cifs: prevent data race in cifs_reconnect_tcon()

Make sure to get an up-to-date TCP_Server_Info::nr_targets value prior
to waiting the server to be reconnected in cifs_reconnect_tcon().  It
is set in cifs_tcp_ses_needs_reconnect() and protected by
TCP_Server_Info::srv_lock.

Create a new cifs_wait_for_server_reconnect() helper that can be used
by both SMB2+ and CIFS reconnect code.
Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/cifsproto.h

@@ -694,5 +694,6 @@ static inline int cifs_create_options(struct cifs_sb_info *cifs_sb, int options)
 
 struct super_block *cifs_get_tcon_super(struct cifs_tcon *tcon);
 void cifs_put_tcon_super(struct super_block *sb);
+int cifs_wait_for_server_reconnect(struct TCP_Server_Info *server, bool retry);
 
 #endif			/* _CIFSPROTO_H */

fs/cifs/cifssmb.c

@@ -72,7 +72,6 @@ cifs_reconnect_tcon(struct cifs_tcon *tcon, int smb_command)
 	struct cifs_ses *ses;
 	struct TCP_Server_Info *server;
 	struct nls_table *nls_codepage;
-	int retries;
 
 	/*
 	 * SMBs NegProt, SessSetup, uLogoff do not have tcon yet so check for
@@ -102,45 +101,9 @@ cifs_reconnect_tcon(struct cifs_tcon *tcon, int smb_command)
 	}
 	spin_unlock(&tcon->tc_lock);
 
-	retries = server->nr_targets;
-
-	/*
-	 * Give demultiplex thread up to 10 seconds to each target available for
-	 * reconnect -- should be greater than cifs socket timeout which is 7
-	 * seconds.
-	 */
-	while (server->tcpStatus == CifsNeedReconnect) {
-		rc = wait_event_interruptible_timeout(server->response_q,
-						      (server->tcpStatus != CifsNeedReconnect),
-						      10 * HZ);
-		if (rc < 0) {
-			cifs_dbg(FYI, "%s: aborting reconnect due to a received signal by the process\n",
-				 __func__);
-			return -ERESTARTSYS;
-		}
-
-		/* are we still trying to reconnect? */
-		spin_lock(&server->srv_lock);
-		if (server->tcpStatus != CifsNeedReconnect) {
-			spin_unlock(&server->srv_lock);
-			break;
-		}
-		spin_unlock(&server->srv_lock);
-
-		if (retries && --retries)
-			continue;
-
-		/*
-		 * on "soft" mounts we wait once. Hard mounts keep
-		 * retrying until process is killed or server comes
-		 * back on-line
-		 */
-		if (!tcon->retry) {
-			cifs_dbg(FYI, "gave up waiting on reconnect in smb_init\n");
-			return -EHOSTDOWN;
-		}
-		retries = server->nr_targets;
-	}
+	rc = cifs_wait_for_server_reconnect(server, tcon->retry);
+	if (rc)
+		return rc;
 
 	spin_lock(&ses->chan_lock);
 	if (!cifs_chan_needs_reconnect(ses, server) && !tcon->need_reconnect) {

fs/cifs/misc.c

@@ -1266,3 +1266,47 @@ int cifs_inval_name_dfs_link_error(const unsigned int xid,
 	return 0;
 }
 #endif
+
+int cifs_wait_for_server_reconnect(struct TCP_Server_Info *server, bool retry)
+{
+	int timeout = 10;
+	int rc;
+
+	spin_lock(&server->srv_lock);
+	if (server->tcpStatus != CifsNeedReconnect) {
+		spin_unlock(&server->srv_lock);
+		return 0;
+	}
+	timeout *= server->nr_targets;
+	spin_unlock(&server->srv_lock);
+
+	/*
+	 * Give demultiplex thread up to 10 seconds to each target available for
+	 * reconnect -- should be greater than cifs socket timeout which is 7
+	 * seconds.
+	 *
+	 * On "soft" mounts we wait once. Hard mounts keep retrying until
+	 * process is killed or server comes back on-line.
+	 */
+	do {
+		rc = wait_event_interruptible_timeout(server->response_q,
+						      (server->tcpStatus != CifsNeedReconnect),
+						      timeout * HZ);
+		if (rc < 0) {
+			cifs_dbg(FYI, "%s: aborting reconnect due to received signal\n",
+				 __func__);
+			return -ERESTARTSYS;
+		}
+
+		/* are we still trying to reconnect? */
+		spin_lock(&server->srv_lock);
+		if (server->tcpStatus != CifsNeedReconnect) {
+			spin_unlock(&server->srv_lock);
+			return 0;
+		}
+		spin_unlock(&server->srv_lock);
+	} while (retry);
+
+	cifs_dbg(FYI, "%s: gave up waiting on reconnect\n", __func__);
+	return -EHOSTDOWN;
+}

