Re: [PATCH v3 3/3] Bluetooth: hidp: fix possible might sleep error in hidp_session_thread

[Dmitry Torokhov]

Hi Jeffy,

On Sun, Feb 12, 2017 at 8:12 PM, Jeffy Chen <jeffy.chen@xxxxxxxxxxxxxx> wrote:
> It looks like hidp_session_thread 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>
> 1/ Fix could not wake up by wake attempts on original wait queues.
> 2/ Remove unnecessary memory barrier before wake_up_* functions.
>
> ---
>
> Changes in v3: None
> Changes in v2: None
>
>  net/bluetooth/hidp/core.c | 33 ++++++++++++++++++++++-----------
>  1 file changed, 22 insertions(+), 11 deletions(-)
>
> diff --git a/net/bluetooth/hidp/core.c b/net/bluetooth/hidp/core.c
> index 0bec458..076bc50 100644
> --- a/net/bluetooth/hidp/core.c
> +++ b/net/bluetooth/hidp/core.c
> @@ -36,6 +36,7 @@
>  #define VERSION "1.2"
>
>  static DECLARE_RWSEM(hidp_session_sem);
> +static DECLARE_WAIT_QUEUE_HEAD(hidp_session_wq);
>  static LIST_HEAD(hidp_session_list);
>
>  static unsigned char hidp_keycode[256] = {
> @@ -1068,12 +1069,12 @@ static int hidp_session_start_sync(struct hidp_session *session)
>   * Wake up session thread and notify it to stop. This is asynchronous and
>   * returns immediately. Call this whenever a runtime error occurs and you want
>   * the session to stop.
> - * Note: wake_up_process() performs any necessary memory-barriers for us.
> + * Note: wake_up_interruptible() performs any necessary memory-barriers for us.
>   */
>  static void hidp_session_terminate(struct hidp_session *session)
>  {
>         atomic_inc(&session->terminate);
> -       wake_up_process(session->task);
> +       wake_up_interruptible(&hidp_session_wq);
>  }
>
>  /*
> @@ -1180,7 +1181,9 @@ static void hidp_session_run(struct hidp_session *session)
>         struct sock *ctrl_sk = session->ctrl_sock->sk;
>         struct sock *intr_sk = session->intr_sock->sk;
>         struct sk_buff *skb;
> +       DEFINE_WAIT_FUNC(wait, woken_wake_function);
>
> +       add_wait_queue(&hidp_session_wq, &wait);
>         for (;;) {
>                 /*
>                  * This thread can be woken up two ways:
> @@ -1188,12 +1191,10 @@ static void hidp_session_run(struct hidp_session *session)
>                  *    session->terminate flag and wakes this thread up.
>                  *  - Via modifying the socket state of ctrl/intr_sock. This
>                  *    thread is woken up by ->sk_state_changed().
> -                *
> -                * Note: set_current_state() performs any necessary
> -                * memory-barriers for us.
>                  */
> -               set_current_state(TASK_INTERRUPTIBLE);
>
> +               /* Ensure session->terminate is updated */
> +               smp_mb__before_atomic();
>                 if (atomic_read(&session->terminate))
>                         break;
>
> @@ -1227,11 +1228,22 @@ static void hidp_session_run(struct hidp_session *session)
>                 hidp_process_transmit(session, &session->ctrl_transmit,
>                                       session->ctrl_sock);
>
> -               schedule();
> +               wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
>         }
> +       remove_wait_queue(&hidp_session_wq, &wait);
>
>         atomic_inc(&session->terminate);
> -       set_current_state(TASK_RUNNING);
> +
> +       /* Ensure session->terminate is updated */
> +       smp_mb__after_atomic();
> +}
> +
> +int hidp_session_wake_function(wait_queue_t *wait, unsigned int mode,
> +                              int sync, void *key)

static?

> +{
> +       wake_up_interruptible(&hidp_session_wq);
> +
> +       return default_wake_function(wait, mode, sync, key);

I do not think you need to call default_wake_function() here: the
process is waiting on hidp_session_wq, so the wakeup above is what
will wake up the session. By the time you get to call
default_wake_function() task will already be in wrong state. I think
we should simply return "false" instead of calling
default_wake_function().

>  }
>
>  /*
> @@ -1244,7 +1256,8 @@ static void hidp_session_run(struct hidp_session *session)
>  static int hidp_session_thread(void *arg)
>  {
>         struct hidp_session *session = arg;
> -       wait_queue_t ctrl_wait, intr_wait;
> +       DEFINE_WAIT_FUNC(ctrl_wait, hidp_session_wake_function);
> +       DEFINE_WAIT_FUNC(intr_wait, hidp_session_wake_function);
>
>         BT_DBG("session %p", session);
>
> @@ -1254,8 +1267,6 @@ static int hidp_session_thread(void *arg)
>         set_user_nice(current, -15);
>         hidp_set_timer(session);
>
> -       init_waitqueue_entry(&ctrl_wait, current);
> -       init_waitqueue_entry(&intr_wait, current);
>         add_wait_queue(sk_sleep(session->ctrl_sock->sk), &ctrl_wait);
>         add_wait_queue(sk_sleep(session->intr_sock->sk), &intr_wait);
>         /* This memory barrier is paired with wq_has_sleeper(). See
> --
> 2.1.4
>
>

Thanks.

-- 
Dmitry