[PATCH v6 5/6] nfsd: count NFSv4 callback operations per netns

[Jeff Layton <jlayton@kernel.org>]

The NFS server tracks per-operation call counts for the forward channel
(proc4ops) but keeps no statistics for the NFSv4 backchannel (callback)
operations it sends to clients.

Add a per-netns array of percpu counters for callback operations, indexed
by RFC 8881 callback opcode (OP_CB_GETATTR..OP_CB_OFFLOAD), and bump the
relevant counter in nfsd4_run_cb(), which is hit exactly once per callback
that is actually queued.

CB_GETATTR is sent when a GETATTR conflicts with an outstanding write
delegation, which is roughly what the dedicated wdeleg_getattr counter
tracked. The two are not identical: the old counter incremented on every
such conflict, whereas the CB_GETATTR counter only counts callbacks that
are actually queued, so concurrent conflicts that coalesce onto an
already in-flight CB_GETATTR are now counted once rather than once per
conflict. Report the procfs "wdeleg_getattr" line from the CB_GETATTR
counter and drop the now-redundant NFSD_STATS_WDELEG_GETATTR counter, its
helper, and its increment site.

Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/nfsd/netns.h        | 12 +++++++++++-
 fs/nfsd/nfs4callback.c | 22 +++++++++++++++++++++-
 fs/nfsd/nfs4state.c    |  2 --
 fs/nfsd/nfsctl.c       | 14 ++++++++++++++
 fs/nfsd/stats.c        |  2 +-
 fs/nfsd/stats.h        |  5 +++--
 6 files changed, 50 insertions(+), 7 deletions(-)

diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index 03724bef10a7..37daba0d4747 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -53,11 +53,16 @@ enum {
 	NFSD_STATS_FIRST_NFS4_OP,	/* count of individual nfsv4 operations */
 	NFSD_STATS_LAST_NFS4_OP = NFSD_STATS_FIRST_NFS4_OP + LAST_NFS4_OP,
 #define NFSD_STATS_NFS4_OP(op)	(NFSD_STATS_FIRST_NFS4_OP + (op))
-	NFSD_STATS_WDELEG_GETATTR,	/* count of getattr conflict with wdeleg */
 #endif
 	NFSD_STATS_COUNTERS_NUM
 };
 
+/*
+ * Per-netns NFSv4 callback (backchannel) per-operation counters, indexed
+ * directly by RFC 8881 callback opcode (OP_CB_GETATTR..OP_CB_OFFLOAD).
+ */
+#define NFSD_STATS_CB_OPS_NUM	(OP_CB_OFFLOAD + 1)
+
 /*
  * Represents a nfsd "container". With respect to nfsv4 state tracking, the
  * fields of interest are the *_id_hashtbls and the *_name_tree. These track
@@ -198,6 +203,11 @@ struct nfsd_net {
 	/* Per-netns stats counters */
 	struct percpu_counter    counter[NFSD_STATS_COUNTERS_NUM];
 
+#ifdef CONFIG_NFSD_V4
+	/* Per-netns NFSv4 callback (backchannel) per-operation counters */
+	struct percpu_counter    cb_counter[NFSD_STATS_CB_OPS_NUM];
+#endif
+
 	/* sunrpc svc stats */
 	struct svc_stat          nfsd_svcstats;
 
diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
index 71dcb448fa0a..b171257da6ba 100644
--- a/fs/nfsd/nfs4callback.c
+++ b/fs/nfsd/nfs4callback.c
@@ -1921,12 +1921,32 @@ void nfsd4_init_cb(struct nfsd4_callback *cb, struct nfs4_client *clp,
 bool nfsd4_run_cb(struct nfsd4_callback *cb)
 {
 	struct nfs4_client *clp = cb->cb_clp;
+	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
+	const struct nfsd4_callback_ops *ops = cb->cb_ops;
+	u32 minorversion = clp->cl_minorversion;
 	bool queued;
 
+	/*
+	 * Snapshot the opcode, minorversion, and the per-net pointer before
+	 * queuing: once nfsd4_queue_cb() has queued the work, the callback (and
+	 * the object that embeds it) may be processed and freed concurrently, so
+	 * neither cb nor clp can be dereferenced afterward.
+	 */
 	nfsd41_cb_inflight_begin(clp);
 	queued = nfsd4_queue_cb(cb);
-	if (!queued)
+	if (queued) {
+		if (ops)
+			nfsd_stats_cb_op_inc(nn, ops->opcode);
+		/*
+		 * Minorversion > 0 callbacks prepend a CB_SEQUENCE op (see
+		 * encode_cb_sequence4args()); count it like the forechannel
+		 * counts SEQUENCE, so it isn't perpetually reported as zero.
+		 */
+		if (minorversion > 0)
+			nfsd_stats_cb_op_inc(nn, OP_CB_SEQUENCE);
+	} else {
 		nfsd41_cb_inflight_end(clp);
+	}
 	return queued;
 }
 