fs/cifs/smb2pdu.c

@@ -139,66 +139,6 @@ smb2_hdr_assemble(struct smb2_hdr *shdr, __le16 smb2_cmd,
 	return;
 }
 
-static int wait_for_server_reconnect(struct TCP_Server_Info *server,
-				     __le16 smb2_command, bool retry)
-{
-	int timeout = 10;
-	int rc;
-
-	spin_lock(&server->srv_lock);
-	if (server->tcpStatus != CifsNeedReconnect) {
-		spin_unlock(&server->srv_lock);
-		return 0;
-	}
-	timeout *= server->nr_targets;
-	spin_unlock(&server->srv_lock);
-
-	/*
-	 * Return to caller for TREE_DISCONNECT and LOGOFF and CLOSE
-	 * here since they are implicitly done when session drops.
-	 */
-	switch (smb2_command) {
-	/*
-	 * BB Should we keep oplock break and add flush to exceptions?
-	 */
-	case SMB2_TREE_DISCONNECT:
-	case SMB2_CANCEL:
-	case SMB2_CLOSE:
-	case SMB2_OPLOCK_BREAK:
-		return -EAGAIN;
-	}
-
-	/*
-	 * Give demultiplex thread up to 10 seconds to each target available for
-	 * reconnect -- should be greater than cifs socket timeout which is 7
-	 * seconds.
-	 *
-	 * On "soft" mounts we wait once. Hard mounts keep retrying until
-	 * process is killed or server comes back on-line.
-	 */
-	do {
-		rc = wait_event_interruptible_timeout(server->response_q,
-						      (server->tcpStatus != CifsNeedReconnect),
-						      timeout * HZ);
-		if (rc < 0) {
-			cifs_dbg(FYI, "%s: aborting reconnect due to received signal\n",
-				 __func__);
-			return -ERESTARTSYS;
-		}
-
-		/* are we still trying to reconnect? */
-		spin_lock(&server->srv_lock);
-		if (server->tcpStatus != CifsNeedReconnect) {
-			spin_unlock(&server->srv_lock);
-			return 0;
-		}
-		spin_unlock(&server->srv_lock);
-	} while (retry);
-
-	cifs_dbg(FYI, "%s: gave up waiting on reconnect\n", __func__);
-	return -EHOSTDOWN;
-}
-
 static int
 smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,
 	       struct TCP_Server_Info *server)
@@ -243,7 +183,27 @@ smb2_reconnect(__le16 smb2_command, struct cifs_tcon *tcon,
 	    (!tcon->ses->server) || !server)
 		return -EIO;
 
-	rc = wait_for_server_reconnect(server, smb2_command, tcon->retry);
+	spin_lock(&server->srv_lock);
+	if (server->tcpStatus == CifsNeedReconnect) {
+		/*
+		 * Return to caller for TREE_DISCONNECT and LOGOFF and CLOSE
+		 * here since they are implicitly done when session drops.
+		 */
+		switch (smb2_command) {
+		/*
+		 * BB Should we keep oplock break and add flush to exceptions?
+		 */
+		case SMB2_TREE_DISCONNECT:
+		case SMB2_CANCEL:
+		case SMB2_CLOSE:
+		case SMB2_OPLOCK_BREAK:
+			spin_unlock(&server->srv_lock);
+			return -EAGAIN;
+		}
+	}
+	spin_unlock(&server->srv_lock);
+
+	rc = cifs_wait_for_server_reconnect(server, tcon->retry);
 	if (rc)
 		return rc;