cifs: make locking consistent around the server session status

There were three places where we were not taking the spinlock
around updates to server->tcpStatus when it was being modified.
To be consistent (also removes Coverity warning) and to remove
possibility of race best to lock all places where it is updated.
Two of the three were in initialization of the field and can't
race - but added lock around the other.

Addresses-Coverity: 1399512 ("Data race condition")
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: smfrench

fs/cifs/cifsglob.h

@@ -577,6 +577,7 @@ struct TCP_Server_Info {
 	char server_RFC1001_name[RFC1001_NAME_LEN_WITH_NULL];
 	struct smb_version_operations	*ops;
 	struct smb_version_values	*vals;
+	/* updates to tcpStatus protected by GlobalMid_Lock */
 	enum statusEnum tcpStatus; /* what we think the status is */
 	char *hostname; /* hostname portion of UNC string */
 	struct socket *ssocket;
@@ -1785,7 +1786,7 @@ require use of the stronger protocol */
  *	list operations on pending_mid_q and oplockQ
  *      updates to XID counters, multiplex id  and SMB sequence numbers
  *      list operations on global DnotifyReqList
- *      updates to ses->status
+ *      updates to ses->status and TCP_Server_Info->tcpStatus
  *      updates to server->CurrentMid
  *  tcp_ses_lock protects:
  *	list operations on tcp and SMB session lists

fs/cifs/connect.c

@@ -1403,6 +1403,11 @@ cifs_get_tcp_session(struct smb3_fs_context *ctx)
 		goto out_err_crypto_release;
 	}
 	tcp_ses->min_offload = ctx->min_offload;
+	/*
+	 * at this point we are the only ones with the pointer
+	 * to the struct since the kernel thread not created yet
+	 * no need to spinlock this update of tcpStatus
+	 */
 	tcp_ses->tcpStatus = CifsNeedNegotiate;
 
 	if ((ctx->max_credits < 20) || (ctx->max_credits > 60000))

fs/cifs/transport.c

@@ -431,7 +431,9 @@ __smb_send_rqst(struct TCP_Server_Info *server, int num_rqst,
 		 * be taken as the remainder of this one. We need to kill the
 		 * socket so the server throws away the partial SMB
 		 */
+		spin_lock(&GlobalMid_Lock);
 		server->tcpStatus = CifsNeedReconnect;
+		spin_unlock(&GlobalMid_Lock);
 		trace_smb3_partial_send_reconnect(server->CurrentMid,
 						  server->conn_id, server->hostname);
 	}