Re: [PATCH 0/4] NFSD: CB_RECALL_ANY fixes and a meaningful keep count

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2026-08-11 at 15:52 -0400, Chuck Lever wrote:
> NFSD sends every CB_RECALL_ANY with craa_objects_to_keep set to
> zero. RFC 8881 Section 20.6.3 reads that as a request to retain no
> delegation at all, whether or not the delegation backs a file an
> application still has open.
> 
> NFSD meant the callback as a signal to return unused delegations.
> Only the Linux client has been tested against it, and that client
> ignores craa_objects_to_keep and returns every unused delegation of
> the named types, so the fixed zero never produced visible
> misbehavior.
> 
> The NFSv4.0 recipient bug is fixed on its own so it can be
> backported to LTS ahead of the rest. An NFSv4.0 callback service
> rejects CB_RECALL_ANY, and nothing brings the callback channel back
> up afterward (patch 1).
> 
> The keep count comes from a new per-client delegation count rather
> than a walk of cl_delegations (patch 2). deleg_reaper() runs under
> nn->client_lock, and cl_delegations is serialized by nn->deleg_lock,
> which nests outside it, so the reaper cannot count the list. It
> reads the counter without the lock and may not depend on the value.
> 
> Each callback asks a client to give up one delegation. A larger
> request reaches delegations that applications still have open, and
> both reaper callers re-arm while their condition lasts. A client
> holding a single delegation is skipped rather than sent the old
> zero. That strands one delegation per client, which this
> best-effort design accepts for now.
> 
> NFSD sets no recall target and remembers nothing across callbacks.
> RFC 8881 Section 20.6.4 prescribes CB_RECALL against specific
> delegations once a client fails to return any. NFSD does not take
> that step yet. CB_RECALL_ANY is asynchronous and reports no
> completion, so NFSD treats it as advisory.
> 
> ---
> Chuck Lever (4):
>       NFSD: Do not send CB_RECALL_ANY to NFSv4.0 clients
>       NFSD: Count the delegations held by each client
>       NFSD: Name directory delegations in the CB_RECALL_ANY type mask
>       NFSD: Send a meaningful CB_RECALL_ANY keep count
> 
>  fs/nfsd/nfs4state.c | 27 +++++++++++++++++++++++----
>  fs/nfsd/state.h     |  2 ++
>  2 files changed, 25 insertions(+), 4 deletions(-)
> ---
> base-commit: 1d479c6b53f684b27da84ec352b7efb97f7f115f
> change-id: 20260810-recall-any-keep-count-f50c2ae1b792
> 
> Best regards,
> --  
> Chuck Lever <cel@kernel.org>

Looks reasonable.

Reviewed-by: Jeff Layton <jlayton@kernel.org>