On Wed, 2016-07-27 at 14:48 -0400, Fields Bruce James wrote:
> On Tue, Jul 26, 2016 at 04:08:29PM +0000, Trond Myklebust wrote:
> >
> > > On Jul 26, 2016, at 11:43, J. Bruce Fields <bfie...@fieldses.org> wrote:
> > >
> > > On Tue, Jul 26, 2016 at 09:51:19AM -0400, Trond Myklebust wrote:
> > >> We're seeing traces of the following form:
> > >>
> > >> [10952.396347] svc: transport ffff88042ba4a 000 dequeued, inuse=2
> > >> [10952.396351] svc: tcp_accept ffff88042ba4 a000 sock ffff88042a6e4c80
> > >> [10952.396362] nfsd: connect from 10.2.6.1, port=187
> > >> [10952.396364] svc: svc_setup_socket ffff8800b99bcf00
> > >> [10952.396368] setting up TCP socket for reading
> > >> [10952.396370] svc: svc_setup_socket created ffff8803eb10a000 (inet
> > >> ffff88042b75b800)
> > >> [10952.396373] svc: transport ffff8803eb10a000 put into queue
> > >> [10952.396375] svc: transport ffff88042ba4a000 put into queue
> > >> [10952.396377] svc: server ffff8800bb0ec000 waiting for data (to =
> > >> 3600000)
> > >> [10952.396380] svc: transport ffff8803eb10a000 dequeued, inuse=2
> > >> [10952.396381] svc_recv: found XPT_CLOSE
> > >> [10952.396397] svc: svc_delete_xprt(ffff8803eb10a000)
> > >> [10952.396398] svc: svc_tcp_sock_detach(ffff8803eb10a000)
> > >> [10952.396399] svc: svc_sock_detach(ffff8803eb10a000)
> > >> [10952.396412] svc: svc_sock_free(ffff8803eb10a000)
> > >>
> > >> i.e. an immediate close of the socket after initialisation.
> > >
> > > Interesting, thanks!
> > >
> > > So the one thing I don't understand is why this is correct behavior for
> > > accept--I thought it wasn't supposed to return a socket until it was
> > > fully established.
> >
> > inet_accept() appears to allow SYN_RECV:
>
> OK. Cc'ing netdev just to make sure we didn't overlook anything.
>
SYN_RECV after accept() is a TCP Fast Open property I think.
Maybe you are playing with some global TCP Fast Open settings ?
> (Also: what were user-visible symptoms? Mounts failing, or unexpected
> delays?)
>
> --b.
>
> >
> > int inet_accept(struct socket *sock, struct socket *newsock, int flags)
> > {
> > struct sock *sk1 = sock->sk;
> > int err = -EINVAL;
> > struct sock *sk2 = sk1->sk_prot->accept(sk1, flags, &err);
> >
> > if (!sk2)
> > goto do_err;
> >
> > lock_sock(sk2);
> >
> > sock_rps_record_flow(sk2);
> > WARN_ON(!((1 << sk2->sk_state) &
> > (TCPF_ESTABLISHED | TCPF_SYN_RECV |
> > TCPF_CLOSE_WAIT | TCPF_CLOSE)));
> >
> > sock_graft(sk2, newsock);
> >
> > newsock->state = SS_CONNECTED;
> > err = 0;
> > release_sock(sk2);
> > do_err:
> > return err;
> > }
