Re: [PATCH 2/2] x86/mce: Add mce=panic_on_ce_count to panic on a corrected error flood

[Luck, Tony]

On Fri, Aug 21, 2026 at 03:24:08AM -0700, Breno Leitao wrote:
> A machine check bank producing corrected errors faster than the kernel can
> drain them is not a machine anyone wants to keep in service, but nothing
> takes it out. mce_track_storm() throttles CMCI for the bank and the
> machine stays up.
> 
> Count corrected errors per bank and add mce=panic_on_ce_count=<count>
> and panic the host if we have more events than set.

FYI. I don't think this needs to be fixed, but you should be aware and
perhaps document the shared bank details.

This won't count accurately for banks that are shared by multiple logical
CPUs (you've inherited this from the storm detection code that introduces
this problem).

E.g. a machine check bank reporting L2 errors is shared by both logical CPUs
on a core on P-core systems, and by all cores on a module on E-core systems.

But the storm code keeps <per-CPU,per-bank> counts. So if an L2 instance
is throwing out many errors, some will be counted by one of the CPUs, while
other errors are counted separately by the other CPUs sharing the bank.

The net effect is that a storm won't be trigged until one of the CPUs tracking
a shared bank hits the threshold.

Similarly there may be more errors logged than you expect before your
panic fires.

-Tony