On Tue, 2023-10-03 at 10:44 -0400, Olga Kornievskaia wrote: > On Sat, Sep 30, 2023 at 7:06 PM Trond Myklebust <trondmy@xxxxxxxxxxxxxxx> wrote: > > > > On Sat, 2023-09-30 at 18:36 -0400, Olga Kornievskaia wrote: > > > On Fri, Sep 29, 2023 at 10:57 PM Trond Myklebust > > > <trondmy@xxxxxxxxxxxxxxx> wrote: > > > > > > > > On Thu, 2023-09-28 at 10:58 -0400, Olga Kornievskaia wrote: > > > > > On Wed, Sep 27, 2023 at 3:35 PM <trondmy@xxxxxxxxxx> wrote: > > > > > > > > > > > > From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> > > > > > > > > > > > > If the TCP connection attempt fails without ever establishing a > > > > > > connection, then assume the problem may be the server is > > > > > > rejecting > > > > > > us > > > > > > due to port reuse. > > > > > > > > > > Doesn't this break 4.0 replay cache? Seems too general to assume > > > > > that > > > > > any unsuccessful SYN was due to a server reboot and it's ok for > > > > > the > > > > > client to change the port. > > > > > > > > This is where things get interesting. Yes, if we change the port > > > > number, then it will almost certainly break NFSv3 and NFSv4.0 > > > > replay > > > > caching on the server. > > > > > > > > However the problem is that once we get stuck in the situation > > > > where we > > > > cannot connect, then each new connection attempt is just causing > > > > the > > > > server's TCP layer to push back and recall that the connection from > > > > this port was closed. > > > > IOW: the problem is that once we're in this situation, we cannot > > > > easily > > > > exit without doing one of the following. Either we have to > > > > > > > > 1. Change the port number, so that the TCP layer allows us to > > > > connect. > > > > 2. Or.. Wait for long enough that the TCP layer has forgotten > > > > altogether about the previous connection. > > > > > > > > The problem is that option (2) is subject to livelock, and so has a > > > > potential infinite time out. I've seen this livelock in action, and > > > > I'm > > > > not seeing a solution that has predictable results. > > > > > > > > So unless there is a solution for the problems in (2), I don't see > > > > how > > > > we can avoid defaulting to option (1) at some point, in which case > > > > the > > > > only question is "when do we switch ports?". > > > > > > I'm not sure how one can justify that regression that will come out > > > of > > > #1 will be less of a problem then the problem in #2. > > > > > > I think I'm still not grasping why the NFS server would > > > (legitimately) > > > be closing a connection that is re-using the port. Can you present a > > > sequence of events that would lead to this? > > > > > > > Yes. It is essentially the problem described in this blog: > > https://blog.davidvassallo.me/2010/07/13/time_wait-and-port-reuse/ > > > > ...and as you can see, it is nothing to do with NFS. This is the TCP > > protocol working as expected. > > What I'm seeing are statements that RFC allows for/provides guidance > on how to transition out of TIME_WAIT state. I'm also hearing that the > reasons that the server can't allow for port reuse is due to broken > client implementation or use of (broken?) NAT implementation. > > I don't see how any of this justifies allowing a regression in the > linux client code. I'm clearly missing something. How are you possibly > OK with breaking the reply cache? > Is it really breaking things