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SubjectRe: [RFT][PATCH] mm: Fix race in kunmap_atomic()
On 10/27/2010 10:54 AM, Peter Zijlstra wrote:

> Christoph reported a nice splat which illustrated a race in the new
> stack based kmap_atomic implementation.
>
> The problem is that we pop our stack slot before we're completely done
> resetting its state -- in particular clearing the PTE (sometimes that's
> CONFIG_DEBUG_HIGHMEM). If an interrupt happens before we actually clear
> the PTE used for the last slot, that interrupt can reuse the slot in a
> dirty state, which triggers a BUG in kmap_atomic().
>
> Fix this by introducing kmap_atomic_idx() which reports the current slot
> index without actually releasing it and use that to find the PTE and
> delay the _pop() until after we're completely done.
>
> Reported-by: Christoph Hellwig<hch@infradead.org>
> Signed-off-by: Peter Zijlstra<a.p.zijlstra@chello.nl>

Acked-by: Rik van Riel <riel@redhat.com>

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