On Thu, May 12, 2022 at 10:54:05AM +0800, Miaohe Lin wrote: > On 2022/5/12 2:35, Mike Kravetz wrote: > > On 5/11/22 08:19, Naoya Horiguchi wrote: > >> From: Naoya Horiguchi <naoya.horiguchi@xxxxxxx> > >> > >> If memory_failure() fails to grab page refcount on a hugetlb page > >> because it's busy, it returns without setting PG_hwpoison on it. > >> This not only loses a chance of error containment, but breaks the rule > >> that action_result() should be called only when memory_failure() do > >> any of handling work (even if that's just setting PG_hwpoison). > >> This inconsistency could harm code maintainability. > >> > >> So set PG_hwpoison and call hugetlb_set_page_hwpoison() for such a case. > > I'm sorry but where is hugetlb_set_page_hwpoison() defined and used ? I can't find it. Sorry, this depends on the unmerged patch https://lore.kernel.org/linux-mm/20220427042841.678351-2-naoya.horiguchi@xxxxxxxxx/ , so should come after that. I'll do both into a single patchset next. ... > >> diff --git a/mm/memory-failure.c b/mm/memory-failure.c > >> index 6a28d020a4da..e3269b991016 100644 > >> --- a/mm/memory-failure.c > >> +++ b/mm/memory-failure.c > >> @@ -1526,7 +1526,8 @@ int __get_huge_page_for_hwpoison(unsigned long pfn, int flags) > >> count_increased = true; > >> } else { > >> ret = -EBUSY; > >> - goto out; > >> + if (!(flags & MF_NO_RETRY)) > >> + goto out; > >> } > > > > Hi Naoya, > > > > We are in the else block because !HPageFreed() and !HPageMigratable(). > > IIUC, this likely means the page is isolated. One common reason for isolation > > is migration. So, the page could be isolated and on a list for migration. > > > > I took a quick look at the hugetlb migration code and did not see any checks > > for PageHWPoison after a hugetlb page is isolated. I could have missed > > something? If there are no checks, we will read the PageHWPoison page > > in kernel mode while copying to the migration target. > > > > Is this an issue? Is is something we need to be concerned with? Memory > > errors can happen at any time, and gracefully handling them is best effort. > > It seems HWPoison hugetlb page will still be accessed before this patch. Can we do a > get_page_unless_zero first here to ensure that hugetlb page migration should fail due > to this extra page reference and thus not access the page content? If hugetlb page is > already freezed, corrupted memory will still be consumed though. :( Right, I have no idea about this ... Thanks, Naoya Horiguchi