though if you can't connect otherwise? Bear in mind that if you're dealing with NAT'ed setup, and you wait until the connection is completely forgotten, then the NAT'ing firewall is likely to change your source port anyway. Chuck brought up an interesting question privately: should knfsd's v3/v4.0 DRC start ignoring the source port? We already check this otherwise: - IP addr - XID - hash of first 256 bytes of the payload That seems like enough discriminators that we could stop comparing the source port without breaking things. > > > But can't we at least arm ourselves in not unnecessarily breaking the > > > reply cache by at least imposing some timeout/number of retries > > > before > > > resetting? If the client was retrying to unsuccessfully re-establish > > > connection for a (fixed) while, then 4.0 client's lease would expire > > > and switching the port after the lease expires makes no difference. > > > There isn't a solution in v3 unfortunately. But a time-based approach > > > would at least separate these 'peculiar' servers vs normal servers. > > > And if this is a 4.1 client, we can reset the port without a timeout. > > > > > > > This is not a 'peculiar server' vs 'normal server' problem. The reuse > > of ports in this way violates the TCP protocol, and has been a problem > > I disagree here. Even the RFC quoted by the blogger says that reuse of > port is allowed. > > > for NFS/TCP since the beginning. However, it was never a problem for > > the older connectionless UDP protocol, which is where the practice of > > tying the replay cache to the source port began in the first place. > > > > NFSv4.1 does not have this problem because it deliberately does not > > reuse TCP ports, and the reason is precisely to avoid the TIME_WAIT > > state problems. > > > > NFSv3 tries to avoid it by doing an incremental back off, but we > > recently saw that does not suffice to avoid live lock, after a system > > got stuck for several hours in this state. > > > > > Am I correct that every unsuccessful SYN causes a new source point to > > > be taken? If so, then a server reboot where multiple SYNs are sent > > > prior to connection re-establishment (times number of mounts) might > > > cause source port exhaustion? > > > > > > > No. Not every unsuccessful SYN: It is every unsuccessful sequence of > > I disagree. Here's a snippet of the network trace with the proposed > patch. The port is changed on EVERY unsuccessful SYN. > > 76 2023-10-03 10:17:04.285731 192.168.1.134 → 192.168.1.106 NFS 238 > V3 WRITE Call, FH: 0x10bedd7c Offset: 0 Len: 4 FILE_SYNC > 77 2023-10-03 10:17:04.328371 192.168.1.106 → 192.168.1.134 TCP 66 > 2049 → 909 [ACK] Seq=1113 Ack=1501 Win=31872 Len=0 TSval=3542359002 > TSecr=3081600630 > 256 2023-10-03 10:18:04.341041 192.168.1.134 → 192.168.1.106 TCP 66 > [TCP Keep-Alive] 909 → 2049 [ACK] Seq=1500 Ack=1113 Win=32000 Len=0 > TSval=3081660681 TSecr=3542359002 > 259 2023-10-03 10:18:04.341500 192.168.1.106 → 192.168.1.134 TCP 54 > 2049 → 909 [RST] Seq=1113 Win=0 Len=0 > 260 2023-10-03 10:18:04.341860 192.168.1.134 → 192.168.1.106 TCP 74 > [TCP Port numbers reused] 909 → 2049 [SYN] Seq=0 Win=32120 Len=0 > MSS=1460 SACK_PERM TSval=3081660681 TSecr=0 WS=128 > 261 2023-10-03 10:18:04.342031 192.168.1.106 → 192.168.1.134 TCP 54 > 2049 → 909 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0 > 266 2023-10-03 10:18:07.380801 192.168.1.134 → 192.168.1.106 