linux-kernel - Re: [PATCH 02/20] x86/mce: Define mce_setup() helpers for global and per-CPU fields

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Date:   Wed, 22 Nov 2023 19:24:51 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Yazen Ghannam <yazen.ghannam@....com>
Cc:     linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org,
        tony.luck@...el.com, x86@...nel.org, Avadhut.Naik@....com,
        Smita.KoralahalliChannabasappa@....com,
        amd-gfx@...ts.freedesktop.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH 02/20] x86/mce: Define mce_setup() helpers for global and
 per-CPU fields

On Sat, Nov 18, 2023 at 01:32:30PM -0600, Yazen Ghannam wrote:
> +void mce_setup_global(struct mce *m)

We usually call those things "common":

mce_setup_common().

> +{
> +	memset(m, 0, sizeof(struct mce));
> +
> +	m->cpuid	= cpuid_eax(1);
> +	m->cpuvendor	= boot_cpu_data.x86_vendor;
> +	m->mcgcap	= __rdmsr(MSR_IA32_MCG_CAP);
> +	/* need the internal __ version to avoid deadlocks */
> +	m->time		= __ktime_get_real_seconds();
> +}
> +
> +void mce_setup_per_cpu(struct mce *m)

And call this

	mce_setup_for_cpu(unsigned int cpu, struct mce *m);

so that it doesn't look like some per_cpu helper.

And yes, you should supply the CPU number as an argument. Because
otherwise, when you look at your next change:

+       mce_setup_global(&m);
+       m.cpu = m.extcpu = cpu;
+       mce_setup_per_cpu(&m);

This contains the "hidden" requirement that m.extcpu happens *always*
*before* the mce_setup_per_cpu() call and that is flaky and error prone.

So make that:

	mce_setup_common(&m);
	mce_setup_for_cpu(m.extcpu, &m);

and do m.cpu = m.extcpu = cpu inside the second function.

And then it JustWorks(tm) and you can't "forget" assigning m.extcpu and
there's no subtlety.

Ok?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette