On Thu, 27 May 2010 13:43:00 -0700 Doug Doan <dougd@xxxxxxxx> wrote:
>
> When a copy-on-write occurs, we take one of two paths in handle_mm_fault:
> through handle_pte_fault for normal pages, or through hugetlb_fault for huge pages.
>
> In the normal page case, we eventually get to do_wp_page and call mmu notifiers
> via ptep_clear_flush_notify. There is no callout to the mmmu notifiers in the
> huge page case. This patch fixes that.
>
> Signed-off-by: Doug Doan <dougd@xxxxxxxx>
> ---
>
> [patch text/plain (802B)]
> --- mm/hugetlb.c.orig 2010-05-27 13:07:58.569546314 -0700
> +++ mm/hugetlb.c 2010-05-26 14:41:06.449296524 -0700
(In patch -p1 form, please. So a/mm/hugetlb.c)
> @@ -2345,11 +2345,17 @@ retry_avoidcopy:
> ptep = huge_pte_offset(mm, address & huge_page_mask(h));
> if (likely(pte_same(huge_ptep_get(ptep), pte))) {
> /* Break COW */
> + mmu_notifier_invalidate_range_start(mm,
> + address & huge_page_mask(h),
> + (address & huge_page_mask(h)) + huge_page_size(h));
> huge_ptep_clear_flush(vma, address, ptep);
> set_huge_pte_at(mm, address, ptep,
> make_huge_pte(vma, new_page, 1));
> /* Make the old page be freed below */
> new_page = old_page;
> + mmu_notifier_invalidate_range_end(mm,
> + address & huge_page_mask(h),
> + (address & huge_page_mask(h)) + huge_page_size(h));
> }
> page_cache_release(new_page);
> page_cache_release(old_page);
This causes mmu_notifier_invalidate_range_start() to be called under
page_table_lock. The immediately preceding code seems to take some
care to avoid doing that. I took a quick look at other callsites and
cannot immediately see other cases where
mmu_notifier_invalidate_range_start/end() are called under that lock.
This may not introduce bugs with current notifier implementations (I
didn't check), but it does lessen flexibility?
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