On Fri, Mar 07, 2014 at 01:35:02AM -0500, Naoya Horiguchi wrote: > 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. Andrew, could you consider picking up this patch (below) and "[PATCH] mm: add pte_present() check on existing hugetlb_entry" (previously posted in this thread) into linux-mm? This patch is to be folded into "mempolicy: apply page table walker on queue_pages_range()," and another one is into "pagewalk: update page table walker core." Or do I need to repost them? Thanks, Naoya > 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> > -- 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>