Re: [PATCH] btrfs: fix a possible umount deadlock

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On Fri, Sep 09, 2016 at 04:31:04PM +0800, Anand Jain wrote:
>  static int __btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
>  {
>  	struct btrfs_device *device, *tmp;
> +	static LIST_HEAD(pending_put);

Why is it static?

> +	INIT_LIST_HEAD(&pending_put);
>  
>  	if (--fs_devices->opened > 0)
>  		return 0;
> @@ -906,9 +904,24 @@ static int __btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
>  	mutex_lock(&fs_devices->device_list_mutex);
>  	list_for_each_entry_safe(device, tmp, &fs_devices->devices, dev_list) {
>  		btrfs_close_one_device(device);
> +		list_add(&device->dev_list, &pending_put);
>  	}
>  	mutex_unlock(&fs_devices->device_list_mutex);
>  
> +	/*
> +	 * btrfs_show_devname() is using the device_list_mutex,
> +	 * sometimes a call to blkdev_put() leads vfs calling
> +	 * into this func. So do put outside of device_list_mutex,
> +	 * as of now.
> +	 */
> +	while (!list_empty(&pending_put)) {
> +		device = list_entry(pending_put.next,
> +					struct btrfs_device, dev_list);
> +		list_del(&device->dev_list);
> +		btrfs_close_bdev(device);
> +		call_rcu(&device->rcu, free_device);
> +	}
> +
>  	WARN_ON(fs_devices->open_devices);
>  	WARN_ON(fs_devices->rw_devices);
>  	fs_devices->opened = 0;
--
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