struct intel_memory_region_ops ttm_system_region_ops = {
 	.init_object = __i915_gem_ttm_object_init,
+	.release = intel_region_ttm_fini,
 };
 
 struct intel_memory_region *

drivers/gpu/drm/i915/gem/selftests/huge_pages.c

@@ -568,7 +568,7 @@ static int igt_mock_memory_region_huge_pages(void *arg)
 out_put:
 	i915_gem_object_put(obj);
 out_region:
-	intel_memory_region_put(mem);
+	intel_memory_region_destroy(mem);
 	return err;
 }
 

drivers/gpu/drm/i915/gt/intel_region_lmem.c

@@ -66,12 +66,16 @@ static void release_fake_lmem_bar(struct intel_memory_region *mem)
 			   DMA_ATTR_FORCE_CONTIGUOUS);
 }
 
-static void
+static int
 region_lmem_release(struct intel_memory_region *mem)
 {
-	intel_region_ttm_fini(mem);
+	int ret;
+
+	ret = intel_region_ttm_fini(mem);
 	io_mapping_fini(&mem->iomap);
 	release_fake_lmem_bar(mem);
+
+	return ret;
 }
 
 static int
@@ -231,7 +235,7 @@ static struct intel_memory_region *setup_lmem(struct intel_gt *gt)
 	return mem;
 
 err_region_put:
-	intel_memory_region_put(mem);
+	intel_memory_region_destroy(mem);
 	return ERR_PTR(err);
 }
 

drivers/gpu/drm/i915/intel_memory_region.c

@@ -126,7 +126,6 @@ intel_memory_region_create(struct drm_i915_private *i915,
 			goto err_free;
 	}
 
-	kref_init(&mem->kref);
 	return mem;
 
 err_free:
@@ -144,28 +143,17 @@ void intel_memory_region_set_name(struct intel_memory_region *mem,
 	va_end(ap);
 }
 
-static void __intel_memory_region_destroy(struct kref *kref)
+void intel_memory_region_destroy(struct intel_memory_region *mem)
 {
-	struct intel_memory_region *mem =
-		container_of(kref, typeof(*mem), kref);
+	int ret = 0;
 
 	if (mem->ops->release)
-		mem->ops->release(mem);
+		ret = mem->ops->release(mem);
 
+	GEM_WARN_ON(!list_empty_careful(&mem->objects.list));
 	mutex_destroy(&mem->objects.lock);
-	kfree(mem);
-}
-
-struct intel_memory_region *
-intel_memory_region_get(struct intel_memory_region *mem)
-{
-	kref_get(&mem->kref);
-	return mem;
-}
-
-void intel_memory_region_put(struct intel_memory_region *mem)
-{
-	kref_put(&mem->kref, __intel_memory_region_destroy);
+	if (!ret)
+		kfree(mem);
 }
 
 /* Global memory region registration -- only slight layer inversions! */
@@ -234,7 +222,7 @@ void intel_memory_regions_driver_release(struct drm_i915_private *i915)
 			fetch_and_zero(&i915->mm.regions[i]);
 
 		if (region)
-			intel_memory_region_put(region);
+			intel_memory_region_destroy(region);
 	}
 }
 

drivers/gpu/drm/i915/intel_memory_region.h

@@ -6,7 +6,6 @@
 #ifndef __INTEL_MEMORY_REGION_H__
 #define __INTEL_MEMORY_REGION_H__
 
-#include <linux/kref.h>
 #include <linux/ioport.h>
 #include <linux/mutex.h>
 #include <linux/io-mapping.h>
@@ -51,7 +50,7 @@ struct intel_memory_region_ops {
 	unsigned int flags;
 
 	int (*init)(struct intel_memory_region *mem);
-	void (*release)(struct intel_memory_region *mem);
+	int (*release)(struct intel_memory_region *mem);
 
 	int (*init_object)(struct intel_memory_region *mem,
 			   struct drm_i915_gem_object *obj,
@@ -71,8 +70,6 @@ struct intel_memory_region {
 	/* For fake LMEM */
 	struct drm_mm_node fake_mappable;
 
-	struct kref kref;
-
 	resource_size_t io_start;
 	resource_size_t min_page_size;
 	resource_size_t total;
@@ -110,9 +107,7 @@ intel_memory_region_create(struct drm_i915_private *i915,
 			   u16 instance,
 			   const struct intel_memory_region_ops *ops);
 
