Re: [PATCH v2 0/6] Automatic NFSv4 state revocation on filesystem unmount

[Jeff Layton <jlayton@kernel.org>]

On Wed, 2026-01-07 at 19:40 -0500, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
> 
> When an NFS server exports a filesystem and clients hold NFSv4 state
> (opens, locks, delegations), unmounting the underlying filesystem
> fails with EBUSY. The /proc/fs/nfsd/unlock_fs interface exists for
> administrators to manually revoke state before retrying the unmount,
> but this approach has significant operational drawbacks.
> 
> Manual intervention breaks automation workflows. Containerized NFS
> servers, orchestration systems, and unattended maintenance scripts
> cannot reliably unmount exported filesystems without implementing
> custom logic to detect the failure and invoke unlock_fs. System
> administrators managing many exports face tedious, error-prone
> procedures when decommissioning storage.
> 
> This series enables the NFS server to detect filesystem unmount
> events and automatically revoke associated state. The mechanism
> uses the kernel's existing fs_pin infrastructure, which provides
> callbacks during mount lifecycle transitions.
> 

(cc'ing the vfs maintainers)

One thing I want to point out here is that the only user of fs_pin is
the BSD process accounting subsystem, which would be really nice to get
rid of at some point:

https://lore.kernel.org/linux-fsdevel/20260106-bsd-acct-v1-1-d15564b52c83@kernel.org/

I suspect the VFS maintainers might want you to use something different
here so fs_pin can eventually go away too.

An alternate idea might be to plumb an srcu notifier chain into the
umount codepath, similar to the lease_notifier_chain in fs/locks.c.
Then nfsd could register to be notified when there is a umount attempt
and do the right thing to tear down state.


> When a filesystem
> is unmounted, all NFSv4 opens, locks, and delegations referencing
> it are revoked, async COPY operations are cancelled with
> NFS4ERR_ADMIN_REVOKED sent to clients, NLM locks are released,
> and cached file handles are closed.
> 
> With automatic revocation, unmount operations complete without
> administrator intervention once the brief state cleanup finishes.
> Clients receive immediate notification of state loss through
> standard NFSv4 error codes, allowing applications to handle the
> situation appropriately rather than encountering silent failures.
> 
> Based on the nfsd-testing branch of:
> 
>   https://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git/
> 
> Changes since v1:
> - Explain why drop_client() is being renamed
> - Finish implementing revocation on umount
> - Rename pin_insert_group
> - Clarified log output and code comments
> - Hold nfsd_mutex while closing nfsd_files
> 
> Chuck Lever (6):
>   nfsd: cancel async COPY operations when admin revokes filesystem state
>   fs: export pin_insert and pin_remove for modular filesystems
>   fs: add pin_insert_sb() for superblock-only pins
>   fs: invoke group_pin_kill() during mount teardown
>   nfsd: revoke NFSv4 state when filesystem is unmounted
>   nfsd: close cached files on filesystem unmount
> 
>  fs/fs_pin.c            |  50 ++++++++
>  fs/namespace.c         |   2 +
>  fs/nfsd/Makefile       |   2 +-
>  fs/nfsd/filecache.c    |  44 +++++++
>  fs/nfsd/filecache.h    |   1 +
>  fs/nfsd/netns.h        |   4 +
>  fs/nfsd/nfs4proc.c     | 124 +++++++++++++++++--
>  fs/nfsd/nfs4state.c    |  46 +++++--
>  fs/nfsd/nfsctl.c       |  11 +-
>  fs/nfsd/pin.c          | 274 +++++++++++++++++++++++++++++++++++++++++
>  fs/nfsd/state.h        |   9 ++
>  fs/nfsd/xdr4.h         |   1 +
>  include/linux/fs_pin.h |   1 +
>  13 files changed, 548 insertions(+), 21 deletions(-)
>  create mode 100644 fs/nfsd/pin.c

-- 
Jeff Layton <jlayton@kernel.org>