From: "Mkrtchyan, Tigran" <tigran.mkrtchyan@desy.de>
To: linux-nfs <linux-nfs@vger.kernel.org>
Subject: Duplicated RPC client initialization with flexfiles layout
Date: Fri, 2 Oct 2026 14:33:00 +0200 (CEST) [thread overview]
Message-ID: <2038989007.1029515.1790944380174.JavaMail.zimbra@desy.de> (raw)
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Dear NFS fellows,
Your users were able to trigger a weird bug in rpc/flexfiles/our server.
The behavior is that the pNFS flexfiles client tries to create connections
to 6 data servers in parallel. However, the initialization to each DS happens
twice; for that, the connection is dropped at the TCP level. The wireshark
packes of one of the DSes and bpftrace-based tracing of rpc_create_xprt
functions are below.
This is with REHL 5.14.0-687.52.1 (at the moment); I will check whether I can reproduce it with the upstream kernel as well.
Any ideas?
Best regards,
Tigran.
1 0.000000000 1xx.yy.182.55 → 1xx.yy.50.150 TCP 76 763 → 24006 [SYN] Seq=0 Win=64240 Len=0 MSS=1460 SACK_PERM=1 TSval=3321872006 TSecr=0 WS=512
2 0.000000000 1xx.yy.182.55 → 1xx.yy.50.150 TCP 76 [TCP Out-Of-Order] 763 → 24006 [SYN] Seq=0 Win=64240 Len=0 MSS=1460 SACK_PERM=1 TSval=3321872006 TSecr=0 WS=512
3 0.000043716 1xx.yy.50.150 → 1xx.yy.182.55 TCP 76 24006 → 763 [SYN, ACK] Seq=0 Ack=1 Win=65160 Len=0 MSS=1460 SACK_PERM=1 TSval=196237843 TSecr=3321872006 WS=128
4 0.000049947 1xx.yy.50.150 → 1xx.yy.182.55 TCP 76 [TCP Out-Of-Order] 24006 → 763 [SYN, ACK] Seq=0 Ack=1 Win=65160 Len=0 MSS=1460 SACK_PERM=1 TSval=196237843 TSecr=3321872006 WS=128
5 0.000101734 1xx.yy.182.55 → 1xx.yy.50.150 TCP 76 941 → 24006 [SYN] Seq=0 Win=64240 Len=0 MSS=1460 SACK_PERM=1 TSval=3321872006 TSecr=0 WS=512
6 0.000101734 1xx.yy.182.55 → 1xx.yy.50.150 TCP 76 [TCP Out-Of-Order] 941 → 24006 [SYN] Seq=0 Win=64240 Len=0 MSS=1460 SACK_PERM=1 TSval=3321872006 TSecr=0 WS=512
7 0.000130403 1xx.yy.50.150 → 1xx.yy.182.55 TCP 76 24006 → 941 [SYN, ACK] Seq=0 Ack=1 Win=65160 Len=0 MSS=1460 SACK_PERM=1 TSval=196237844 TSecr=3321872006 WS=128
8 0.000135463 1xx.yy.50.150 → 1xx.yy.182.55 TCP 76 [TCP Out-Of-Order] 24006 → 941 [SYN, ACK] Seq=0 Ack=1 Win=65160 Len=0 MSS=1460 SACK_PERM=1 TSval=196237844 TSecr=3321872006 WS=128
9 0.000134812 1xx.yy.182.55 → 1xx.yy.50.150 TCP 62 763 → 24006 [RST] Seq=1 Win=0 Len=0
10 0.000134812 1xx.yy.182.55 → 1xx.yy.50.150 TCP 62 763 → 24006 [RST] Seq=1 Win=0 Len=0
11 0.000243066 1xx.yy.182.55 → 1xx.yy.50.150 TCP 68 941 → 24006 [ACK] Seq=1 Ack=1 Win=64512 Len=0 TSval=3321872006 TSecr=196237844
12 0.000243066 1xx.yy.182.55 → 1xx.yy.50.150 TCP 68 [TCP Dup ACK 11#1] 941 → 24006 [ACK] Seq=1 Ack=1 Win=64512 Len=0 TSval=3321872006 TSecr=196237844
13 0.000479359 1xx.yy.182.55 → 1xx.yy.50.150 TCP 68 941 → 24006 [FIN, ACK] Seq=1 Ack=1 Win=64512 Len=0 TSval=3321872006 TSecr=196237844
14 0.000479359 1xx.yy.182.55 → 1xx.yy.50.150 TCP 68 [TCP Out-Of-Order] 941 → 24006 [FIN, ACK] Seq=1 Ack=1 Win=64512 Len=0 TSval=3321872006 TSecr=196237844
15 0.000595959 1xx.yy.50.150 → 1xx.yy.182.55 TCP 68 24006 → 941 [FIN, ACK] Seq=1 Ack=2 Win=65280 Len=0 TSval=196237844 TSecr=3321872006
16 0.000603322 1xx.yy.50.150 → 1xx.yy.182.55 TCP 68 [TCP Out-Of-Order] 24006 → 941 [FIN, ACK] Seq=1 Ack=2 Win=65280 Len=0 TSval=196237844 TSecr=3321872006
17 0.000688326 1xx.yy.182.55 → 1xx.yy.50.150 TCP 68 941 → 24006 [ACK] Seq=2 Ack=2 Win=64512 Len=0 TSval=3321872007 TSecr=196237844
