linux-kernel - Re: [PATCH 0/1] Slightly relax the type checking done by min() and max().

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Date:   Fri, 25 Nov 2022 17:58:13 +0200
From:   'Andy Shevchenko' <andriy.shevchenko@...ux.intel.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        'Joe Perches' <joe@...ches.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 0/1] Slightly relax the type checking done by min() and
 max().

On Fri, Nov 25, 2022 at 03:27:07PM +0000, David Laight wrote:
> From: Andy Shevchenko
> > Sent: 25 November 2022 15:21
> > On Fri, Nov 25, 2022 at 03:00:40PM +0000, David Laight wrote:
> > > The min() and max() defines include a type check to avoid the unexpected
> > >   behaviour when a negative value is compared against and unsigned value.
> > > However a lot of code hits this check and uses min_t() to avoid the error.
> > > Many of these are just plain wrong.
> > >
> > > Those casting to u8 or u16 are particularly suspect, eg:
> > > drivers/usb/misc/usb251xb.c:528:
> > > 		hub->max_current_sp = min_t(u8, property_u32 / 2000, 50);
> > 
> > I don't buy this. What's exactly wrong with this code?
> 
> Consider what happens if propery_u32 is 512000.
> The returned value is 0 not 50.

I considered that and there are two things to consider on your side:
1) it's coming from device property;
2) device property is validated using YAML schema.

On top of that, the wrong property is on the user. We have a lot of stuff that
user may put wrongly, but it's user's choice.

Any better example, please?

-- 
With Best Regards,
Andy Shevchenko