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

[jeffy]

Hi Dmitry,

On 02/14/2017 05:27 AM, Dmitry Torokhov wrote:
> 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?
Oops, sure.
> > +{
> > +       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().
Ok, thanx.
> >   }
> >
> >   /*
> > @@ -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.