ext4: cache NULL when both default_acl and acl are NULL

default_acl and acl of newly created inode will be initiated as
ACL_NOT_CACHED in vfs function inode_init_always() and later will be
updated by calling xxx_init_acl() in specific filesystems.  However,
when default_acl and acl are NULL then they keep the value of
ACL_NOT_CACHED.  This patch changes the code to cache NULL for acl /
default_acl in this case to save unnecessary ACL lookup attempt.
Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>

fs/ext4/acl.c

@@ -284,12 +284,16 @@ ext4_init_acl(handle_t *handle, struct inode *inode, struct inode *dir)
 		error = __ext4_set_acl(handle, inode, ACL_TYPE_DEFAULT,
 				       default_acl, XATTR_CREATE);
 		posix_acl_release(default_acl);
+	} else {
+		inode->i_default_acl = NULL;
 	}
 	if (acl) {
 		if (!error)
 			error = __ext4_set_acl(handle, inode, ACL_TYPE_ACCESS,
 					       acl, XATTR_CREATE);
 		posix_acl_release(acl);
+	} else {
+		inode->i_acl = NULL;
 	}
 	return error;
 }