Re: [PATCH 4/4] NFSD: Send a meaningful CB_RECALL_ANY keep count

On Tue, 11 Aug 2026 at 21:57, Chuck Lever <[email protected]> wrote:
>
> deleg_reaper() sets craa_objects_to_keep to zero on every
> CB_RECALL_ANY. Per RFC 8881 Section 20.6.3, that asks the client to
> retain no read or write delegation at all, whether or not the
> delegation backs an open file.
>
> The field names a count the client may keep. The client picks which
> objects to return, because the server cannot read lack of recent
> use as lack of usefulness. Zero leaves nothing to choose among. A
> client that complies returns the delegations backing its open files
> and reopens each one with CLAIM_DELEGATE_CUR, so NFSD trades a
> delegation for an open stateid and recovers nothing. A client that
> reads the zero as "unspecified" does nothing instead, and
> nfsd4_cb_recall_any_done() inspects only the reply status, so NFSD
> cannot tell the two apart.
>
> Derive the keep count from cl_deleg_count and ask each client for a
> single delegation. A larger request reaches delegations an
> application still has open, and both callers re-arm while their
> condition lasts. Skip a client holding one delegation rather than
> send the zero again. That gate subsumes the list_empty() test above
> it, and it belongs above the NFSD4_CALLBACK_RUNNING test_and_set. A
> continue below that point latches the bit with no callback in
> flight to clear it.
>
> The Linux client ignores craa_objs_to_keep and returns unused
> delegations from the type mask alone, so the count changes nothing
> for it. The gate does. The reaper goes quiet for a client walked
> down to one delegation.
>
> Fixes: 44df6f439a17 ("NFSD: add delegation reaper to react to low memory condition")
> Signed-off-by: Chuck Lever <[email protected]>

ms-nfs41-client hit that bug when implementing CB_RECALL_ANY
(https://github.com/kofemann/ms-nfs41-client/commit/3abe73c8ab0d924450a1c1c480f0b14f963f9531)
with Linux 7.0 nfsd.
What should existing NFSv4.1 clients do if they encounter a
objects_to_keep value of 0? Right now it recalls ALL delegations,
which basically is a "reset" of all delegations.

Ced
-- 
Cedric Blancher <[email protected]>
[https://plus.google.com/u/0/+CedricBlancher/]
Institute Pasteur