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

[jeffy]

Hi brian,

On 02/11/2017 09:40 AM, Brian Norris wrote:
> 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 <jeffy.chen@xxxxxxxxxxxxxx>
> > ---
> >
> >   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.
Got it, thanx!
> Other than that, I this looks ok:
>
> Reviewed-by: Brian Norris <briannorris@xxxxxxxxxxx>
>
> But I haven't been testing BNEP.
>
> Brian
>
> > +		wake_up_interruptible(sk_sleep(s->sock->sk));
> >   	} else
> >   		err = -ENOENT;
> >   
> > --
> > 2.1.4