[PATCH v7 5/6] nfsd: count NFSv4 callback operations per netns

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: LLM
Signed-off-by: Jeff Layton <[email protected]>
---
 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 a7bd7b67fa4f..71eebfea020d 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
@@ -200,6 +205,11 @@ 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..a901bbe67e03 100644
--- a/fs/nfsd/nfs4callback.c
+++ b/fs/nfsd/nfs4callback.c
@@ -39,6 +39,7 @@
 #include "nfsd.h"
 #include "state.h"
 #include "netns.h"
+#include "stats.h"
 #include "trace.h"
 #include "xdr4cb.h"
 #include "xdr4.h"
@@ -1921,12 +1922,31 @@ 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;
 
 	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.  CB_NULL probes (ops == NULL) carry
+			 * no CB_SEQUENCE -- and on 4.1+ they are dropped without
+			 * sending any RPC (see nfsd4_run_cb_work()) -- so they
+			 * must not be counted here.
+			 */
+			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 19810419f457..18e17232cf94 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -10122,7 +10122,6 @@ __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;
@@ -10162,7 +10161,6 @@ 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 7731051105c9..93e18426039d 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -2736,6 +2736,13 @@ 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);
@@ -2764,6 +2771,10 @@ 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);
@@ -2804,6 +2815,9 @@ 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 9a03e097cfe5..f16559813292 100644
--- a/fs/nfsd/stats.c
+++ b/fs/nfsd/stats.c
@@ -65,7 +65,7 @@ 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 87736b7fbf28..70eaf5f20bda 100644
--- a/fs/nfsd/stats.h
+++ b/fs/nfsd/stats.h
@@ -71,9 +71,10 @@ 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 */

-- 
2.55.0