-struct intel_memory_region *
-intel_memory_region_get(struct intel_memory_region *mem);
-void intel_memory_region_put(struct intel_memory_region *mem);
+void intel_memory_region_destroy(struct intel_memory_region *mem);
 
 int intel_memory_regions_hw_probe(struct drm_i915_private *i915);
 void intel_memory_regions_driver_release(struct drm_i915_private *i915);

drivers/gpu/drm/i915/intel_region_ttm.c

@@ -104,14 +104,45 @@ int intel_region_ttm_init(struct intel_memory_region *mem)
  * memory region, and if it was registered with the TTM device,
  * removes that registration.
  */
-void intel_region_ttm_fini(struct intel_memory_region *mem)
+int intel_region_ttm_fini(struct intel_memory_region *mem)
 {
-	int ret;
+	struct ttm_resource_manager *man = mem->region_private;
+	int ret = -EBUSY;
+	int count;
+
+	/*
+	 * Put the region's move fences. This releases requests that
+	 * may hold on to contexts and vms that may hold on to buffer
+	 * objects placed in this region.
+	 */
+	if (man)
+		ttm_resource_manager_cleanup(man);
+
+	/* Flush objects from region. */
+	for (count = 0; count < 10; ++count) {
+		i915_gem_flush_free_objects(mem->i915);
+
+		mutex_lock(&mem->objects.lock);
+		if (list_empty(&mem->objects.list))
+			ret = 0;
+		mutex_unlock(&mem->objects.lock);
+		if (!ret)
+			break;
+
+		msleep(20);
+		flush_delayed_work(&mem->i915->bdev.wq);
+	}
+
+	/* If we leaked objects, Don't free the region causing use after free */
+	if (ret || !man)
+		return ret;
 
 	ret = i915_ttm_buddy_man_fini(&mem->i915->bdev,
 				      intel_region_to_ttm_type(mem));
 	GEM_WARN_ON(ret);
 	mem->region_private = NULL;
+
+	return ret;
 }
 
 /**

drivers/gpu/drm/i915/intel_region_ttm.h

@@ -20,7 +20,7 @@ void intel_region_ttm_device_fini(struct drm_i915_private *dev_priv);
 
 int intel_region_ttm_init(struct intel_memory_region *mem);
 
-void intel_region_ttm_fini(struct intel_memory_region *mem);
+int intel_region_ttm_fini(struct intel_memory_region *mem);
 
 struct i915_refct_sgt *
 intel_region_ttm_resource_to_rsgt(struct intel_memory_region *mem,

drivers/gpu/drm/i915/selftests/intel_memory_region.c

@@ -225,7 +225,7 @@ static int igt_mock_reserve(void *arg)
 
 out_close:
 	close_objects(mem, &objects);
-	intel_memory_region_put(mem);
+	intel_memory_region_destroy(mem);
 out_free_order:
 	kfree(order);
 	return err;
@@ -439,7 +439,7 @@ static int igt_mock_splintered_region(void *arg)
 out_close:
 	close_objects(mem, &objects);
 out_put:
-	intel_memory_region_put(mem);
+	intel_memory_region_destroy(mem);
 	return err;
 }
 
@@ -507,7 +507,7 @@ static int igt_mock_max_segment(void *arg)
 out_close:
 	close_objects(mem, &objects);
 out_put:
-	intel_memory_region_put(mem);
+	intel_memory_region_destroy(mem);
 	return err;
 }
 
@@ -1196,7 +1196,7 @@ int intel_memory_region_mock_selftests(void)
 
 	err = i915_subtests(tests, mem);
 
-	intel_memory_region_put(mem);
+	intel_memory_region_destroy(mem);
 out_unref:
 	mock_destroy_device(i915);
 	return err;

drivers/gpu/drm/i915/selftests/mock_region.c

@@ -84,13 +84,16 @@ static int mock_object_init(struct intel_memory_region *mem,
 	return 0;
 }
 
-static void mock_region_fini(struct intel_memory_region *mem)
+static int mock_region_fini(struct intel_memory_region *mem)
 {
 	struct drm_i915_private *i915 = mem->i915;
 	int instance = mem->instance;
+	int ret;
 
-	intel_region_ttm_fini(mem);
+	ret = intel_region_ttm_fini(mem);
 	ida_free(&i915->selftest.mock_region_instances, instance);
+
+	return ret;
 }
 
 static const struct intel_memory_region_ops mock_region_ops = {