18 0.000688326 1xx.yy.182.55 → 1xx.yy.50.150 TCP 68 [TCP Dup ACK 17#1] 941 → 24006 [ACK] Seq=2 Ack=2 Win=64512 Len=0 TSval=3321872007 TSecr=196237844
19 1.023913451 1xx.yy.182.55 → 1xx.yy.50.150 TCP 76 716 → 24006 [SYN] Seq=0 Win=64240 Len=0 MSS=1460 SACK_PERM=1 TSval=3321873030 TSecr=0 WS=512
20 1.023913451 1xx.yy.182.55 → 1xx.yy.50.150 TCP 76 [TCP Out-Of-Order] 716 → 24006 [SYN] Seq=0 Win=64240 Len=0 MSS=1460 SACK_PERM=1 TSval=3321873030 TSecr=0 WS=512
21 1.023967704 1xx.yy.50.150 → 1xx.yy.182.55 TCP 76 24006 → 716 [SYN, ACK] Seq=0 Ack=1 Win=65160 Len=0 MSS=1460 SACK_PERM=1 TSval=196238867 TSecr=3321873030 WS=128
22 1.023976295 1xx.yy.50.150 → 1xx.yy.182.55 TCP 76 [TCP Out-Of-Order] 24006 → 716 [SYN, ACK] Seq=0 Ack=1 Win=65160 Len=0 MSS=1460 SACK_PERM=1 TSval=196238867 TSecr=3321873030 WS=128
23 1.023981641 1xx.yy.182.55 → 1xx.yy.50.150 TCP 76 708 → 24006 [SYN] Seq=0 Win=64240 Len=0 MSS=1460 SACK_PERM=1 TSval=3321873030 TSecr=0 WS=512
24 1.023981641 1xx.yy.182.55 → 1xx.yy.50.150 TCP 76 [TCP Out-Of-Order] 708 → 24006 [SYN] Seq=0 Win=64240 Len=0 MSS=1460 SACK_PERM=1 TSval=3321873030 TSecr=0 WS=512
25 1.024021399 1xx.yy.50.150 → 1xx.yy.182.55 TCP 76 24006 → 708 [SYN, ACK] Seq=0 Ack=1 Win=65160 Len=0 MSS=1460 SACK_PERM=1 TSval=196238867 TSecr=3321873030 WS=128
26 1.024027734 1xx.yy.50.150 → 1xx.yy.182.55 TCP 76 [TCP Out-Of-Order] 24006 → 708 [SYN, ACK] Seq=0 Ack=1 Win=65160 Len=0 MSS=1460 SACK_PERM=1 TSval=196238867 TSecr=3321873030 WS=128
27 1.024056233 1xx.yy.182.55 → 1xx.yy.50.150 TCP 62 716 → 24006 [RST] Seq=1 Win=0 Len=0
28 1.024056233 1xx.yy.182.55 → 1xx.yy.50.150 TCP 62 716 → 24006 [RST] Seq=1 Win=0 Len=0
2026-10-02 14:14:25: rpc_create_xprt failed: 1xx.yy.51.163:24010 err=-512
2026-10-02 14:14:25: rpc_create_xprt failed: 1xx.yy.51.163:24010 err=-512
2026-10-02 14:14:25: rpc_create_xprt failed: 1xx.yy.50.147:24001 err=-512
2026-10-02 14:14:25: rpc_create_xprt failed: 1xx.yy.50.147:24001 err=-512
2026-10-02 14:14:25: rpc_create_xprt failed: 1xx.yy.50.150:24006 err=-512
2026-10-02 14:14:25: rpc_create_xprt failed: 1xx.yy.50.150:24006 err=-512
2026-10-02 14:14:25: rpc_create_xprt failed: 1xx.yy.51.218:24011 err=-512
2026-10-02 14:14:25: rpc_create_xprt failed: 1xx.yy.51.218:24011 err=-512
2026-10-02 14:14:25: rpc_create_xprt failed: 1xx.yy.50.59:24005 err=-512
2026-10-02 14:14:25: rpc_create_xprt failed: 1xx.yy.50.59:24005 err=-512
2026-10-02 14:14:25: rpc_create_xprt failed: 1xx.yy.52.47:24001 err=-512
2026-10-02 14:14:25: rpc_create_xprt failed: 1xx.yy.52.47:24001 err=-512
2026-10-02 14:14:26: rpc_create_xprt failed: 1xx.yy.51.163:24010 err=-512
2026-10-02 14:14:26: rpc_create_xprt failed: 1xx.yy.51.163:24010 err=-512
2026-10-02 14:14:26: rpc_create_xprt failed: 1xx.yy.50.147:24001 err=-512
2026-10-02 14:14:26: rpc_create_xprt failed: 1xx.yy.50.147:24001 err=-512
2026-10-02 14:14:26: rpc_create_xprt failed: 1xx.yy.50.150:24006 err=-512
2026-10-02 14:14:26: rpc_create_xprt failed: 1xx.yy.50.150:24006 err=-512
2026-10-02 14:14:26: rpc_create_xprt failed: 1xx.yy.51.218:24011 err=-512
2026-10-02 14:14:26: rpc_create_xprt failed: 1xx.yy.51.218:24011 err=-512
2026-10-02 14:14:26: rpc_create_xprt failed: 1xx.yy.50.59:24005 err=-512
2026-10-02 14:14:26: rpc_create_xprt failed: 1xx.yy.50.59:24005 err=-512
2026-10-02 14:14:26: rpc_create_xprt failed: 1xx.yy.52.47:24001 err=-512
2026-10-02 14:14:26: rpc_create_xprt failed: 1xx.yy.52.47:24001 err=-512
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