cifs: fix max_credits implementation

The current implementation of max_credits on the client does
not work because the CreditRequest logic for several commands
does not take max_credits into account.

Still, we can end up asking the server for more credits, depending
on the number of credits in flight. For this, we need to
limit the credits while parsing the responses too.

Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: sprasad-microsoft

fs/smb/client/smb2ops.c

@@ -34,6 +34,8 @@ static int
 change_conf(struct TCP_Server_Info *server)
 {
 	server->credits += server->echo_credits + server->oplock_credits;
+	if (server->credits > server->max_credits)
+		server->credits = server->max_credits;
 	server->oplock_credits = server->echo_credits = 0;
 	switch (server->credits) {
 	case 0:

fs/smb/client/smb2pdu.c

@@ -1305,7 +1305,12 @@ SMB2_sess_alloc_buffer(struct SMB2_sess_data *sess_data)
 	}
 
 	/* enough to enable echos and oplocks and one max size write */
-	req->hdr.CreditRequest = cpu_to_le16(130);
+	if (server->credits >= server->max_credits)
+		req->hdr.CreditRequest = cpu_to_le16(0);
+	else
+		req->hdr.CreditRequest = cpu_to_le16(
+			min_t(int, server->max_credits -
+			      server->credits, 130));
 
 	/* only one of SMB2 signing flags may be set in SMB2 request */
 	if (server->sign)
@@ -1899,7 +1904,12 @@ SMB2_tcon(const unsigned int xid, struct cifs_ses *ses, const char *tree,
 	rqst.rq_nvec = 2;
 
 	/* Need 64 for max size write so ask for more in case not there yet */
-	req->hdr.CreditRequest = cpu_to_le16(64);
+	if (server->credits >= server->max_credits)
+		req->hdr.CreditRequest = cpu_to_le16(0);
+	else
+		req->hdr.CreditRequest = cpu_to_le16(
+			min_t(int, server->max_credits -
+			      server->credits, 64));
 
 	rc = cifs_send_recv(xid, ses, server,
 			    &rqst, &resp_buftype, flags, &rsp_iov);
@@ -4227,6 +4237,7 @@ smb2_async_readv(struct cifs_readdata *rdata)
 	struct TCP_Server_Info *server;
 	struct cifs_tcon *tcon = tlink_tcon(rdata->cfile->tlink);
 	unsigned int total_len;
+	int credit_request;
 
 	cifs_dbg(FYI, "%s: offset=%llu bytes=%u\n",
 		 __func__, rdata->offset, rdata->bytes);
@@ -4258,7 +4269,13 @@ smb2_async_readv(struct cifs_readdata *rdata)
 	if (rdata->credits.value > 0) {
 		shdr->CreditCharge = cpu_to_le16(DIV_ROUND_UP(rdata->bytes,
 						SMB2_MAX_BUFFER_SIZE));
-		shdr->CreditRequest = cpu_to_le16(le16_to_cpu(shdr->CreditCharge) + 8);
+		credit_request = le16_to_cpu(shdr->CreditCharge) + 8;
+		if (server->credits >= server->max_credits)
+			shdr->CreditRequest = cpu_to_le16(0);
+		else
+			shdr->CreditRequest = cpu_to_le16(
+				min_t(int, server->max_credits -
+						server->credits, credit_request));
 
 		rc = adjust_credits(server, &rdata->credits, rdata->bytes);
 		if (rc)
@@ -4468,6 +4485,7 @@ smb2_async_writev(struct cifs_writedata *wdata,
 	unsigned int total_len;
 	struct cifs_io_parms _io_parms;
 	struct cifs_io_parms *io_parms = NULL;
+	int credit_request;
 
 	if (!wdata->server)
 		server = wdata->server = cifs_pick_channel(tcon->ses);
@@ -4572,7 +4590,13 @@ smb2_async_writev(struct cifs_writedata *wdata,
 	if (wdata->credits.value > 0) {
 		shdr->CreditCharge = cpu_to_le16(DIV_ROUND_UP(wdata->bytes,
 						    SMB2_MAX_BUFFER_SIZE));
-		shdr->CreditRequest = cpu_to_le16(le16_to_cpu(shdr->CreditCharge) + 8);
+		credit_request = le16_to_cpu(shdr->CreditCharge) + 8;
+		if (server->credits >= server->max_credits)
+			shdr->CreditRequest = cpu_to_le16(0);
+		else
+			shdr->CreditRequest = cpu_to_le16(
+				min_t(int, server->max_credits -
+						server->credits, credit_request));
 
 		rc = adjust_credits(server, &wdata->credits, io_parms->length);
 		if (rc)