On Thu, Dec 03, 2015 at 07:16:10PM -0500, Ashok Raj wrote:
> Linux has logical cpu offline capability. That can be triggered by:
>
> # echo 0 > /sys/devices/system/cpu/cpuX/online
>
> In Intel Architecture, MCE's are broadcasted to all CPUs in the system.
>
> This includes the CPUs marked offline by Linux. Unless the CPU's were removed
> via an ACPI notification, in which case the cpu's are removed from the
> cpu_present_map.
>
> This patch ensures offline CPU's don't participate in MCE rendezvous, but
> simply perform clearing some status bits to ensure a second MCE wont cause
> automatic shutdown.
>
> Without the patch, mce_start will increment mce_callin, but mce_start would
> wait for all online_cpus. So offline cpu's should avoid participating in the
> rendezvous process.
>
> Reviewed-by: Tony Luck <[email protected]>
> Signed-off-by: Ashok Raj <[email protected]>
> ---
> arch/x86/kernel/cpu/mcheck/mce.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/cpu/mcheck/mce.c
> b/arch/x86/kernel/cpu/mcheck/mce.c
> index c5b0d56..82a0c8b 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> @@ -998,6 +998,7 @@ void do_machine_check(struct pt_regs *regs, long
> error_code)
> u64 recover_paddr = ~0ull;
> int flags = MF_ACTION_REQUIRED;
> int lmce = 0;
> + unsigned int cpu = smp_processor_id();
>
> ist_enter(regs);
>
> @@ -1008,6 +1009,14 @@ void do_machine_check(struct pt_regs *regs, long
> error_code)
>
> mce_gather_info(&m, regs);
>
> + /*
> + * if this cpu is offline, just bail out.
> + * TBD: looking into adding any logs this offline CPU might have,
> + * to be collected and reported by the rendezvous master.
> + */
> + if (cpu_is_offline(cpu) && (m.mcgstatus & MCG_STATUS_RIPV))
> + goto out;
This CPU - it being offline and all - is not doing the minimal amount of
work possible IMO.
Why does it have to do ist_enter(), this_cpu_inc(mce_exception_count),
etc?
IMO the only things it should do is this:
if (cpu_is_offline(smp_processor_id())) {
mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
return;
}
and that should be at the very beginning of do_machine_check(). So
that the hardware is happy. Concerning Linux, it is offline so no data
structures on it are valid.
Hmmm?
P.S., please don't put stable@ to CC - add it as a "CC: " line in the
SOB section instead.
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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