Re: [patch] staging: ion: use two separate locks for heaps and clients in ion_device

[Laura Abbott]

On 09/30/2016 01:18 AM, Xu YiPing wrote:
> ion_alloc may get into slow path to get free page,
> the call stack:
>
> __alloc_pages_slowpath
> ion_page_pool_alloc_pages
> alloc_buffer_page
> ion_system_heap_allocate
> ion_buffer_create  <-- hold ion_device->lock
> ion_alloc
>
> after that, kernel invokes low-memory killer to kill some apps in
> order to free memory in android system. However, sometimes, the
> killing is blocked,
> the app's call stack:
>
> rwsem_down_write_failed
> down_write
> ion_client_destroy
> ion_release
> fput
> do_signal
>
> the killing is blocked because ion_device->lock is held by ion_alloc.
>
> ion_alloc hold the lock for accessing the heaps list,
> ion_destroy_client hold the lock for accessing the clients list.
>
> so, we can use two separate locks for heaps and clients, to avoid the
> unnecessary race.

I've reviewed this and it looks okay at first pass but I don't want it
applied just yet. Ion locking is a bit of a mess and has been added
once piece at a time. It needs a fundamental review. There will be Ion
discussions at plumbers at the end of October. Let's come back to this
after plumbers.

> Signed-off-by: Xu YiPing <xuyiping@xxxxxxxxxxxxx>
> ---
>  drivers/staging/android/ion/ion.c | 37 ++++++++++++++++++++-----------------
>  1 file changed, 20 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
> index a2cf93b..331ad0f 100644
> --- a/drivers/staging/android/ion/ion.c
> +++ b/drivers/staging/android/ion/ion.c
> @@ -46,7 +46,8 @@
>   * @dev:		the actual misc device
>   * @buffers:		an rb tree of all the existing buffers
>   * @buffer_lock:	lock protecting the tree of buffers
> - * @lock:		rwsem protecting the tree of heaps and clients
> + * @client_lock:	rwsem protecting the tree of clients
> + * @heap_lock:		rwsem protecting the tree of heaps
>   * @heaps:		list of all the heaps in the system
>   * @user_clients:	list of all the clients created from userspace
>   */
> @@ -54,7 +55,8 @@ struct ion_device {
>  	struct miscdevice dev;
>  	struct rb_root buffers;
>  	struct mutex buffer_lock;
> -	struct rw_semaphore lock;
> +	struct rw_semaphore client_lock;
> +	struct rw_semaphore heap_lock;
>  	struct plist_head heaps;
>  	long (*custom_ioctl)(struct ion_client *client, unsigned int cmd,
>  			     unsigned long arg);
> @@ -146,7 +148,7 @@ static inline void ion_buffer_page_clean(struct page **page)
>  	*page = (struct page *)((unsigned long)(*page) & ~(1UL));
>  }
>
> -/* this function should only be called while dev->lock is held */
> +/* this function should only be called while dev->heap_lock is held */
>  static void ion_buffer_add(struct ion_device *dev,
>  			   struct ion_buffer *buffer)
>  {
> @@ -172,7 +174,7 @@ static void ion_buffer_add(struct ion_device *dev,
>  	rb_insert_color(&buffer->node, &dev->buffers);
>  }
>
> -/* this function should only be called while dev->lock is held */
> +/* this function should only be called while dev->heap_lock is held */
>  static struct ion_buffer *ion_buffer_create(struct ion_heap *heap,
>  				     struct ion_device *dev,
>  				     unsigned long len,
> @@ -511,7 +513,7 @@ struct ion_handle *ion_alloc(struct ion_client *client, size_t len,
