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?