Re: [Crash-utility] [Patch 1/4][kernel][slimdump] Add new elf-note of type NT_NOCOREDUMP to capture slimdump

----- Original Message ----- > On Wed, Oct 05, 2011 at 07:20:37PM +0200, Borislav Petkov wrote: > > On Wed, Oct 05, 2011 at 01:10:07PM -0400, Vivek Goyal wrote: > > > On Wed, Oct 05, 2011 at 08:58:53AM -0700, Luck, Tony wrote: > > > > > > The plan is to pass-down the list of poisoned memory pages > > > > > > to the second > > > > > > kernel using an elf-note so that these pages are left > > > > > > untouched during > > > > > > dump capture. I'm working on an implementation of the same > > > > > > and should > > > > > > have patches soon. > > > > > > > > > > I would say let us first figure out what happens while > > > > > reading a poisoned > > > > > page and is this a problem before working on a solution. > > > > > > > > If the page is poisoned because of a real uncorrectable error > > > > in memory > > > > (reported as SRAO machine check today, or by SRAR > > > > real-soon-now). Then > > > > accessing the page from the processor while taking a memory > > > > dump will > > > > result in a machine check. > > > > > > > > Note that a large memory system that had been running for a > > > > long time > > > > may have built up a small stash of these land-mine pages - and > > > > we need > > > > to worry about them even in the case where the panic is not > > > > machine > > > > check related (in fact especially in this case ... we are in a > > > > case > > > > where we actually do want the dump to diagnose the cause of the > > > > panic, > > > > and we don't want to risk losing the crash dump because we > > > > aborted when > > > > touching a page that the OS had safely avoided for > > > > days/weeks/months). > > > > > > > > So passing a list of poisoned pages from the old kernel to the > > > > new kernel > > > > is a good idea - and is independent of the cause of the crash > > > > (except that > > > > in the fatal machine check case due to memory error the list is > > > > guaranteed > > > > to be non-empty). > > > > > > Whre is this poisoned page info stored? In struct page? If yes, then > > > user space can walk through it and make sure not to touch poisoned pages. > > > Anyway user space filtering utility "makedumpfile" walks through struct > > > pages to filter out the pages. It should be able to filter out > > > poisoned pages unconditionally. So there should be no need for kernel > > > to export a list of these pages. > > > > Does this utility work on a vmcore dump? If so, Tony refers to the > > creation of the vmcore itself from the memory used by the first > > kernel. > > No, this utitlity can directly work on /proc/vmcore where first kernel's > image is still in memory and not on disk. > > > If there are poisoned pages, merely accessing that portion of DRAM > > containing the poisoned data would cause further MCEs in the freshly > > booted kernel so you won't be able to finish creating the dump. > > As long as you can get to your struct page arrays, one should be able > to filter out poisoned pages without saving the whole dump. It's still going to require a minimal kernel change because the PG_hwpoison flag's bit number differs depending upon the kernel configuration, if it exists at all. An additional vmcoreinfo item probably...