Re: [Crash-utility] [Patch 1/4][kernel][slimdump] Add new elf-note of type NT_NOCOREDUMP to capture slimdump
On Wed, Oct 05, 2011 at 12:48:44PM +0530, K.Prasad wrote:
On Tue, Oct 04, 2011 at 10:04:37AM -0400, Vivek Goyal wrote:
> On Mon, Oct 03, 2011 at 01:02:03PM +0530, K.Prasad wrote:
> > There are certain types of crashes induced by faulty hardware in which
> > capturing crashing kernel's memory (through kdump) makes no sense (or
sometimes
> > dangerous).
> >
> > A case in point, is unrecoverable memory errors (resulting in fatal machine
> > check exceptions) in which reading from the faulty memory location from the
> > kexec'ed kernel will cause double fault and system reset (leaving no
> > information for the user).
>
> Prasad,
>
> I am just trying to remember what was wrong with Andi's approach of
> disable MCE while copying the dump?
>
Hi Vivek,
The behaviour upon a read operation on an UC memory location is
undefined and so we want to avoid it (previously discussed here:
http://article.gmane.org/gmane.linux.kernel/1146799). When we disable
MCE and copy the dump, we will invariably read the faulty memory
location.
Right, from the message above:
"- To disable MCE exceptions as done by the patches cited above. However
the result of a read operation on corrupted memory is unknown and the
system behaviour is undefined. We're unsure if this is a safe thing to
do."
Can you elaborate more on that? Are we talking poisoned memory here or
undetected and uncorrectable memory errors?
Thanks.
--
Regards/Gruss,
Boris.