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    SubjectRe: doublefault debugging (was Re: Linux v2.5.62 --- spontaneous reboots)
    On Wed, Feb 19, 2003 at 08:52:46PM -0800, Linus Torvalds wrote:
    > Whee. So the double-fault patch actually ends up being useful? It didn't
    > help with Chris' problem, but hey, if it helps with something else..
    > Anyway, that %esp is crap, which also explains this:
    >> 0xc01181c4 <do_page_fault+20>: mov %eax,0xc(%esp,1)
    > Took a page fault because 0xc(%esp) wasn't there, and the page fault
    > couldn't write the fault trace to the stack (same reason), so you got a
    > double fault.

    Not sure where he got his %esp, but I extracted the following:

    <zwane> MAXMEM=0x33e00000
    <zwane> vmalloc: start = 0xf3e1f000, end = 0xfbe21000
    <zwane> fixaddr: start = 0xfbe23000, end = 0xfffff000

    which means somehow %esp landed in an unmapped tidbit in the middle of
    of vmallocspace that isn't even mapped. I highly suspect rounding
    errors of mine since I squished vmallocspace, fixmapspace, and the
    physical mapping so close together they might share L3 pagetables, i.e.
    they're separated by 2*MMUPAGE_SIZE instead of customary 8MB or so.

    -- wli
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