[bug report] drm: Warn about negative sizes when calculating scale factor

[Dan Carpenter]

On Fri, Oct 20, 2023 at 02:55:37PM +0300, Ville Syrjälä wrote:
> On Fri, Oct 20, 2023 at 02:39:04PM +0300, Dan Carpenter wrote:
> > On Wed, Oct 18, 2023 at 05:17:42PM +0300, Dan Carpenter wrote:
> > > drivers/gpu/drm/drm_rect.c
> > >    134  static int drm_calc_scale(int src, int dst)
> > >    135  {
> > >    136          int scale = 0;
> > >    137  
> > >    138          if (WARN_ON(src < 0 || dst < 0))
> > >                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > > These days, with automated fuzz testing, this WARN_ON() is problematic.
> > > WARN() is considered a kernel bug, and pr_warn() is the hip new way to
> > > alert the user about issues.
> > 
> > Btw, a lot of people (Greg claims it's the majority of Linux users)
> > these days have run kernels with panic on warn enabled so that's another
> > reason to avoid using WARN_ON() for stuff that it known to be possible.
> 
> This is not possible, unless there is a serious bug somewhere else.

Ah.  That's fine then.  This is kunit which is deliberately triggering
the WARN_ON().  The KASAN testing also deliberately triggers WARN_ON()s
so it's a necessary thing.

I just wonder if there is some way to mark these kinds of warnings as
expected.  Perhaps we could add a comment in the kunit test?

regards,
dan carpenter