[CIFS] fix for incorrect session reconnects

cifs reconnect could end up happening incorrectly due to
the small initial tcp recvmsg response. When the socket
was within three bytes of being full and the recvmsg
returned only 1 to 3 bytes of the initial 4 byte
read of the RFC1001 length field. Fortunately this
seems to be less common on more current kernels, but
this fixes it so cifs tries to retrieve all 4 bytes
of the initial tcp read.
Signed-off-by: NShirish Pargoankar <shirishp@us.ibm.com>
Signed-off-by: NSteve French <sfrench@us.ibm.com>

fs/cifs/connect.c

@@ -400,9 +400,11 @@ cifs_demultiplex_thread(struct TCP_Server_Info *server)
 		iov.iov_len = 4;
 		smb_msg.msg_control = NULL;
 		smb_msg.msg_controllen = 0;
+		pdu_length = 4; /* enough to get RFC1001 header */
+incomplete_rcv:
 		length =
 		    kernel_recvmsg(csocket, &smb_msg,
-				 &iov, 1, 4, 0 /* BB see socket.h flags */);
+				&iov, 1, pdu_length, 0 /* BB other flags? */);
 
 		if ( kthread_should_stop() ) {
 			break;
@@ -437,13 +439,12 @@ cifs_demultiplex_thread(struct TCP_Server_Info *server)
 			wake_up(&server->response_q);
 			continue;
 		} else if (length < 4) {
-			cFYI(1,
-			    ("Frame under four bytes received (%d bytes long)",
+			cFYI(1, ("less than four bytes received (%d bytes)",
 			      length));
+			pdu_length -= length;
 			cifs_reconnect(server);
-			csocket = server->ssocket;
-			wake_up(&server->response_q);
-			continue;
+			msleep(1);
+			goto incomplete_rcv;
 		}
 
 		/* The right amount was read from socket - 4 bytes */