From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>, Uros Bizjak <ubizjak@gmail.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
llvm@lists.linux.dev, Dennis Zhou <dennis@kernel.org>,
Tejun Heo <tj@kernel.org>, Christoph Lameter <cl@linux.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Bill Wendling <morbo@google.com>,
Justin Stitt <justinstitt@google.com>
Subject: Re: [PATCH v1 1/1] x86/percpu: Cast -1 to argument type when comparing in percpu_add_op()
Date: Wed, 16 Oct 2024 21:20:03 +0300 [thread overview]
Message-ID: <ZxAD0-kQJ0_lDxje@smile.fi.intel.com> (raw)
In-Reply-To: <ZxAAlEyvxzWpwQQ0@smile.fi.intel.com>
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
next prev parent reply other threads:[~2024-10-16 18:20 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-09-05 17:03 Andy Shevchenko
2024-10-16 13:37 ` Andy Shevchenko
2024-10-16 15:44 ` Dave Hansen
2024-10-16 17:03 ` Nick Desaulniers
2024-10-16 18:06 ` Andy Shevchenko
2024-10-16 18:20 ` Andy Shevchenko [this message]
2024-10-16 19:43 ` Dave Hansen
2024-10-16 19:20 ` Peter Zijlstra
2024-10-16 19:44 ` Dave Hansen
2024-10-17 18:18 ` Peter Zijlstra
2024-10-18 12:21 ` Andy Shevchenko
2024-10-22 19:53 ` Dave Hansen
2024-10-22 23:24 ` Christoph Lameter (Ampere)
2024-10-23 17:15 ` Dave Hansen
2024-10-23 21:40 ` H. Peter Anvin
2024-10-23 14:24 ` Andy Shevchenko
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