On Thu, Jul 21, 2016 at 09:43:40AM +0200, Michal Hocko wrote: > We have further discussed the patch and I believe it is not correct. See [1]. > I am proposing the following alternative. > > [1] http://lkml.kernel.org/r/20160720132431.GM11249@xxxxxxxxxxxxxx > --- > From b1e9b3214f1859fdf7d134cdcb56f5871933539c Mon Sep 17 00:00:00 2001 > From: Michal Hocko <mhocko@xxxxxxxx> > Date: Thu, 21 Jul 2016 09:28:13 +0200 > Subject: [PATCH] mm, hugetlb: fix huge_pte_alloc BUG_ON > > Zhong Jiang has reported a BUG_ON from huge_pte_alloc hitting when he > runs his database load with memory online and offline running in > parallel. The reason is that huge_pmd_share might detect a shared pmd > which is currently migrated and so it has migration pte which is > !pte_huge. > > There doesn't seem to be any easy way to prevent from the race and in > fact seeing the migration swap entry is not harmful. Both callers of > huge_pte_alloc are prepared to handle them. copy_hugetlb_page_range > will copy the swap entry and make it COW if needed. hugetlb_fault will > back off and so the page fault is retries if the page is still under > migration and waits for its completion in hugetlb_fault. > > That means that the BUG_ON is wrong and we should update it. Let's > simply check that all present ptes are pte_huge instead. > > Reported-by: zhongjiang <zhongjiang@xxxxxxxxxx> > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> In the early days of hugetlb, we had an assumption that !pte_none is equivalent to pmd_present() because there was no valid non-present entry on huge_pte. Situation has changed by hugepage migration and/or hwpoison, so we have to care about the separation of these two, and make sure that pte_present is true before checking pte_huge. So I think this change is right. Thank you Zhong, Michal. Acked-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> -- 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