cifs: Tracepoints and logs for tracing credit changes.

There is at least one suspected bug in crediting changes in cifs.ko
which has come up a few times in the discussions and in a customer
case.

This change adds tracepoints to the code which modifies the server
credit values in any way. The goal is to be able to track the changes
to the credit values of the session to be able to catch when there is
a crediting bug.
Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/connect.c

@@ -845,6 +845,7 @@ static void
 smb2_add_credits_from_hdr(char *buffer, struct TCP_Server_Info *server)
 {
 	struct smb2_sync_hdr *shdr = (struct smb2_sync_hdr *)buffer;
+	int scredits = server->credits;
 
 	/*
 	 * SMB1 does not use credits.
@@ -857,6 +858,13 @@ smb2_add_credits_from_hdr(char *buffer, struct TCP_Server_Info *server)
 		server->credits += le16_to_cpu(shdr->CreditRequest);
 		spin_unlock(&server->req_lock);
 		wake_up(&server->request_q);
+
+		trace_smb3_add_credits(server->CurrentMid,
+				server->hostname, scredits,
+				le16_to_cpu(shdr->CreditRequest));
+		cifs_server_dbg(FYI, "%s: added %u credits total=%d\n",
+				__func__, le16_to_cpu(shdr->CreditRequest),
+				scredits);
 	}
 }
 

fs/cifs/smb2ops.c

@@ -100,9 +100,10 @@ smb2_add_credits(struct TCP_Server_Info *server,
 	spin_unlock(&server->req_lock);
 	wake_up(&server->request_q);
 
-	if (reconnect_detected)
+	if (reconnect_detected) {
 		cifs_dbg(FYI, "trying to put %d credits from the old server instance %d\n",
 			 add, instance);
+	}
 
 	if (server->tcpStatus == CifsNeedReconnect
 	    || server->tcpStatus == CifsExiting)
@@ -124,7 +125,7 @@ smb2_add_credits(struct TCP_Server_Info *server,
 	default:
 		trace_smb3_add_credits(server->CurrentMid,
 			server->hostname, rc, add);
-		cifs_dbg(FYI, "add %u credits total=%d\n", add, rc);
+		cifs_dbg(FYI, "%s: added %u credits total=%d\n", __func__, add, rc);
 	}
 }
 
@@ -136,6 +137,11 @@ smb2_set_credits(struct TCP_Server_Info *server, const int val)
 	if (val == 1)
 		server->reconnect_instance++;
 	spin_unlock(&server->req_lock);
+
+	trace_smb3_set_credits(server->CurrentMid,
+			server->hostname, val, val);
+	cifs_dbg(FYI, "%s: set %u credits\n", __func__, val);
+
 	/* don't log while holding the lock */
 	if (val == 1)
 		cifs_dbg(FYI, "set credits to 1 due to smb2 reconnect\n");
@@ -202,6 +208,7 @@ smb2_wait_mtu_credits(struct TCP_Server_Info *server, unsigned int size,
 				DIV_ROUND_UP(*num, SMB2_MAX_BUFFER_SIZE);
 			credits->instance = server->reconnect_instance;
 			server->credits -= credits->value;
+			scredits = server->credits;
 			server->in_flight++;
 			if (server->in_flight > server->max_in_flight)
 				server->max_in_flight = server->in_flight;
@@ -209,6 +216,12 @@ smb2_wait_mtu_credits(struct TCP_Server_Info *server, unsigned int size,
 		}
 	}
 	spin_unlock(&server->req_lock);
+
+	trace_smb3_add_credits(server->CurrentMid,
+			server->hostname, scredits, -(credits->value));
+	cifs_dbg(FYI, "%s: removed %u credits total=%d\n",
+			__func__, credits->value, scredits);
+
 	return rc;
 }
 
@@ -218,13 +231,17 @@ smb2_adjust_credits(struct TCP_Server_Info *server,
 		    const unsigned int payload_size)
 {
 	int new_val = DIV_ROUND_UP(payload_size, SMB2_MAX_BUFFER_SIZE);
+	int scredits;
 
 	if (!credits->value || credits->value == new_val)
 		return 0;
 
 	if (credits->value < new_val) {
-		WARN_ONCE(1, "request has less credits (%d) than required (%d)",
-			  credits->value, new_val);
+		trace_smb3_too_many_credits(server->CurrentMid,
+				server->hostname, 0, credits->value - new_val);
+		cifs_server_dbg(VFS, "request has less credits (%d) than required (%d)",
+				credits->value, new_val);
+
 		return -ENOTSUPP;
 	}
 
