Return-Path: Received: from fieldses.org ([173.255.197.46]:42228 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757156AbcG0SsH (ORCPT ); Wed, 27 Jul 2016 14:48:07 -0400 Date: Wed, 27 Jul 2016 14:48:06 -0400 From: Fields Bruce James To: Trond Myklebust Cc: List Linux NFS Mailing , netdev@vger.kernel.org Subject: Re: [PATCH 1/2] SUNRPC: accept() may return sockets that are still in SYN_RECV Message-ID: <20160727184806.GA19229@fieldses.org> References: <1469541080-4184-1-git-send-email-trond.myklebust@primarydata.com> <20160726154354.GA6692@fieldses.org> <7C18520C-D486-4466-8D9D-FF2052B03F0E@primarydata.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <7C18520C-D486-4466-8D9D-FF2052B03F0E@primarydata.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Tue, Jul 26, 2016 at 04:08:29PM +0000, Trond Myklebust wrote: > > > On Jul 26, 2016, at 11:43, J. Bruce Fields 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. (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; > }