Re: [PATCH v4 3/3] Bluetooth: hidp: fix possible might sleep error in hidp_session_thread

[AL Yu-Chen Cho]

On Tue, 2017-02-14 at 08:55 +0800, Jeffy Chen 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.
> 
> 1/ Make hidp_session_wake_function static.
> 2/ Remove unnecessary default_wake_function.
> 

Tested-by: AL Yu-Chen Cho <acho@xxxxxxxx>

> ---
> 
> 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..1fc0764 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();
> +}
> +
> +static int hidp_session_wake_function(wait_queue_t *wait,
> +				      unsigned int mode,
> +				      int sync, void *key)
> +{
> +	wake_up_interruptible(&hidp_session_wq);
> +	return false;
>  }
>  
>  /*
> @@ -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