Subject: Re: [PATCH 2/3] Bluetooth: cmtp: fix possible might sleep error in cmtp_session

From: Brian Norris <[email-masked]>
Date: Fri, 10 Feb 2017 17:43:17 -0800

Hi,

On Tue, Jan 24, 2017 at 12:07:50PM +0800, Jeffy Chen wrote:
> It looks like cmtp_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/cmtp/core.c | 21 ++++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/net/bluetooth/cmtp/core.c b/net/bluetooth/cmtp/core.c
> index 9e59b66..6b03f2b 100644
> --- a/net/bluetooth/cmtp/core.c
> +++ b/net/bluetooth/cmtp/core.c
> @@ -280,16 +280,16 @@ static int cmtp_session(void *arg)
>  	struct cmtp_session *session = arg;
>  	struct sock *sk = session->sock->sk;
>  	struct sk_buff *skb;
> -	wait_queue_t wait;
> +	DEFINE_WAIT_FUNC(wait, woken_wake_function);
>  
>  	BT_DBG("session %p", session);
>  
>  	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(&session->terminate))
>  			break;
> @@ -306,9 +306,8 @@ static int cmtp_session(void *arg)
>  
>  		cmtp_process_transmit(session);
>  
> -		schedule();
> +		wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
>  	}
> -	__set_current_state(TASK_RUNNING);
>  	remove_wait_queue(sk_sleep(sk), &wait);
>  
>  	down_write(&cmtp_session_sem);
> @@ -393,7 +392,11 @@ int cmtp_add_connection(struct cmtp_connadd_req *req, struct socket *sock)
>  		err = cmtp_attach_device(session);
>  		if (err < 0) {
>  			atomic_inc(&session->terminate);
> -			wake_up_process(session->task);
> +
> +			/* Ensure session->terminate is updated */
> +			smp_mb__after_atomic();
> +

Same comment about the barrier.

> +			wake_up_interruptible(sk_sleep(session->sock->sk));
>  			up_write(&cmtp_session_sem);
>  			return err;
>  		}
> @@ -431,7 +434,11 @@ int cmtp_del_connection(struct cmtp_conndel_req *req)
>  
>  		/* Stop session thread */
>  		atomic_inc(&session->terminate);
> -		wake_up_process(session->task);
> +
> +		/* Ensure session->terminate is updated */
> +		smp_mb__after_atomic();

And again.

But otherwise I think this looks OK, again with the caveat that I don't
know Bluetooth/CMTP that well:

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

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