On Thu 21-07-16 08:13:55, Naoya Horiguchi wrote: > 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> Thank you for double checking Naoya! IIUC Fixes: 290408d4a250 ("hugetlb: hugepage migration core") should help. Maybe we should even tag that for stable? -- Michal Hocko SUSE Labs -- 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>