Re: doublefault debugging (was Re: Linux v2.5.62 --- spontaneous reboots)

[William Lee Irwin III]

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