drm/i915: Track i915_active using debugobjects

Provide runtime asserts and tracking of i915_active via debugobjects.
For example, this should allow us to check that the i915_active is only
active when we expect it to be and is never freed too early.

One consequence is that, for simplicity, we no longer allow i915_active
to be on-stack which only affected the selftests.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190621183801.23252-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_active.c

@@ -4,6 +4,8 @@
  * Copyright © 2019 Intel Corporation
  */
 
+#include <linux/debugobjects.h>
+
 #include "gt/intel_engine_pm.h"
 
 #include "i915_drv.h"
@@ -31,6 +33,55 @@ struct active_node {
 	u64 timeline;
 };
 
+#if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM) && IS_ENABLED(CONFIG_DEBUG_OBJECTS)
+
+static void *active_debug_hint(void *addr)
+{
+	struct i915_active *ref = addr;
+
+	return (void *)ref->retire ?: (void *)ref;
+}
+
+static struct debug_obj_descr active_debug_desc = {
+	.name = "i915_active",
+	.debug_hint = active_debug_hint,
+};
+
+static void debug_active_init(struct i915_active *ref)
+{
+	debug_object_init(ref, &active_debug_desc);
+}
+
+static void debug_active_activate(struct i915_active *ref)
+{
+	debug_object_activate(ref, &active_debug_desc);
+}
+
+static void debug_active_deactivate(struct i915_active *ref)
+{
+	debug_object_deactivate(ref, &active_debug_desc);
+}
+
+static void debug_active_fini(struct i915_active *ref)
+{
+	debug_object_free(ref, &active_debug_desc);
+}
+
+static void debug_active_assert(struct i915_active *ref)
+{
+	debug_object_assert_init(ref, &active_debug_desc);
+}
+
+#else
+
+static inline void debug_active_init(struct i915_active *ref) { }
+static inline void debug_active_activate(struct i915_active *ref) { }
+static inline void debug_active_deactivate(struct i915_active *ref) { }
+static inline void debug_active_fini(struct i915_active *ref) { }
+static inline void debug_active_assert(struct i915_active *ref) { }
+
+#endif
+
 static void
 __active_park(struct i915_active *ref)
 {
@@ -50,6 +101,8 @@ __active_retire(struct i915_active *ref)
 	if (--ref->count)
 		return;
 
+	debug_active_deactivate(ref);
+
 	/* return the unused nodes to our slabcache */
 	__active_park(ref);
 
@@ -155,6 +208,8 @@ void i915_active_init(struct drm_i915_private *i915,
 		      struct i915_active *ref,
 		      void (*retire)(struct i915_active *ref))
 {
+	debug_active_init(ref);
+
 	ref->i915 = i915;
 	ref->retire = retire;
 	ref->tree = RB_ROOT;
@@ -191,13 +246,21 @@ int i915_active_ref(struct i915_active *ref,
 
 bool i915_active_acquire(struct i915_active *ref)
 {
+	debug_active_assert(ref);
 	lockdep_assert_held(BKL(ref));
-	return !ref->count++;
+
+	if (ref->count++)
+		return false;
+
+	debug_active_activate(ref);
+	return true;
 }
 
 void i915_active_release(struct i915_active *ref)
 {
+	debug_active_assert(ref);
 	lockdep_assert_held(BKL(ref));
+
 	__active_retire(ref);
 }
 
@@ -260,6 +323,7 @@ int i915_request_await_active(struct i915_request *rq, struct i915_active *ref)
 #if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)
 void i915_active_fini(struct i915_active *ref)
 {
+	debug_active_fini(ref);
 	GEM_BUG_ON(i915_active_request_isset(&ref->last));
 	GEM_BUG_ON(!RB_EMPTY_ROOT(&ref->tree));
 	GEM_BUG_ON(ref->count);

drivers/gpu/drm/i915/selftests/i915_active.c

@@ -16,28 +16,51 @@ struct live_active {
 	bool retired;
 };
 
