Re: [PATCH 2/3] hwmon: surface_temp: Add support for sensor names

[Maximilian Luz]

Hi,

On 4/16/24 11:08 PM, Guenter Roeck wrote:
> On Tue, Apr 16, 2024 at 09:00:05PM +0200, Maximilian Luz wrote:
> > On 4/16/24 3:30 PM, Guenter Roeck wrote:
> > > On Sat, Mar 30, 2024 at 12:24:01PM +0100, Maximilian Luz wrote:
> >
> > [...]
> >
> > > > +static int ssam_tmp_get_name(struct ssam_device *sdev, u8 iid, char *buf, size_t buf_len)
> > > > +{
> > > > +	struct ssam_tmp_get_name_rsp name_rsp;
> > > > +	int status;
> > > > +
> > > > +	status =  __ssam_tmp_get_name(sdev->ctrl, sdev->uid.target, iid, &name_rsp);
> > > > +	if (status)
> > > > +		return status;
> > > > +
> > > > +	/*
> > > > +	 * This should not fail unless the name in the returned struct is not
> > > > +	 * null-terminated or someone changed something in the struct
> > > > +	 * definitions above, since our buffer and struct have the same
> > > > +	 * capacity by design. So if this fails blow this up with a warning.
> > > > +	 * Since the more likely cause is that the returned string isn't
> > > > +	 * null-terminated, we might have received garbage (as opposed to just
> > > > +	 * an incomplete string), so also fail the function.
> > > > +	 */
> > > > +	status = strscpy(buf, name_rsp.name, buf_len);
> > > > +	WARN_ON(status < 0);
> > >
> > > Not acceptable. From include/asm-generic/bug.h:
> > >
> > >    * Do not use these macros when checking for invalid external inputs
> > >    * (e.g. invalid system call arguments, or invalid data coming from
> > >    * network/devices), and on transient conditions like ENOMEM or EAGAIN.
> > >    * These macros should be used for recoverable kernel issues only.
> >
> > Hmm, I always interpreted that as "do not use for checking user-defined
> > input", which this is not.
>
> "invalid data coming from network/devices" is not user-defined input.
>
> > The reason I added/requested it here was to check for "bugs" in how we
> > think the interface behaves (and our definitions related to it) as the
> > interface was reverse-engineered. Generally, when this fails I expect
> > that we made some mistake in our code (or the things we assume about the
> > interface), which likely causes us to interpret the received data as
> > "garbage" (and not the EC sending corrupted data, which it is generally
> > not due to CRC checking and validation in the SAM driver). Hence, I
> > personally would prefer if this blows up in a big warning with a trace
> > attached to it, so that an end-user can easily report this to us and
> > that we can appropriately deal with it. As opposed to some one-line
> > error message that will likely get overlooked or not taken as seriously.
>
> I have heard the "This backtrace is absolutely essential" argument before,
> including the "will be fixed" part. Chromebooks report more than 500,000
> warning backtraces _every single day_. None of them is getting fixed.
>
> > If you still insist, I could change that to a dev_err() message. Or
> > maybe make the comment a bit clearer.
>
> dev_err() would be acceptable. WARN() or WARN_ON() are no-go.

Sorry for the delayed response. I will change this to a dev_err() then
and try to re-spin the patches this weekend.

Best regards,
Max