Re: [PATCH v7 8/9] powerpc/mce: Add sysctl control for recovery action on MCE.

On Thu, 09 Aug 2018 00:56:00 +1000
Michael Ellerman [off-list ref] wrote:

Mahesh J Salgaonkar [off-list ref] writes:

quoted

From: Mahesh Salgaonkar <redacted>

Introduce recovery action for recovered memory errors (MCEs). There are
soft memory errors like SLB Multihit, which can be a result of a bad
hardware OR software BUG. Kernel can easily recover from these soft errors
by flushing SLB contents. After the recovery kernel can still continue to
function without any issue. But in some scenario's we may keep getting
these soft errors until the root cause is fixed. To be able to analyze and
find the root cause, best way is to gather enough data and system state at
the time of MCE. Hence this patch introduces a sysctl knob where user can
decide either to continue after recovery or panic the kernel to capture the
dump.  

I'm not convinced we want this.

As we've discovered it's often not possible to reconstruct what happened
based on a dump anyway.

The key thing you need is the content of the SLB and that's not included
in a dump.

So I think we should dump the SLB content when we get the MCE (which
this series does) and any other useful info, and then if we can recover
we should.

Yeah it's a lot of knobs that administrators can hardly be expected to
tune. Hypervisor or firmware should really eventually make the MCE
unrecoverable if we aren't making progress.

That said, x86 has a bunch of options, and for debugging a rare crash
or specialised installations it might be useful. But we should follow
the normal format, /proc/sys/kernel/panic_on_mce.

Thanks,
Nick