Bug 407931

http://fedorapeople.org/~wtogami/temp/mkinitrd-kernel-oops/
SRPM and x86_64 build of mkinitrd that exposes this kernel bug.  If you are
running a different arch, simply rebuild the SRPM.  So far I only know it
happens on my x86_64 laptop, I haven't tested it on i386 yet.

http://wtogami.livejournal.com/21452.html
You can follow instructions from here in order to safely use the above
experimental mkinitrd to expose this bug.  Note that the system DOES boot even
with the kernel oopses.  It *is* a bug in this experimental mkinitrd, but
according to hpa and riel this is a genuine kernel bug.

Here are more debug tips:
1) yum install busybox
Then mkinitrd will pull in busybox into the initrd so you have more utilities to
use while debugging from the initrd shell.
2) Remove "quiet" and add "verbose shell" to your kernel args.
This will display everything that is run as it happens, and drop to a shell
before it boots the system.  "busybox dmesg"

Another thing...
It isn't clear exactly where the kernel oops occurs or what initrd or nash is
doing at the time of the oops.  Because if you let it boot into the OS, then
subsequently use dmesg, then you see the oopses after "Freeing initrd memory". 
But if you use "shell" arg and drop into the shell before it boots your system,
you see the kernel oopses earlier during the initrd.  I am a bit confused by this.

pages is NULL here, implying vma->vm_private_data was NULL:

static struct page *special_mapping_nopage(struct vm_area_struct *vma,
                                           unsigned long address, int *type)
{
        struct page **pages;

        BUG_ON(address < vma->vm_start || address >= vma->vm_end);

        address -= vma->vm_start;
        for (pages = vma->vm_private_data; address > 0 && *pages; ++pages)
                address -= PAGE_SIZE;

===>    if (*pages) {
                struct page *page = *pages;
                get_page(page);
                return page;
        }

        return NOPAGE_SIGBUS;
}

Does booting with kernel option 'vdso=0' make any difference?

vdso=0 avoids this kernel oops!

hotplug is apparently being run before the vdso is initialized.

Workaround: don't put an executable called /sbin/hotplug in the initrd.

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