On Thu, Mar 06, 2014 at 04:16:29PM -0500, Sasha Levin wrote: > On 03/06/2014 11:08 AM, Naoya Horiguchi wrote: > > And I found my patch was totally wrong because it should check > > !pte_present(), not pte_present(). > > I'm testing fixed one (see below), and the problem seems not to reproduce > > in my environment at least for now. > > But I'm not 100% sure, so I need your double checking. > > Nope, I still see the problem. Same NULL deref and trace as before. Hmm, that's unfortunate. I tried to find out how this reproduces and the root cause, but no luck. So I suggest to add !PageHuge check before entering isolate_huge_page(), which certainly gets over this problem. I think "[PATCH] mm: add pte_present() check on existing hugetlb_entry" is correct itself although it didn't fix this race. Thanks, Naoya --- From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> Date: Fri, 7 Mar 2014 00:59:41 -0500 Subject: [PATCH] mm/mempolicy.c: add comment in queue_pages_hugetlb() We have a race where we try to migrate an invalid page, resulting in hitting VM_BUG_ON_PAGE in isolate_huge_page(). queue_pages_hugetlb() is OK to fail, so let's check !PageHuge before queuing it with some comment as a todo reminder. Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> --- mm/mempolicy.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 494f401bbf6c..175353eb7396 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -530,6 +530,17 @@ static int queue_pages_hugetlb(pte_t *pte, unsigned long addr, if (!pte_present(entry)) return 0; page = pte_page(entry); + + /* + * TODO: Trinity found that page could be a non-hugepage. This is an + * unexpected behavior, but it's not clear how this problem happens. + * So let's simply skip such corner case. Page migration can often + * fail for various reasons, so it's ok to just skip the address + * unsuitable to hugepage migration. + */ + if (!PageHeadHuge(page)) + return 0; + nid = page_to_nid(page); if (node_isset(nid, *qp->nmask) == !!(flags & MPOL_MF_INVERT)) return 0; -- 1.8.5.3 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>