Re: [tipc-discussion] [PATCH v1 2/2] tipc: improve function tipc_wait_for_rcvmsg()

[Ying X. <yin...@wi...>]

On 2/13/19 4:18 PM, Tung Nguyen wrote:
> This commit replaces schedule_timeout() with wait_woken()
> in function tipc_wait_for_rcvmsg(). wait_woken() uses
> memory barriers in its implementation to avoid potential
> race condition when putting a process into sleeping state
> and then waking it up.
> 
> Signed-off-by: Tung Nguyen <tun...@de...>

Acked-by: Ying Xue <yin...@wi...>

> ---
>  net/tipc/socket.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/net/tipc/socket.c b/net/tipc/socket.c
> index 81b87916a0eb..684f2125fc6b 100644
> --- a/net/tipc/socket.c
> +++ b/net/tipc/socket.c
> @@ -1677,7 +1677,7 @@ static void tipc_sk_send_ack(struct tipc_sock *tsk)
>  static int tipc_wait_for_rcvmsg(struct socket *sock, long *timeop)
>  {
>  	struct sock *sk = sock->sk;
> -	DEFINE_WAIT(wait);
> +	DEFINE_WAIT_FUNC(wait, woken_wake_function);
>  	long timeo = *timeop;
>  	int err = sock_error(sk);
>  
> @@ -1685,15 +1685,17 @@ static int tipc_wait_for_rcvmsg(struct socket *sock, long *timeop)
>  		return err;
>  
>  	for (;;) {
> -		prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
>  		if (timeo && skb_queue_empty(&sk->sk_receive_queue)) {
>  			if (sk->sk_shutdown & RCV_SHUTDOWN) {
>  				err = -ENOTCONN;
>  				break;
>  			}
> +			add_wait_queue(sk_sleep(sk), &wait);
>  			release_sock(sk);
> -			timeo = schedule_timeout(timeo);
> +			timeo = wait_woken(&wait, TASK_INTERRUPTIBLE, timeo);
> +			sched_annotate_sleep();
>  			lock_sock(sk);
> +			remove_wait_queue(sk_sleep(sk), &wait);
>  		}
>  		err = 0;
>  		if (!skb_queue_empty(&sk->sk_receive_queue))
> @@ -1709,7 +1711,6 @@ static int tipc_wait_for_rcvmsg(struct socket *sock, long *timeop)
>  		if (err)
>  			break;
>  	}
> -	finish_wait(sk_sleep(sk), &wait);
>  	*timeop = timeo;
>  	return err;
>  }
>