[regression] Large rsize/wsize (1MB) causes EIO after 2b092175f5e3 ("NFS: Fix inheritance of the block sizes when automounting")

Salvatore Bonaccorso
2026-03-14T12:23:06Z

Control: forwarded -1 https://lore.kernel.org/regressions/177349021750.3039212.10211295677877269201@eldamar.lan
Control: tags -1 + upstream

Hi Trond, hi Anna

In Debian we got reports of a NFS client regression where large
rsize/wsize (1MB) causes EIO after the commit 2b092175f5e3 ("NFS: Fix
inheritance of the block sizes when automounting") and its backports
to the stable series. The report in full is at:
https://bugs.debian.org/1128834

Maik reported:
> after upgrading from Linux 6.1.158 to 6.1.162, NFS client writes fail with input/output errors (EIO).
>
> Environment:
> - Debian Bookworm
> - Kernel: 6.1.0-43-amd64 (6.1.162-1)
> - NFSv4.2 (also reproducible with 4.1)
> - Default mount options include rsize=1048576,wsize=1048576
>
> Reproducer:
> dd if=/dev/zero of=~/testfile bs=1M count=500
> or
> dd if=/dev/zero of=~/testfile bs=4k count=100000
>
> On different computers and VMs!
>
>
> Result:
> dd: closing output file: Input/output error
>
> Workaround:
> Mount with:
> rsize=65536,wsize=65536
>
> With reduced I/O size, the issue disappears completely.
>
> Impact:
> - File writes fail (file >1M)
> - KDE Plasma crashes due to corrupted cache/config writes
>
> The issue does NOT occur on kernel 6.1.0-42 (6.1.158).

I was not able to reproduce the problem, and it turned out that it
seems to be triggerable when on NFS server side a Dell EMC (Isilion)
system was used. So the issue was not really considered initially as
beeing "our" issue.

Valentin SAMIR, a second user affected, did as well report the issue
to Dell, and Dell seems to point at a client issue instead. Valentin
writes:

> We are facing the same issue. Dell seems to point to a client issue:
> The kernel treats the max size as the nfs payload max size whereas
> OneFs treat the max size as the overall compound packet max size
> (everything related to NFS in the call). Hence when OneFS receives a
> call with a payload of 1M, the overall NFS packet is slightly bigger
> and it returns an NFS4ERR_REQ_TOO_BIG.
>
> So the question is: should max req size/max resp size be treated as the
> nfs payload max size or the whole nfs packet max size?

His reply in https://bugs.debian.org/1128834#55 contains a quote from
the response Valentin got from Dell, I'm full quoting it here for
easier followup in case needed:

