Message-ID: <49B9E725.3060103@davidnewall.com>
Date: Fri, 13 Mar 2009 15:25:01 +1030
From: David Newall <davidn@davidnewall.com>
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To: Gene Heskett <gene.heskett@gmail.com>
CC: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: I just got got another Oops
References: <200903120133.11583.gene.heskett@gmail.com> <200903121348.43477.gene.heskett@gmail.com> <49B96471.8070602@davidnewall.com> <200903121928.00746.gene.heskett@gmail.com>
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Gene,

I think it's a null page pointer passed to prep_new_page.  It's
difficult to be certain, because it's compiled with -O2, but that's what
it looks like.

Let's test that hypothesis.  Let's also compile page_alloc.c with
debugging.  Do that by executing the commands in the attached file, and
then doing a make install (or whatever you do.)

But first, let's also sidestep the optimiser by making prep_new_page
public. Do that by changing:

   static int prep_new_page(struct page *page, int order, gfp_t gfp_flags)**


in mm/page_alloc.c, near line 637, to:

   int my_prep_new_page(struct page *page, int order, gfp_t gfp_flags)**

and by changing:

	if (prep_new_page(page, order, gfp_flags))


near line 1137, to:

	if (my_prep_new_page(page, order, gfp_flags))


This will prevent the optimiser from inlining that function, and we
would expect to see the error change from
"get_page_from_freelist+0x24b/0x4c0" to "my_prep_new_page+0x0yy/0x0zz".

David

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