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

[jeffy]

Hi brian,

On 02/11/2017 09:43 AM, Brian Norris wrote:
> 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 <jeffy.chen@xxxxxxxxxxxxxx>
> > ---
> >
> >   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.
Done, there are barriers in wake functions indeed, thanx!
> > +			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 <briannorris@xxxxxxxxxxxx>
>
> > +
> > +		wake_up_interruptible(sk_sleep(session->sock->sk));
> >   	} else
> >   		err = -ENOENT;
> >   
> > --
> > 2.1.4