FreeBSD 16.0-CURRENT nfsd causes kernel panic when ms-nfs41-client runs WinZFS from file

Aurélien Couderc <[email protected]> Tue, 16 Jun 2026 10:41:33 +0200
Newsgroups gmane.os.freebsd.devel.hackers
Message-ID <CA+1jF5qAwz0=Uj7U=E2B4pTm+6fuyxakz6HK2W7o0xxuHrxRPg@mail.gmail.com>
FreeBSD NFSD causes repeated kernel panics with ms-nfs41-client, but
only if we run a Windows OpenZFS zpool from a NFS filesystem.

Steps to use OpenZFS on NFS (I've send the instructions to Roland):
cd nfs_subdir_on_freebsd26
truncate -s $((512*1024*1024*1024)) poolfile1.bin
chmod a+rw poolfile1.bin
zpool.exe create -o ashift=15 -o autotrim=on -O
casesensitivity=insensitive -O driveletter=Z nfspool1
"\\\\?\\$(cygpath -w "$PWD/poolfile1.bin")"

The ZFS filesystem on Windows works for a while until the FreeBSD
kernel drops into the kernel debugger prompt, warning that NFSD had
become unresponsive.

How can I debug this?


FreeBSD version: FreeBSD 16.0-CURRENT installed from
FreeBSD-16.0-CURRENT-amd64-20260505-8e8d87856241-285702
uname -a
FreeBSD fbsd7283 16.0-CURRENT FreeBSD 16.0-CURRENT
main-n285769-1d24638d3e88 GENERIC amd64
Delegations are ENABLED for nfsd.

Windows version: Win11
OpenZFS version:
https://github.com/openzfsonwindows/openzfs/releases/download/zfswin-2.4.1rc11/OpenZFSOnWindows-debug-2.4.1rc11b.exe
ms-nfs41-client version: ms-nfs41-client-release-2026-06-01

Aurélien
-- 
Aurélien Couderc <[email protected]>
Big Data/Data mining expert, chess enthusiast