cifs: fix credits leak for SMB1 oplock breaks

For SMB1 oplock breaks we would grab one credit while sending the PDU
but we would never relese the credit back since we will never receive a
response to this from the server. Eventuallt this would lead to a hang
once all credits are leaked.

Fix this by defining a new flag CIFS_NO_SRV_RSP which indicates that there
is no server response to this command and thus we need to add any credits back
immediately after sending the PDU.

CC: Stable <stable@vger.kernel.org> #v5.0+
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/cifsglob.h

@@ -1703,6 +1703,7 @@ static inline bool is_retryable_error(int error)
 
 #define   CIFS_HAS_CREDITS 0x0400    /* already has credits */
 #define   CIFS_TRANSFORM_REQ 0x0800    /* transform request before sending */
+#define   CIFS_NO_SRV_RSP    0x1000    /* there is no server response */
 
 /* Security Flags: indicate type of session setup needed */
 #define   CIFSSEC_MAY_SIGN	0x00001

fs/cifs/cifssmb.c

@@ -2540,7 +2540,7 @@ CIFSSMBLock(const unsigned int xid, struct cifs_tcon *tcon,
 
 	if (lockType == LOCKING_ANDX_OPLOCK_RELEASE) {
 		/* no response expected */
-		flags = CIFS_ASYNC_OP | CIFS_OBREAK_OP;
+		flags = CIFS_NO_SRV_RSP | CIFS_ASYNC_OP | CIFS_OBREAK_OP;
 		pSMB->Timeout = 0;
 	} else if (waitFlag) {
 		flags = CIFS_BLOCKING_OP; /* blocking operation, no timeout */

fs/cifs/transport.c

@@ -1073,8 +1073,11 @@ compound_send_recv(const unsigned int xid, struct cifs_ses *ses,
 
 	mutex_unlock(&ses->server->srv_mutex);
 
-	if (rc < 0) {
-		/* Sending failed for some reason - return credits back */
+	/*
+	 * If sending failed for some reason or it is an oplock break that we
+	 * will not receive a response to - return credits back
+	 */
+	if (rc < 0 || (flags & CIFS_NO_SRV_RSP)) {
 		for (i = 0; i < num_rqst; i++)
 			add_credits(ses->server, &credits[i], optype);
 		goto out;
@@ -1095,9 +1098,6 @@ compound_send_recv(const unsigned int xid, struct cifs_ses *ses,
 		smb311_update_preauth_hash(ses, rqst[0].rq_iov,
 					   rqst[0].rq_nvec);
 
-	if ((flags & CIFS_TIMEOUT_MASK) == CIFS_ASYNC_OP)
-		goto out;
-
 	for (i = 0; i < num_rqst; i++) {
 		rc = wait_for_response(ses->server, midQ[i]);
 		if (rc != 0)