Hi Trond-
> On Feb 19, 2019, at 9:06 AM, Trond Myklebust <trondmy@xxxxxxxxx> wrote:
>
> Because we clear XPRT_SOCK_DATA_READY before reading, we can end up
> with a situation where new data arrives, causing xs_data_ready() to
> queue up a second receive worker job for the same socket, which then
> immediately gets stuck waiting on the transport receive mutex.
> The fix is to only clear XPRT_SOCK_DATA_READY once we're done reading,
> and then to use poll() to check if we might need to queue up a new
> job in order to deal with any new data.
Does this fix an application-visible hang, or is it merely a performance
optimization?
> Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
> ---
> net/sunrpc/xprtsock.c | 17 +++++++++++++++--
> 1 file changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> index f5d7dcd9e8d9..a721c843d5d3 100644
> --- a/net/sunrpc/xprtsock.c
> +++ b/net/sunrpc/xprtsock.c
> @@ -656,13 +656,25 @@ xs_read_stream(struct sock_xprt *transport, int flags)
> return ret != 0 ? ret : -ESHUTDOWN;
> }
>
> +static void xs_poll_check_readable(struct sock_xprt *transport)
> +{
> + struct socket *sock = transport->sock;
> + __poll_t events;
> +
> + clear_bit(XPRT_SOCK_DATA_READY, &transport->sock_state);
> + events = sock->ops->poll(NULL, sock, NULL);
> + if (!(events & (EPOLLIN | EPOLLRDNORM)) || events & EPOLLRDHUP)
> + return;
> + if (!test_and_set_bit(XPRT_SOCK_DATA_READY, &transport->sock_state))
> + queue_work(xprtiod_workqueue, &transport->recv_worker);
> +}
> +
> static void xs_stream_data_receive(struct sock_xprt *transport)
> {
> size_t read = 0;
> ssize_t ret = 0;
>
> mutex_lock(&transport->recv_mutex);
> - clear_bit(XPRT_SOCK_DATA_READY, &transport->sock_state);
> if (transport->sock == NULL)
> goto out;
> for (;;) {
> @@ -672,6 +684,7 @@ static void xs_stream_data_receive(struct sock_xprt *transport)
> read += ret;
> cond_resched();
> }
> + xs_poll_check_readable(transport);
> out:
> mutex_unlock(&transport->recv_mutex);
> trace_xs_stream_read_data(&transport->xprt, ret, read);
> @@ -1362,7 +1375,6 @@ static void xs_udp_data_receive(struct sock_xprt *transport)
> int err;
>
> mutex_lock(&transport->recv_mutex);
> - clear_bit(XPRT_SOCK_DATA_READY, &transport->sock_state);
> sk = transport->inet;
> if (sk == NULL)
> goto out;
> @@ -1374,6 +1386,7 @@ static void xs_udp_data_receive(struct sock_xprt *transport)
> consume_skb(skb);
> cond_resched();
> }
> + xs_poll_check_readable(transport);
> out:
> mutex_unlock(&transport->recv_mutex);
> }
> --
> 2.20.1
>
--
Chuck Lever
