From mboxrd@z Thu Jan 1 00:00:00 1970 From: akpm@linux-foundation.org Subject: [merged] mm-userfaultfd-thp-avoid-waiting-when-pmd-under-thp-migration.patch removed from -mm tree Date: Thu, 01 Feb 2018 11:31:52 -0800 Message-ID: <20180201193152.siStuxAzd%akpm@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.linuxfoundation.org ([140.211.169.12]:58308 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753060AbeBATby (ORCPT ); Thu, 1 Feb 2018 14:31:54 -0500 Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: aarcange@redhat.com, kirill.shutemov@linux.intel.com, mike.kravetz@oracle.com, mm-commits@vger.kernel.org, n-horiguchi@ah.jp.nec.com, rppt@linux.vnet.ibm.com, viro@zeniv.linux.org.UK, ying.huang@intel.com, zi.yan@cs.rutgers.edu The patch titled Subject: mm, userfaultfd, THP: avoid waiting when PMD under THP migration has been removed from the -mm tree. Its filename was mm-userfaultfd-thp-avoid-waiting-when-pmd-under-thp-migration.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Huang Ying Subject: mm, userfaultfd, THP: avoid waiting when PMD under THP migration If THP migration is enabled, for a VMA handled by userfaultfd, consider the following situation, do_page_fault() __do_huge_pmd_anonymous_page() handle_userfault() userfault_msg() /* a huge page is allocated and mapped at fault address */ /* the huge page is under migration, leaves migration entry in page table */ userfaultfd_must_wait() /* return true because !pmd_present() */ /* may wait in loop until fatal signal */ That is, it may be possible for userfaultfd_must_wait() encounters a PMD entry which is !pmd_none() && !pmd_present(). In the current implementation, we will wait for such PMD entries, which may cause unnecessary waiting, and potential soft lockup. This is fixed via avoiding to wait when !pmd_none() && !pmd_present(), only wait when pmd_none(). This may be not a problem in practice, because userfaultfd_must_wait() is always called with mm->mmap_sem read-locked. mremap() will write-lock mm->mmap_sem. And UFFDIO_COPY doesn't support to copy THP mapping. But the change introduced still makes the code more correct, and makes the PMD and PTE code more consistent. Link: http://lkml.kernel.org/r/20171207011752.3292-1-ying.huang@intel.com Signed-off-by: "Huang, Ying" Reviewed-by: Andrea Arcangeli Cc: Mike Kravetz Cc: Mike Rapoport Cc: "Kirill A. Shutemov" Cc: Alexander Viro Cc: Zi Yan Cc: Naoya Horiguchi Signed-off-by: Andrew Morton --- fs/userfaultfd.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff -puN fs/userfaultfd.c~mm-userfaultfd-thp-avoid-waiting-when-pmd-under-thp-migration fs/userfaultfd.c --- a/fs/userfaultfd.c~mm-userfaultfd-thp-avoid-waiting-when-pmd-under-thp-migration +++ a/fs/userfaultfd.c @@ -294,10 +294,13 @@ static inline bool userfaultfd_must_wait * pmd_trans_unstable) of the pmd. */ _pmd = READ_ONCE(*pmd); - if (!pmd_present(_pmd)) + if (pmd_none(_pmd)) goto out; ret = false; + if (!pmd_present(_pmd)) + goto out; + if (pmd_trans_huge(_pmd)) goto out; _ Patches currently in -mm which might be from ying.huang@intel.com are