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

  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 <briannor...@chromium.or>

But I haven't been testing BNEP.

Brian

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

--

2.1.4