mm/ksm.c seems to be doing an unneeded _notify.

[Robin Holt <holt@xxxxxxx>]

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?

Thanks,
Robin Holt

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