From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3E00CC48BDF for ; Fri, 18 Jun 2021 06:20:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1CE696120A for ; Fri, 18 Jun 2021 06:20:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231137AbhFRGWq (ORCPT ); Fri, 18 Jun 2021 02:22:46 -0400 Received: from ms-10.1blu.de ([178.254.4.101]:57598 "EHLO ms-10.1blu.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231789AbhFRGUq (ORCPT ); Fri, 18 Jun 2021 02:20:46 -0400 Received: from [37.209.98.109] (helo=marius.localnet) by ms-10.1blu.de with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lu7pf-0006Pf-RR; Fri, 18 Jun 2021 08:18:23 +0200 From: Marius Zachmann To: Aleksandr Mezin , Wilken Gottwalt Cc: Guenter Roeck , linux-hwmon@vger.kernel.org, Jiri Kosina Subject: Re: corsair-cpro and hidraw Date: Fri, 18 Jun 2021 08:18:23 +0200 Message-ID: <4451002.svKJrzdh7d@marius> In-Reply-To: <20210618074500.7215532b@monster.powergraphx.local> References: <20210618074500.7215532b@monster.powergraphx.local> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Con-Id: 241080 X-Con-U: 0-mail X-Originating-IP: 37.209.98.109 Precedence: bulk List-ID: X-Mailing-List: linux-hwmon@vger.kernel.org On 18.06.21 at 07:45:00 CEST, Wilken Gottwalt wrote > On Fri, 18 Jun 2021 05:56:29 +0600 > Aleksandr Mezin wrote: > > > I've looked through corsair-psu sources, and I think filtering in > > raw_event won't be enough. > > > > For example, in corsairpsu_request, there are 2 commands, and they > > should be executed consecutively: > > 1) corsairpsu_usb_cmd(priv, 2, PSU_CMD_SELECT_RAIL, rail, NULL); > > 2) corsairpsu_usb_cmd(priv, 3, cmd, 0, data); > > > > If the userspace will squeeze another PSU_CMD_SELECT_RAIL between (1) > > and (2), the driver will get data for a wrong rail (and with the > > current code won't even notice it). > > > > So unless there is a way to "lock" hidraw (and it seems that there > > isn't - looking at the code, hidraw calls the low-level hid driver > > directly, as far as I understand), it won't work correctly. > > > > And if a driver can't work correctly with hidraw enabled - maybe it > > shouldn't enable hidraw? So that the user can 1) notice that something > > is wrong 2) blacklist or unbind the driver (or userspace tools that > > use hidraw can unbind automatically). Otherwise everything seems to be > > silently broken. > > > > On the other hand, maybe races between the kernel driver and userspace > > tools are unlikely, because the driver doesn't talk to the device > > continuously - only when sysfs reads happen. > > I never noticed any issues of that kind. I actually did quite a lot of > userspace testing. A result of this a userspace tool you can find here: > https://github.com/wgottwalt/corsair-psu/tree/main/tools/rmi-hxi-query > > Though, if you find a way to trigger such a race condition I have no > problem to remove the hidraw part. > > greetings > Will It is possible. Making a userspace tool with just a loop of read/writes will get you wrong readings in the driver sometimes. Removing hidraw from the drivers is not a solution, because there are many userspace tools for these devices and it should be an expected use case to have them running at the same time (eg OpenRGB for rgb) I think the correct solution would be to lock hidraw while the drivers are doing requests. After a (short) look: Introducing a mutex in the hidraw struct which would be locked in hidraw_ioctl and could also be locked in the corsair-psu and corsair-cpro drivers could be a solution. If there are no objections or better suggestions, I will try this over the weekend. Greetings Marius Added Jiri Kosina for hidraw to Cc: > > > Added corsair-psu maintainer to Cc: > > > > On Thu, Jun 17, 2021 at 7:14 PM Guenter Roeck wrote: > > > > > > On Thu, Jun 17, 2021 at 01:11:38PM +0600, Aleksandr Mezin wrote: > > > > On Thu, Jun 17, 2021 at 12:27 PM Marius Zachmann wrote: > > > > ... > > > > > This device uses an echo of the command > > > > > in the answer and if they don't match it returns an error. This could > > > > > maybe lead to a false error when the replies are switched, but is > > > > > probably preferable. > > > > > > > > Hm... If the response includes the id of the request, it should be > > > > possible to filter reports in raw_event, i. e. don't signal completion > > > > if the report doesn't match, and wait more. Yes, there is a corner > > > > case, "if a command is not supported, the length value in the reply is > > > > okay, but the command value is set to 0". But timing out (250 ms) in > > > > this case should probably be fine... Actually I have a compatible > > > > Corsair PSU so maybe I'll send a patch. > > > > > > Patches to improve the situation are welcome. My understanding is > > > that with the current driver users should disable the kernel driver > > > if they plan to use userspace tools to access the device. > > > > > > Guenter > >