From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f54.google.com (mail-wm0-f54.google.com [74.125.82.54]) by kanga.kvack.org (Postfix) with ESMTP id 54DBE82F99 for ; Thu, 24 Dec 2015 17:56:27 -0500 (EST) Received: by mail-wm0-f54.google.com with SMTP id p187so193842160wmp.0 for ; Thu, 24 Dec 2015 14:56:27 -0800 (PST) Received: from mail-wm0-x22f.google.com (mail-wm0-x22f.google.com. [2a00:1450:400c:c09::22f]) by mx.google.com with ESMTPS id l6si74562943wje.171.2015.12.24.14.56.25 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 24 Dec 2015 14:56:25 -0800 (PST) Received: by mail-wm0-x22f.google.com with SMTP id p187so190812058wmp.1 for ; Thu, 24 Dec 2015 14:56:25 -0800 (PST) Date: Fri, 25 Dec 2015 00:56:23 +0200 From: "Kirill A. Shutemov" Subject: Re: [PATCH 2/4] thp: fix regression in handling mlocked pages in __split_huge_pmd() Message-ID: <20151224225623.GA22707@node.shutemov.name> References: <1450957883-96356-1-git-send-email-kirill.shutemov@linux.intel.com> <1450957883-96356-3-git-send-email-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Dan Williams Cc: "Kirill A. Shutemov" , Andrew Morton , Sasha Levin , Linux MM On Thu, Dec 24, 2015 at 10:51:43AM -0800, Dan Williams wrote: > On Thu, Dec 24, 2015 at 3:51 AM, Kirill A. Shutemov > wrote: > > This patch fixes regression caused by patch > > "mm, dax: dax-pmd vs thp-pmd vs hugetlbfs-pmd" > > > > The patch makes pmd_trans_huge() check and "page = pmd_page(*pmd)" after > > __split_huge_pmd_locked(). It can never succeed, since the pmd already > > points to a page table. As result the page is never get munlocked. > > > > It causes crashes like this: > > http://lkml.kernel.org/r/5661FBB6.6050307@oracle.com > > > > Signed-off-by: Kirill A. Shutemov > > Reported-by: Sasha Levin > > Cc: Dan Williams > > --- > > mm/huge_memory.c | 8 +++----- > > 1 file changed, 3 insertions(+), 5 deletions(-) > > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > index 99f2a0ecb621..1a988d9b86ef 100644 > > --- a/mm/huge_memory.c > > +++ b/mm/huge_memory.c > > @@ -3024,14 +3024,12 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > > ptl = pmd_lock(mm, pmd); > > if (unlikely(!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd))) > > goto out; > > - __split_huge_pmd_locked(vma, pmd, haddr, false); > > - > > - if (pmd_trans_huge(*pmd)) > > - page = pmd_page(*pmd); > > - if (page && PageMlocked(page)) > > + page = pmd_page(*pmd); > > + if (PageMlocked(page)) > > get_page(page); > > else > > page = NULL; > > + __split_huge_pmd_locked(vma, pmd, haddr, false); > > Since dax pmd mappings may not have a backing struct page I think this > additionally needs the following: > > 8<----- > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 4eae97325e95..c4eccfa836f4 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3025,11 +3025,13 @@ void __split_huge_pmd(struct vm_area_struct > *vma, pmd_t *pmd, > ptl = pmd_lock(mm, pmd); > if (unlikely(!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd))) > goto out; > - page = pmd_page(*pmd); > - if (PageMlocked(page)) > - get_page(page); > - else > - page = NULL; > + else if (pmd_trans_huge(*pmd)) { > + page = pmd_page(*pmd); > + if (PageMlocked(page)) > + get_page(page); > + else > + page = NULL; > + } > __split_huge_pmd_locked(vma, pmd, haddr, false); > out: > spin_unlock(ptl); > Right, I've missed that. Here's updated patch.