linux-kernel - Re: [PATCH] driver core: fix race between creating/querying glue dir and its cleanup

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Date:	Tue, 26 Apr 2016 22:57:28 +0530
From:	Chandra Sekhar Lingutla <clingutla@...eaurora.org>
To:	Ming Lei <ming.lei@...onical.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org, Yijing Wang <wangyijing@...wei.com>
Subject: Re: [PATCH] driver core: fix race between creating/querying glue dir
 and its cleanup

Hi Ming,

On 03/28/2016 01:57 PM, Ming Lei wrote:
> The global mutex of 'gdp_mutex' is used to serialize creating/querying
> glue dir and its cleanup. Turns out it isn't a perfect way because
> part(kobj_kset_leave()) of the actual cleanup action() is done inside
> the release handler of the glue dir kobject. That means gdp_mutex has
> to be held before releasing the last reference count of the glue dir
> kobject.
>
> This patch moves glue dir's cleanup after kobject_del() in device_del()
> for avoiding the race.
>
> Cc: Yijing Wang <wangyijing@...wei.com>
> Reported-by: Chandra Sekhar Lingutla <clingutla@...eaurora.org>
> Signed-off-by: Ming Lei <ming.lei@...onical.com>
> ---
>   drivers/base/core.c | 41 +++++++++++++++++++++++++++++++----------
>   1 file changed, 31 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 0a8bdad..3f2e1f8 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -836,11 +836,31 @@ static struct kobject *get_device_parent(struct device *dev,
>   	return NULL;
>   }
>
> +static inline bool live_in_glue_dir(struct kobject *kobj,
> +				    struct device *dev)
> +{
> +	if (!kobj || !dev->class ||
> +	    kobj->kset != &dev->class->p->glue_dirs)
> +		return true;
> +	return false;
> +}
I think we should return false if kobj->kset != &dev->class->p->glue_dirs.
If kboj->kset points to dev->class->p->glue_dirs, then we live in glue dir.
So logic should be:
	if (!kobj || !dev->class ||
		kobj->kset != &dev->class->p->glue_dirs)
			return false;
	return true;

> +
> +static inline struct kobject *get_glue_dir(struct device *dev)
> +{
> +	if (live_in_glue_dir(&dev->kobj, dev))
> +		return dev->kobj.parent;
> +	return NULL;
> +}
> +
> +/*
> + * make sure cleaning up dir as the last step, we need to make
> + * sure .release handler of kobject is run with holding the
> + * global lock
> + */
>   static void cleanup_glue_dir(struct device *dev, struct kobject *glue_dir)
>   {
>   	/* see if we live in a "glue" directory */
> -	if (!glue_dir || !dev->class ||
> -	    glue_dir->kset != &dev->class->p->glue_dirs)
> +	if (!live_in_glue_dir(glue_dir, dev))
>   		return;
>
>   	mutex_lock(&gdp_mutex);
> @@ -848,11 +868,6 @@ static void cleanup_glue_dir(struct device *dev, struct kobject *glue_dir)
>   	mutex_unlock(&gdp_mutex);
>   }
>
> -static void cleanup_device_parent(struct device *dev)
> -{
> -	cleanup_glue_dir(dev, dev->kobj.parent);
> -}
> -
>   static int device_add_class_symlinks(struct device *dev)
>   {
>   	struct device_node *of_node = dev_of_node(dev);
> @@ -1028,6 +1043,7 @@ int device_add(struct device *dev)
>   	struct kobject *kobj;
>   	struct class_interface *class_intf;
>   	int error = -EINVAL;
> +	struct kobject *glue_dir = NULL;
>
>   	dev = get_device(dev);
>   	if (!dev)
> @@ -1072,8 +1088,10 @@ int device_add(struct device *dev)
>   	/* first, register with generic layer. */
>   	/* we require the name to be set before, and pass NULL */
>   	error = kobject_add(&dev->kobj, dev->kobj.parent, NULL);
> -	if (error)
> +	if (error) {
> +		glue_dir = get_glue_dir(dev);
>   		goto Error;
> +	}
>
>   	/* notify platform of device entry */
>   	if (platform_notify)
> @@ -1154,9 +1172,10 @@ done:
>   	device_remove_file(dev, &dev_attr_uevent);
>    attrError:
>   	kobject_uevent(&dev->kobj, KOBJ_REMOVE);
> +	glue_dir = get_glue_dir(dev);
>   	kobject_del(&dev->kobj);
>    Error:
> -	cleanup_device_parent(dev);
> +	cleanup_glue_dir(dev, glue_dir);
>   	put_device(parent);
>   name_error:
>   	kfree(dev->p);
> @@ -1232,6 +1251,7 @@ EXPORT_SYMBOL_GPL(put_device);
>   void device_del(struct device *dev)
>   {
>   	struct device *parent = dev->parent;
> +	struct kobject *glue_dir = NULL;
>   	struct class_interface *class_intf;
>
>   	/* Notify clients of device removal.  This call must come
> @@ -1276,8 +1296,9 @@ void device_del(struct device *dev)
>   		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
>   					     BUS_NOTIFY_REMOVED_DEVICE, dev);
>   	kobject_uevent(&dev->kobj, KOBJ_REMOVE);
> -	cleanup_device_parent(dev);
> +	glue_dir = get_glue_dir(dev);
>   	kobject_del(&dev->kobj);
> +	cleanup_glue_dir(dev, glue_dir);
>   	put_device(parent);
>   }
>   EXPORT_SYMBOL_GPL(device_del);
>