nfsd: add tracepoint in mark_client_expired_locked

Show client info alongside the number of cl_rpc_users. If that's
elevated, then we can infer that this function returned nfserr_jukebox.

[ cel: For additional debugging of RPC user refcounting ]
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Tested-by: Vladimir Benes <vbenes@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4state.c

@@ -2347,7 +2347,11 @@ unhash_client(struct nfs4_client *clp)
 
 static __be32 mark_client_expired_locked(struct nfs4_client *clp)
 {
-	if (atomic_read(&clp->cl_rpc_users))
+	int users = atomic_read(&clp->cl_rpc_users);
+
+	trace_nfsd_mark_client_expired(clp, users);
+
+	if (users)
 		return nfserr_jukebox;
 	unhash_client_locked(clp);
 	return nfs_ok;

fs/nfsd/trace.h

@@ -848,6 +848,30 @@ DEFINE_CLIENTID_EVENT(purged);
 DEFINE_CLIENTID_EVENT(renew);
 DEFINE_CLIENTID_EVENT(stale);
 
+TRACE_EVENT(nfsd_mark_client_expired,
+	TP_PROTO(
+		const struct nfs4_client *clp,
+		int cl_rpc_users
+	),
+	TP_ARGS(clp, cl_rpc_users),
+	TP_STRUCT__entry(
+		__field(int, cl_rpc_users)
+		__field(u32, cl_boot)
+		__field(u32, cl_id)
+		__sockaddr(addr, clp->cl_cb_conn.cb_addrlen)
+	),
+	TP_fast_assign(
+		__entry->cl_rpc_users = cl_rpc_users;
+		__entry->cl_boot = clp->cl_clientid.cl_boot;
+		__entry->cl_id = clp->cl_clientid.cl_id;
+		__assign_sockaddr(addr, &clp->cl_cb_conn.cb_addr,
+				  clp->cl_cb_conn.cb_addrlen)
+	),
+	TP_printk("addr=%pISpc client %08x:%08x cl_rpc_users=%d",
+		__get_sockaddr(addr), __entry->cl_boot, __entry->cl_id,
+		__entry->cl_rpc_users)
+);
+
 DECLARE_EVENT_CLASS(nfsd_net_class,
 	TP_PROTO(const struct nfsd_net *nn),
 	TP_ARGS(nn),