On Wed, Sep 16, 2015 at 9:58 AM, Benjamin Coddington
<bcodding@xxxxxxxxxx> wrote:
> After a network segmentation that times out the socket, we can get stuck in
> a loop where the client repeatedly sends a SYN, then a RST, with the result
> that the client will never successfully reconnect to the server.
>
> When there's a need to re-establish a TCP connection, the scheduled
> connect_worker does xs_tcp_setup_socket(), which sends a SYN, then
> immediately wakes the waiting task to call_connect_status with a status of
> EAGAIN, which proceeds to xprt_connect() and kernel_sock_shutdown() which
> will send a RST.
>
> Fix this loop by deferring xprt_clear_connecting() until the TCP state
> change of ESTALISHED or CLOSED, thereby ensuring that we do not race into
> xs_connect() while waiting for SYN,ACK from the server.
>
> Fixes: 099392048c (SUNRPC: Prevent SYN+SYNACK+RST storms)
> Signed-off-by: Benjamin Coddington <bcodding@xxxxxxxxxx>
> ---
> net/sunrpc/xprtsock.c | 6 ++++--
> 1 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> index 7be90bc..6df51df 100644
> --- a/net/sunrpc/xprtsock.c
> +++ b/net/sunrpc/xprtsock.c
> @@ -1450,6 +1450,7 @@ static void xs_tcp_state_change(struct sock *sk)
> switch (sk->sk_state) {
> case TCP_ESTABLISHED:
> spin_lock(&xprt->transport_lock);
> + xprt_clear_connecting(xprt);
> if (!xprt_test_and_set_connected(xprt)) {
> struct sock_xprt *transport = container_of(xprt,
> struct sock_xprt, xprt);
> @@ -1496,6 +1497,7 @@ static void xs_tcp_state_change(struct sock *sk)
> smp_mb__after_atomic();
> break;
> case TCP_CLOSE:
> + xprt_clear_connecting(xprt);
> xs_sock_mark_closed(xprt);
> }
> out:
> @@ -2237,10 +2239,10 @@ static void xs_tcp_setup_socket(struct work_struct *work)
> xs_tcp_force_close(xprt);
> break;
> case 0:
> - case -EINPROGRESS:
> + xprt_clear_connecting(xprt);
> case -EALREADY:
> + case -EINPROGRESS:
> xprt_unlock_connect(xprt, transport);
> - xprt_clear_connecting(xprt);
> return;
> case -EINVAL:
> /* Happens, for instance, if the user specified a link
>
This introduces races. The call to xprt_clear_connecting in TCP_CLOSE
can trigger pretty much at any time, and so could interfere with a
subsequent connection attempt.
I have an alternative patch which addresses this problem and which is
undergoing testing.
--
To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
