From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197]) by kanga.kvack.org (Postfix) with ESMTP id 5897C6B007E for ; Tue, 19 Apr 2016 11:19:20 -0400 (EDT) Received: by mail-pf0-f197.google.com with SMTP id e190so34618118pfe.3 for ; Tue, 19 Apr 2016 08:19:20 -0700 (PDT) Received: from mail-pa0-x231.google.com (mail-pa0-x231.google.com. [2607:f8b0:400e:c03::231]) by mx.google.com with ESMTPS id d68si9029630pfc.68.2016.04.19.08.19.19 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 19 Apr 2016 08:19:19 -0700 (PDT) Received: by mail-pa0-x231.google.com with SMTP id fs9so7658480pac.2 for ; Tue, 19 Apr 2016 08:19:19 -0700 (PDT) Date: Tue, 19 Apr 2016 11:19:04 -0400 From: Jerome Glisse Subject: Re: [PATCH 17/18] dax: Use radix tree entry lock to protect cow faults Message-ID: <20160419151904.GA17318@gmail.com> References: <1461015341-20153-1-git-send-email-jack@suse.cz> <1461015341-20153-18-git-send-email-jack@suse.cz> <20160419114609.GA13932@gmail.com> <20160419143343.GC22413@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20160419143343.GC22413@quack2.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Jan Kara Cc: linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-mm@kvack.org, Ross Zwisler , Dan Williams , linux-nvdimm@lists.01.org, Matthew Wilcox On Tue, Apr 19, 2016 at 04:33:43PM +0200, Jan Kara wrote: > On Tue 19-04-16 07:46:09, Jerome Glisse wrote: > > On Mon, Apr 18, 2016 at 11:35:40PM +0200, Jan Kara wrote: > > > diff --git a/mm/memory.c b/mm/memory.c > > > index 93897f23cc11..f09cdb8d48fa 100644 > > > --- a/mm/memory.c > > > +++ b/mm/memory.c > > > @@ -63,6 +63,7 @@ > > > #include > > > #include > > > #include > > > +#include > > > > > > #include > > > #include > > > @@ -2785,7 +2786,8 @@ oom: > > > */ > > > static int __do_fault(struct vm_area_struct *vma, unsigned long address, > > > pgoff_t pgoff, unsigned int flags, > > > - struct page *cow_page, struct page **page) > > > + struct page *cow_page, struct page **page, > > > + void **entry) > > > { > > > struct vm_fault vmf; > > > int ret; > > > @@ -2800,8 +2802,10 @@ static int __do_fault(struct vm_area_struct *vma, unsigned long address, > > > ret = vma->vm_ops->fault(vma, &vmf); > > > if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY))) > > > return ret; > > > - if (!vmf.page) > > > - goto out; > > > > Removing the above sounds seriously bogus to me as it means that below > > if (unlikely(PageHWPoison(vmf.page))) could dereference a NULL pointer. > > If you do not return a valid page, you must return appropriate return code > from the ->fault handler. That being VM_FAULT_NOPAGE, VM_FAULT_DAX_LOCKED, > or some error. That has always been the case except for DAX abuse which was > added by commit 2e4cdab0584f "mm: allow page fault handlers to perform the > COW" about an year ago. And my patch fixes this abuse. > > I'm not aware of any other code that would start abusing the return value > from the ->fault handler. If some such code indeed got merged during the > last year, it should be fixed as well. > Ok my bad i missed that. Cheers, Jerome -- 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