linux-kernel - 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

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Date:   Thu, 12 May 2022 13:42:26 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Hans de Goede <hdegoede@...hat.com>,
        kernel test robot <lkp@...el.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     llvm@...ts.linux.dev, kbuild-all@...ts.01.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-kernel@...r.kernel.org, Tony Luck <tony.luck@...el.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

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.