Re: [PATCH drm-misc-next v8 09/12] drm/gpuvm: reference count drm_gpuvm structures

Christian König <christian.koenig@xxxxxxx> · Fri, 3 Nov 2023 08:18:35 +0100

Am 02.11.23 um 00:31 schrieb Danilo Krummrich:
Implement reference counting for struct drm_gpuvm.

From the design point of view what is that good for?

Background is that the most common use case I see is that this object is 
embedded into something else and a reference count is then not really a 
good idea.

Thanks,
Christian.


Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
---
  drivers/gpu/drm/drm_gpuvm.c            | 44 +++++++++++++++++++-------
  drivers/gpu/drm/nouveau/nouveau_uvmm.c | 20 +++++++++---
  include/drm/drm_gpuvm.h                | 31 +++++++++++++++++-
  3 files changed, 78 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/drm_gpuvm.c b/drivers/gpu/drm/drm_gpuvm.c
index 53e2c406fb04..6a88eafc5229 100644
--- a/drivers/gpu/drm/drm_gpuvm.c
+++ b/drivers/gpu/drm/drm_gpuvm.c
@@ -746,6 +746,8 @@ drm_gpuvm_init(struct drm_gpuvm *gpuvm, const char *name,
  	gpuvm->rb.tree = RB_ROOT_CACHED;
  	INIT_LIST_HEAD(&gpuvm->rb.list);
  
+	kref_init(&gpuvm->kref);
+
  	gpuvm->name = name ? name : "unknown";
  	gpuvm->flags = flags;
  	gpuvm->ops = ops;
@@ -770,15 +772,8 @@ drm_gpuvm_init(struct drm_gpuvm *gpuvm, const char *name,
  }
  EXPORT_SYMBOL_GPL(drm_gpuvm_init);
  
-/**
- * drm_gpuvm_destroy() - cleanup a &drm_gpuvm
- * @gpuvm: pointer to the &drm_gpuvm to clean up
- *
- * Note that it is a bug to call this function on a manager that still
- * holds GPU VA mappings.
- */
-void
-drm_gpuvm_destroy(struct drm_gpuvm *gpuvm)
+static void
+drm_gpuvm_fini(struct drm_gpuvm *gpuvm)
  {
  	gpuvm->name = NULL;
  
@@ -790,7 +785,33 @@ drm_gpuvm_destroy(struct drm_gpuvm *gpuvm)
  
  	drm_gem_object_put(gpuvm->r_obj);
  }
-EXPORT_SYMBOL_GPL(drm_gpuvm_destroy);
+
+static void
+drm_gpuvm_free(struct kref *kref)
+{
+	struct drm_gpuvm *gpuvm = container_of(kref, struct drm_gpuvm, kref);
+
+	if (drm_WARN_ON(gpuvm->drm, !gpuvm->ops->vm_free))
+		return;
+
+	drm_gpuvm_fini(gpuvm);
+
+	gpuvm->ops->vm_free(gpuvm);
+}
+
+/**
+ * drm_gpuvm_bo_put() - drop a struct drm_gpuvm reference
+ * @gpuvm: the &drm_gpuvm to release the reference of
+ *
+ * This releases a reference to @gpuvm.
+ */
+void
+drm_gpuvm_put(struct drm_gpuvm *gpuvm)
+{
+	if (gpuvm)
+		kref_put(&gpuvm->kref, drm_gpuvm_free);
+}
+EXPORT_SYMBOL_GPL(drm_gpuvm_put);
  
  static int
  __drm_gpuva_insert(struct drm_gpuvm *gpuvm,
@@ -843,7 +864,7 @@ drm_gpuva_insert(struct drm_gpuvm *gpuvm,
  	if (unlikely(!drm_gpuvm_range_valid(gpuvm, addr, range)))
  		return -EINVAL;
  
-	return __drm_gpuva_insert(gpuvm, va);
+	return __drm_gpuva_insert(drm_gpuvm_get(gpuvm), va);
  }
  EXPORT_SYMBOL_GPL(drm_gpuva_insert);
  
@@ -876,6 +897,7 @@ drm_gpuva_remove(struct drm_gpuva *va)
  	}
  
  	__drm_gpuva_remove(va);
+	drm_gpuvm_put(va->vm);
  }
  EXPORT_SYMBOL_GPL(drm_gpuva_remove);
  
diff --git a/drivers/gpu/drm/nouveau/nouveau_uvmm.c b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
index 54be12c1272f..cb2f06565c46 100644
--- a/drivers/gpu/drm/nouveau/nouveau_uvmm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
@@ -1780,6 +1780,18 @@ nouveau_uvmm_bo_unmap_all(struct nouveau_bo *nvbo)
  	}
  }
  
+static void
+nouveau_uvmm_free(struct drm_gpuvm *gpuvm)
+{
+	struct nouveau_uvmm *uvmm = uvmm_from_gpuvm(gpuvm);
+
+	kfree(uvmm);
+}
+
+static const struct drm_gpuvm_ops gpuvm_ops = {
+	.vm_free = nouveau_uvmm_free,
+};
+
  int
  nouveau_uvmm_ioctl_vm_init(struct drm_device *dev,
  			   void *data,
@@ -1830,7 +1842,7 @@ nouveau_uvmm_ioctl_vm_init(struct drm_device *dev,
  		       NOUVEAU_VA_SPACE_END,
  		       init->kernel_managed_addr,
  		       init->kernel_managed_size,
-		       NULL);
+		       &gpuvm_ops);
  	/* GPUVM takes care from here on. */
  	drm_gem_object_put(r_obj);
  
@@ -1849,8 +1861,7 @@ nouveau_uvmm_ioctl_vm_init(struct drm_device *dev,
  	return 0;
  
  out_gpuvm_fini:
-	drm_gpuvm_destroy(&uvmm->base);
-	kfree(uvmm);
+	drm_gpuvm_put(&uvmm->base);
  out_unlock:
  	mutex_unlock(&cli->mutex);
  	return ret;
@@ -1902,7 +1913,6 @@ nouveau_uvmm_fini(struct nouveau_uvmm *uvmm)
  
  	mutex_lock(&cli->mutex);
  	nouveau_vmm_fini(&uvmm->vmm);
-	drm_gpuvm_destroy(&uvmm->base);
-	kfree(uvmm);
+	drm_gpuvm_put(&uvmm->base);
  	mutex_unlock(&cli->mutex);
  }
diff --git a/include/drm/drm_gpuvm.h b/include/drm/drm_gpuvm.h
index 0c2e24155a93..4e6e1fd3485a 100644
--- a/include/drm/drm_gpuvm.h
+++ b/include/drm/drm_gpuvm.h
@@ -247,6 +247,11 @@ struct drm_gpuvm {
  		struct list_head list;
  	} rb;
  
+	/**
+	 * @kref: reference count of this object
+	 */
+	struct kref kref;
+
  	/**
  	 * @kernel_alloc_node:
  	 *
@@ -273,7 +278,23 @@ void drm_gpuvm_init(struct drm_gpuvm *gpuvm, const char *name,
  		    u64 start_offset, u64 range,
  		    u64 reserve_offset, u64 reserve_range,
  		    const struct drm_gpuvm_ops *ops);
-void drm_gpuvm_destroy(struct drm_gpuvm *gpuvm);
+
+/**
+ * drm_gpuvm_get() - acquire a struct drm_gpuvm reference
+ * @gpuvm: the &drm_gpuvm to acquire the reference of
+ *
+ * This function acquires an additional reference to @gpuvm. It is illegal to
+ * call this without already holding a reference. No locks required.
+ */
+static inline struct drm_gpuvm *
+drm_gpuvm_get(struct drm_gpuvm *gpuvm)
+{
+	kref_get(&gpuvm->kref);
+
+	return gpuvm;
+}
+
+void drm_gpuvm_put(struct drm_gpuvm *gpuvm);
  
  bool drm_gpuvm_range_valid(struct drm_gpuvm *gpuvm, u64 addr, u64 range);
  bool drm_gpuvm_interval_empty(struct drm_gpuvm *gpuvm, u64 addr, u64 range);
@@ -673,6 +694,14 @@ static inline void drm_gpuva_init_from_op(struct drm_gpuva *va,
   * operations to drivers.
   */
  struct drm_gpuvm_ops {
+	/**
+	 * @vm_free: called when the last reference of a struct drm_gpuvm is
+	 * dropped
+	 *
+	 * This callback is mandatory.
+	 */
+	void (*vm_free)(struct drm_gpuvm *gpuvm);
+
  	/**
  	 * @op_alloc: called when the &drm_gpuvm allocates
  	 * a struct drm_gpuva_op







