Re: [PATCH 02/13] vfio/mdev: embedd struct mdev_parent in the parent data structure

From: Kirti Wankhede <kwankhede@nvidia.com>
To: Christoph Hellwig <hch@lst.de>,
	Tony Krowiak <akrowiak@linux.ibm.com>,
	Halil Pasic <pasic@linux.ibm.com>,
	Jason Herne <jjherne@linux.ibm.com>,
	Eric Farman <farman@linux.ibm.com>,
	Matthew Rosato <mjrosato@linux.ibm.com>,
	Zhenyu Wang <zhenyuw@linux.intel.com>,
	Zhi Wang <zhi.a.wang@intel.com>,
	Alex Williamson <alex.williamson@redhat.com>
Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org,
	intel-gvt-dev@lists.freedesktop.org, Neo Jia <cjia@nvidia.com>,
	Dheeraj Nigam <dnigam@nvidia.com>,
	Tarun Gupta <targupta@nvidia.com>
Subject: Re: [PATCH 02/13] vfio/mdev: embedd struct mdev_parent in the parent data structure
Date: Thu, 16 Jun 2022 00:59:47 +0530	[thread overview]
Message-ID: <ab47e216-f027-2083-308b-89c6aaa2e806@nvidia.com> (raw)
In-Reply-To: <20220614045428.278494-3-hch@lst.de>

On 6/14/2022 10:24 AM, Christoph Hellwig wrote:
<snip>

>   /*
> - * mdev_register_device : Register a device
> + * mdev_register_parent: Register a device as parent for mdevs
> + * @parent: parent structure registered
>    * @dev: device structure representing parent device.
>    * @mdev_driver: Device driver to bind to the newly created mdev
>    *
> - * Add device to list of registered parent devices.
>    * Returns a negative value on error, otherwise 0.
>    */
> -int mdev_register_device(struct device *dev, struct mdev_driver *mdev_driver)
> +int mdev_register_parent(struct mdev_parent *parent, struct device *dev,
> +		struct mdev_driver *mdev_driver)
>   {
> -	int ret;
> -	struct mdev_parent *parent;
>   	char *env_string = "MDEV_STATE=registered";
>   	char *envp[] = { env_string, NULL };
> +	int ret;
>   
>   	/* check for mandatory ops */
>   	if (!mdev_driver->supported_type_groups)
>   		return -EINVAL;
>   
> -	dev = get_device(dev);
> -	if (!dev)
> -		return -EINVAL;
> -

Hold the reference for device here once rather than helding multiple 
times while adding sysfs for each mdev_types below. See more below

