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Subject: Re: 2.6.15-rc4 panic in __nr_to_section() with CONFIG_SPARSEMEM
From: Dave Hansen <haveblue@us.ibm.com>
To: Badari Pulavarty <pbadari@us.ibm.com>
Cc: Andy Whitcroft <andyw@uk.ibm.com>, lkml <linux-kernel@vger.kernel.org>
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Date: Wed, 07 Dec 2005 14:52:15 -0800
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On Wed, 2005-12-07 at 14:37 -0800, Badari Pulavarty wrote:
> Hi Andy,
> 
> I getting a panic while doing "cat /proc/<pid>/smaps" on
> a process. I debugged a little to find out that faulting
> IP is in _nr_to_section() - seems to be getting somehow
> called by  pte_offset_map_lock() from smaps_pte_range
> (which show_smaps) calls.
> 
> Any ideas on why or how to debug further ? 

You're sure it's inside of the pte_offset_map_lock()?

It's probably this call chain:

        pte_offset_map_lock()
        pte_offset_map()
        pmd_page()
        pfn_to_page()
        __pfn_to_section()
        __nr_to_section()

I'd probably take a hard look at the PMD first to make sure it looks
good.  Then, maybe go through some of the conversions in
pte_offset_map_lock() from that chain and print out each step inside of
smaps_pte_range().  Can you trigger it easily?

-- Dave

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