cifs: change iface_list from array to sorted linked list

A server's published interface list can change over time, and needs
to be updated. We've storing iface_list as a simple array, which
makes it difficult to manipulate an existing list.

With this change, iface_list is modified into a linked list of
interfaces, which is kept sorted by speed.

Also added a reference counter for an iface entry, so that each
channel can maintain a backpointer to the iface and drop it
easily when needed.

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

1 files changed, 40 insertions, 38 deletions

diff --git a/fs/cifs/sess.c b/fs/cifs/sess.c
index d417de354d9d..d7b6e5687df2 100644
--- a/fs/cifs/sess.c
+++ b/fs/cifs/sess.c
@@ -58,7 +58,7 @@ bool is_ses_using_iface(struct cifs_ses *ses, struct cifs_server_iface *iface)
 
 	spin_lock(&ses->chan_lock);
 	for (i = 0; i < ses->chan_count; i++) {
-		if (is_server_using_iface(ses->chans[i].server, iface)) {
+		if (ses->chans[i].iface == iface) {
 			spin_unlock(&ses->chan_lock);
 			return true;
 		}
@@ -151,11 +151,9 @@ int cifs_try_adding_channels(struct cifs_sb_info *cifs_sb, struct cifs_ses *ses)
 {
 	int old_chan_count, new_chan_count;
 	int left;
-	int i = 0;
 	int rc = 0;
 	int tries = 0;
-	struct cifs_server_iface *ifaces = NULL;
-	size_t iface_count;
+	struct cifs_server_iface *iface = NULL, *niface = NULL;
 
 	spin_lock(&ses->chan_lock);
 
@@ -185,32 +183,16 @@ int cifs_try_adding_channels(struct cifs_sb_info *cifs_sb, struct cifs_ses *ses)
 	spin_unlock(&ses->chan_lock);
 
 	/*
-	 * Make a copy of the iface list at the time and use that
-	 * instead so as to not hold the iface spinlock for opening
-	 * channels
-	 */
-	spin_lock(&ses->iface_lock);
-	iface_count = ses->iface_count;
-	if (iface_count <= 0) {
-		spin_unlock(&ses->iface_lock);
-		cifs_dbg(VFS, "no iface list available to open channels\n");
-		return 0;
-	}
-	ifaces = kmemdup(ses->iface_list, iface_count*sizeof(*ifaces),
-			 GFP_ATOMIC);
-	if (!ifaces) {
-		spin_unlock(&ses->iface_lock);
-		return 0;
-	}
-	spin_unlock(&ses->iface_lock);
-
-	/*
 	 * Keep connecting to same, fastest, iface for all channels as
 	 * long as its RSS. Try next fastest one if not RSS or channel
 	 * creation fails.
 	 */
+	spin_lock(&ses->iface_lock);
+	iface = list_first_entry(&ses->iface_list, struct cifs_server_iface,
+				 iface_head);
+	spin_unlock(&ses->iface_lock);
+
 	while (left > 0) {
-		struct cifs_server_iface *iface;
 
 		tries++;
 		if (tries > 3*ses->chan_max) {
@@ -219,27 +201,46 @@ int cifs_try_adding_channels(struct cifs_sb_info *cifs_sb, struct cifs_ses *ses)
 			break;
 		}
 
-		iface = &ifaces[i];
-		if (is_ses_using_iface(ses, iface) && !iface->rss_capable) {
-			i = (i+1) % iface_count;
-			continue;
+		spin_lock(&ses->iface_lock);
+		if (!ses->iface_count) {
+			spin_unlock(&ses->iface_lock);
+			break;
 		}
 
-		rc = cifs_ses_add_channel(cifs_sb, ses, iface);
-		if (rc) {
-			cifs_dbg(FYI, "failed to open extra channel on iface#%d rc=%d\n",
-				 i, rc);
-			i = (i+1) % iface_count;
-			continue;
+		list_for_each_entry_safe_from(iface, niface, &ses->iface_list,
+				    iface_head) {
+			/* skip ifaces that are unusable */
+			if (!iface->is_active ||
+			    (is_ses_using_iface(ses, iface) &&
+			     !iface->rss_capable)) {
+				continue;
+			}
+
+			/* take ref before unlock */
+			kref_get(&iface->refcount);
+
+			spin_unlock(&ses->iface_lock);
+			rc = cifs_ses_add_channel(cifs_sb, ses, iface);
+			spin_lock(&ses->iface_lock);
+
+			if (rc) {
+				cifs_dbg(VFS, "failed to open extra channel on iface:%pIS rc=%d\n",
+					 &iface->sockaddr,
+					 rc);
+				kref_put(&iface->refcount, release_iface);
+				continue;
+			}
+
+			cifs_dbg(FYI, "successfully opened new channel on iface:%pIS\n",
+				 &iface->sockaddr);
+			break;
 		}
+		spin_unlock(&ses->iface_lock);
 
-		cifs_dbg(FYI, "successfully opened new channel on iface#%d\n",
-			 i);
 		left--;
 		new_chan_count++;
 	}
 
-	kfree(ifaces);
 	return new_chan_count - old_chan_count;
 }
 
@@ -355,6 +356,7 @@ cifs_ses_add_channel(struct cifs_sb_info *cifs_sb, struct cifs_ses *ses,
 		spin_unlock(&ses->chan_lock);
 		goto out;
 	}
+	chan->iface = iface;
 	ses->chan_count++;
 	atomic_set(&ses->chan_seq, 0);