Re: [PATCH v15 05/32] v4l: async: Correctly serialise async sub-device unregistration

[Hans Verkuil <hverkuil@xxxxxxxxx>]

On 04/10/17 23:50, Sakari Ailus wrote:
> The check whether an async sub-device is bound to a notifier was performed
> without list_lock held, making it possible for another process to
> unbind the async sub-device before the sub-device unregistration function
> proceeds to take the lock.
> 
> Fix this by first acquiring the lock and then proceeding with the check.
> 
> Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>

Acked-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>

> ---
>  drivers/media/v4l2-core/v4l2-async.c | 18 +++++++-----------
>  1 file changed, 7 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-async.c b/drivers/media/v4l2-core/v4l2-async.c
> index 4924481451ca..cde2cf2ab4b0 100644
> --- a/drivers/media/v4l2-core/v4l2-async.c
> +++ b/drivers/media/v4l2-core/v4l2-async.c
> @@ -298,20 +298,16 @@ EXPORT_SYMBOL(v4l2_async_register_subdev);
>  
>  void v4l2_async_unregister_subdev(struct v4l2_subdev *sd)
>  {
> -	struct v4l2_async_notifier *notifier = sd->notifier;
> -
> -	if (!sd->asd) {
> -		if (!list_empty(&sd->async_list))
> -			v4l2_async_cleanup(sd);
> -		return;
> -	}
> -
>  	mutex_lock(&list_lock);
>  
> -	list_add(&sd->asd->list, &notifier->waiting);
> +	if (sd->asd) {
> +		struct v4l2_async_notifier *notifier = sd->notifier;
>  
> -	if (notifier->unbind)
> -		notifier->unbind(notifier, sd, sd->asd);
> +		list_add(&sd->asd->list, &notifier->waiting);
> +
> +		if (notifier->unbind)
> +			notifier->unbind(notifier, sd, sd->asd);
> +	}
>  
>  	v4l2_async_cleanup(sd);
>  
>