nfsd: dedup nfs4_client_to_reclaim inserts

nfs4_client_to_reclaim() unconditionally allocates a new
nfs4_client_reclaim, prepends it to reclaim_str_hashtbl[], and bumps
reclaim_str_hashtbl_size with no check for an existing entry for the
same client name.  After a reboot with a populated recovery directory
that inflates the counter by one for every client that reclaims:

    boot:    load_recdir()
               nfs4_client_to_reclaim(name)   /* entry #1, size++ */

    grace:   RECLAIM_COMPLETE
               __nfsd4_create_reclaim_record_grace()
                 nfs4_client_to_reclaim(name) /* entry #2, size++ */

inc_reclaim_complete() ends the grace period early only when

    atomic_inc_return(&nn->nr_reclaim_complete) ==
        nn->reclaim_str_hashtbl_size

With reclaim_str_hashtbl_size at 2N and nr_reclaim_complete capped at
N, the equality never holds and the fast end-of-grace path is dead.
The grace period always runs out the full 90-second laundromat timer,
and the shadow entry left in the hash table carries a dangling cr_clp
for any reader that walks it.

Fix nfs4_client_to_reclaim() to look the name up with
nfsd4_find_reclaim_client() first and, on a hit, fold the new
princhash into the existing record (if it lacks one) and return that
record without allocating or touching reclaim_str_hashtbl_size.  On
kmemdup() failure during the fold-in, return NULL so
__cld_pipe_inprogress_downcall() surfaces -EFAULT to nfsdcld, matching
the miss-path contract.

Add an rw_semaphore (reclaim_str_hashtbl_lock) to struct nfsd_net that
serialises all access to reclaim_str_hashtbl[] and
reclaim_str_hashtbl_size.  Writers (nfs4_client_to_reclaim,
nfs4_remove_reclaim_record callers) hold the write side; readers
(nfsd4_cld_check*, inc_reclaim_complete, clients_still_reclaiming,
nfs4_has_reclaimed_state, nfsd4_check_legacy_client) hold the read
side.  All call sites are in sleepable context, and none is a hot
path, so the rwsem cost is negligible.

Reported-by: Chris Mason <clm@meta.com>
Fixes: 362063a595be ("nfsd: keep a tally of RECLAIM_COMPLETE operations when using nfsdcld")
Cc: stable@vger.kernel.org
Assisted-by: kres:claude-opus-4-7
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260530-nfsd-fixes-v2-4-f27e8eb4d974@kernel.org
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

0 files changed, 0 insertions, 0 deletions