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? > > 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 > >
