cifs: handle cases where a channel is closed

So far, SMB multichannel could only scale up, but not
scale down the number of channels. In this series of
patch, we now allow the client to deal with the case
of multichannel disabled on the server when the share
is mounted. With that change, we now need the ability
to scale down the channels.

This change allows the client to deal with cases of
missing channels more gracefully.

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

fs/smb/client/cifs_debug.c

@@ -136,6 +136,11 @@ cifs_dump_channel(struct seq_file *m, int i, struct cifs_chan *chan)
 {
 	struct TCP_Server_Info *server = chan->server;
 
+	if (!server) {
+		seq_printf(m, "\n\n\t\tChannel: %d DISABLED", i+1);
+		return;
+	}
+
 	seq_printf(m, "\n\n\t\tChannel: %d ConnectionId: 0x%llx"
 		   "\n\t\tNumber of credits: %d,%d,%d Dialect 0x%x"
 		   "\n\t\tTCP status: %d Instance: %d"

fs/smb/client/cifsglob.h

@@ -1050,6 +1050,7 @@ struct cifs_ses {
 	spinlock_t chan_lock;
 	/* ========= begin: protected by chan_lock ======== */
 #define CIFS_MAX_CHANNELS 16
+#define CIFS_INVAL_CHAN_INDEX (-1)
 #define CIFS_ALL_CHANNELS_SET(ses)	\
 	((1UL << (ses)->chan_count) - 1)
 #define CIFS_ALL_CHANS_GOOD(ses)		\

fs/smb/client/cifsproto.h

@@ -616,7 +616,7 @@ bool is_server_using_iface(struct TCP_Server_Info *server,
 bool is_ses_using_iface(struct cifs_ses *ses, struct cifs_server_iface *iface);
 void cifs_ses_mark_for_reconnect(struct cifs_ses *ses);
 
-unsigned int
+int
 cifs_ses_get_chan_index(struct cifs_ses *ses,
 			struct TCP_Server_Info *server);
 void

fs/smb/client/connect.c

@@ -173,8 +173,12 @@ cifs_signal_cifsd_for_reconnect(struct TCP_Server_Info *server,
 	list_for_each_entry(ses, &pserver->smb_ses_list, smb_ses_list) {
 		spin_lock(&ses->chan_lock);
 		for (i = 0; i < ses->chan_count; i++) {
+			if (!ses->chans[i].server)
+				continue;
+
 			spin_lock(&ses->chans[i].server->srv_lock);
-			ses->chans[i].server->tcpStatus = CifsNeedReconnect;
+			if (ses->chans[i].server->tcpStatus != CifsExiting)
+				ses->chans[i].server->tcpStatus = CifsNeedReconnect;
 			spin_unlock(&ses->chans[i].server->srv_lock);
 		}
 		spin_unlock(&ses->chan_lock);

fs/smb/client/sess.c

@@ -69,7 +69,7 @@ bool is_ses_using_iface(struct cifs_ses *ses, struct cifs_server_iface *iface)
 
 /* channel helper functions. assumed that chan_lock is held by caller. */
 
-unsigned int
+int
 cifs_ses_get_chan_index(struct cifs_ses *ses,
 			struct TCP_Server_Info *server)
 {
@@ -85,14 +85,17 @@ cifs_ses_get_chan_index(struct cifs_ses *ses,
 		cifs_dbg(VFS, "unable to get chan index for server: 0x%llx",
 			 server->conn_id);
 	WARN_ON(1);
-	return 0;
+	return CIFS_INVAL_CHAN_INDEX;
 }
 
 void
 cifs_chan_set_in_reconnect(struct cifs_ses *ses,
 			     struct TCP_Server_Info *server)
 {
-	unsigned int chan_index = cifs_ses_get_chan_index(ses, server);
+	int chan_index = cifs_ses_get_chan_index(ses, server);
+
+	if (chan_index == CIFS_INVAL_CHAN_INDEX)
+		return;
 
 	ses->chans[chan_index].in_reconnect = true;
 }
@@ -102,6 +105,8 @@ cifs_chan_clear_in_reconnect(struct cifs_ses *ses,
 			     struct TCP_Server_Info *server)
 {
 	unsigned int chan_index = cifs_ses_get_chan_index(ses, server);
+	if (chan_index == CIFS_INVAL_CHAN_INDEX)
+		return;
 
