smb3: add tracepoint to catch cases where credit refund of failed op overlaps reconnect

Add tracepoint to catch potential cases where a pending operation overlapping a
reconnect could fail and incorrectly refund its credits causing the client
to think it has more credits available than the server thinks it does.
Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>

fs/cifs/smb2ops.c

@@ -74,6 +74,12 @@ smb2_add_credits(struct TCP_Server_Info *server, const unsigned int add,
 	int *val, rc = 0;
 	spin_lock(&server->req_lock);
 	val = server->ops->get_credits_field(server, optype);
+
+	/* eg found case where write overlapping reconnect messed up credits */
+	if (((optype & CIFS_OP_MASK) == CIFS_NEG_OP) && (*val != 0))
+		trace_smb3_reconnect_with_invalid_credits(server->CurrentMid,
+			server->hostname, *val);
+
 	*val += add;
 	if (*val > 65000) {
 		*val = 65000; /* Don't get near 64K credits, avoid srv bugs */

fs/cifs/trace.h

@@ -486,6 +486,36 @@ DEFINE_EVENT(smb3_reconnect_class, smb3_##name,  \
 DEFINE_SMB3_RECONNECT_EVENT(reconnect);
 DEFINE_SMB3_RECONNECT_EVENT(partial_send_reconnect);
 
+DECLARE_EVENT_CLASS(smb3_credit_class,
+	TP_PROTO(__u64	currmid,
+		char *hostname,
+		int credits),
+	TP_ARGS(currmid, hostname, credits),
+	TP_STRUCT__entry(
+		__field(__u64, currmid)
+		__field(char *, hostname)
+		__field(int, credits)
+	),
+	TP_fast_assign(
+		__entry->currmid = currmid;
+		__entry->hostname = hostname;
+		__entry->credits = credits;
+	),
+	TP_printk("server=%s current_mid=0x%llx credits=%d",
+		__entry->hostname,
+		__entry->currmid,
+		__entry->credits)
+)
+
+#define DEFINE_SMB3_CREDIT_EVENT(name)        \
+DEFINE_EVENT(smb3_credit_class, smb3_##name,  \
+	TP_PROTO(__u64	currmid,		\
+		char *hostname,			\
+		int  credits),			\
+	TP_ARGS(currmid, hostname, credits))
+
+DEFINE_SMB3_CREDIT_EVENT(reconnect_with_invalid_credits);
+
 #endif /* _CIFS_TRACE_H */
 
 #undef TRACE_INCLUDE_PATH