Re: Hardware Error Kernel Mini-Summit

From: Eric W. Biederman
Date: Tue May 18 2010 - 18:14:28 EST

Borislav Petkov <bp@xxxxxxxxx> writes:

> From: "Luck, Tony" <tony.luck@xxxxxxxxx>
> Date: Tue, May 18, 2010 at 03:08:58PM -0400
>> > It makes sense to use the kernel's performance events
>> > logging framework when we are logging events about how the
>> > system performs.
>> Perhaps it makes more sense to say that the Linux "performance
>> events logging framework" has become more generic and is really
>> now an "event logging framework".
> Yep, that's the idea.
>> > Furthermore it's NMI safe, offers structured logging, has
>> > various streaming, multiplexing and filtering capabilities
>> > that come handy for RAS purposes and more.
>> Those of us present at the mini-summit were not familiar with
>> all the features available. One area of concern was how to be
>> sure that something is in fact listening to and logging the
>> error events. My understanding is that if there is no process
>> attached to an event, the kernel will just drop it. This is
>> of particular concern because the kernel's first scan of the
>> machine check banks occurs before there are any processes.
>> So errors found early in boot (which might be saved fatal
>> errors from before the boot) might be lost.
> Well, we have a trace_mce_record tracepoint in the mcheck code which
> calls all the necessary callbacks when an mcheck occurs. For the time
> being, the idea is to use the mce.c ring buffer for early mchecks and
> copy them to the regular ftrace per-cpu buffer after the last has been
> initialized. Later, we could switch to a another early bootmem buffer if
> there's need to.
> Also, we want to have a userspace daemon that reads out the mces from
> the trace buffer and does further processing like thresholding etc in
> userspace.
> Concerning critical errors, there we bypass the perf subsystem and
> execute the smallest amount of code possible while trying to shutdown
> gracefully if the error type allows that.
> These are the rough ideas at least...

Can someone please tell me why everyone is eager to squirrel
correctable error reports away and not report them in dmesg? aka

I have had on several occasions a machine with memory errors that
mcelog or the BIOS was eating the error reports and not putting them
anywhere a normal human being would look.

If your system isn't broken correctable errors are rare. People look
at syslog. People look in /var/log/messages and dmesg when something
goes weird.

I have no problem with additional interfaces to provide additional
functionality but please can we put errors where people can find them.

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