TCP 74 > 954 → 2049 [SYN] Seq=0 Win=32120 Len=0 MSS=1460 SACK_PERM > TSval=3081663720 TSecr=0 WS=128 > 267 2023-10-03 10:18:07.380971 192.168.1.106 → 192.168.1.134 TCP 54 > 2049 → 954 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0 > 275 2023-10-03 10:18:10.423352 192.168.1.134 → 192.168.1.106 TCP 74 > 856 → 2049 [SYN] Seq=0 Win=32120 Len=0 MSS=1460 SACK_PERM > TSval=3081666760 TSecr=0 WS=128 > 276 2023-10-03 10:18:10.423621 192.168.1.106 → 192.168.1.134 TCP 54 > 2049 → 856 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0 > 286 2023-10-03 10:18:13.466277 192.168.1.134 → 192.168.1.106 TCP 74 > 957 → 2049 [SYN] Seq=0 Win=32120 Len=0 MSS=1460 SACK_PERM > TSval=3081669801 TSecr=0 WS=128 > 287 2023-10-03 10:18:13.466812 192.168.1.106 → 192.168.1.134 TCP 54 > 2049 → 957 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0 > 289 2023-10-03 10:18:16.509229 192.168.1.134 → 192.168.1.106 TCP 74 > 695 → 2049 [SYN] Seq=0 Win=32120 Len=0 MSS=1460 SACK_PERM > TSval=3081672841 TSecr=0 WS=128 > 290 2023-10-03 10:18:16.509845 192.168.1.106 → 192.168.1.134 TCP 54 > 2049 → 695 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0 > 294 2023-10-03 10:18:19.551062 192.168.1.134 → 192.168.1.106 TCP 74 > 940 → 2049 [SYN] Seq=0 Win=32120 Len=0 MSS=1460 SACK_PERM > TSval=3081675881 TSecr=0 WS=128 > 295 2023-10-03 10:18:19.551434 192.168.1.106 → 192.168.1.134 TCP 54 > 2049 → 940 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0 > 300 2023-10-03 10:18:22.590380 192.168.1.134 → 192.168.1.106 TCP 74 > 810 → 2049 [SYN] Seq=0 Win=32120 Len=0 MSS=1460 SACK_PERM > TSval=3081678921 TSecr=0 > WS=128 > 301 2023-10-03 10:18:22.590726 192.168.1.106 → 192.168.1.134 TCP 54 > 2049 → 810 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0 > 308 2023-10-03 10:18:25.628256 192.168.1.134 → 192.168.1.106 TCP 74 > 877 → 2049 [SYN] Seq=0 Win=32120 Len=0 MSS=1460 SACK_PERM > TSval=3081681961 TSecr=0 WS=128 > 309 2023-10-03 10:18:25.628724 192.168.1.106 → 192.168.1.134 TCP 54 > 2049 → 877 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0 > 312 2023-10-03 10:18:28.665682 192.168.1.134 → 192.168.1.106 TCP 74 > 934 → 2049 [SYN] Seq=0 Win=32120 Len=0 MSS=1460 SACK_PERM > TSval=3081685001 TSecr=0 WS=128 > 313 2023-10-03 10:18:28.666374 192.168.1.106 → 192.168.1.134 TCP 54 > 2049 → 934 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0 > 320 2023-10-03 10:18:31.702236 192.168.1.134 → 192.168.1.106 TCP 74 > 803 → 2049 [SYN] Seq=0 Win=32120 Len=0 MSS=1460 SACK_PERM > TSval=3081688040 TSecr=0 WS=128 > 321 2023-10-03 10:18:31.702490 192.168.1.106 → 192.168.1.134 TCP 74 > 2049 → 803 [SYN, ACK] Seq=0 Ack=1 Win=31856 Len=0 MSS=1460 SACK_PERM > TSval=1993141756 TSecr=3081688040 WS=128 > 322 2023-10-03 10:18:31.702729 192.168.1.134 → 192.168.1.106 TCP 66 > 803 → 2049 [ACK] Seq=1 Ack=1 Win=32128 Len=0 TSval=3081688040 > TSecr=1993141756 > 323 2023-10-03 10:18:31.702737 192.168.1.134 → 192.168.1.106 NFS 238 > V3 WRITE Call, FH: 0x10bedd7c Offset: 0 Len: 4 FILE_SYNC > 324 2023-10-03 10:18:31.702893 192.168.1.106 → 192.168.1.134 TCP 66 > 2049 → 803 [ACK] Seq=1 Ack=173 Win=31872 Len=0 TSval=1993141756 > TSecr=3081688040 > 749 2023-10-03 10:19:01.880214 192.168.1.106 → 192.168.1.134 NFS 206 > V3 WRITE Reply (Call In 323) Len: 4 FILE_SYNC > > This is the same without the patch. Port is successfully reused. > Replay cache OK here not above. > > 76 2023-10-03 10:17:04.285731 192.168.1.134 → 