Re: [PATCH v1 1/1] x86/percpu: Cast -1 to argument type when comparing in percpu_add_op()

Andy Shevchenko
2024-10-16T18:20:11Z

On Wed, Oct 16, 2024 at 09:06:13PM +0300, Andy Shevchenko wrote:
> On Wed, Oct 16, 2024 at 08:44:56AM -0700, Dave Hansen wrote:

...

> > This doesn't _look_ right.

See below.

...

> Maybe more readable, but wouldn't it be theoretically buggy for u64?
> I'm talking about the case when u64 == UINT_MAX, which will be true
> in your case and false in mine.
>
> > const int pao_ID__ = (__builtin_constant_p(val) &&
> > ((val) == 1 || (int)(val) == -1)) ?
> >
> > (int)(val) : 0;

This code _is_ buggy, thanks to my new test case.

[ 66.161375] pcp -1 (0xffffffffffffffff) != expected 4294967295 (0xffffffff)

Hence, I'll send a v2 with the test case and updated Subject.

--
With Best Regards,
Andy Shevchenko