Re: [ 08/82] mm: pmd_read_atomic: fix 32bit PAE pmd walk vspmd_populate SMP race condition

[Josh Boyer]

On Thu, Jun 7, 2012 at 12:03 AM, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> 3.4-stable review patch.  If anyone has any objections, please let me know.
>
> ------------------
>
> From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
>
> commit 26c191788f18129af0eb32a358cdaea0c7479626 upstream.
>
> When holding the mmap_sem for reading, pmd_offset_map_lock should only
> run on a pmd_t that has been read atomically from the pmdp pointer,
> otherwise we may read only half of it leading to this crash.

This one is important, but it can break Xen apparently:

http://permalink.gmane.org/gmane.comp.emulators.xen.devel/132522
https://bugzilla.redhat.com/show_bug.cgi?id=829016

Not sure if you want to hold off on it or see if Andrea comes up with
a follow up fix?

josh
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