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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Hans de Goede <hdegoede@redhat.com>,
        kernel test robot <lkp@intel.com>,
        Peter Zijlstra <peterz@infradead.org>
Cc:     llvm@lists.linux.dev, kbuild-all@lists.01.org,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        linux-kernel@vger.kernel.org, Tony Luck <tony.luck@intel.com>
Subject: Re: [pdx86-platform-drivers-x86:review-hans 46/59]
 kernel/stop_machine.c:638:35: error: call to undeclared function
 'cpu_smt_mask'; ISO C99 and later do not support implicit function
 declarations
In-Reply-To: <ce8e9601-f514-5227-f9f7-87594218f95f@redhat.com>
References: <202205120904.Gr9HEY5E-lkp@intel.com> <87zgjnw1bg.ffs@tglx>
 <ce8e9601-f514-5227-f9f7-87594218f95f@redhat.com>
Date:   Thu, 12 May 2022 13:42:26 +0200
Message-ID: <87r14zvuxp.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On Thu, May 12 2022 at 11:53, Hans de Goede wrote:
> On 5/12/22 11:24, Thomas Gleixner wrote:
>> On Thu, May 12 2022 at 09:29, kernel test robot wrote:
>>>>> kernel/stop_machine.c:638:35: error: call to undeclared function 'cpu_smt_mask'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
>>>            const struct cpumask *smt_mask = cpu_smt_mask(cpu);
>> 
>> This warning with W=1 is not the worst of the problems.
>> 
>> The build will simply fail for CONFIG_SMP=y && CONFIG_SCHED_SMT=n
>> because cpu_smt_mask() cannot be resolved.
>> 
>> The other issue is CONFIG_SMP=n. This will fail to build the IFS driver
>> because stop_core_cpuslocked() is not available for SMP=n.
>
> The IFS Kconfig already depends on SMP :
>
> config INTEL_IFS
>         tristate "Intel In Field Scan"
>         depends on X86 && 64BIT && SMP
>         select INTEL_IFS_DEVICE
>         help
>           Enable ...
>
>
> So I don't think we need the non-SMP implementation inside
> include/linux/stop_machine.h, we only need the #ifdef you
> suggest in kernel/stop_machine.c  ?

For the case at hand that's sufficient.

> I think it is best to just squash this into the original
> patch, do you agree ?

Yes.