>  	if (!len)
>  		return ERR_PTR(-EINVAL);
>
> -	down_read(&dev->lock);
> +	down_read(&dev->heap_lock);
>  	plist_for_each_entry(heap, &dev->heaps, node) {
>  		/* if the caller didn't specify this heap id */
>  		if (!((1 << heap->id) & heap_id_mask))
> @@ -520,7 +522,7 @@ struct ion_handle *ion_alloc(struct ion_client *client, size_t len,
>  		if (!IS_ERR(buffer))
>  			break;
>  	}
> -	up_read(&dev->lock);
> +	up_read(&dev->heap_lock);
>
>  	if (buffer == NULL)
>  		return ERR_PTR(-ENODEV);
> @@ -713,7 +715,7 @@ static int is_client_alive(struct ion_client *client)
>  	node = ion_root_client->rb_node;
>  	dev = container_of(ion_root_client, struct ion_device, clients);
>
> -	down_read(&dev->lock);
> +	down_read(&dev->client_lock);
>  	while (node) {
>  		tmp = rb_entry(node, struct ion_client, node);
>  		if (client < tmp) {
> @@ -721,12 +723,12 @@ static int is_client_alive(struct ion_client *client)
>  		} else if (client > tmp) {
>  			node = node->rb_right;
>  		} else {
> -			up_read(&dev->lock);
> +			up_read(&dev->client_lock);
>  			return 1;
>  		}
>  	}
>
> -	up_read(&dev->lock);
> +	up_read(&dev->client_lock);
>  	return 0;
>  }
>
> @@ -841,12 +843,12 @@ struct ion_client *ion_client_create(struct ion_device *dev,
>  	if (!client->name)
>  		goto err_free_client;
>
> -	down_write(&dev->lock);
> +	down_write(&dev->client_lock);
>  	client->display_serial = ion_get_client_serial(&dev->clients, name);
>  	client->display_name = kasprintf(
>  		GFP_KERNEL, "%s-%d", name, client->display_serial);
>  	if (!client->display_name) {
> -		up_write(&dev->lock);
> +		up_write(&dev->client_lock);
>  		goto err_free_client_name;
>  	}
>  	p = &dev->clients.rb_node;
> @@ -873,7 +875,7 @@ struct ion_client *ion_client_create(struct ion_device *dev,
>  			path, client->display_name);
>  	}
>
> -	up_write(&dev->lock);
> +	up_write(&dev->client_lock);
>
>  	return client;
>
> @@ -903,12 +905,12 @@ void ion_client_destroy(struct ion_client *client)
>
>  	idr_destroy(&client->idr);
>
> -	down_write(&dev->lock);
> +	down_write(&dev->client_lock);
>  	if (client->task)
>  		put_task_struct(client->task);
>  	rb_erase(&client->node, &dev->clients);
>  	debugfs_remove_recursive(client->debug_root);
> -	up_write(&dev->lock);
> +	up_write(&dev->client_lock);
>
>  	kfree(client->display_name);
>  	kfree(client->name);
> @@ -1603,7 +1605,7 @@ void ion_device_add_heap(struct ion_device *dev, struct ion_heap *heap)
>  		ion_heap_init_shrinker(heap);
>
>  	heap->dev = dev;
> -	down_write(&dev->lock);
> +	down_write(&dev->heap_lock);
>  	/*
>  	 * use negative heap->id to reverse the priority -- when traversing
>  	 * the list later attempt higher id numbers first
> @@ -1638,7 +1640,7 @@ void ion_device_add_heap(struct ion_device *dev, struct ion_heap *heap)
>  		}
>  	}
>
> -	up_write(&dev->lock);
> +	up_write(&dev->heap_lock);
>  }
>  EXPORT_SYMBOL(ion_device_add_heap);
>
> @@ -1685,7 +1687,8 @@ debugfs_done:
>  	idev->custom_ioctl = custom_ioctl;
>  	idev->buffers = RB_ROOT;
>  	mutex_init(&idev->buffer_lock);
> -	init_rwsem(&idev->lock);
> +	init_rwsem(&idev->client_lock);
> +	init_rwsem(&idev->heap_lock);
>  	plist_head_init(&idev->heaps);
>  	idev->clients = RB_ROOT;
>  	ion_root_client = &idev->clients;
> --
> 2.7.4