Re: [PATCH v3] x86/mce: Try printing all machine check banks known before panic

From: Borislav Petkov
Date: Wed Nov 19 2014 - 05:30:07 EST

On Wed, Nov 19, 2014 at 05:22:41PM +0800, wrote:
> From: Rui Wang <>
> There are cases when an machine check panics without giving any information
> about the error:
> [ 177.806166] Kernel panic - not syncing: Machine check from unknown source
> No information besides that it is a machine check. This happens in two cases:
> 1) The CPU logs the error with the MCi_STATUS.EN bit set to zero, and Linux
> ignores EN=0 entries (as it should).

Well, I guess we shouldn't anymore. Apparently hw forgets to set the
bit when raising an MCE so then we should ignore it too in mce-severity
and delete that piece or grade it as higher severity based on, I dunno,
b0rked hardware family/model/stepping or whatever bit we set...

NO, "Not enabled",

> 2) In normal processing the MCE handler ignores banks that do not contain fatal
> or unrecoverable errors (these would later be found and logged by the CMCI
> handler). If we panic, these will never be logged, but could be important
> to diagnose the problem.

Well, we do this:

* Non uncorrected or non signaled errors are handled by
* machine_check_poll. Leave them alone, unless this panics.
if (!(m.status & (cfg->ser ? MCI_STATUS_S : MCI_STATUS_UC)) &&

so no_way_out gets indirectly controlled by mce-severity too. So I guess
mce-severity would need adjusting instead of adding more stuff to the #MC

Btw, the panic message comes from

* No machine check event found. Must be some external
* source or one CPU is hung. Panic.
if (global_worst <= MCE_KEEP_SEVERITY && mca_cfg.tolerant < 3)
mce_panic("Machine check from unknown source", NULL, NULL);

so fixing mce_severity is what should happen here instead, IMO.



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