192.168.1.106 NFS 238 > V3 WRITE Call, FH: 0x10bedd7c Offset: 0 Len: 4 FILE_SYNC > 77 2023-10-03 10:17:04.328371 192.168.1.106 → 192.168.1.134 TCP 66 > 2049 → 909 [ACK] Seq=1113 Ack=1501 Win=31872 Len=0 TSval=3542359002 > TSecr=3081600630 > 256 2023-10-03 10:18:04.341041 192.168.1.134 → 192.168.1.106 TCP 66 > [TCP Keep-Alive] 909 → 2049 [ACK] Seq=1500 Ack=1113 Win=32000 Len=0 > TSval=3081660681 TSecr=3542359002 > 259 2023-10-03 10:18:04.341500 192.168.1.106 → 192.168.1.134 TCP 54 > 2049 → 909 [RST] Seq=1113 Win=0 Len=0 > 260 2023-10-03 10:18:04.341860 192.168.1.134 → 192.168.1.106 TCP 74 > [TCP Port numbers reused] 909 → 2049 [SYN] Seq=0 Win=32120 Len=0 > MSS=1460 SACK_PERM TSval=3081660681 TSecr=0 WS=128 > 261 2023-10-03 10:18:04.342031 192.168.1.106 → 192.168.1.134 TCP 54 > 2049 → 909 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0 > 266 2023-10-03 10:18:07.380801 192.168.1.134 → 192.168.1.106 TCP 74 > 954 → 2049 [SYN] Seq=0 Win=32120 Len=0 MSS=1460 SACK_PERM > TSval=3081663720 TSecr=0 WS=128 > 267 2023-10-03 10:18:07.380971 192.168.1.106 → 192.168.1.134 TCP 54 > 2049 → 954 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0 > 275 2023-10-03 10:18:10.423352 192.168.1.134 → 192.168.1.106 TCP 74 > 856 → 2049 [SYN] Seq=0 Win=32120 Len=0 MSS=1460 SACK_PERM > TSval=3081666760 TSecr=0 WS=128 > 276 2023-10-03 10:18:10.423621 192.168.1.106 → 192.168.1.134 TCP 54 > 2049 → 856 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0 > 286 2023-10-03 10:18:13.466277 192.168.1.134 → 192.168.1.106 TCP 74 > 957 → 2049 [SYN] Seq=0 Win=32120 Len=0 MSS=1460 SACK_PERM > TSval=3081669801 TSecr=0 WS=128 > 287 2023-10-03 10:18:13.466812 192.168.1.106 → 192.168.1.134 TCP 54 > 2049 → 957 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0 > 289 2023-10-03 10:18:16.509229 192.168.1.134 → 192.168.1.106 TCP 74 > 695 → 2049 [SYN] Seq=0 Win=32120 Len=0 MSS=1460 SACK_PERM > TSval=3081672841 TSecr=0 WS=128 > 290 2023-10-03 10:18:16.509845 192.168.1.106 → 192.168.1.134 TCP 54 > 2049 → 695 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0 > 294 2023-10-03 10:18:19.551062 192.168.1.134 → 192.168.1.106 TCP 74 > 940 → 2049 [SYN] Seq=0 Win=32120 Len=0 MSS=1460 SACK_PERM > TSval=3081675881 TSecr=0 WS=128 > 295 2023-10-03 10:18:19.551434 192.168.1.106 → 192.168.1.134 TCP 54 > 2049 → 940 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0 > 300 2023-10-03 10:18:22.590380 192.168.1.134 → 192.168.1.106 TCP 74 > 810 → 2049 [SYN] Seq=0 Win=32120 Len=0 MSS=1460 SACK_PERM > TSval=3081678921 TSecr=0 WS=128 > 301 2023-10-03 10:18:22.590726 192.168.1.106 → 192.168.1.134 TCP 54 > 2049 → 810 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0 > 308 2023-10-03 10:18:25.628256 192.168.1.134 → 192.168.1.106 TCP 74 > 877 → 2049 [SYN] Seq=0 Win=32120 Len=0 MSS=1460 SACK_PERM > TSval=3081681961 TSecr=0 WS=128 > 309 2023-10-03 10:18:25.628724 192.168.1.106 → 192.168.1.134 TCP 54 > 2049 → 877 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0 > 312 2023-10-03 10:18:28.665682 192.168.1.134 → 192.168.1.106 TCP 74 > 934 → 2049 [SYN] Seq=0 Win=32120 Len=0 MSS=1460 SACK_PERM > TSval=3081685001 TSecr=0 WS=128 > 313 2023-10-03 10:18:28.666374 192.168.1.106 → 192.168.1.134 TCP 54 > 2049 → 934 [RST, ACK] Seq=1 Ack=1 Win=0 Len=0 > 320 2023-10-03 10:18:31.702236 192.168.1.134 → 192.168.1.106 TCP 74 > 803 → 2049 [SYN] Seq=0 Win=32120 Len=0 MSS=1460 SACK_PERM > TSval=3081688040 TSecr=0 WS=128 > 321 2023-10-03 10:18:31.702490 192.168.1.106 → 192.168.1.134 TCP 74 > 2049 → 803 [SYN, ACK] Seq=0 Ack=1 Win=31856 Len=0 MSS=1460 SACK_PERM > TSval=1993141756 TSecr=3081688040 WS=128 > 322 2023-10-03 10:18:31.702729 192.168.1.134 → 192.168.1.106 TCP 66 > 803 → 2049 [ACK] Seq=1 Ack=1 Win=32128 Len=0 TSval=3081688040 > TSecr=1993141756 > 323 2023-10-03 10:18:31.702737 192.168.1.134 → 192.168.1.106 NFS 238 > V3 WRITE Call, FH: 0x10bedd7c Offset: 0 Len: 4 FILE_SYNC > 324 2023-10-03 10:18:31.702893 192.168.1.106 → 192.168.1.134 TCP 66 > 2049 → 803 [ACK] Seq=1 Ack=173 Win=31872 Len=0 TSval=1993141756 > TSecr=3081688040 > 749 2023-10-03 10:19:01.880214 192.168.1.106 → 192.168.1.134 NFS 206 > V3 WRITE Reply (Call In 323) Len: 4 FILE_SYNC > 750 2023-10-03 10:19:01.880616 192.168.1.134 → 192.168.1.106 TCP 66 > 803 → 2049 [ACK] Seq=173 Ack=141 Win=32000 Len=0 TSval=3081718241 > TSecr=1993171927 > > > > SYNs. If the server is not replying to our SYN packets, then the TCP > > layer will back off and retransmit. So there is already a backoff-retry > > happening at that level. > > > > > > > > > > > > > > > > > > > > > > > > > > Signed-off-by: Trond Myklebust > > > > > > <trond.myklebust@xxxxxxxxxxxxxxx> > > > > > > --- > > > > > > net/sunrpc/xprtsock.c | 10 +++++++++- > > > > > > 1 file changed, 9 insertions(+), 1 deletion(-) > > > > > > > > > > > > diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c > > > > > > index 71848ab90d13..1a96777f0ed5 100644 > > > > > > --- a/net/sunrpc/xprtsock.c > > > > > > +++ b/net/sunrpc/xprtsock.c > > > > > > @@ -62,6 +62,7 @@ > > > > > > #include "sunrpc.h" > > > > > > > > > > > > static void xs_close(struct rpc_xprt *xprt); > > > > > > +static void xs_reset_srcport(struct sock_xprt *transport); > > > > > > static void xs_set_srcport(struct sock_xprt *transport, struct > > > > > > socket *sock); > > > > > > static void xs_tcp_set_socket_timeouts(struct rpc_xprt *xprt, > > > > > > struct socket *sock); > > > > > > @@ -1565,8 +1566,10 @@ static void xs_tcp_state_change(struct > > > > > > sock > > > > > > *sk) > > > > > > break; > > > > > > case TCP_CLOSE: > > > > > > if (test_and_clear_bit(XPRT_SOCK_CONNECTING, > > > > > > - &transport- > > > > > > > sock_state)) > > > > > > + &transport->sock_state)) > > > > > > { > > > > > > + xs_reset_srcport(transport); > > > > > > xprt_clear_connecting(xprt); > > > > > > + } > > > > > > clear_bit(XPRT_CLOSING, &xprt->state); > > > > > > /* Trigger the socket release */ > > > > > > xs_run_error_worker(transport, > > > > > > XPRT_SOCK_WAKE_DISCONNECT); > > > > > > @@ -1722,6 +1725,11 @@ static void xs_set_port(struct rpc_xprt > > > > > > *xprt, unsigned short port) > > > > > > xs_update_peer_port(xprt); > > > > > > } > > > > > > > > > > > > +static void xs_reset_srcport(struct sock_xprt *transport) > > > > > > +{ > > > > > > + transport->srcport = 0; > > > > > > +} > > > > > > + > > > > > > static void xs_set_srcport(struct sock_xprt *transport, struct > > > > > > socket *sock) > > > > > > { > > > > > > if (transport->srcport == 0 && transport- > > > > > > > xprt.reuseport) > > > > > > -- > > > > > > 2.41.0 > > > > > > > > > > > > > > -- > > > > Trond Myklebust Linux NFS client maintainer, Hammerspace > > > > trond.myklebust@xxxxxxxxxxxxxxx > > > > -- > > Trond Myklebust > > Linux NFS client maintainer, Hammerspace > > trond.myklebust@xxxxxxxxxxxxxxx > > > > -- Jeff Layton <jlayton@xxxxxxxxxx>
