Subject: Re: [PATCH 1/3] Bluetooth: bnep: fix possible might sleep error in bnep_session

From: Brian Norris <[email-masked]>
Date: Fri, 10 Feb 2017 17:40:45 -0800

Hi,

On Tue, Jan 24, 2017 at 12:07:49PM +0800, Jeffy Chen wrote:
> It looks like bnep_session has same pattern as the issue reported in
> old rfcomm:
> 
> 	while (1) {
> 		set_current_state(TASK_INTERRUPTIBLE);
> 		if (condition)
> 			break;
> 		// may call might_sleep here
> 		schedule();
> 	}
> 	__set_current_state(TASK_RUNNING);
> 
> Which fixed at:
> 	dfb2fae Bluetooth: Fix nested sleeps
> 
> So let's fix it at the same way, also follow the suggestion of:
> https://lwn.net/Articles/628628/
> 
> Signed-off-by: Jeffy Chen <[email-masked]>
> ---
> 
>  net/bluetooth/bnep/core.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/net/bluetooth/bnep/core.c b/net/bluetooth/bnep/core.c
> index fbf251f..da04d51 100644
> --- a/net/bluetooth/bnep/core.c
> +++ b/net/bluetooth/bnep/core.c
> @@ -484,16 +484,16 @@ static int bnep_session(void *arg)
>  	struct net_device *dev = s->dev;
>  	struct sock *sk = s->sock->sk;
>  	struct sk_buff *skb;
> -	wait_queue_t wait;
> +	DEFINE_WAIT_FUNC(wait, woken_wake_function);
>  
>  	BT_DBG("");
>  
>  	set_user_nice(current, -15);
>  
> -	init_waitqueue_entry(&wait, current);
>  	add_wait_queue(sk_sleep(sk), &wait);
>  	while (1) {
> -		set_current_state(TASK_INTERRUPTIBLE);
> +		/* Ensure session->terminate is updated */
> +		smp_mb__before_atomic();
>  
>  		if (atomic_read(&s->terminate))
>  			break;
> @@ -515,9 +515,8 @@ static int bnep_session(void *arg)
>  				break;
>  		netif_wake_queue(dev);
>  
> -		schedule();
> +		wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
>  	}
> -	__set_current_state(TASK_RUNNING);
>  	remove_wait_queue(sk_sleep(sk), &wait);
>  
>  	/* Cleanup session */
> @@ -666,7 +665,11 @@ int bnep_del_connection(struct bnep_conndel_req *req)
>  	s = __bnep_get_session(req->dst);
>  	if (s) {
>  		atomic_inc(&s->terminate);
> -		wake_up_process(s->task);
> +
> +		/* Ensure session->terminate is updated */
> +		smp_mb__after_atomic();
> +

__wake_up() suggests:

 * It may be assumed that this function implies a write memory barrier before
 * changing the task state if and only if any tasks are woken up.

so the above barrier is probably unnecessary. I'm not so sure about the
one before atomic_read(); seems fine.

Other than that, I this looks ok:

Reviewed-by: Brian Norris <[email-masked]>

But I haven't been testing BNEP.

Brian

> +		wake_up_interruptible(sk_sleep(s->sock->sk));
>  	} else
>  		err = -ENOENT;
>  
> -- 
> 2.1.4
> 
>