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Subject: Re: Unsafe pte_update() in do_page_fault() (4xx and Book-E)
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Eugene Surovegin <ebs@ebshome.net>
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Date: Fri, 03 Mar 2006 14:43:02 +1100
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Cc: linuxppc-dev@ozlabs.org, Kumar Gala <kumar.gala@freescale.com>
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> If this happens, pte_update() sets _PAGE_HWEXEC bit in just cleared 
> PTE. Sometime later, another page fault happens for this page, but 
> because of that set bit, pte_none() test in handle_pte_fault() fails, 
> and we continue along the wrong path, thinking that this PTE was 
> swapped out to the swap file, and this triggers swap_dup error I 
> mentioned at the beginning.

Can we preempt at that point ? As tehre is no SMP 4xx that I know of
preempt would be the only cause for such a race ...

Ben.