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.c...@rock-chips.com>
---

  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 <briannor...@chromium.org>

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

--

2.1.4