From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f180.google.com (mail-wi0-f180.google.com [209.85.212.180]) by kanga.kvack.org (Postfix) with ESMTP id D85B66B0254 for ; Thu, 17 Sep 2015 11:46:58 -0400 (EDT) Received: by wicfx3 with SMTP id fx3so33080419wic.0 for ; Thu, 17 Sep 2015 08:46:58 -0700 (PDT) Received: from mail-wi0-f173.google.com (mail-wi0-f173.google.com. [209.85.212.173]) by mx.google.com with ESMTPS id ir10si4818033wjb.206.2015.09.17.08.46.57 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 17 Sep 2015 08:46:57 -0700 (PDT) Received: by wicgb1 with SMTP id gb1so123739313wic.1 for ; Thu, 17 Sep 2015 08:46:57 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20150917154131.GA27791@linux.intel.com> References: <1438948423-128882-1-git-send-email-kirill.shutemov@linux.intel.com> <20150916111218.GB23026@node.dhcp.inet.fi> <20150917154131.GA27791@linux.intel.com> Date: Thu, 17 Sep 2015 08:46:57 -0700 Message-ID: Subject: Re: [PATCH] mm: take i_mmap_lock in unmap_mapping_range() for DAX From: Dan Williams Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Ross Zwisler , "Kirill A. Shutemov" , Matthew Wilcox , Dan Williams , "Kirill A. Shutemov" , Andrew Morton , Linux MM , linux-fsdevel , Linux Kernel Mailing List , "linux-nvdimm@lists.01.org" On Thu, Sep 17, 2015 at 8:41 AM, Ross Zwisler wrote: > On Wed, Sep 16, 2015 at 02:12:18PM +0300, Kirill A. Shutemov wrote: >> On Tue, Sep 15, 2015 at 04:52:42PM -0700, Dan Williams wrote: >> > Hi Kirill, >> > >> > On Fri, Aug 7, 2015 at 4:53 AM, Kirill A. Shutemov >> > wrote: >> > > DAX is not so special: we need i_mmap_lock to protect mapping->i_mmap. >> > > >> > > __dax_pmd_fault() uses unmap_mapping_range() shoot out zero page from >> > > all mappings. We need to drop i_mmap_lock there to avoid lock deadlock. >> > > >> > > Re-aquiring the lock should be fine since we check i_size after the >> > > point. >> > > >> > > Not-yet-signed-off-by: Matthew Wilcox >> > > Signed-off-by: Kirill A. Shutemov >> > > --- >> > > fs/dax.c | 35 +++++++++++++++++++---------------- >> > > mm/memory.c | 11 ++--------- >> > > 2 files changed, 21 insertions(+), 25 deletions(-) >> > > >> > > diff --git a/fs/dax.c b/fs/dax.c >> > > index 9ef9b80cc132..ed54efedade6 100644 >> > > --- a/fs/dax.c >> > > +++ b/fs/dax.c >> > > @@ -554,6 +554,25 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, >> > > if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE) >> > > goto fallback; >> > > >> > > + if (buffer_unwritten(&bh) || buffer_new(&bh)) { >> > > + int i; >> > > + for (i = 0; i < PTRS_PER_PMD; i++) >> > > + clear_page(kaddr + i * PAGE_SIZE); >> > >> > This patch, now upstream as commit 46c043ede471, moves the call to >> > clear_page() earlier in __dax_pmd_fault(). However, 'kaddr' is not >> > set at this point, so I'm not sure this path was ever tested. >> >> Ughh. It's obviously broken. >> >> I took fs/dax.c part of the patch from Matthew. And I'm not sure now we >> would need to move this "if (buffer_unwritten(&bh) || buffer_new(&bh)) {" >> block around. It should work fine where it was before. Right? >> Matthew? > > Moving the "if (buffer_unwritten(&bh) || buffer_new(&bh)) {" block back seems > correct to me. Matthew is out for a while, so we should probably take care of > this without him. I'd say leave it at its current location and add a local call to bdev_direct_access() as I'm not sure you'd want to trigger one of the failure conditions without having zeroed the page. I.e. right before vmf_insert_pfn_pmd() is probably too late. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org