On 2022/10/25 13:35, Naoya Horiguchi wrote: > On Tue, Oct 25, 2022 at 10:38:11AM +0800, Miaohe Lin wrote: >> On 2022/10/24 14:20, Naoya Horiguchi wrote: >>> From: Naoya Horiguchi <naoya.horiguchi@xxxxxxx> >>> >>> HWPoisoned page is not supposed to be accessed once marked, but currently >>> such accesses can happen during memory hotremove because do_migrate_range() >>> can be called before dissolve_free_huge_pages() is called. >>> >>> Clear HPageMigratable for hwpoisoned hugepages to prevent them from being >>> migrated. This should be done in hugetlb_lock to avoid race against >>> isolate_hugetlb(). >>> >>> get_hwpoison_huge_page() needs to have a flag to show it's called from >>> unpoison to take refcount of hwpoisoned hugepages, so add it. >>> >>> Reported-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> >>> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx> >>> Reviewed-by: Oscar Salvador <osalvador@xxxxxxx> >>> Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> >>> --- >>> ChangeLog v3 -> v7: >>> - introduce TESTCLEARHPAGEFLAG() to determine the value of migratable_cleared >> >> Many thanks for update, Naoya. I'm sorry but TestClearHPageMigratable() might be somewhat >> overkill. As we discussed in previous thread: >> >> """ >> I think I might be nitpicking... But it seems ClearHPageMigratable is not enough here. >> 1. In MF_COUNT_INCREASED case, we don't know whether HPageMigratable is set. >> 2. Even if HPageMigratable is set, there might be a race window before we clear HPageMigratable? >> So "*migratable_cleared = TestClearHPageMigratable" might be better? But I might be wrong. >> """ >> >> The case 2 should be a dumb problem(sorry about it). HPageMigratable() is always cleared while holding >> the hugetlb_lock which is already held by get_huge_page_for_hwpoison(). So the only case we should care >> about is case 1 and that can be handled by below more efficient pattern: >> if (HPageMigratable) >> ClearHPageMigratable() >> >> So the overhead of test and clear atomic ops can be avoided. But this is trival. >> >> Anyway, this patch still looks good to me. And my Reviewed-by tag still applies. Many thanks. > > OK, so I replace this 1/4 with the following one, thank you. Many thanks for your update, Naoya. ;) This version looks good to me too. Thanks, Miaohe Lin
