From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S932211AbdEUD0Y (ORCPT <rfc822;w@1wt.eu>);
        Sat, 20 May 2017 23:26:24 -0400
Received: from zeniv.linux.org.uk ([195.92.253.2]:36958 "EHLO
        ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751848AbdEUD0W (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Sat, 20 May 2017 23:26:22 -0400
Date: Sun, 21 May 2017 04:25:10 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Geliang Tang <geliangtang@gmail.com>, Felipe Balbi <balbi@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Michal Nazarewicz <mina86@mina86.com>,
        Vincent Pelletier <plr.vincent@gmail.com>,
        Felix =?iso-8859-1?Q?H=E4dicke?= <felixhaedicke@web.de>,
        Jim Lin <jilin@nvidia.com>, linux-usb@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] usb: gadget: f_fs: use memdup_user
Message-ID: <20170521032453.GW390@ZenIV.linux.org.uk>
References: <908fa521decaf3703e172c3734c0d498741f3ddb.1494580404.git.geliangtang@gmail.com>
 <694b8a4beb2ec1e087321bc423e5cd0c69e5a717.1494576863.git.geliangtang@gmail.com>
 <20170513080530.2rsqs3apd6w3psve@mwanda>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20170513080530.2rsqs3apd6w3psve@mwanda>
User-Agent: Mutt/1.8.0 (2017-02-23)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Sat, May 13, 2017 at 11:05:30AM +0300, Dan Carpenter wrote:

> > +	data = memdup_user(buf, len);
> > +	if (unlikely(IS_ERR(data)))
> 
> Don't use likely/unlikely() here.  It's not a fast path.

More to the point,

#define IS_ERR_VALUE(x) unlikely((unsigned long)(void *)(x) >= (unsigned long)-MAX_ERRNO)
static inline bool __must_check IS_ERR(__force const void *ptr)
{
	return IS_ERR_VALUE((unsigned long)ptr);
}

IOW, IS_ERR() already produces unlikely(....), fast path or not.