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SubjectRe: [PATCH] SUNRPC: fix shutdown of NFS TCP client socket
Date


> On Mar 8, 2023, at 14:01, Siddharth Kawar <Siddharth.Kawar@microsoft.com> wrote:
>
> [You don't often get email from siddharth.kawar@microsoft.com. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
>
> Subject: [PATCH] SUNRPC: fix shutdown of NFS TCP client socket
>
> NFS server Duplicate Request Cache (DRC) algorithms rely on NFS clients
> reconnecting using the same local TCP port. Unique NFS operations are
> identified by the per-TCP connection set of XIDs. This prevents file
> corruption when non-idempotent NFS operations are retried.
>
> Currently, NFS client TCP connections are using different local TCP ports
> when reconnecting to NFS servers.
>
> After an NFS server initiates shutdown of the TCP connection, the NFS
> client's TCP socket is set to NULL after the socket state has reached
> TCP_LAST_ACK(9). When reconnecting, the new socket attempts to reuse
> the same local port but fails with EADDRNOTAVAIL (99). This forces the
> socket to use a different local TCP port to reconnect to the remote NFS
> server.
>
> State Transition and Events:
> TCP_CLOSING(8)

No: TCP state == 8 is TCP_CLOSE_WAIT

> TCP_LAST_ACK(9)
> connect(fail EADDRNOTAVAIL(99))
> TCP_CLOSE(7)
> bind on new port
> connect success
>
> dmesg excerpts showing reconnect switching from local port of 688 to 1014:
> [590701.200229] NFS: mkdir(0:61/560857152), testQ
> [590701.200231] NFS call mkdir testQ
> [590701.200259] RPC: xs_tcp_send_request(224) = 0
> [590751.883111] RPC: xs_tcp_state_change client 0000000051f4e000...
> [590751.883146] RPC: state 8 conn 1 dead 0 zapped 1 sk_shutdown 1
> [590751.883160] RPC: xs_data_ready...
> [590751.883232] RPC: xs_tcp_state_change client 0000000051f4e000...
> [590751.883235] RPC: state 9 conn 0 dead 0 zapped 1 sk_shutdown 3
> [590751.883238] RPC: xs_tcp_state_change client 0000000051f4e000...
> [590751.883239] RPC: state 9 conn 0 dead 0 zapped 1 sk_shutdown 3
> [590751.883283] RPC: xs_connect scheduled xprt 0000000051f4e000
> [590751.883314] RPC: xs_bind 0.0.0.0:688: ok (0)
> [590751.883321] RPC: worker connecting xprt 0000000051f4e000 via tcp
> to 10.101.1.30 (port 2049)
> [590751.883330] RPC: 0000000051f4e000 connect status 99 connected 0
> sock state 7
> [590751.883342] RPC: xs_tcp_state_change client 0000000051f4e000...
> [590751.883343] RPC: state 7 conn 0 dead 0 zapped 1 sk_shutdown 3
> [590751.883356] RPC: xs_connect scheduled xprt 0000000051f4e000
> [590751.883383] RPC: xs_bind 0.0.0.0:1014: ok (0)
> [590751.883388] RPC: worker connecting xprt 0000000051f4e000 via tcp
> to 10.101.1.30 (port 2049)
> [590751.883420] RPC: 0000000051f4e000 connect status 115 connected 0
> sock state 2
> ...
>
>
> State Transition and Events with patch applied:
> TCP_CLOSING(8)
> TCP_LAST_ACK(9)
> TCP_CLOSE(7)
> connect(reuse of port succeeds)
>
> dmesg excerpts showing reconnect on same port (936):
> [ 257.139935] NFS: mkdir(0:59/560857152), testQ
> [ 257.139937] NFS call mkdir testQ
> ...
> [ 307.822702] RPC: state 8 conn 1 dead 0 zapped 1 sk_shutdown 1
> [ 307.822714] RPC: xs_data_ready...
> [ 307.822817] RPC: xs_tcp_state_change client 00000000ce702f14...
> [ 307.822821] RPC: state 9 conn 0 dead 0 zapped 1 sk_shutdown 3
> [ 307.822825] RPC: xs_tcp_state_change client 00000000ce702f14...
> [ 307.822826] RPC: state 9 conn 0 dead 0 zapped 1 sk_shutdown 3
> [ 307.823606] RPC: xs_tcp_state_change client 00000000ce702f14...
> [ 307.823609] RPC: state 7 conn 0 dead 0 zapped 1 sk_shutdown 3
> [ 307.823629] RPC: xs_tcp_state_change client 00000000ce702f14...
> [ 307.823632] RPC: state 7 conn 0 dead 0 zapped 1 sk_shutdown 3
> [ 307.823676] RPC: xs_connect scheduled xprt 00000000ce702f14
> [ 307.823704] RPC: xs_bind 0.0.0.0:936: ok (0)
> [ 307.823709] RPC: worker connecting xprt 00000000ce702f14 via tcp
> to 10.101.1.30 (port 2049)
> [ 307.823748] RPC: 00000000ce702f14 connect status 115 connected 0
> sock state 2
> ...
> [ 314.916193] RPC: state 7 conn 0 dead 0 zapped 1 sk_shutdown 3
> [ 314.916251] RPC: xs_connect scheduled xprt 00000000ce702f14
> [ 314.916282] RPC: xs_bind 0.0.0.0:936: ok (0)
> [ 314.916292] RPC: worker connecting xprt 00000000ce702f14 via tcp
> to 10.101.1.30 (port 2049)
> [ 314.916342] RPC: 00000000ce702f14 connect status 115 connected 0
> sock state 2
>
> Fixes: 7c81e6a9d75b (SUNRPC: Tweak TCP socket shutdown in the RPC client)
> Signed-off-by: Siddharth Rajendra Kawar <sikawar@microsoft.com>
> ---
> diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> index d8ee06a9650a..e55e380bc10c 100644
> --- a/net/sunrpc/xprtsock.c
> +++ b/net/sunrpc/xprtsock.c
> @@ -2094,6 +2094,7 @@ static void xs_tcp_shutdown(struct rpc_xprt *xprt)
> break;
> case TCP_ESTABLISHED:
> case TCP_CLOSE_WAIT:
> + case TCP_LAST_ACK:
> kernel_sock_shutdown(sock, SHUT_RDWR);
> trace_rpc_socket_shutdown(xprt, sock);
> break;

The only way to transition from TCP_CLOSE_WAIT to TCP_LAST_ACK is by closing the socket ( see https://www.ibm.com/docs/en/zos/2.1.0?topic=SSLTBW_2.1.0/com.ibm.zos.v2r1.halu101/constatus.html ), so closing it while in TCP_LAST_ACK is redundant.


_________________________________
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com

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