 	ses->chans[chan_index].in_reconnect = false;
 }
@@ -111,6 +116,8 @@ cifs_chan_in_reconnect(struct cifs_ses *ses,
 			  struct TCP_Server_Info *server)
 {
 	unsigned int chan_index = cifs_ses_get_chan_index(ses, server);
+	if (chan_index == CIFS_INVAL_CHAN_INDEX)
+		return true;	/* err on the safer side */
 
 	return CIFS_CHAN_IN_RECONNECT(ses, chan_index);
 }
@@ -120,6 +127,8 @@ cifs_chan_set_need_reconnect(struct cifs_ses *ses,
 			     struct TCP_Server_Info *server)
 {
 	unsigned int chan_index = cifs_ses_get_chan_index(ses, server);
+	if (chan_index == CIFS_INVAL_CHAN_INDEX)
+		return;
 
 	set_bit(chan_index, &ses->chans_need_reconnect);
 	cifs_dbg(FYI, "Set reconnect bitmask for chan %u; now 0x%lx\n",
@@ -131,6 +140,8 @@ cifs_chan_clear_need_reconnect(struct cifs_ses *ses,
 			       struct TCP_Server_Info *server)
 {
 	unsigned int chan_index = cifs_ses_get_chan_index(ses, server);
+	if (chan_index == CIFS_INVAL_CHAN_INDEX)
+		return;
 
 	clear_bit(chan_index, &ses->chans_need_reconnect);
 	cifs_dbg(FYI, "Cleared reconnect bitmask for chan %u; now 0x%lx\n",
@@ -142,6 +153,8 @@ cifs_chan_needs_reconnect(struct cifs_ses *ses,
 			  struct TCP_Server_Info *server)
 {
 	unsigned int chan_index = cifs_ses_get_chan_index(ses, server);
+	if (chan_index == CIFS_INVAL_CHAN_INDEX)
+		return true;	/* err on the safer side */
 
 	return CIFS_CHAN_NEEDS_RECONNECT(ses, chan_index);
 }
@@ -151,6 +164,8 @@ cifs_chan_is_iface_active(struct cifs_ses *ses,
 			  struct TCP_Server_Info *server)
 {
 	unsigned int chan_index = cifs_ses_get_chan_index(ses, server);
+	if (chan_index == CIFS_INVAL_CHAN_INDEX)
+		return true;	/* err on the safer side */
 
 	return ses->chans[chan_index].iface &&
 		ses->chans[chan_index].iface->is_active;
@@ -269,7 +284,7 @@ cifs_chan_update_iface(struct cifs_ses *ses, struct TCP_Server_Info *server)
 
 	spin_lock(&ses->chan_lock);
 	chan_index = cifs_ses_get_chan_index(ses, server);
-	if (!chan_index) {
+	if (chan_index == CIFS_INVAL_CHAN_INDEX) {
 		spin_unlock(&ses->chan_lock);
 		return 0;
 	}
@@ -319,6 +334,11 @@ cifs_chan_update_iface(struct cifs_ses *ses, struct TCP_Server_Info *server)
 
 	spin_lock(&ses->chan_lock);
 	chan_index = cifs_ses_get_chan_index(ses, server);
+	if (chan_index == CIFS_INVAL_CHAN_INDEX) {
+		spin_unlock(&ses->chan_lock);
+		return 0;
+	}
+
 	ses->chans[chan_index].iface = iface;
 
 	/* No iface is found. if secondary chan, drop connection */

fs/smb/client/smb2transport.c

@@ -413,7 +413,13 @@ generate_smb3signingkey(struct cifs_ses *ses,
 		      ses->ses_status == SES_GOOD);
 
 	chan_index = cifs_ses_get_chan_index(ses, server);
-	/* TODO: introduce ref counting for channels when the can be freed */
+	if (chan_index == CIFS_INVAL_CHAN_INDEX) {
+		spin_unlock(&ses->chan_lock);
+		spin_unlock(&ses->ses_lock);
+
+		return -EINVAL;
+	}
+
 	spin_unlock(&ses->chan_lock);
 	spin_unlock(&ses->ses_lock);