linux-kernel - Re: [RFC PATCH v2 3/4] acpi: apei: Do not panic() when correctable errors are marked as fatal.

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Date:   Wed, 25 Apr 2018 10:00:53 -0500
From:   "Alex G." <mr.nuke.me@...il.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     linux-acpi@...r.kernel.org, linux-edac@...r.kernel.org,
        rjw@...ysocki.net, lenb@...nel.org, tony.luck@...el.com,
        tbaicar@...eaurora.org, will.deacon@....com, james.morse@....com,
        shiju.jose@...wei.com, zjzhang@...eaurora.org,
        gengdongjiu@...wei.com, linux-kernel@...r.kernel.org,
        alex_gagniuc@...lteam.com, austin_bolen@...l.com,
        shyam_iyer@...l.com, devel@...ica.org, mchehab@...nel.org,
        robert.moore@...el.com, erik.schmauss@...el.com,
        Yazen Ghannam <yazen.ghannam@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [RFC PATCH v2 3/4] acpi: apei: Do not panic() when correctable
 errors are marked as fatal.



On 04/25/2018 09:01 AM, Borislav Petkov wrote:
> On Mon, Apr 23, 2018 at 11:19:25PM -0500, Alex G. wrote:
>> That tells you what FFS said about the error.
> 
> I betcha those status and command values have a human-readable counterparts.
> 
> Btw, what do you abbreviate with "FFS"?

Firmware-first.

>> It's immediately obvious if there's a glaring FFS bug and if we get bogus
>> data. If you distrust firmware as much as I do, then you will find great
>> value in having such info in the logs. It's probably not too useful to a
>> casual user, but then neither is a majority of the system log.
> 
> No no, you're missing the point - I *want* all data in the error log
> which helps debug a hardware issue. I just want it humanly readable so
> that I don't have to jot down the values and go scour the manuals to map
> what it actually means.

We could probably use more of the native AER print functions, but that's
beyond the scope of this patch. I tried something like this [1], but
have given up following the PCI maintainer's radio silence. I don't care
_that_ much about the log format.

[1] http://www.spinics.net/lists/linux-pci/msg71422.html

>> You're missing the timing and assuming you will get the hotplug interrupt.
>> In this example, you have 22ms between the link down and presence detect
>> state change. This is a fairly fast removal.
>>
>> Hotplug dependencies aside (you can have the kernel run without PCIe hotplug
>> support), I don't think you want to just linger in NMI for dozens of
>> milliseconds waiting for presence detect confirmation.
> 
> No, I don't mean that. I mean something like deferred processing:

Like the exact thing that this patch series implements? :)

> you
> get an error, you notice it is a device which supports physical removal
> so you exit the NMI handler and process the error in normal, process
> context which allows you to query the device and say, "Hey device, are
> you still there?"

Like the exact way the AER handler works?

> If it is not, you drop all the hw I/O errors reported for it.

Like the PCI error recovery mechanisms that AER invokes?

> Hmmm?
Hmmm