linux-kernel - Re: [PATCH] iio: imu: adis16550: rework clock range test

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Message-ID: <20250702163126.000007ac@huawei.com>
Date: Wed, 2 Jul 2025 16:31:26 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Andy Shevchenko <andriy.shevchenko@...el.com>
CC: David Lechner <dlechner@...libre.com>, Lars-Peter Clausen
	<lars@...afoo.de>, Michael Hennerich <Michael.Hennerich@...log.com>, Jonathan
 Cameron <jic23@...nel.org>, Nuno Sá <nuno.sa@...log.com>,
	Robert Budai <robert.budai@...log.com>, "Andy Shevchenko" <andy@...nel.org>,
	<linux-iio@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iio: imu: adis16550: rework clock range test

On Wed, 2 Jul 2025 18:17:24 +0300
Andy Shevchenko <andriy.shevchenko@...el.com> wrote:

> On Wed, Jul 02, 2025 at 10:07:17AM -0500, David Lechner wrote:
> > On 7/2/25 9:59 AM, Andy Shevchenko wrote:  
> > > On Wed, Jul 02, 2025 at 05:53:57PM +0300, Andy Shevchenko wrote:  
> > >> On Wed, Jul 02, 2025 at 09:27:45AM -0500, David Lechner wrote:  
> > >>> Rework the clock rate range test to test if sync_mode_data != NULL
> > >>> instead of testing if the for loop index variable. This makes it easier
> > >>> for static analyzers to see that we aren't using an uninitialized
> > >>> sync_mode_data [1].  
> > >>
> > >> But at the same time it makes it not to be the usual pattern.,,  
> > > 
> > > Reading the static analyser output I think the first hunk is only what we need,
> > > but this is still false positive and it's problem of that static
> > > analyser. Have you filed a bug there? (My point is that modifying the code for
> > > the advantage of false positives of some static analyser is wrong road to go
> > > in my opinion.)  
> > 
> > I agree that we shouldn't fix this _only_ to make the static analyzer
> > happy. But I had to think quite a bit harder to see that the existing
> > code was correct compared to what I have proposed here.
> > 
> > But if this is a common pattern that I just haven't learned to identify
> > at a glance yet and everybody else can easily see that the existing code
> > is correct, then perhaps it isn't worth the change.  
> 
> To me checking against index variable (when it's integer, obviously) is correct
> thing to do and regular pattern. OTOH, if the "index" is a pointer and rather
> we call it "iterator", the angle of view is different because in some cases
> it may lead to stale or invalid value which might be mistakenly dereferenced or
> speculated (see more in the discussion about list entry APIs [entry is a
> keyword here] and if list_entry_is_head() is a good approach.)
> 

Original code looks fine to me and is a very common pattern.  So I'd argue
the static analyzer needs some work.

Jonathan