Subject: Re: [PATCH] Bluetooth: hidp: might sleep error in hidp_session_thread

From: Brian Norris <[email-masked]>
Date: Mon, 23 Jan 2017 18:31:01 -0800

Hi Jeffy,

On Fri, Jan 20, 2017 at 09:52:08PM +0800, Jeffy Chen wrote:
> [   39.044329] do not call blocking ops when !TASK_RUNNING; state=1 set
> at [<ffffffbffc290358>] hidp_session_thread+0x110/0x568 [hidp]
> ...
> [   40.159664] Call trace:
> [   40.162122] [<ffffffc00024ae08>] __might_sleep+0x64/0x90
> [   40.167443] [<ffffffc00080568c>] lock_sock_nested+0x30/0x78
> [   40.173047] [<ffffffbffc1b3ca0>] l2cap_sock_sendmsg+0x90/0xf0
> [bluetooth]
> [   40.179842] [<ffffffc0008012c4>] sock_sendmsg+0x4c/0x68
> [   40.185072] [<ffffffc000801414>] kernel_sendmsg+0x54/0x68
> [   40.190477] [<ffffffbffc28f4d0>] hidp_send_frame+0x78/0xa0 [hidp]
> [   40.196574] [<ffffffbffc28f53c>] hidp_process_transmit+0x44/0x98
> [hidp]
> [   40.203191] [<ffffffbffc2905ac>] hidp_session_thread+0x364/0x568
> [hidp]

Am I crazy, or are several other protocols broken like this too? I see a
similar structure in net/bluetooth/bnep/core.c and
net/bluetooth/cmtp/core.c, at least, each of which also call
kernel_sendmsg(), which might be an l2cap socket (...I think? I'm not a
bluetooth expert really).

> 
> Following (https://lwn.net/Articles/628628/).
> 
> Signed-off-by: Jeffy Chen <[email-masked]>
> ---
> 
>  net/bluetooth/hidp/core.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/net/bluetooth/hidp/core.c b/net/bluetooth/hidp/core.c
> index 0bec458..bfd3fb8 100644
> --- a/net/bluetooth/hidp/core.c
> +++ b/net/bluetooth/hidp/core.c
> @@ -1180,7 +1180,9 @@ 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(sk_sleep(intr_sk), &wait);
>  	for (;;) {
>  		/*
>  		 * This thread can be woken up two ways:
> @@ -1188,12 +1190,10 @@ 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 +1227,14 @@ 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);

I think this looks mostly good, except what about the
hidp_session_terminate() condition? In that case, you're running
wake_up_process() -- which won't set WQ_FLAG_WOKEN for us. So what
happens if we see a hidp_session_terminate() call in between the check
for the ->terminate count, but before we call wait_woken()? IIUC, I
think we'll just ignore the call and keep waiting for the next wake
signal.

I think you might need to rework hidp_session_terminate() too, to
actually target the wait queue and not just the processes.

IIUC, of course. I could be wrong...

Brian

>  	}
> +	remove_wait_queue(sk_sleep(intr_sk), &wait);
>  
>  	atomic_inc(&session->terminate);
> -	set_current_state(TASK_RUNNING);
> +
> +	/* Ensure session->terminate is updated */
> +	smp_mb__after_atomic();
>  }
>  
>  /*
> -- 
> 2.1.4
> 
>