Why write CPER_NOTIFY_MCE to ERST when reboot

Why write CPER_NOTIFY_MCE to ERST when reboot

[Joe Jin]

Hi Tony,

With commit 0bb77c46 "pstore: X86 platform interface using ACPI/APEI/ERST"
when reboot the server kernel will call erst_writer() to write CPER_NOTIFY_MCE
to ERST, if reboot the server to Windows we find MCE from system event logs.
Any reason write this to ERST when reboot?

Any input will appreciate!

Regards,
Joe

Re: Why write CPER_NOTIFY_MCE to ERST when reboot

[Jiang Liu]

On Fri 31 May 2013 04:22:36 PM CST, Joe Jin wrote:
> Hi Tony,
>
> With commit 0bb77c46 "pstore: X86 platform interface using ACPI/APEI/ERST"
> when reboot the server kernel will call erst_writer() to write CPER_NOTIFY_MCE
> to ERST, if reboot the server to Windows we find MCE from system event logs.
> Any reason write this to ERST when reboot?
>
> Any input will appreciate!
>
> Regards,
> Joe
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Hi Joe,
     I guess this is used to handle an uncorrectable MCE. When 
uncorrectable MCE happens,
the whole disk io stack is unreliable so we couldn't write MCE record 
to disk, ERST is the
last method to store the MCE record and OS could retrieve this record 
from ERST on next
reboot.
Regards!
Gerry

RE: Why write CPER_NOTIFY_MCE to ERST when reboot

[Luck, Tony]

Gerry has this right - we want to preserve the error information, but we
don't trust our kernel enough to have it write to a regular disk (perhaps
it has no access to I/O because of the error - or worse, perhaps it might
write to the wrong place or the wrong disk).

In theory data the information in the machine check banks is preserved
across a warm reset for the reboot - but in practice we may sometimes
need a power-cycle and full cold reset. Also I've heard that on some systems
the BIOS clears the banks before the OS can see them.

-Tony

Re: Why write CPER_NOTIFY_MCE to ERST when reboot

[Joe Jin]

Tony and Gerry, thanks!

Regards,
Joe

On 06/01/13 02:29, Luck, Tony wrote:
> Gerry has this right - we want to preserve the error information, but we
> don't trust our kernel enough to have it write to a regular disk (perhaps
> it has no access to I/O because of the error - or worse, perhaps it might
> write to the wrong place or the wrong disk).
> 
> In theory data the information in the machine check banks is preserved
> across a warm reset for the reboot - but in practice we may sometimes
> need a power-cycle and full cold reset. Also I've heard that on some systems
> the BIOS clears the banks before the OS can see them.
> 
> -Tony
> 


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