Re: [PATCH v3 6/6] loop: be paranoid on exit and prevent new additions / removals

[Greg KH]

On Wed, Apr 29, 2020 at 07:46:27AM +0000, Luis Chamberlain wrote:
> Be pedantic on removal as well and hold the mutex.
> This should prevent uses of addition while we exit.
> 
> Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
> ---
>  drivers/block/loop.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index da693e6a834e..6dccba22c9b5 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -2333,6 +2333,8 @@ static void __exit loop_exit(void)
>  
>  	range = max_loop ? max_loop << part_shift : 1UL << MINORBITS;
>  
> +	mutex_lock(&loop_ctl_mutex);
> +
>  	idr_for_each(&loop_index_idr, &loop_exit_cb, NULL);
>  	idr_destroy(&loop_index_idr);
>  
> @@ -2340,6 +2342,8 @@ static void __exit loop_exit(void)
>  	unregister_blkdev(LOOP_MAJOR, "loop");
>  
>  	misc_deregister(&loop_misc);
> +
> +	mutex_unlock(&loop_ctl_mutex);
>  }
>  
>  module_init(loop_init);

What type of issue is this helping with?  Can it be triggered today?  if
so, shouldn't it be backported to stable kernels?

thanks,

greg k-h