Subject: Re: [PATCH 2/3] Bluetooth: cmtp: fix possible might sleep error in cmtp_session

From: jeffy <[email-masked]>
Date: Mon, 13 Feb 2017 12:14:37 +0800

Hi brian,

On 02/11/2017 09:43 AM, Brian Norris wrote:
> Hi,
>
> On Tue, Jan 24, 2017 at 12:07:50PM +0800, Jeffy Chen wrote:
>> It looks like cmtp_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 <[email-masked]>
>> ---
>>
>>   net/bluetooth/cmtp/core.c | 21 ++++++++++++++-------
>>   1 file changed, 14 insertions(+), 7 deletions(-)
>>
>> diff --git a/net/bluetooth/cmtp/core.c b/net/bluetooth/cmtp/core.c
>> index 9e59b66..6b03f2b 100644
>> --- a/net/bluetooth/cmtp/core.c
>> +++ b/net/bluetooth/cmtp/core.c
>> @@ -280,16 +280,16 @@ static int cmtp_session(void *arg)
>>   	struct cmtp_session *session = arg;
>>   	struct sock *sk = session->sock->sk;
>>   	struct sk_buff *skb;
>> -	wait_queue_t wait;
>> +	DEFINE_WAIT_FUNC(wait, woken_wake_function);
>>   
>>   	BT_DBG("session %p", session);
>>   
>>   	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(&session->terminate))
>>   			break;
>> @@ -306,9 +306,8 @@ static int cmtp_session(void *arg)
>>   
>>   		cmtp_process_transmit(session);
>>   
>> -		schedule();
>> +		wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
>>   	}
>> -	__set_current_state(TASK_RUNNING);
>>   	remove_wait_queue(sk_sleep(sk), &wait);
>>   
>>   	down_write(&cmtp_session_sem);
>> @@ -393,7 +392,11 @@ int cmtp_add_connection(struct cmtp_connadd_req *req, struct socket *sock)
>>   		err = cmtp_attach_device(session);
>>   		if (err < 0) {
>>   			atomic_inc(&session->terminate);
>> -			wake_up_process(session->task);
>> +
>> +			/* Ensure session->terminate is updated */
>> +			smp_mb__after_atomic();
>> +
> Same comment about the barrier.
Done, there are barriers in wake functions indeed, thanx!
>
>> +			wake_up_interruptible(sk_sleep(session->sock->sk));
>>   			up_write(&cmtp_session_sem);
>>   			return err;
>>   		}
>> @@ -431,7 +434,11 @@ int cmtp_del_connection(struct cmtp_conndel_req *req)
>>   
>>   		/* Stop session thread */
>>   		atomic_inc(&session->terminate);
>> -		wake_up_process(session->task);
>> +
>> +		/* Ensure session->terminate is updated */
>> +		smp_mb__after_atomic();
> And again.
>
> But otherwise I think this looks OK, again with the caveat that I don't
> know Bluetooth/CMTP that well:
>
> Reviewed-by: Brian Norris <[email-masked]>
>
>> +
>> +		wake_up_interruptible(sk_sleep(session->sock->sk));
>>   	} else
>>   		err = -ENOENT;
>>   
>> -- 
>> 2.1.4
>>
>>
>
>