-static void __live_active_retire(struct i915_active *base)
+static void __live_free(struct live_active *active)
+{
+	i915_active_fini(&active->base);
+	kfree(active);
+}
+
+static void __live_retire(struct i915_active *base)
 {
 	struct live_active *active = container_of(base, typeof(*active), base);
 
 	active->retired = true;
 }
 
-static int __live_active_setup(struct drm_i915_private *i915,
-			       struct live_active *active)
+static struct live_active *__live_alloc(struct drm_i915_private *i915)
+{
+	struct live_active *active;
+
+	active = kzalloc(sizeof(*active), GFP_KERNEL);
+	if (!active)
+		return NULL;
+
+	i915_active_init(i915, &active->base, __live_retire);
+
+	return active;
+}
+
+static struct live_active *
+__live_active_setup(struct drm_i915_private *i915)
 {
 	struct intel_engine_cs *engine;
 	struct i915_sw_fence *submit;
+	struct live_active *active;
 	enum intel_engine_id id;
 	unsigned int count = 0;
 	int err = 0;
 
-	submit = heap_fence_create(GFP_KERNEL);
-	if (!submit)
-		return -ENOMEM;
+	active = __live_alloc(i915);
+	if (!active)
+		return ERR_PTR(-ENOMEM);
 
-	i915_active_init(i915, &active->base, __live_active_retire);
-	active->retired = false;
+	submit = heap_fence_create(GFP_KERNEL);
+	if (!submit) {
+		kfree(active);
+		return ERR_PTR(-ENOMEM);
+	}
 
 	if (!i915_active_acquire(&active->base)) {
 		pr_err("First i915_active_acquire should report being idle\n");
@@ -84,64 +107,79 @@ static int __live_active_setup(struct drm_i915_private *i915,
 	i915_sw_fence_commit(submit);
 	heap_fence_put(submit);
 
-	return err;
+	/* XXX leaks live_active on error */
+	return err ? ERR_PTR(err) : active;
 }
 
 static int live_active_wait(void *arg)
 {
 	struct drm_i915_private *i915 = arg;
-	struct live_active active;
+	struct live_active *active;
 	intel_wakeref_t wakeref;
-	int err;
+	int err = 0;
 
 	/* Check that we get a callback when requests retire upon waiting */
 
 	mutex_lock(&i915->drm.struct_mutex);
 	wakeref = intel_runtime_pm_get(&i915->runtime_pm);
 
-	err = __live_active_setup(i915, &active);
+	active = __live_active_setup(i915);
+	if (IS_ERR(active)) {
+		err = PTR_ERR(active);
+		goto err;
+	}
 
-	i915_active_wait(&active.base);
-	if (!active.retired) {
+	i915_active_wait(&active->base);
+	if (!active->retired) {
 		pr_err("i915_active not retired after waiting!\n");
 		err = -EINVAL;
 	}
 
-	i915_active_fini(&active.base);
+	__live_free(active);
+
 	if (igt_flush_test(i915, I915_WAIT_LOCKED))
 		err = -EIO;
 
+err:
 	intel_runtime_pm_put(&i915->runtime_pm, wakeref);
 	mutex_unlock(&i915->drm.struct_mutex);
+
 	return err;
 }
 
 static int live_active_retire(void *arg)
 {
 	struct drm_i915_private *i915 = arg;
-	struct live_active active;
+	struct live_active *active;
 	intel_wakeref_t wakeref;
-	int err;
+	int err = 0;
 
 	/* Check that we get a callback when requests are indirectly retired */
 
 	mutex_lock(&i915->drm.struct_mutex);
 	wakeref = intel_runtime_pm_get(&i915->runtime_pm);
 
-	err = __live_active_setup(i915, &active);
+	active = __live_active_setup(i915);
+	if (IS_ERR(active)) {
+		err = PTR_ERR(active);
+		goto err;
+	}
 
 	/* waits for & retires all requests */
 	if (igt_flush_test(i915, I915_WAIT_LOCKED))
 		err = -EIO;
 
-	if (!active.retired) {
+	if (!active->retired) {
 		pr_err("i915_active not retired after flushing!\n");
 		err = -EINVAL;
 	}
 
-	i915_active_fini(&active.base);
+	__live_free(active);
+
+err:
 	intel_runtime_pm_put(&i915->runtime_pm, wakeref);
 	mutex_unlock(&i915->drm.struct_mutex);
+
 	return err;
 }