Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965327AbdDSP0I (ORCPT ); Wed, 19 Apr 2017 11:26:08 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:45582 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934796AbdDSOjC (ORCPT ); Wed, 19 Apr 2017 10:39:02 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Kirill A. Shutemov" , Minchan Kim , Andrea Arcangeli , Hillf Danton , Andrew Morton , Linus Torvalds Subject: [PATCH 4.10 06/69] thp: fix MADV_DONTNEED vs. MADV_FREE race Date: Wed, 19 Apr 2017 16:36:35 +0200 Message-Id: <20170419141555.381841254@linuxfoundation.org> X-Mailer: git-send-email 2.12.2 In-Reply-To: <20170419141555.114738231@linuxfoundation.org> References: <20170419141555.114738231@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2070 Lines: 60 4.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Kirill A. Shutemov commit 58ceeb6bec86d9140f9d91d71a710e963523d063 upstream. Both MADV_DONTNEED and MADV_FREE handled with down_read(mmap_sem). It's critical to not clear pmd intermittently while handling MADV_FREE to avoid race with MADV_DONTNEED: CPU0: CPU1: madvise_free_huge_pmd() pmdp_huge_get_and_clear_full() madvise_dontneed() zap_pmd_range() pmd_trans_huge(*pmd) == 0 (without ptl) // skip the pmd set_pmd_at(); // pmd is re-established It results in MADV_DONTNEED skipping the pmd, leaving it not cleared. It violates MADV_DONTNEED interface and can result is userspace misbehaviour. Basically it's the same race as with numa balancing in change_huge_pmd(), but a bit simpler to mitigate: we don't need to preserve dirty/young flags here due to MADV_FREE functionality. [kirill.shutemov@linux.intel.com: Urgh... Power is special again] Link: http://lkml.kernel.org/r/20170303102636.bhd2zhtpds4mt62a@black.fi.intel.com Link: http://lkml.kernel.org/r/20170302151034.27829-4-kirill.shutemov@linux.intel.com Signed-off-by: Kirill A. Shutemov Acked-by: Minchan Kim Cc: Minchan Kim Cc: Andrea Arcangeli Cc: Hillf Danton Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/huge_memory.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1393,8 +1393,7 @@ bool madvise_free_huge_pmd(struct mmu_ga deactivate_page(page); if (pmd_young(orig_pmd) || pmd_dirty(orig_pmd)) { - orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd, - tlb->fullmm); + pmdp_invalidate(vma, addr, pmd); orig_pmd = pmd_mkold(orig_pmd); orig_pmd = pmd_mkclean(orig_pmd);