smb: client: short-circuit in open_cached_dir_by_dentry() if !dentry

When dentry is NULL, the current code acquires the spinlock and traverses
the entire list, but the condition (dentry && cfid->dentry == dentry)
ensures no match will ever be found.

Return -ENOENT early in this case, avoiding unnecessary lock acquisition
and list traversal.

Signed-off-by: Henrique Carvalho <henrique.carvalho@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: hac-v

fs/smb/client/cached_dir.c

@@ -416,9 +416,12 @@ int open_cached_dir_by_dentry(struct cifs_tcon *tcon,
 	if (cfids == NULL)
 		return -EOPNOTSUPP;
 
+	if (!dentry)
+		return -ENOENT;
+
 	spin_lock(&cfids->cfid_list_lock);
 	list_for_each_entry(cfid, &cfids->entries, entry) {
-		if (dentry && cfid->dentry == dentry) {
+		if (cfid->dentry == dentry) {
 			if (!is_valid_cached_dir(cfid))
 				break;
 			cifs_dbg(FYI, "found a cached file handle by dentry\n");