Re: [PATCH v4] vmcoreinfo: Track and log recoverable hardware errors

Dave Hansen
2025-08-01T16:24:44Z

On 8/1/25 08:13, Breno Leitao wrote:
> Hello Dave,
>
> On Fri, Aug 01, 2025 at 07:52:17AM -0700, Dave Hansen wrote:
>> On 8/1/25 05:31, Breno Leitao wrote:
>>> Introduce a generic infrastructure for tracking recoverable hardware
>>> errors (HW errors that are visible to the OS but does not cause a panic)
>>> and record them for vmcore consumption.
>> ...
>>
>> Are there patches for the consumer side of this, too? Or do humans
>> looking at crash dumps have to know what to go digging for?
>>
>> In either case, don't we need documentation for this new ABI?
>
> I have considered this, but the documentation for vmcoreinfo
> (admin-guide/kdump/vmcoreinfo.rst) solely documents what is explicitly
> exposed by vmcore, which differs from the nature of these counters.
>
> Where would be a good place to document it?

I'm not picky. But you also didn't quite answer the question I was asking.

Is this new data for humans or machines to read?

>>> @@ -1690,6 +1691,9 @@ noinstr void do_machine_check(struct pt_regs *regs)
>>> }
>>>
>>> out:
>>> + /* Given it didn't panic, mark it as recoverable */
>>> + hwerr_log_error_type(HWERR_RECOV_MCE);
>>> +
>>
>> Does "MCE" mean anything outside of x86?
>
> AFAIK this is a MCE concept.

I'm not really sure what that response means.

There are two problems here. First is that HWERR_RECOV_MCE is defined in
arch-generic code, but it may never get used by anything other than x86
when CONFIG_X86_MCE.

That also completely wastes space in your data structure when
HWERR_RECOV_MCE=n. Not a huge deal as-is, but it's still a bit sloppy
and wasteful.

...
>>> + hwerr_data[src].count++;
>>> + hwerr_data[src].timestamp = ktime_get_real_seconds();
>>> +}
>>> +EXPORT_SYMBOL_GPL(hwerr_log_error_type);
>>
>> I'd also love to hear more about _actual_ users of this. Surely, someone
>> hit a real world problem and thought this would be a nifty solution. Who
>> was that? What problem did they hit? How does this help them?
>
> Yes, this has been extensively discussed in the very first version of
> the patch. Borislav raised the same question, which was discussed in the
> following link:
>
> https://lore.kernel.org/all/20250715125327.GGaHZPRz9QLNNO-7q8@fat_crate.local/

When someone raises a concern, we usually try to alleviate the concern
in a way that is self-contained in the next posting. A cover letter with
a full explanation would be one place to put the reasoning, for example.

But expecting future reviewers to plod through all the old threads isn't
really feasible.