Re: [Xen-devel] Xen dom0 crash in get_phys_to_machine

["Alan J. Wylie" <NDA5OWUy@xxxxxxxxxxx>]

at 14:05 on Fri 22-Oct-2010 Gianni Tedesco (gianni.tedesco@xxxxxxxxxx) wrote:

> FWIW, when I was checking for any call where pfn > max_pfn - and I got:
> 
>   p2m_top[0][10][104] max_pfn=0
> 
> The p2m seems to have been correctly initialised:
> 
>  xen_build_dynamic_phys_to_machine: topidx=0 mididx=375 max_pfn=192512
> 
> But then it looks like something is trampling max_pfn and possibly other
> important data structures.

I've just been reading through the Documentation/development-process
and discovered "sparse".

Five minutes ago I ran it on mmu.c and got the following interesting
output:

/usr/src/jeremy-git-xen/arch/x86/xen/mmu.c:385:23: warning: symbol 'max_pfn' 
shadows an earlier one
/usr/src/jeremy-git-xen/arch/x86/include/asm/page_64_types.h:58:22: originally 
declared here
/usr/src/jeremy-git-xen/arch/x86/xen/mmu.c:289:47: warning: potentially 
expensive pointer subtraction
/usr/src/jeremy-git-xen/arch/x86/include/asm/xen/page.h:84:9: warning: 
incorrect type in argument 1 (different address spaces)
/usr/src/jeremy-git-xen/arch/x86/include/asm/xen/page.h:84:9:    expected void 
const volatile [noderef] <asn:1>*<noident>
/usr/src/jeremy-git-xen/arch/x86/include/asm/xen/page.h:84:9:    got unsigned 
long *
/usr/src/jeremy-git-xen/arch/x86/include/asm/xen/page.h:84:9: warning: cast 
adds address space to expression (<asn:1>)
/usr/src/jeremy-git-xen/arch/x86/include/asm/xen/page.h:84:9: warning: cast 
adds address space to expression (<asn:1>)
/usr/src/jeremy-git-xen/arch/x86/include/asm/xen/page.h:84:9: warning: cast 
adds address space to expression (<asn:1>)
/usr/src/jeremy-git-xen/arch/x86/include/asm/xen/page.h:84:9: warning: cast 
adds address space to expression (<asn:1>)
/usr/src/jeremy-git-xen/include/linux/mm.h:603:16: warning: potentially 
expensive pointer subtraction
/usr/src/jeremy-git-xen/arch/x86/xen/mmu.c:1269:37: warning: potentially 
expensive pointer subtraction
/usr/src/jeremy-git-xen/include/linux/mm.h:603:16: warning: potentially 
expensive pointer subtraction
/usr/src/jeremy-git-xen/include/linux/mm.h:603:16: warning: potentially 
expensive pointer subtraction
/usr/src/jeremy-git-xen/arch/x86/xen/mmu.c:1410:37: warning: potentially 
expensive pointer subtraction
/usr/src/jeremy-git-xen/include/linux/mm.h:603:16: warning: potentially 
expensive pointer subtraction
/usr/src/jeremy-git-xen/arch/x86/xen/mmu.c:1684:17: error: bad constant 
expression

Is it just a co-incidence that the first two lines refer to the same
symbol that you have just mentioned?

I'm going to try renaming the local symbol and see if things still crash.

The trouble is that the box I've been testing on is supposed to be our
backup file server and is currently doing a rsync of 280GB of files
from a 7 year old windows box. At least I'll be able to leave it
running undisturbed over the weekend.

-- 
Alan J. Wylie                                          http://www.wylie.me.uk/


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