On Sat, Sep 10, 2016 at 07:03:38AM +0800, Anand Jain wrote:
>  static int __btrfs_close_devices(struct btrfs_fs_devices *fs_devices)
>  {
>       struct btrfs_device *device, *tmp;
> +     LIST_HEAD(pending_put);
> +     INIT_LIST_HEAD(&pending_put);

LIST_HEAD declares and initializes the list to an empty one, not
necessary to call INIT_LIST_HEAD.

>  
>       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,

Could be list_first_entry
> +                                     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;

After this patch, the function btrfs_close_one_device no longer does
what it says, ie. it does not close the device. I'd have to look closer
why it allocates a new structure and replaces it in the list, but this
looks weird.
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