[RFC] drm/tests: annotate intentional stack trace in drm_test_rect_calc_hscale()

[mripard at kernel.org]

Hi,

On Wed, Nov 01, 2023 at 12:08:00PM +0300, Dan Carpenter wrote:
> Let me add Richard to the CC list.  See lore for more details.
> https://lore.kernel.org/all/CA+G9fYuA643RHHpPnz9Ww7rr3zV5a0y=7_uFcybBSL=QP_sQvQ@mail.gmail.com/
> 
> On Tue, Oct 31, 2023 at 09:57:48PM +0530, Naresh Kamboju wrote:
> > On Mon, 30 Oct 2023 at 14:33, Dan Carpenter <dan.carpenter at linaro.org> wrote:
> > >
> > > We have started printing more and more intentional stack traces.  Whether
> > > it's testing KASAN is able to detect use after frees or it's part of a
> > > kunit test.
> > >
> > > These stack traces can be problematic.  They suddenly show up as a new
> > > failure.  Now the test team has to contact the developers.  A bunch of
> > > people have to investigate the bug.  We finally decide that it's
> > > intentional so now the test team has to update their filter scripts to
> > > mark it as intentional.  These filters are ad-hoc because there is no
> > > standard format for warnings.
> > >
> > > A better way would be to mark it as intentional from the start.
> > >
> > > Here, I have marked the beginning and the end of the trace.  It's more
> > > tricky for things like lkdtm_FORTIFY_MEM_MEMBER() where the flow doesn't
> > > reach the end of the function.  I guess I would print a different
> > > warning for stack traces that can't have a
> > > "Intentional warning finished\n" message at the end.
> > >
> > > I haven't actually tested this patch...  Daniel, do you have a
> > > list of intentional stack traces we could annotate?
> > 
> > [My two cents]
> > 
> > I have been noticing following kernel warnings / BUGs
> 
> Some are intentional and some are not.  I had a similar thing happen to
> me last week where I had too many Smatch false positives in my devel
> code so I accidentally sent a patch with a stupid bug.  I've since
> updated my QC process to run both the devel and released versions of
> Smatch.
> 
> But a similar thing is happening here where we have so many bogus
> warnings that we missed a real bug.

IIRC, there was a similar discussion for lockdep issues. IMO, any
(unintended) warning should trigger a test failure.

I guess that would require adding some intrumentation to __WARN somehow,
and also allowing tests to check whether a warning had been generated
during their execution for tests that want to trigger one.

Maxime
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