cifs: improve handlecaching

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2151418
commit 47fc249

Only track the dentry for the root handle

    Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
    Signed-off-by: Steve French <stfrench@microsoft.com>
    (cherry picked from commit 47fc249)
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>

Author: Ronnie Sahlberg

fs/cifs/cached_dir.c

@@ -47,11 +47,11 @@ int open_cached_dir(unsigned int xid, struct cifs_tcon *tcon,
 	if (cifs_sb->root == NULL)
 		return -ENOENT;
 
-	if (strlen(path))
+	if (!path[0])
+		dentry = cifs_sb->root;
+	else
 		return -ENOENT;
 
-	dentry = cifs_sb->root;
-
 	cfid = &tcon->cfids->cfid;
 	mutex_lock(&cfid->fid_mutex);
 	if (cfid->is_valid) {
@@ -177,7 +177,8 @@ int open_cached_dir(unsigned int xid, struct cifs_tcon *tcon,
 	cfid->tcon = tcon;
 	cfid->is_valid = true;
 	cfid->dentry = dentry;
-	dget(dentry);
+	if (dentry)
+		dget(dentry);
 	kref_init(&cfid->refcount);
 
 	/* BB TBD check to see if oplock level check can be removed below */