* Robin Holt (holt@xxxxxxx) wrote:
> While reviewing ksm.c, I noticed that ksm.c does:
>
> if (pte_write(*ptep)) {
> pte_t entry;
>
> swapped = PageSwapCache(page);
> flush_cache_page(vma, addr, page_to_pfn(page));
> /*
> * Ok this is tricky, when get_user_pages_fast() run it doesnt
> * take any lock, therefore the check that we are going to make
> * with the pagecount against the mapcount is racey and
> * O_DIRECT can happen right after the check.
> * So we clear the pte and flush the tlb before the check
> * this assure us that no O_DIRECT can happen after the check
> * or in the middle of the check.
> */
> entry = ptep_clear_flush(vma, addr, ptep);
> /*
> * Check that no O_DIRECT or similar I/O is in progress on the
> * page
> */
> if (page_mapcount(page) + 1 + swapped != page_count(page)) {
> set_pte_at_notify(mm, addr, ptep, entry);
> goto out_unlock;
> }
> entry = pte_wrprotect(entry);
> set_pte_at_notify(mm, addr, ptep, entry);
>
>
> I would think the error case (where the page has an elevated page_count)
> should not be using set_pte_at_notify. In that event, you are simply
> restoring the previous value. Have I missed something or is this an
> extraneous _notify?
It does look extraneous to me as well.
thanks,
-chris
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