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index b830aed7ae39..8f8da1312231 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -9904,7 +9904,6 @@ __be32
 nfsd4_deleg_getattr_conflict(struct svc_rqst *rqstp, struct dentry *dentry,
 			     struct nfs4_delegation **pdp)
 {
-	struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
 	struct nfsd_thread_local_info *ntli = rqstp->rq_private;
 	struct file_lock_context *ctx;
 	struct nfs4_delegation *dp = NULL;
@@ -9944,7 +9943,6 @@ nfsd4_deleg_getattr_conflict(struct svc_rqst *rqstp, struct dentry *dentry,
 		return 0;
 	}
 
-	nfsd_stats_wdeleg_getattr_inc(nn);
 	refcount_inc(&dp->dl_stid.sc_count);
 	ncf = &dp->dl_cb_fattr;
 	nfs4_cb_getattr(&dp->dl_cb_fattr);
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index f0514d8149cd..4710415790e2 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -2691,6 +2691,13 @@ static __net_init int nfsd_net_init(struct net *net)
 	if (retval)
 		goto out_repcache_error;
 
+#ifdef CONFIG_NFSD_V4
+	retval = percpu_counter_init_many(nn->cb_counter, 0, GFP_KERNEL,
+					  NFSD_STATS_CB_OPS_NUM);
+	if (retval)
+		goto out_cb_counter_error;
+#endif
+
 	memset(&nn->nfsd_svcstats, 0, sizeof(nn->nfsd_svcstats));
 	nn->nfsd_svcstats.program = &nfsd_programs[0];
 	retval = svc_stat_alloc_counts(&nn->nfsd_svcstats);
@@ -2719,6 +2726,10 @@ static __net_init int nfsd_net_init(struct net *net)
 out_svcstats_error:
 	svc_stat_free_counts(&nn->nfsd_svcstats);
 out_proc_error:
+#ifdef CONFIG_NFSD_V4
+	percpu_counter_destroy_many(nn->cb_counter, NFSD_STATS_CB_OPS_NUM);
+out_cb_counter_error:
+#endif
 	percpu_counter_destroy_many(nn->counter, NFSD_STATS_COUNTERS_NUM);
 out_repcache_error:
 	nfsd_idmap_shutdown(net);
@@ -2759,6 +2770,9 @@ static __net_exit void nfsd_net_exit(struct net *net)
 	nfsd_net_cb_shutdown(nn);
 	nfsd_proc_stat_shutdown(net);
 	svc_stat_free_counts(&nn->nfsd_svcstats);
+#ifdef CONFIG_NFSD_V4
+	percpu_counter_destroy_many(nn->cb_counter, NFSD_STATS_CB_OPS_NUM);
+#endif
 	percpu_counter_destroy_many(nn->counter, NFSD_STATS_COUNTERS_NUM);
 	nfsd_idmap_shutdown(net);
 	nfsd_export_shutdown(net);
diff --git a/fs/nfsd/stats.c b/fs/nfsd/stats.c
index f7eaf95e20fc..35d9a5571946 100644
--- a/fs/nfsd/stats.c
+++ b/fs/nfsd/stats.c
@@ -63,7 +63,7 @@ static int nfsd_show(struct seq_file *seq, void *v)
 			   percpu_counter_sum_positive(&nn->counter[NFSD_STATS_NFS4_OP(i)]));
 	}
 	seq_printf(seq, "\nwdeleg_getattr %lld",
-		percpu_counter_sum_positive(&nn->counter[NFSD_STATS_WDELEG_GETATTR]));
+		percpu_counter_sum_positive(&nn->cb_counter[OP_CB_GETATTR]));
 
 	seq_putc(seq, '\n');
 #endif
diff --git a/fs/nfsd/stats.h b/fs/nfsd/stats.h
index e4efb0e4e56d..f90cd565f7cb 100644
--- a/fs/nfsd/stats.h
+++ b/fs/nfsd/stats.h
@@ -68,9 +68,10 @@ static inline void nfsd_stats_drc_mem_usage_sub(struct nfsd_net *nn, s64 amount)
 }
 
 #ifdef CONFIG_NFSD_V4
-static inline void nfsd_stats_wdeleg_getattr_inc(struct nfsd_net *nn)
+static inline void nfsd_stats_cb_op_inc(struct nfsd_net *nn, u32 opcode)
 {
-	percpu_counter_inc(&nn->counter[NFSD_STATS_WDELEG_GETATTR]);
+	if (opcode >= OP_CB_GETATTR && opcode <= OP_CB_OFFLOAD)
+		percpu_counter_inc(&nn->cb_counter[opcode]);
 }
 #endif
 #endif /* _NFSD_STATS_H */

-- 
2.54.0