> I have been looking at the action plan output we captured.
> Specifically around when you first mounted and then repro'ed the
> error.
>
> Looking at the pcap we gathered, firstly, lets concentrate on the
> "create session" calls between Client / Node.
> Here we can these max sizes advertised - per screenshot.
>
>
> Frame 17: 306 bytes on wire (2448 bits), 306 bytes captured (2448
> bits)
> Ethernet II, Src: SuperMicroCo_1d:7d:b2 (ac:1f:6b:1d:7d:b2), Dst:
> MellanoxTech_bd:8c:7a (c4:70:bd:bd:8c:7a)
> Internet Protocol Version 4, Src: 172.22.1.132, Dst: 172.22.16.29
> Transmission Control Protocol, Src Port: 810, Dst Port: 2049, Seq:
> 613, Ack: 277, Len: 240
> Remote Procedure Call, Type:Call XID:0x945b7e1d
> Network File System, Ops(1): CREATE_SESSION
> [Program Version: 4]
> [V4 Procedure: COMPOUND (1)]
> Tag: <EMPTY>
> minorversion: 2
> Operations (count: 1): CREATE_SESSION
> Opcode: CREATE_SESSION (43)
> clientid: 0x36adef626e919bf4
> seqid: 0x00000001
> csa_flags: 0x00000003, CREATE_SESSION4_FLAG_PERSIST,
> CREATE_SESSION4_FLAG_CONN_BACK_CHAN
> csa_fore_chan_attrs
> hdr pad size: 0
> max req size: 1049620
> max resp size: 1049480
> max resp size cached: 7584
> max ops: 8
> max reqs: 64
> csa_back_chan_attrs
> hdr pad size: 0
> max req size: 4096
> max resp size: 4096
> max resp size cached: 0
> max ops: 2
> max reqs: 16
> cb_program: 0x40000000
> flavor: 1
> stamp: 2087796144
> machine name: srv-transfert.ad.phedre.fr
> uid: 0
> gid: 0
> [Main Opcode: CREATE_SESSION (43)]
>
>
> And the Node responds, as expected confirming the max size of
> 1048576.
>
>
> Frame 19: 194 bytes on wire (1552 bits), 194 bytes captured (1552
> bits)
> Ethernet II, Src: MellanoxTech_bd:8c:7a (c4:70:bd:bd:8c:7a), Dst:
> IETF-VRRP-VRID_3f (00:00:5e:00:01:3f)
> Internet Protocol Version 4, Src: 172.22.16.29, Dst: 172.22.1.132
> Transmission Control Protocol, Src Port: 2049, Dst Port: 810, Seq:
> 321, Ack: 853, Len: 128
> Remote Procedure Call, Type:Reply XID:0x945b7e1d
> Network File System, Ops(1): CREATE_SESSION
> [Program Version: 4]
> [V4 Procedure: COMPOUND (1)]
> Status: NFS4_OK (0)
> Tag: <EMPTY>
> Operations (count: 1)
> Opcode: CREATE_SESSION (43)
> Status: NFS4_OK (0)
> sessionid: f49b916e62efad36f200000006000000
> seqid: 0x00000001
> csr_flags: 0x00000002,
> CREATE_SESSION4_FLAG_CONN_BACK_CHAN
> csr_fore_chan_attrs
> hdr pad size: 0
> max req size: 1048576
> max resp size: 1048576
> max resp size cached: 7584
> max ops: 8
> max reqs: 64
> csr_back_chan_attrs
> hdr pad size: 0
> max req size: 4096
> max resp size: 4096
> max resp size cached: 0
> max ops: 2
> max reqs: 16
> [Main Opcode: CREATE_SESSION (43)]
>
>
> Now if we look later on in the sequence when the Client sends the
> write request to the Node - we see in the frame, the max size is as
> expected 1048576
>
>
> Frame 747: 1998 bytes on wire (15984 bits), 1998 bytes captured
> (15984 bits)
> Ethernet II, Src: SuperMicroCo_1d:7d:b2 (ac:1f:6b:1d:7d:b2), Dst:
> MellanoxTech_bd:8c:7a (c4:70:bd:bd:8c:7a)
> Internet Protocol Version 4, Src: 172.22.1.132, Dst: 172.22.16.29
> Transmission Control Protocol, Src Port: 810, Dst Port: 2049, Seq:
> 1054149, Ack: 6009, Len: 1932
> [345 Reassembled TCP Segments (1048836 bytes): #84(1448), #85(5792),
> #87(5792), #89(1448), #90(1448), #92(4344), #94(4344), #96(2896),
> #98(1448), #99(2896), #101(4344), #103(4344), #105(1448), #106(1448),
> #108(2896), #110(1448), #111(2896)]
> Remote Procedure Call, Type:Call XID:0xb45b7e1d
> Network File System, Ops(4): SEQUENCE, PUTFH, WRITE, GETATTR
> [Program Version: 4]
> [V4 Procedure: COMPOUND (1)]
> Tag: <EMPTY>
> minorversion: 2
> Operations (count: 4): SEQUENCE, PUTFH, WRITE, GETATTR
> Opcode: SEQUENCE (53)
> Opcode: PUTFH (22)
> Opcode: WRITE (38)
> StateID
> offset: 0
> stable: FILE_SYNC4 (2)
> Write length: 1048576
> Data: <DATA>
> Opcode: GETATTR (9)
> [Main Opcode: WRITE (38)]
>
>
> However we then see the Node reply a short time later with (as below)
> REQ_TOO_BIG - meaning the max size has been exceeded.
>
> Frame 749: 114 bytes on wire (912 bits), 114 bytes captured (912
> bits)
> Ethernet II, Src: MellanoxTech_bd:8c:7a (c4:70:bd:bd:8c:7a), Dst:
> IETF-VRRP-VRID_3f (00:00:5e:00:01:3f)
> Internet Protocol Version 4, Src: 172.22.16.29, Dst: 172.22.1.132
> Transmission Control Protocol, Src Port: 2049, Dst Port: 810, Seq:
> 6009, Ack: 1056081, Len: 48
> Remote Procedure Call, Type:Reply XID:0xb45b7e1d
> Network File System, Ops(1): SEQUENCE(NFS4ERR_REQ_TOO_BIG)
> [Program Version: 4]
> [V4 Procedure: COMPOUND (1)]
> Status: NFS4ERR_REQ_TOO_BIG (10065)
> Tag: <EMPTY>
> Operations (count: 1)
> Opcode: SEQUENCE (53)
> Status: NFS4ERR_REQ_TOO_BIG (10065)
> [Main Opcode: SEQUENCE (53)]
>
>
> Why is this?
>
> The reason for this seems to be related to the Client.
>
> From the Cluster side, the max rsize/wsize is the overall compound
> packet max size (everything related to NFS in the call)
>
> So for example with a compound call in nfsv4.2 - this might include
> the below type detail which does not exceed the overall size 1048576:
>
> [
> COMPOUND header
> SEQUENCE ....
> PUTFH ...
> WRITE header
> WRITE payload
> ] (overall) < 1mb
>
>
> However the Client instead uses r/wsize from mount option, as a limit
> for the write payload.
>
> So with the same example
> COMPOUND header
> SEQUENCE ....
> PUTFH ...
> WRITE header
>
> [
> WRITE payload
> ] (write) < 1mb
>
> But overall this ends up being 1mb + all the overhead of write
> header, compound header, putfh etc
> Puts it over the channel limit of 1048576 and hence the error
> returned.
>
> So it seems here the Client ignores that value and insists on the
> WRITE with a payload == wszie; which in total with WRITE overhead and
> all other requests in COMPOUND (PUTFH, etc) exceeds maxrequestsize,
> which prompts NFS4ERR_REQ_TOO_BIG.
>
>
> And as you can see, once you reduce the size within the mount options
> on the Client side, it no longer exceeds its limits.
> Meaning you don't get the I/O error.

So question, are we behaving here correctly or is it our Problem, or is the
issue still considered on Dell's side?

#regzbot introduced: 2b092175f5e301cdaa935093edfef2be9defb6df
#regzbot monitor: https://bugs.debian.org/1128834

How to proceeed from here?

Regards,
Salvatore