[PATCH v2 15/19] NFS4: Add a trace event to record invalid CB sequence IDs

[Chuck Lever <chuck.lever@xxxxxxxxxx>]

Help debug NFSv4 callback failures.

Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
 fs/nfs/callback_proc.c |   28 ++++++++++++++++++++--------
 fs/nfs/nfs4trace.h     |   38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+), 8 deletions(-)

diff --git a/fs/nfs/callback_proc.c b/fs/nfs/callback_proc.c
index 3159673..f39924b 100644
--- a/fs/nfs/callback_proc.c
+++ b/fs/nfs/callback_proc.c
@@ -414,27 +414,39 @@ __be32 nfs4_callback_devicenotify(void *argp, void *resp,
 validate_seqid(const struct nfs4_slot_table *tbl, const struct nfs4_slot *slot,
 		const struct cb_sequenceargs * args)
 {
+	__be32 ret;
+
+	ret = cpu_to_be32(NFS4ERR_BADSLOT);
 	if (args->csa_slotid > tbl->server_highest_slotid)
-		return htonl(NFS4ERR_BADSLOT);
+		goto out_err;
 
 	/* Replay */
 	if (args->csa_sequenceid == slot->seq_nr) {
+		ret = cpu_to_be32(NFS4ERR_DELAY);
 		if (nfs4_test_locked_slot(tbl, slot->slot_nr))
-			return htonl(NFS4ERR_DELAY);
+			goto out_err;
+
 		/* Signal process_op to set this error on next op */
+		ret = cpu_to_be32(NFS4ERR_RETRY_UNCACHED_REP);
 		if (args->csa_cachethis == 0)
-			return htonl(NFS4ERR_RETRY_UNCACHED_REP);
+			goto out_err;
 
 		/* Liar! We never allowed you to set csa_cachethis != 0 */
-		return htonl(NFS4ERR_SEQ_FALSE_RETRY);
+		ret = cpu_to_be32(NFS4ERR_SEQ_FALSE_RETRY);
+		goto out_err;
 	}
 
 	/* Note: wraparound relies on seq_nr being of type u32 */
-	if (likely(args->csa_sequenceid == slot->seq_nr + 1))
-		return htonl(NFS4_OK);
-
 	/* Misordered request */
-	return htonl(NFS4ERR_SEQ_MISORDERED);
+	ret = cpu_to_be32(NFS4ERR_SEQ_MISORDERED);
+	if (args->csa_sequenceid != slot->seq_nr + 1)
+		goto out_err;
+
+	return cpu_to_be32(NFS4_OK);
+
+out_err:
+	trace_nfs4_cb_seqid_err(args, ret);
+	return ret;
 }
 
 /*
diff --git a/fs/nfs/nfs4trace.h b/fs/nfs/nfs4trace.h
index cd1a5c0..6beb1f2 100644
--- a/fs/nfs/nfs4trace.h
+++ b/fs/nfs/nfs4trace.h
@@ -490,6 +490,44 @@
 			__entry->highest_slotid
 		)
 );
+
+TRACE_EVENT(nfs4_cb_seqid_err,
+		TP_PROTO(
+			const struct cb_sequenceargs *args,
+			__be32 status
+		),
+		TP_ARGS(args, status),
+
+		TP_STRUCT__entry(
+			__field(unsigned int, session)
+			__field(unsigned int, slot_nr)
+			__field(unsigned int, seq_nr)
+			__field(unsigned int, highest_slotid)
+			__field(unsigned int, cachethis)
+			__field(int, error)
+		),
+
+		TP_fast_assign(
+			__entry->session = nfs_session_id_hash(&args->csa_sessionid);
+			__entry->slot_nr = args->csa_slotid;
+			__entry->seq_nr = args->csa_sequenceid;
+			__entry->highest_slotid = args->csa_highestslotid;
+			__entry->cachethis = args->csa_cachethis;
+			__entry->error = -be32_to_cpu(status);
+		),
+
+		TP_printk(
+			"error=%d (%s) session=0x%08x slot_nr=%u seq_nr=%u "
+			"highest_slotid=%u",
+			__entry->error,
+			show_nfsv4_errors(__entry->error),
+			__entry->session,
+			__entry->slot_nr,
+			__entry->seq_nr,
+			__entry->highest_slotid
+		)
+);
+
 #endif /* CONFIG_NFS_V4_1 */
 
 TRACE_EVENT(nfs4_setup_sequence,