cifs: do not let cifs_chan_update_iface deallocate channels

cifs_chan_update_iface is meant to check and update the server
interface used for a channel when the existing server interface
is no longer available.

So far, this handler had the code to remove an interface entry
even if a new candidate interface is not available. Allowing
this leads to several corner cases to handle.

This change makes the logic much simpler by not deallocating
the current channel interface entry if a new interface is not
found to replace it with.

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

Author: sprasad-microsoft

fs/smb/client/sess.c

@@ -439,15 +439,15 @@ cifs_chan_update_iface(struct cifs_ses *ses, struct TCP_Server_Info *server)
 		cifs_dbg(FYI, "unable to find a suitable iface\n");
 	}
 
-	if (!chan_index && !iface) {
+	if (!iface) {
 		cifs_dbg(FYI, "unable to get the interface matching: %pIS\n",
 			 &ss);
 		spin_unlock(&ses->iface_lock);
 		return 0;
 	}
 
 	/* now drop the ref to the current iface */
-	if (old_iface && iface) {
+	if (old_iface) {
 		cifs_dbg(FYI, "replacing iface: %pIS with %pIS\n",
 			 &old_iface->sockaddr,
 			 &iface->sockaddr);
@@ -460,44 +460,32 @@ cifs_chan_update_iface(struct cifs_ses *ses, struct TCP_Server_Info *server)
 
 		kref_put(&old_iface->refcount, release_iface);
 	} else if (old_iface) {
-		cifs_dbg(FYI, "releasing ref to iface: %pIS\n",
+		/* if a new candidate is not found, keep things as is */
+		cifs_dbg(FYI, "could not replace iface: %pIS\n",
 			 &old_iface->sockaddr);
-
-		old_iface->num_channels--;
-		if (old_iface->weight_fulfilled)
-			old_iface->weight_fulfilled--;
-
-		kref_put(&old_iface->refcount, release_iface);
 	} else if (!chan_index) {
 		/* special case: update interface for primary channel */
-		cifs_dbg(FYI, "referencing primary channel iface: %pIS\n",
-			 &iface->sockaddr);
-		iface->num_channels++;
-		iface->weight_fulfilled++;
-	} else {
-		WARN_ON(!iface);
-		cifs_dbg(FYI, "adding new iface: %pIS\n", &iface->sockaddr);
+		if (iface) {
+			cifs_dbg(FYI, "referencing primary channel iface: %pIS\n",
+				 &iface->sockaddr);
+			iface->num_channels++;
+			iface->weight_fulfilled++;
+		}
 	}
 	spin_unlock(&ses->iface_lock);
 
-	spin_lock(&ses->chan_lock);
-	chan_index = cifs_ses_get_chan_index(ses, server);
-	if (chan_index == CIFS_INVAL_CHAN_INDEX) {
+	if (iface) {
+		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;
 		spin_unlock(&ses->chan_lock);
-		return 0;
 	}
 
-	ses->chans[chan_index].iface = iface;
-
-	/* No iface is found. if secondary chan, drop connection */
-	if (!iface && SERVER_IS_CHAN(server))
-		ses->chans[chan_index].server = NULL;
-
-	spin_unlock(&ses->chan_lock);
-
-	if (!iface && SERVER_IS_CHAN(server))
-		cifs_put_tcp_session(server, false);
-
 	return rc;
 }