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

[jeffy <jeffy.chen@rock-chips.com>]

Hi brian,

On 02/11/2017 09:26 AM, Brian Norris wrote:
> Hi Jeffy,
>
> I'm really not an expert on bluetooth or HIDP, but I can't bring myself
> to say that this is correct. I still think you have a problem.
>
> On Tue, Jan 24, 2017 at 12:07:51PM +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@rock-chips.com>
>> ---
>>
>>   net/bluetooth/hidp/core.c | 23 +++++++++++++++--------
>>   1 file changed, 15 insertions(+), 8 deletions(-)
>>
>> diff --git a/net/bluetooth/hidp/core.c b/net/bluetooth/hidp/core.c
>> index 0bec458..43d6e6a 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 +1069,15 @@ 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.
>>    */
>>   static void hidp_session_terminate(struct hidp_session *session)
>>   {
>>   	atomic_inc(&session->terminate);
>> -	wake_up_process(session->task);
>> +
>> +	/* Ensure session->terminate is updated */
>> +	smp_mb__after_atomic();
>> +
>> +	wake_up_interruptible(&hidp_session_wq);
> So, you're adding a whole new wait queue here.
>
>>   }
>>   
>>   /*
>> @@ -1180,7 +1184,9 @@ 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 +1194,10 @@ 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 +1231,14 @@ 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);
> And you're waiting on it here.
>
> But you're already on two other wait queues (hidp_session_thread()). So
> the nice WQ_FLAG_WOKEN handling will only happen if you get woken via
> the new hidp_session_wq queue. But what about the other two? Seems like
> again you might have a race condition that would lead you to
> (temporarily, at least?) missing a wake-up attempt.
Thanx for point that out.
>
> I'm not really sure what the best way to resolve this would be. My best
> guess would be to either consolidate the use of these wait queues, or
> lese roll a version of wait_woken() to handle 2 or more wait heads...
>
> Am I wrong? I easily could be.
>
> Brian
>
>>   	}
>> +	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();
>>   }
>>   
>>   /*
>> -- 
>> 2.1.4
>>
>>
>
>