@@ -232,15 +249,24 @@ smb2_adjust_credits(struct TCP_Server_Info *server,
 
 	if (server->reconnect_instance != credits->instance) {
 		spin_unlock(&server->req_lock);
+		trace_smb3_reconnect_detected(server->CurrentMid,
+			server->hostname, 0, 0);
 		cifs_server_dbg(VFS, "trying to return %d credits to old session\n",
 			 credits->value - new_val);
 		return -EAGAIN;
 	}
 
 	server->credits += credits->value - new_val;
+	scredits = server->credits;
 	spin_unlock(&server->req_lock);
 	wake_up(&server->request_q);
 	credits->value = new_val;
+
+	trace_smb3_add_credits(server->CurrentMid,
+			server->hostname, scredits, credits->value - new_val);
+	cifs_dbg(FYI, "%s: adjust added %u credits total=%d\n",
+			__func__, credits->value - new_val, scredits);
+
 	return 0;
 }
 
@@ -2343,6 +2369,7 @@ static bool
 smb2_is_status_pending(char *buf, struct TCP_Server_Info *server)
 {
 	struct smb2_sync_hdr *shdr = (struct smb2_sync_hdr *)buf;
+	int scredits;
 
 	if (shdr->Status != STATUS_PENDING)
 		return false;
@@ -2350,8 +2377,14 @@ smb2_is_status_pending(char *buf, struct TCP_Server_Info *server)
 	if (shdr->CreditRequest) {
 		spin_lock(&server->req_lock);
 		server->credits += le16_to_cpu(shdr->CreditRequest);
+		scredits = server->credits;
 		spin_unlock(&server->req_lock);
 		wake_up(&server->request_q);
+
+		trace_smb3_add_credits(server->CurrentMid,
+				server->hostname, scredits, le16_to_cpu(shdr->CreditRequest));
+		cifs_dbg(FYI, "%s: status pending add %u credits total=%d\n",
+				__func__, le16_to_cpu(shdr->CreditRequest), scredits);
 	}
 
 	return true;

fs/cifs/trace.h

@@ -909,8 +909,12 @@ DEFINE_EVENT(smb3_credit_class, smb3_##name,  \
 	TP_ARGS(currmid, hostname, credits, credits_to_add))
 
 DEFINE_SMB3_CREDIT_EVENT(reconnect_with_invalid_credits);
+DEFINE_SMB3_CREDIT_EVENT(reconnect_detected);
 DEFINE_SMB3_CREDIT_EVENT(credit_timeout);
+DEFINE_SMB3_CREDIT_EVENT(insufficient_credits);
+DEFINE_SMB3_CREDIT_EVENT(too_many_credits);
 DEFINE_SMB3_CREDIT_EVENT(add_credits);
+DEFINE_SMB3_CREDIT_EVENT(set_credits);
 
 #endif /* _CIFS_TRACE_H */
 

fs/cifs/transport.c

@@ -527,6 +527,7 @@ wait_for_free_credits(struct TCP_Server_Info *server, const int num_credits,
 	int *credits;
 	int optype;
 	long int t;
+	int scredits = server->credits;
 
 	if (timeout < 0)
 		t = MAX_JIFFY_OFFSET;
@@ -624,12 +625,18 @@ wait_for_free_credits(struct TCP_Server_Info *server, const int num_credits,
 			/* update # of requests on the wire to server */
 			if ((flags & CIFS_TIMEOUT_MASK) != CIFS_BLOCKING_OP) {
 				*credits -= num_credits;
+				scredits = *credits;
 				server->in_flight += num_credits;
 				if (server->in_flight > server->max_in_flight)
 					server->max_in_flight = server->in_flight;
 				*instance = server->reconnect_instance;
 			}
 			spin_unlock(&server->req_lock);
+
+			trace_smb3_add_credits(server->CurrentMid,
+					server->hostname, scredits, -(num_credits));
+			cifs_dbg(FYI, "%s: remove %u credits total=%d\n",
+					__func__, num_credits, scredits);
 			break;
 		}
 	}
@@ -649,10 +656,14 @@ wait_for_compound_request(struct TCP_Server_Info *server, int num,
 			  const int flags, unsigned int *instance)
 {
 	int *credits;
+	int scredits, sin_flight;
 
 	credits = server->ops->get_credits_field(server, flags & CIFS_OP_MASK);
 
 	spin_lock(&server->req_lock);
+	scredits = *credits;
+	sin_flight = server->in_flight;
+
 	if (*credits < num) {
 		/*
 		 * Return immediately if not too many requests in flight since
@@ -660,6 +671,10 @@ wait_for_compound_request(struct TCP_Server_Info *server, int num,
 		 */
 		if (server->in_flight < num - *credits) {
 			spin_unlock(&server->req_lock);
+			trace_smb3_insufficient_credits(server->CurrentMid,
+					server->hostname, scredits, sin_flight);
+			cifs_dbg(FYI, "%s: %d requests in flight, needed %d total=%d\n",
+					__func__, sin_flight, num, scredits);
 			return -ENOTSUPP;
 		}
 	}