On 18.06.21 at 08:47:37 CEST, Wilken Gottwalt wrote > On Fri, 18 Jun 2021 08:18:23 +0200 > Marius Zachmann <mail@xxxxxxxxxxxxxxxxx> wrote: > > > On 18.06.21 at 07:45:00 CEST, Wilken Gottwalt wrote > > > On Fri, 18 Jun 2021 05:56:29 +0600 > > > Aleksandr Mezin <mezin.alexander@xxxxxxxxx> 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. > > Hmm, did you read the comments in the driver? I warn about writing nonsense > values to the micro-controller because you can make it stall. If I let you > access the device by hidraw I assume you know what you are doing. You > actually can damage your PSU by this, something I also warn about. I even > mention that I may remove the hidraw feature in future versions. Sorry for the confusion. I did not test with corsair-psu. (Do not have the hardware) I tested with corsair-cpro. Reading temps with userspace and reading fan speed with the driver simultaneously. But you are right. This is also not, what a userspace tool should do this fast and if it doesn't, races are really unlikely. > > > 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) > > corsair-psu is a hwmon driver, not a gadget driver. This driver does not > have to provide hidraw, only hwmon api access. The hidraw is just a nice > to have feature. And like my query tool shows, you actually don't need the > driver to query it from userspace. The first prototypes of the driver did > locking in the hidraw part which sometimes resulted in lockups. I will > not increase complexity for a nice-to-have feature. So the only option is, > I remove the feature if it causes trouble. > > Guenter, what do you think? > > greetings, > Will > > > 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 <linux@xxxxxxxxxxxx> 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 <mail@xxxxxxxxxxxxxxxxx> 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 > > > > > > > > > > > > > > > >
