Upstream commit 4cc9b9f2bf4dfe13fe573 "nfsd: refine and rename
NFSD_MAY_LOCK" and
stable v6.12.54 commit 18744bc56b0ec (re)moves checks from
fs/nfsd/vfs.c::nfsd_permission().
This causes NFS clients to see
$ flock -e -w 4 /srv/NAS/test/debian-13.3.0-amd64-netinst.iso sleep 1
flock: /srv/NAS/test/debian-13.3.0-amd64-netinst.iso: No locks available
Keeping the check in nfsd_permission() whilst also copying it to
fs/nfsd/nfsfh.c::__fh_verify() resolves the issue.
This was discovered on the Debian openQA infrastructure server when
upgrading kernel from v6.12.48 to later v6.12.y where worker hosts (with
any earlier or later kernel version) pass NFSv3 mounted ISO images to
qemu-system-x86_64 and it reports:
!!! : qemu-system-x86_64: -device
scsi-cd,id=cd0-device,drive=cd0-overlay0,serial=cd0: Failed to get
"consistent read" lock: No locks available
QEMU: Is another process using the image
[/var/lib/openqa/pool/2/20260223-1-debian-testing-amd64-netinst.iso]?
A simple reproducer with the server using:
# cat /etc/exports.d/test.exports
/srv/NAS/test
fdff::/64(fsid=0,rw,no_root_squash,sync,no_subtree_check,auth_nlm)
and clients using:
# mount -t nfs [fdff::2]:/srv/NAS/test /srv/NAS/test -o
proto=tcp6,ro,fsc,soft
will trigger the error as shown above:
$ flock -e -w 4 /srv/NAS/test/debian-13.3.0-amd64-netinst.iso sleep 1
flock: /srv/NAS/test/debian-13.3.0-amd64-netinst.iso: No locks available
A simple test program calling fcntl() with the same arguments QEMU uses
also fails in the same way.
$ ./nfs3_range_lock_test
/srv/NAS/test/debian-13.3.0-amd64-netinst.{iso,overlay}
Opened base file: /srv/NAS/test/debian-13.3.0-amd64-netinst.iso
Opened overlay file: /srv/NAS/test/debian-13.3.0-amd64-netinst.overlay
Attempting lock at 4 on /srv/NAS/test/debian-13.3.0-amd64-netinst.iso
fcntl(fd, F_GETLK, &fl) failed on base: No locks available
Attempting lock at 8 on /srv/NAS/test/debian-13.3.0-amd64-netinst.overlay
fcntl(fd, F_GETLK, &fl) failed on overlay: No locks available
