Re: [PATCH v2] block: avoid incorrect bdi_unregiter call

[Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>]

Hi Jens,

Could you add this patch for 4.10?

- Masayoshi Mizuma

On Fri, 2 Dec 2016 14:08:34 +0900 Masayoshi Mizuma wrote:
> bdi_unregister() should be called after bdi_register() is called,
> so we should check whether WB_registered flag is set.
> 
> For example of the situation, error path in device driver may call
> blk_cleanup_queue() before the driver calls bdi_register().
> 
> Signed-off-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
> ---
>   mm/backing-dev.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index 8fde443..f8b07d4 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -853,6 +853,9 @@ static void bdi_remove_from_list(struct backing_dev_info *bdi)
>   
>   void bdi_unregister(struct backing_dev_info *bdi)
>   {
> +	if (!test_bit(WB_registered, &bdi->wb.state))
> +		return;
> +
>   	/* make sure nobody finds us on the bdi_list anymore */
>   	bdi_remove_from_list(bdi);
>   	wb_shutdown(&bdi->wb);
>