linux-kernel - Re: [PATCH] x86/mce: drop cpu_missing since we have more capable mce_missing

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Date:   Tue, 9 Nov 2021 10:07:35 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Zhaolong Zhang <zhangzl2013@....com>
Cc:     Tony Luck <tony.luck@...el.com>, x86@...nel.org,
        linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH] x86/mce: drop cpu_missing since we have more capable
 mce_missing_cpus

On Tue, Nov 09, 2021 at 04:31:23PM +0800, Zhaolong Zhang wrote:
> If there is a non-recoverable mce as well, just let it print that
> reason. No need to bring the timeout message indeed. Because since
> the tolerant was set to a high level to ignore the timeout, we can
> eventually ignore them.

Here's how I see it:

	/*
	 * Tolerant levels:
	 * 0: always panic on uncorrected errors, log corrected errors
	 * 1: panic or SIGBUS on uncorrected errors, log corrected errors
	 * 2: SIGBUS or log uncorrected errors (if possible), log corr. errors
	 * 3: never panic or SIGBUS, log all errors (for testing only)
	 */

So on normal deployments, no one should fiddle with tolerant levels - so
you'll be running at tolerance level 0 by default and all should print
out. Same for level 1.

Levels 2 and 3 are, to me at least, purely for testing *only*. And,
actually, that error message should be issued regardless of the
tolerance level - only the panicking should be controlled by that. IOW,
that code should do:

        if ((s64)*t < SPINUNIT) {
                if (cpumask_and(&mce_missing_cpus, cpu_online_mask, &mce_missing_cpus))
                        pr_emerg("CPUs not responding to MCE broadcast (may include false positives): %*pbl\n",
                                 cpumask_pr_args(&mce_missing_cpus));
                if (mca_cfg.tolerant <= 1)
                        mce_panic(msg, NULL, NULL);
                return 1;
        }

because, regardless of tolerance level, saying that some cores didn't
respond is important info.

You could do that as a separate patch, on top, if you feel like it.

> I am not sure whether it should be authored by you or suggested by
> you.

Suggested is fine.

> Anyway, I will post a new patch exactly as you suggested. Please pick
> it or ignore it as appropriate :)

Thx.

-- 
Regards/Gruss,
    Boris.

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