> -	mutex_lock(&parent_list_lock);
> -
> -	/* Check for duplicate */
> -	parent = __find_parent_device(dev);
> -	if (parent) {
> -		parent = NULL;
> -		ret = -EEXIST;
> -		goto add_dev_err;
> -	}
> -
> -	parent = kzalloc(sizeof(*parent), GFP_KERNEL);
> -	if (!parent) {
> -		ret = -ENOMEM;
> -		goto add_dev_err;
> -	}
> -
> -	kref_init(&parent->ref);
> +	memset(parent, 0, sizeof(*parent));
>   	init_rwsem(&parent->unreg_sem);
> -
>   	parent->dev = dev;
>   	parent->mdev_driver = mdev_driver;
>   
>   	if (!mdev_bus_compat_class) {
>   		mdev_bus_compat_class = class_compat_register("mdev_bus");
> -		if (!mdev_bus_compat_class) {
> -			ret = -ENOMEM;
> -			goto add_dev_err;
> -		}
> +		if (!mdev_bus_compat_class)
> +			return -ENOMEM;
>   	}
>   
>   	ret = parent_create_sysfs_files(parent);
>   	if (ret)
> -		goto add_dev_err;
> +		return ret;
>   
>   	ret = class_compat_create_link(mdev_bus_compat_class, dev, NULL);
>   	if (ret)
>   		dev_warn(dev, "Failed to create compatibility class link\n");
>   
> -	list_add(&parent->next, &parent_list);
> -	mutex_unlock(&parent_list_lock);
> -
>   	dev_info(dev, "MDEV: Registered\n");
>   	kobject_uevent_env(&dev->kobj, KOBJ_CHANGE, envp);
> -
>   	return 0;
> -
> -add_dev_err:
> -	mutex_unlock(&parent_list_lock);
> -	if (parent)
> -		mdev_put_parent(parent);
> -	else
> -		put_device(dev);
> -	return ret;
>   }
> -EXPORT_SYMBOL(mdev_register_device);
> +EXPORT_SYMBOL(mdev_register_parent);
>   
>   /*
> - * mdev_unregister_device : Unregister a parent device
> - * @dev: device structure representing parent device.
> - *
> - * Remove device from list of registered parent devices. Give a chance to free
> - * existing mediated devices for given device.
> + * mdev_unregister_parent : Unregister a parent device
> + * @parent: parent structure to unregister
>    */
> -
> -void mdev_unregister_device(struct device *dev)
> +void mdev_unregister_parent(struct mdev_parent *parent)
>   {
> -	struct mdev_parent *parent;
>   	char *env_string = "MDEV_STATE=unregistered";
>   	char *envp[] = { env_string, NULL };
>   
> -	mutex_lock(&parent_list_lock);
> -	parent = __find_parent_device(dev);
> -
> -	if (!parent) {
> -		mutex_unlock(&parent_list_lock);
> -		return;
> -	}
> -	dev_info(dev, "MDEV: Unregistering\n");
> -
> -	list_del(&parent->next);
> -	mutex_unlock(&parent_list_lock);
> +	dev_info(parent->dev, "MDEV: Unregistering\n");
>   
>   	down_write(&parent->unreg_sem);
> -
> -	class_compat_remove_link(mdev_bus_compat_class, dev, NULL);
> -
> -	device_for_each_child(dev, NULL, mdev_device_remove_cb);
> -
> +	class_compat_remove_link(mdev_bus_compat_class, parent->dev, NULL);
> +	device_for_each_child(parent->dev, NULL, mdev_device_remove_cb);
>   	parent_remove_sysfs_files(parent);
>   	up_write(&parent->unreg_sem);
>   
> -	mdev_put_parent(parent);
> -
> -	/* We still have the caller's reference to use for the uevent */
> -	kobject_uevent_env(&dev->kobj, KOBJ_CHANGE, envp);
> +	kobject_uevent_env(&parent->dev->kobj, KOBJ_CHANGE, envp);
>   }
> -EXPORT_SYMBOL(mdev_unregister_device);
> +EXPORT_SYMBOL(mdev_unregister_parent);
>   
>   static void mdev_device_release(struct device *dev)
>   {
> diff --git a/drivers/vfio/mdev/mdev_private.h b/drivers/vfio/mdev/mdev_private.h
> index 7c9fc79f3d838..297f911fdc890 100644
> --- a/drivers/vfio/mdev/mdev_private.h
> +++ b/drivers/vfio/mdev/mdev_private.h
> @@ -13,17 +13,6 @@
>   int  mdev_bus_register(void);
>   void mdev_bus_unregister(void);
>   
> -struct mdev_parent {
> -	struct device *dev;
> -	struct mdev_driver *mdev_driver;
> -	struct kref ref;
> -	struct list_head next;
> -	struct kset *mdev_types_kset;
> -	struct list_head type_list;
> -	/* Synchronize device creation/removal with parent unregistration */
> -	struct rw_semaphore unreg_sem;
> -};
> -
>   struct mdev_type {
>   	struct kobject kobj;
>   	struct kobject *devices_kobj;
> @@ -48,16 +37,4 @@ void mdev_remove_sysfs_files(struct mdev_device *mdev);
>   int mdev_device_create(struct mdev_type *kobj, const guid_t *uuid);
>   int  mdev_device_remove(struct mdev_device *dev);
>   
> -void mdev_release_parent(struct kref *kref);
> -
> -static inline void mdev_get_parent(struct mdev_parent *parent)
> -{
> -	kref_get(&parent->ref);
> -}
> -
> -static inline void mdev_put_parent(struct mdev_parent *parent)
> -{
> -	kref_put(&parent->ref, mdev_release_parent);
> -}
> -
>   #endif /* MDEV_PRIVATE_H */
> diff --git a/drivers/vfio/mdev/mdev_sysfs.c b/drivers/vfio/mdev/mdev_sysfs.c
> index 4bfbf49aaa66a..b71ffc5594870 100644
> --- a/drivers/vfio/mdev/mdev_sysfs.c
> +++ b/drivers/vfio/mdev/mdev_sysfs.c
> @@ -81,7 +81,7 @@ static void mdev_type_release(struct kobject *kobj)
>   
>   	pr_debug("Releasing group %s\n", kobj->name);
>   	/* Pairs with the get in add_mdev_supported_type() */
> -	mdev_put_parent(type->parent);
> +	put_device(type->parent->dev);
>   	kfree(type);
>   }
>   
> @@ -110,7 +110,7 @@ static struct mdev_type *add_mdev_supported_type(struct mdev_parent *parent,
>   	type->kobj.kset = parent->mdev_types_kset;
>   	type->parent = parent;
>   	/* Pairs with the put in mdev_type_release() */
> -	mdev_get_parent(parent);
> +	get_device(parent->dev);
>   	type->type_group_id = type_group_id;
>

Here device reference is held and release multiple times for each 
mdev_type. It should be held once from mdev_register_parent() and 
released from mdev_unregister_parent().

Thanks,
Kirti